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Quantitative reconstruction of Holocene sea ice and sea surface temperature off West Greenland from the first regional diatom dataset
Abstract
Holocene oceanographic conditions in Disko Bay, West Greenland were reconstructed from high-resolution diatom records derived from two marine sediment cores. A modern dataset composed of 35 dated surface sediment samples collected along the entire West Greenland coast accompanied by remote sensing data were used to develop a diatom transfer function to reconstruct April Sea Ice Concentration (SIC) supported by July Sea Surface Temperature (SST) in the area. Our quantitative reconstruction shows that oceanographic changes recorded throughout the last c. 11000 years reflect seasonal interplay between spring (April SIC) and summer (July SST) conditions. Our records show clear correlation with climate patterns identified from ice core data from GISP2 and Agassiz-Renland for the early to mid Holocene. The early Holocene deglaciation of western Greenland Ice Sheet was characterised in Disko Bay by initial strong centennial-scale fluctuations in April SIC with amplitude of over 40%, followed by high April SIC and July SST. These conditions correspond to a general warming of the climate in the Northern Hemisphere. A decrease in April SIC and July SST was recorded during the Holocene Thermal Optimum reflecting more stable spring-summer conditions in Disko Bay. During the late Holocene, high April SIC characterised the Medieval Climate Anomaly, while high July SST prevailed during the Little Ice Age, supporting previously identified anti-phase relationship between surface waters in West Greenland and climate in NW Europe. This anti-phase pattern might reflect seasonal variations in regional oceanographic conditions and large-scale fluctuations within the North Atlantic Oscillation and Atlantic Meridional Overturning Circulation.
... A total of 40 surface sediment samples (Table 1) were analyzed. They were collected from the uppermost 0-2 cm of sediment box cores and multicores recovered during multiple research cruises (Paaimut 2014: Krawczyk et al., 2017Krawczyk et al., , 2021MSM45: Schneider et al., 2015;MSM46: Pollehne, 2015;MSM66: Dorschel et al., 2017). These samples have already been the target of micropaleontological and geochemical analyses, including those of dinoflagellate cysts (Allan et al., 2018, open-water phytoplankton biomarkers (brassicasterol, dinosterol, and highly branched isoprenoid [HBI] III) concentrations (33 of 40 samples; Kolling et al., 2020), and diatoms (16 of 40 samples; Krawczyk et al., 2017Krawczyk et al., , 2021. ...
... They were collected from the uppermost 0-2 cm of sediment box cores and multicores recovered during multiple research cruises (Paaimut 2014: Krawczyk et al., 2017Krawczyk et al., , 2021MSM45: Schneider et al., 2015;MSM46: Pollehne, 2015;MSM66: Dorschel et al., 2017). These samples have already been the target of micropaleontological and geochemical analyses, including those of dinoflagellate cysts (Allan et al., 2018, open-water phytoplankton biomarkers (brassicasterol, dinosterol, and highly branched isoprenoid [HBI] III) concentrations (33 of 40 samples; Kolling et al., 2020), and diatoms (16 of 40 samples; Krawczyk et al., 2017Krawczyk et al., , 2021. All wet samples were stored in a refrigerator at 4°C before treatment and were freeze-dried prior to lipid extraction and analysis. ...
... The color of the dots and the number by their side refer to the site ID (see also Figure 1 and Table 1). studies already addressed this issue Kolling et al., 2020;Krawczyk et al., 2017Krawczyk et al., , 2021, the following discussion will avoid comparing single sites and focus on general patterns. ...
Palmitic acid (PA) is ubiquitous in the biosphere and its hydrogen isotopic composition (δ²HPA) was proposed as a potential paleoenvironmental proxy for salinity, with δ²HPA values increasing with salinity. In this study, we analyzed 40 surface sediment samples from Baffin Bay and the Labrador Sea to examine the isotopic composition of PA in relation to local environmental variables, including salinity. In contrast to expectations, our results show a negative relationship between the δ²HPA and sea‐surface salinity, raising questions about its pertinence and usefulness as a salinity proxy. Instead, our results suggest that the relative abundance of distinct organisms that employ different metabolisms is the key in determining the hydrogen isotopic fractionations in PA. While we show that PA is mostly produced through photoautotrophic metabolisms by diatoms and dinoflagellates, varying contributions from heterotrophic metabolisms may obscure the stable isotope composition of PA. Surprisingly, we found no correlation between the stable carbon isotopic composition of the sedimentary organic matter (δ¹³Corg) and PA (δ¹³CPA), implying major differences in either the dominant organisms producing sedimentary PA or in carbon isotope fractionation during lipid biosynthesis. We also found that the presence of extended sea‐ice cover leads to enriched carbon and hydrogen isotopic compositions in PA. These enriched values suggest heterotrophic biodegradation in the water column and/or in the sediment as well as an increase in grazing activities. We propose that sea‐ice cover and surface water oxygenation modulate the relative impact of phototrophic and heterotrophic metabolisms, and therefore the isotopic composition of marine sedimentary PA.
... In the Baffin Bay region, there is a long tradition of expanding our knowledge of present-day marine environmental conditions by looking at the geological time scale, mostly based on qualitative studies of proxies such as diatoms, dinoflagellates and foraminifera (Seidenkrantz et al. 2007Knudsen et al. 2008;Ren et al. 2009;Andresen et al. 2011;Perner et al. 2011;Krawczyk et al. 2013;Allan et al. 2018;Hansen et al. 2020;Limoges et al. 2020). Recently, more quantitative studies from around Greenland (Sha et al., 2014(Sha et al., , 2016(Sha et al., , 2017Krawczyk et al. 2017;Oksman et al. 2017;Allan et al. 2018Allan et al. , 2019 have utilised surface sediment datasets from both regional and large-scale areas. Such studies reveal the potential to reconstruct past oceanographic conditions more precisely by combining information on species distribution patterns relative to specific environmental conditions obtained from satellite observations. ...
... The present-day oceanographic conditions in the Baffin Bay-Labrador Sea area are governed by a complex system of currents, seasonal sea ice cover and freshwater input from the Greenland Ice Sheet (Zweng and Münchow 2006;Tivy et al. 2011;Krawczyk et al. 2017). Cold and fresh Arctic water masses enter Baffin Bay via Nares Strait, move southwards along the western margins of Baffin Bay as the Baffin Current and then exit via the Labrador Sea as the Labrador Current. ...
... The monthly average extracts are from grid points covering the surface D.W. Krawczyk et al. sediment sample locations (see Fig. 1 and Table S1). Krawczyk et al. (2017) describe the SIC and SST data reanalysis. A spatial resolution of 0.05 degrees was used for the SST product, and 10 km for the SIC product. ...
Evaluating and understanding bio-environmental relationships at different spatial and temporal scales is important for accurately assessing marine productivity in relation to oceanographic conditions in changing Arctic ecosystems. In this paper, we compare four different bio-environmental datasets, in order to shed new light on the complex marine ecosystem of the Baffin Bay-Labrador Sea region, as well as the historical links between environmental changes and the ecosystem. Satellite dataset was used to describe the regional distribution of chlorophyll a, sea ice concentration (SIC), sea surface temperature (SST) and sea surface salinity (SSS). Chlorophyll a data were also analysed together with shrimp assessment dataset to examine the relationship between marine pelagic productivity and bottom feeders off the Greenland coast. A microfossil dataset (diatom valves) from 57 surface sediment stations was used to describe diatom concentration and diversity across the study region. It was also used in combination with satellite data from the same sites to analyse species-environment relationships and develop a diatom-based transfer function for reconstructing past changes in SIC, SST and SSS. Subsequently, we applied the diatom transfer function on three short sediment cores from off SW and W Greenland spanning the last few centuries. A monitoring dataset of sea ice observations and instrumental measurements of water temperature and salinity, together with atmospheric data (air temperature and wind conditions) from Greenland, were used to develop a more complete picture of 20th and 21st century changes in ocean-climate conditions. Our comparative analyses show clear spatial distribution patterns of marine phytoplankton and identify key ecological groups linked to oceanic conditions. In addition, we find a significant correlation between the different trophic levels, culminating in a ‘productivity boom’ in 2001 CE. On a longer temporal scale, the transfer function reconstructions reveal a good correlation with the satellite, monitoring and observational trends, as well as a consistent, long-term decrease in sea ice linked to ocean-climate variability.
... This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. assemblages of microfossils, such as foraminifera (e.g., Aagaard-Sørensen et al., 2010;Seidenkrantz, 2013;Werner et al., 2011), ostracods (e.g., Cronin et al., 2010), diatoms (e.g., Koç et al., 1993;Krawczyk et al., 2017;Miettinen et al., 2015), and organic-walled dinoflagellate cysts (e.g., Bonnet et al., 2010;de Vernal, Eynaud, et al., 2005;de Vernal, Rochon, et al., 2013;de Vernal et al., 2001;Pieńkowski et al., 2017;Ribeiro et al., 2012). However, most of these proxies are indirectly related to sea ice (de Vernal, Gersonde, et al., 2013), and preservation can be a problem in Arctic and sub-Arctic settings (Armand & Leventer, 2010;Wollenburg et al., 2001Wollenburg et al., , 2004. ...
... Further, different age representation by sediments from these regions may limit the direct comparison between both regions. In Baffin Bay, it can be assumed that most surface samples from shelf areas represent modern sediments (Krawczyk et al., 2017), whereas sedimentation rates from Fram Strait and the East Greenland Shelf may differ to a large extent depending on the region (e.g., Andrews & Syvitski, 1994;Mienert et al., 1992;Nam et al., 1995;Stein, 2008). Hence, samples from these areas could represent different age intervals, which make a direct comparison difficult. ...
... Lowest concentrations are observed in the deeper central Baffin Bay where sea ice remains longest during summer ( Figure 4). This may be caused by the extensive sea ice cover, which hampers productivity and causes lower sedimentation rates than observed on the high-productivity West Greenland Shelf (e.g., Krawczyk et al., 2017, Simon et al., 2016, which may cause these sediments to be older than those on the shelf. Its distribution supports the association of HBI III (Z) to productivity along the MIZ as suggested by Belt et al. (2015) from the Barents Sea. ...
To evaluate the present sea ice changes in a longer-term perspective, the knowledge of sea ice variability on preindustrial and geological time scales is essential. For the interpretation of proxy reconstructions it is necessary to understand the recent signals of different sea ice proxies from various regions. We present 260 new sediment surface samples collected in the (sub-)Arctic Oceans that were analyzed for specific sea ice (IP25) and open-water phytoplankton biomarkers (brassicasterol, dinosterol, and highly branched isoprenoid [HBI] III). This new biomarker data set was combined with 615 previously published biomarker surface samples into a pan-Arctic database. The resulting pan-Arctic biomarker and sea ice index (PIP25) database shows a spatial distribution correlating well with the diverse modern sea ice concentrations. We find correlations of PBIP25, PDIP25, and PIIIIP25 with spring and autumn sea ice concentrations. Similar correlations with modern sea ice concentrations are observed in Baffin Bay. However, the correlations of the PIP25 indices with modern sea ice concentrations differ in Fram Strait from those of the (sub-)Arctic data set, which is likely caused by region-specific differences in sea ice variability, nutrient availability, and other environmental conditions. The extended (sea ice) biomarker database strengthens the validity of biomarker sea ice reconstructions in different Arctic regions and shows how different sea ice proxies combined may resolve specific seasonal sea ice conditions.
... In the North Atlantic regionour study areaa prime focus is the reconstruction of past climate and ocean variability (e.g., Andersen et al., 2004;Hald et al., 2004;Berner et al., 2011;Spielhagen et al., 2011;Müller et al., 2012;Miettinen et al., 2012;Pearce et al., 2013;Krawczyk et al., 2017;Falardeau et al., 2018). At higher latitudes, due to the rapid decline in the extent and thickness of Arctic sea ice and the resulting transition of the Arctic into a seasonally sea-ice free region https://doi.org/10.1016/j.marmicro.2020.101860 ...
... Fragilariopsis oceanica and Fragilariopsis cylindrus were described already in the 19th century (Cleve, 1873(Cleve, , 1883, and are often cited as sea-ice indicator species in the Northern Hemisphere (e.g., Jiang et al., 2001;Justwan and Koç, 2008;Sha et al., 2014;Miettinen et al., 2015;Krawczyk et al., 2017). However, the latter has been shown to have a far more complex response to sea ice than previously assumed (von Quillfeldt, 2004;Oksman et al., 2019). ...
... For this purpose, modern marine diatom training sets are highly useful. These data sets consist of both modern species assemblages analyzed from surface sediments and environmental data collected at the sea surface from the same locations, and they usually cover relatively large geographic areas (e.g., Caissie 2012;Sha et al., 2014;Ren et al. 2014;Miettinen et al., 2015;Krawczyk et al., 2017). Our study focuses on the North Atlantic, which hosts to date the largest and geographically most extensive training set in the Northern Hemisphere (the North Atlantic training set; Koc et al. 1993;Andersen et al., 2004;Miettinen et al., 2015), covering the main areas of the region between 42°N and 79°N. ...
A long-term perspective is essential for understanding environmental change. To be able to access the past, environmental archives such as marine and lake sediments that store information in the form of diverse proxy records are used. Whilst many analytical techniques exist to extract the information stored in these proxy records, the critical assessment and refinement of current methods in addition to developing new methods is crucial to improving our understanding. This study aims to improve our knowledge on diatom species used for reconstructing ocean surface conditions, especially temperature and sea ice variability over time. We define the distribution and the relationship to sea surface temperature (SST) and sea ice concentrations (SIC) of the species Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica using diatom training sets from the northern North Atlantic. We further assess the effect of separating these species compared to grouping them under F. oceanica, as has been done in the past. Our results suggest that while these three species share similarities such as the preference for stratified waters induced by sea ice or glacier meltwater, they also exhibit heterogeneous distributions across the northern North Atlantic, with individual optima for SST and SIC. This also affects quantitative reconstructions based on our data, resulting in lower SST and higher SIC estimates when the species are separated in the surface sediment and down-core diatom assemblages.
... Additionally, the increase in the amount Fig. 7 Comparison of different environmental proxy records around and from Greenland. a P B IP 25 record from the Melville Bugt (Core GeoB19927-3, this study), b P B IP 25 record from East Greenland Shelf (Core PS2641; [60]), c Fram Strait (Core MSM5/5-712-2; [88]), d dinocyst-based sea ice cover reconstruction (months of sea ice/year) from Disko Bay (Core MSM343300; [96]), e dinocyst-based sea ice cover reconstruction (months of sea ice/year) from Upernavik (Core AMD14-204C; [22]), f diatom-based SST reconstruction from West Greenland (Core MSM343300; [64]), g the Agassiz Melt Layer Record [37], h the δ 18 O record of the NGRIP ice core from Greenland [124] and i the summer insolation at 70° N [68]. Black solid triangles mark the AMS 14 C-datings arktos of pollen grains from Ellesmere Island could also indicate the maximum summer melting between ~ 9.8 and 8.5 ka BP [17,66]. ...
... Black solid triangles mark the AMS 14 C-datings arktos of pollen grains from Ellesmere Island could also indicate the maximum summer melting between ~ 9.8 and 8.5 ka BP [17,66]. This characteristic warming, reduction of spring/ summer sea ice and deglacial melting of the GIS have been widely reported in the areas such as Fram Strait and Disko Bay based on PIP 25 (Fig. 7c) and SST record (Fig. 7e) [64,88,132]. ...
... Thomas et al. [120] have shown a major increase in winter snowfall during mid Holocene caused by reduced sea ice and open surface water conditions in Baffin Bay and the Labrador Sea, consistent with the occurrence of polynya-type (winter) ice-edge variability. Slightly less pronounced, but warming trend is also observed from the Disko Bay area, based on diatomsbased SST data (Fig. 7f) [64]. Many marine and terrestrial records have also reported the GIS retreat from Disko Bay during this time interval [77,79,115], in agreement with our reconstructions in NE Baffin Bay. ...
Arctic sea ice is a critical component of the climate system, known to influence ocean circulation, earth’s albedo, and ocean–atmosphere heat and gas exchange. Current developments in the use of IP25 (a sea ice proxy with 25 carbon atoms only synthesized by Arctic sea ice diatoms) have proven it to be a suitable proxy for paleo-sea ice reconstructions over hundreds of thousands to even millions of years. In the NE Baffin Bay, off NW Greenland, Melville Bugt is a climate-sensitive region characterized by strong seasonal sea ice variability and strong melt-water discharge from the Greenland Ice Sheet (GIS). Here, we present a centennial-scale resolution Holocene sea ice record, based on IP25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III) using core GeoB19927-3 (73° 35.26′ N, 58° 05.66′ W). Seasonal to ice-edge conditions near the core site are documented for most of the Holocene period with some significant variability. In the lower-most part, a cold interval characterized by extensive sea ice cover and very low local productivity is succeeded by an interval (~ 9.4–8.5 ka BP) with reduced sea ice cover, enhanced GIS spring melting, and strong influence of the West Greenland Current (WGC). From ~ 8.5 until ~ 7.8 ka BP, a cooling event is recorded by ice algae and phytoplankton biomarkers. They indicate an extended sea ice cover, possibly related to the opening of Nares Strait, which may have led to an increased influx of Polar Water into NE-Baffin Bay. The interval between ~ 7.8 and ~ 3.0 ka BP is characterized by generally reduced sea ice cover with millennial-scale variability of the (late winter/early spring) ice-edge limit, increased open-water conditions (polynya type), and a dominant WGC carrying warm waters at least as far as the Melville Bugt area. During the last ~ 3.0 ka BP, our biomarker records do not reflect the late Holocene ‘Neoglacial cooling’ observed elsewhere in the Northern Hemisphere, possibly due to the persistent influence of the WGC and interactions with the adjacent fjords. Peaks in HBI III at about ~ 2.1 and ~ 1.3 ka BP, interpreted as persistent ice-edge situations, might correlate with the Roman Warm Period (RWP) and Medieval Climate Anomaly (MCA), respectively, in-phase with the North Atlantic Oscillation (NAO) mode. When integrated with marine and terrestrial records from other circum-Baffin Bay areas (Disko Bay, the Canadian Arctic, the Labrador Sea), the Melville Bugt biomarker records point to close ties with high Arctic and Northern Hemispheric climate conditions, driven by solar and oceanic circulation forcings.
... Although numerous studies have reconstructed Holocene paleoceanographic changes around Greenland (e.g. Andrews et al., 2016;Jennings, Knudsen, et al., 2002;Jennings & Weiner, 1996;Kolling et al., 2017Kolling et al., , 2018Krawczyk et al., 2010Krawczyk et al., , 2013Krawczyk et al., , 2016Moros et al., 2016Moros et al., , 2006Perner, Moros, Snowball, et al., 2013;Ribeiro et al., 2012) marine and glaciological proxies have rarely been combined into one study to directly investigate ice-ocean interaction in Greenlandic fjords. These studies demonstrated that the connection between ocean and glacier is a highly complex system and varies largely between different fjords in Greenland Andrews et al., 2014;Jennings, Knudsen, et al., 2002;. ...
... As this is controlled by the incursion of the WGC it represents a proxy for remote oceanographic changes (e.g. Krawczyk et al., 2016;. Figure 6e shows the percentage of WWIs superimposed on the PCA scores on Axis 1. ...
... The foraminifera data show a general decrease in relative temperatures from the onset of the record, at 100 BC, until the minimum values at around AD 1690 (Figure 6e), and suggest a progressive weakening of the IC component in the WGC throughout this interval. This trend is consistent with previous studies from the Disko Bugt area Krawczyk et al., 2016; and is part of a wider atmospheric cooling trend since the Holocene Thermal Maximum at around 6500 yr BP Kobashi et al., 2011;Krawczyk et al., 2016;McGregor et al., 2015;Perner et al., 2012;Vinther et al., 2010). ...
In recent years, the Greenland Ice Sheet has experienced persistent mass loss, contributing significantly to global sea level rise. About a third of this mass loss is attributed to dynamical discharge via marine terminating glaciers. In order to understand the current processes better and to put these changes into a longer-term perspective it is important to study past environmental conditions and the glacier response to them.
In this thesis, marine sediment cores from five different fjords in West- and South-East Greenland were investigated to determine the dynamics of marine terminating glaciers in response to ocean temperature variability. The annual deposition of iceberg rafted debris was used to gain understanding of glaciological change, such as iceberg productivity, margin changes and margin type (calving or floating glacier). Ocean temperature was reconstructed using either benthic foraminifera assemblages or alkenone based paleo-thermometry. In West Greenland, the studies reconstructing ocean and glacier change of the last 2000 years in Disko Bugt, and the last 100 years in Upernavik Isfjord, reveal a link between bottom water temperature within the West Greenland Current and glacier stability of Jakobshavn Isbræ and Upernavik Glacier, respectively. Moreover, a lack of IRD sedimentation in Disko Bugt between
1500 to 1850 CE indicates the development of a floating glacier tongue at Jakobshavn Isbræ during the Little Ice Age.
In South-East Greenland, the study reconstructing the last 2000 years of ocean and glacier change in Sermilik Fjord shows relatively minor changes in IRD sedimentation from Helheim Glacier, although SSTs warmed significantly during the Little Ice Age. Besides persistent sea-ice, this was again linked to the existence of a floating glacier tongue. At the onset of the 20th century SSTs raised and Helheim and Kangerlugssuaq glaciers responded with ice tongue collapses. In contrast to that, the study of Thrym Glacier by Nørre Skjoldungesund shows limited response to similar changes in SSTs, which was mostly linked to its glacier configuration limiting ice-ocean interaction.
Furthermore, this thesis also discusses the applicability of established proxies, such as alkenone paleothermometry, foraminifera assemblage and IRD, in complex fjord systems of Greenland. A focus on observations of the processes behind of these proxies in the present day environment may help to reduce uncertainties in the interpretation of the longer-term data set.
... Green dots and asterisks next to station names indicate sediment samples, which are considered "modern", while red dots correspond to other samples, which were either not analyzed for their radiometric content or are regarded as "submodern" (cf. Krawczyk et al., 2017). The sea-ice cover, with data from the National Snow and Ice Data Center (NSIDC; http://nsidc.org/data/bist/), is represented as follows: less than 3 months per year, 3 to 6 months per year and more than 6 months per year. ...
... The sediment samples analyzed here have been subjected to 210 Pb and 137 Cs measurements, which allow us to make a distinction between "modern" and "sub-modern" and to better evaluate the relationships that could be established with oceanographic data compiled from instrumental observations and remote sensing (cf. Krawczyk et al., 2017). ...
... 72°N) (Fig. 1). The samples were collected during a three-leg cruise of the R/V Paamiut in June-July 2014 (Krawczyk et al., 2017). ...
We present a new version of the standardized Northern Hemisphere “modern” dinoflagellate cyst (“dinocyst”) database, which includes abundances of 71 taxa at 1968 sites across the Northern Hemisphere, cross-referenced with 17 environmental parameters extracted mostly from the 2013 World Ocean Atlas. Several taxa with tropical to warm temperate affinities were added to the previous database version. Dinocyst concentrations in the surface sediments reach 10⁶ cysts g⁻¹, with maximum values along the continental margins and minimum values offshore in distal open ocean settings. Assemblages are characterized by the co-occurrence of phototrophic (n = 41) and heterotrophic taxa (n = 30), with maximum proportions of heterotrophic taxa in high productivity regions, notably at the sea-ice edge and in upwelling regions. The main pattern of assemblage distributions includes north–south and nearshore–offshore gradients, with maximum diversity of species along the continental margins and towards the south, in warm temperate and tropical areas. Canonical correspondence analyses performed on heterotrophic and phototrophic taxa independently yield consistent results, hence suggesting similar, but not identical, ecological affinities for both taxonomic groups. For both groups, sea-surface temperature and sea-ice are the most determining parameters, but the phototrophic taxa seem more sensitive to onshore–offshore gradients marked by salinity changes. Productivity-related parameters also determine dinocyst distribution, especially primary productivity in the fall and winter, with a stronger relationship for the combined dataset of phototrophic and heterotrophic taxa.
... These species have previously been inferred to all simply represent the presence of sea ice and so, coupled with their resemblances, are grouped together under one species -as F. oceanica in the North Atlantic training set used in a large number of diatom-inferred sea surface temperature and sea ice reconstructions in the region (e.g. Miettinen et al. 2015;Krawczyk et al. 2016;Oksman et al. 2017a;2017b). Further, Fossula arctica and Fragilariopsis reginae-jahniae were described as separate species relatively lately (Hasle et al. 1996;Witkowski et al. 2000 -respectively), which is also a contributing factor as to why they are not included in the dataset as a significant part of the Miettinen et al. (2015) training set was collected and analysed in the 1990s. ...
... Warming in the Nordic Seas and decreased sea ice is attributed to higher insolation and stronger fluxes of North Atlantic Drift in the north-eastern Atlantic (Andersen et al. 2004a (Alley et al. 1997;Kobashi et al. 2007;Hoffman et al. 2012). April sea-ice concentrations in Baffin Bay were depressed during the Holocene Climate Optimum (~7.5-3.5 Ka) coinciding with minimum extents of the Greenland Ice Sheet Krawczyk et al. 2016). A cooler period followed with increased sea ice in both Baffin Bay and the Greenland Sea Oksman et al. 2017b). ...
... An antiphase climatic relationship developed to the west and east of Greenland during the Medieval Climate Anomaly (~1.2-0.7 Ka), when sea ice to the east of Greenland decreased coincidentally to increased sea ice west of Greenland and In the Labrador Sea (Seidenkrantz et al. 2008;Mann et al. 2009;Miettinen et al. 2015;. the increase in sea ice concentration, significantly cooler waters off Disko Bay and advance of the Jakobshavn Isbrae glacier, indicate a decreased influence of Atlantic Water (Seidenkrantz et al. 2008;Krawczyk et al. 2016). An inverse antiphase climate relationship developed to the west and east of Greenland during the Little Ice Age (~0.7-0.15 ...
... These species have previously been inferred to all simply represent the presence of sea ice and so, coupled with their resemblances, are grouped together under one species -as F. oceanica in the North Atlantic training set used in a large number of diatom-inferred sea surface temperature and sea ice reconstructions in the region (e.g. Miettinen et al. 2015;Krawczyk et al. 2016;Oksman et al. 2017a;2017b). Further, Fossula arctica and Fragilariopsis reginae-jahniae were described as separate species relatively lately (Hasle et al. 1996;Witkowski et al. 2000 -respectively), which is also a contributing factor as to why they are not included in the dataset as a significant part of the Miettinen et al. (2015) training set was collected and analysed in the 1990s. ...
... Warming in the Nordic Seas and decreased sea ice is attributed to higher insolation and stronger fluxes of North Atlantic Drift in the north-eastern Atlantic (Andersen et al. 2004a (Alley et al. 1997;Kobashi et al. 2007;Hoffman et al. 2012). April sea-ice concentrations in Baffin Bay were depressed during the Holocene Climate Optimum (~7.5-3.5 Ka) coinciding with minimum extents of the Greenland Ice Sheet Krawczyk et al. 2016). A cooler period followed with increased sea ice in both Baffin Bay and the Greenland Sea Oksman et al. 2017b). ...
... An antiphase climatic relationship developed to the west and east of Greenland during the Medieval Climate Anomaly (~1.2-0.7 Ka), when sea ice to the east of Greenland decreased coincidentally to increased sea ice west of Greenland and In the Labrador Sea (Seidenkrantz et al. 2008;Mann et al. 2009;Miettinen et al. 2015;. the increase in sea ice concentration, significantly cooler waters off Disko Bay and advance of the Jakobshavn Isbrae glacier, indicate a decreased influence of Atlantic Water (Seidenkrantz et al. 2008;Krawczyk et al. 2016). An inverse antiphase climate relationship developed to the west and east of Greenland during the Little Ice Age (~0.7-0.15 ...
Significant changes in sea-ice variability have occurred in the northern North Atlantic since the last deglaciation, resulting in global scale shifts in climate. By inferring the dynamic changes of palaeo sea-ice to past changes in climate, it is possible to predict future changes in response to anthropogenic climate change. Diatoms allow for detailed reconstructions of palaeoceanographic and sea-ice conditions, both qualitatively, using information of species ecologies and quantitatively, via a transfer function based upon diatom species optima and tolerances of the variable to be reconstructed. Three diatom species comprising a large portion of the training set are proxies for the presence of sea ice: Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica, have currently been grouped into one species – F. oceanica – in the large diatom training set of the northern North Atlantic region. The clustering of the species may result in an imprecise reconstruction of sea ice that does not take into account all the available ecological information.
The proportions of the three species were recounted from the original surface sediment slides alongside the additional chrysophyte cyst Archaeomonas sp. and statistically analysed using Canoco and the R software package eHOF. A core from Kangerlussuaq Trough comprising the Late Holocene (~690–1498 Common Era) was also recounted and analysed using C2.
The separated diatom species and chrysophyte cyst Archaeomonas sp. exhibited different relationships to both sea-ice concentration (aSIC) and sea surface temperature (aSST). The separated F. oceanica is a ‘cold-mixed’ water species occurring at cold aSST and both low and high aSIC. High abundances occur in the marginal ice zone (MIZ) where surficial meltwater is high during the spring bloom, with additional inputs from glacial meltwaters nearshore. F. reginae-jahniae is a sea-ice associated species related to cold aSST and high aSIC. High abundances occur in the low salinity Arctic Water dominated MIZ which experiences significant aSIC. F. arctica is a sea-ice associated species related to cold aSST and high aSIC. High abundances occur in the low salinity Arctic Water dominated MIZ which experiences high aSIC, particularly in polynya conditions. F. arctica can be considered a characteristic polynya species at high abundances. Archaeomonas sp. is a ‘cold-mixed’ water species related to both cold and relatively warm aSST and low and high aSIC. High abundances occur in both relatively warm ice-free Atlantic Water and also in cold high aSIC Arctic Water conditions rendering it a more complex indicator for aSST or aSIC proxy. However, the aversion to MIZ conditions indicates that Archaeomonas sp. is associated with a relatively saline unstratified water column. This is the first time that the distribution and ecology of Archaeomonas sp. has been presented. As such, the ecology described here can be used in future studies. The separation of the three diatom species is crucial for the ecological interpretation of downcore assemblage changes. It is also crucial for the application of transfer functions in order to have greater precision in reconstructing aSIC and assessing the influence of Arctic Water or Atlantic Water, even at low abundances.
... Telford and Birks (2011),22 Adey et al. (2013),23 Halfar et al. (2013),24 Juggins (2013),25 Rosell-Melé andPrahl (2013),26 Jonkers and Kučera (2015),27 Featherstone et al. (2017),28 Freitas et al. (2017),29 Jonkers and Kučera (2017),30 Krawczyk et al. (2017),31 Li et al. (2017),32 Moore et al. (2017),33 Rebotim et al. (2017),34 Reynolds et al. (2017), 35 ...
... ;Perner et al., 2011) a relatively strong and warm WGC-induced melting of marine-based outlet glaciers causing surface freshening and warming(Andresen et al., 2011;Krawczyk et al., 2013;Ouellet-Bernier et al., 2014;Sha et al., 2014;Moros et al., 2016;Krawczyk et al., 2017;Allan et al., 2018;Kolling et al., 2018; Figure 6). From~800 CE the WGC cooled Figure 6b) in parallel to atmospheric cooling and favored a readvance of the ice sheet margin and major outlet glaciers extended again into the fjords. ...
... From~800 CE the WGC cooled Figure 6b) in parallel to atmospheric cooling and favored a readvance of the ice sheet margin and major outlet glaciers extended again into the fjords. This led to an overall surface cooling and increased sea ice(Krawczyk et al., 2013;Ouellet-Bernier et al., 2014;Sha et al., 2014;Moros et al., 2016;Krawczyk et al., 2017;Allan et al., 2018;Kolling et al., 2018; Figures 6c-6e). However, around 1300 CE, despite the clear cooling in the WGC(Figure 6b;Perner et al., 2011), the surface records at Disco Bugt show diverging trends in the temperatures and sea ice cover(Krawczyk et al., 2013;Moros et al., 2016;Ribeiro et al., 2012;Seidenkrantz et al., 2008). ...
The climate of the last two millennia was characterized by decadal to multicentennial variations, which were recorded in terrestrial records and had important societal impacts. The cause of these climatic events is still under debate, but changes in the North Atlantic circulation have often been proposed to play an important role. In this review we compile available high‐resolution paleoceanographic data sets from the northern North Atlantic and Nordic Seas. The records are grouped into regions related to modern ocean conditions, and their variability is discussed. We additionally discuss our current knowledge from modeling studies, with a specific focus on the dynamical changes that are not well inferred from the proxy records. An illustration is provided through the analysis of two climate model ensembles and an individual simulation of the last millennium. This review thereby provides an up‐to‐date paleoperspective on the North Atlantic multidecadal to multicentennial ocean variability across the last two millennia.
... The demand for paleoclimate records is especially crucial in the Arctic region because of the amplified polar warming (e.g., Pithan and Mauritsen, 2014) and associated strong relationship to surface water hydrography and thus are excellent indicators of ocean surface conditions and variability of water masses. Diatoms are diverse and abundant at high latitudes and today, a large number of studies exist from various parts of the northern North Atlantic region: the Nordic Seas (Koç Karpuz and Schrader, 1990;Koç and Jansen, 1994;Miettinen et al., 2012), around Iceland (Jiang et al., 2001(Jiang et al., , 2002(Jiang et al., , 2005(Jiang et al., , 2015Witak et al., 2005;Miettinen et al., 2011;Xiao et al., 2017), northern Svalbard Oksman et al., 2017a), around Greenland (Andersen et al., 2004a(Andersen et al., , 2004bBerner et al., 2008Berner et al., , 2011Justwan and Koç, 2009;Ren et al., 2009;Miettinen et al., 2015), Baffin Bay (Williams, 1986(Williams, , 1990(Williams, , 1993Krawczyk et al., 2010Krawczyk et al., , 2014Krawczyk et al., , 2016Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Oksman et al., 2017b) and the Labrador Sea (De Sève, 1999;Weckström et al., 2013;Pearce et al., 2014a). Some diatom species are associated with sea ice and this link has been used to reconstruct past sea ice variability Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Miettinen et al., 2015;Krawczyk et al., 2016). ...
... Diatoms are diverse and abundant at high latitudes and today, a large number of studies exist from various parts of the northern North Atlantic region: the Nordic Seas (Koç Karpuz and Schrader, 1990;Koç and Jansen, 1994;Miettinen et al., 2012), around Iceland (Jiang et al., 2001(Jiang et al., , 2002(Jiang et al., , 2005(Jiang et al., , 2015Witak et al., 2005;Miettinen et al., 2011;Xiao et al., 2017), northern Svalbard Oksman et al., 2017a), around Greenland (Andersen et al., 2004a(Andersen et al., , 2004bBerner et al., 2008Berner et al., , 2011Justwan and Koç, 2009;Ren et al., 2009;Miettinen et al., 2015), Baffin Bay (Williams, 1986(Williams, , 1990(Williams, , 1993Krawczyk et al., 2010Krawczyk et al., , 2014Krawczyk et al., , 2016Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Oksman et al., 2017b) and the Labrador Sea (De Sève, 1999;Weckström et al., 2013;Pearce et al., 2014a). Some diatom species are associated with sea ice and this link has been used to reconstruct past sea ice variability Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Miettinen et al., 2015;Krawczyk et al., 2016). The earliest diatombased reconstructions were conducted using qualitative diatom assemblage data (e.g., Williams, 1993;Witak et al., 2005;Krawczyk et al., 2010), but in the past few decades, the use (as well as the number) of calibration datasets, consisting of surface sediment diatom assemblages and associated measured environmental data for quantitative reconstructions of SST and sea ice, has increased remarkably (Koç Karpuz and Schrader, 1990;Jiang et al., 2001Jiang et al., , 2005Andersen et al., 2004a;Sha et al., 2014;Miettinen et al., 2015;Krawczyk et al., 2016). ...
... Some diatom species are associated with sea ice and this link has been used to reconstruct past sea ice variability Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Miettinen et al., 2015;Krawczyk et al., 2016). The earliest diatombased reconstructions were conducted using qualitative diatom assemblage data (e.g., Williams, 1993;Witak et al., 2005;Krawczyk et al., 2010), but in the past few decades, the use (as well as the number) of calibration datasets, consisting of surface sediment diatom assemblages and associated measured environmental data for quantitative reconstructions of SST and sea ice, has increased remarkably (Koç Karpuz and Schrader, 1990;Jiang et al., 2001Jiang et al., , 2005Andersen et al., 2004a;Sha et al., 2014;Miettinen et al., 2015;Krawczyk et al., 2016). ...
Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiatus, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.
... release (Schumann et al., 2012). Previous studies of the Holocene in Disko Bugt, Egedesminde Dyb and Vaigat Strait have focused on palaeo-oceanographic variability (Krawczyk et al., 2013(Krawczyk et al., , 2016Moros et al., 2016;Ouellet-Bernier et al., 2014;Perner et al., 2011;Ribeiro et al., 2012;Sha et al., 2014;Sheldon et al., 2015) and in some cases also glaciological changes (Andresen et al., 2011;Lloyd et al., 2006aLloyd et al., , 2011. The glaciological changes at Jakobshavn Isbrae have also been reconstructed from a land-based perspective using threshold lakes as well as from mapping and dating glacial landforms (Briner et al., 2010;Corbett et al., 2011;Kelley et al., 2013;Weidick and Bennike, 2007;Young et al., 2011). ...
... As this is controlled by the incursion of the WGC it represents a proxy for remote oceanographic changes (e.g. Krawczyk et al., 2016;Lloyd, 2006a;Perner et al., 2011). Figure 6e shows the percentage of WWIs superimposed on the PCA scores on Axis 1. ...
... The foraminifera data show a general decrease in relative temperatures from the onset of the record, at 100 BC, until the minimum values at around AD 1690 (Figure 6e), and suggest a progressive weakening of the IC component in the WGC throughout this interval. This trend is consistent with previous studies from the Disko Bugt area (Andresen et al., 2011;Krawczyk et al., 2016;Lloyd, 2006a;Perner et al., 2011) and is part of a wider atmospheric cooling trend since the Holocene Thermal Maximum at around 6500 yr BP (Dahl-Jensen et al., 1998;Kobashi et al., 2011;Krawczyk et al., 2016;Lloyd et al., 2007;McGregor et al., 2015;Perner et al., 2012;Vinther et al., 2010). ...
The Greenland Ice Sheet has experienced significant mass loss in recent years. A substantial component of this is attributable to the retreat of marine-terminating outlet glaciers, which lose mass through increases in calving, submarine melting and terrestrial meltwater discharge. In terms of iceberg production, Jakobshavn Isbræ is the largest marine-terminating glacier in Greenland, yet relatively little is known about its history before the first glacier margin observations in 1851. Two marine sediment cores obtained 15 and 19 km northwest from the mouth of Jakobshavn Isfjord were analysed to reconstruct the past behaviour of Jakobshavn Isbræ and to investigate the response of the glacier system to ocean forcing. These records provide long-term (~2000) context for assessing the significance of the rapid changes in glacier stability over the last century. The X-ray imagery and high-resolution grain size analysis from both cores reveal distinct multi-centennial-scale changes in the flux of iceberg-rafted debris (IRD) from Jakobshavn Isbræ. Foraminiferal analysis shows that variability in the relatively warm West Greenland Current (WGC) may have been an important driver of calving activity at Jakobshavn Isbræ. We find that iceberg rafting and WGC inflow were relatively high from onset of the record, at 60 BC, until AD 1100. Subsequently, the inflow of the WGC into Disko Bugt decreased. This was accompanied by a dramatic reduction in IRD from AD 1500 to 1850, which is attributed to the establishment of a floating ice tongue. We also show that ocean warming in the 20th century is part of a longer-term warming trend in the WGC which started at around AD 1700. Finally, these new records underline the complexity of glaciomarine sediments; IRD variability was driven by the inflow of the WGC but was also modulated by a complex interplay of air temperature, sea-ice coverage and ice margin proximity.
... We use the PIP 25 index [137] and b atmospheric temperatures derived from the GISP2 ice core (°C; [60]). Sea ice related proxies: c IP 25 concentrations (µg/TOC; this study) d sea ice index P D IP 25 (this study), e reconstructed April sea ice concentrations (SIC) from diatoms (%; [61]), f abundances of sea-ice-associated diatoms (%; [60]) and g principal component analysis based on dinoflagellates correlating with sea ice [105]. Surface water proxies: Concentrations of phytoplankton sterols h brassicasterol and i dinosterol and j terrigenous sterol concentrations (all in µg/ TOC; this study), k alkenone C 37:4 (%, [80]) and l alkenone index U K 37 [80]. ...
... However, surface water proxies, i.e., diatoms and dinocysts, reveal contradictory surface water conditions. Whilst diatom assemblages indicate a gradual warming of surface waters around 1.7 kyr BP and only a minor increase in sea ice conditions (Fig. 4e, f; [60,61]) dinocyst reconstructions point towards a gradual cooling with reduced sea ice conditions (Fig. 4g) and relatively high phytoplankton productivity [105]. However, recent dinocyst reconstructions indicate a major change in surface water conditions at ~ 1.5 kyr BP towards cooler conditions and prolonged sea ice cover (up to 8 month/year; [2]). ...
... Our new biomarker record supports a slight increase in sea ice conditions at the core site from 1.7 to 1.2 kyr BP, indicated by a minor increase in IP 25 concentrations and PIP 25 values (Fig. 4c, d), similar to findings from diatom assemblages (Fig. 4e, f; [60,61]). Increased sedimentation rates and higher terrigenous sterol concentrations are observed during this interval (Figs. ...
Past sea ice conditions and open water phytoplankton production were reconstructed from a sediment core taken in Disko Bugt, West Greenland, using the sea ice biomarker IP25 and other specific phytoplankton biomarker (i.e., brassicasterol, dinosterol, HBI III) records. Our biomarker record indicates that Disko Bugt experienced a gradual expansion of seasonal sea ice during the last 2.2 kyr. Maximum sea ice extent was reached during the Little Ice Age around 0.2 kyr BP. Superimposed on this longer term trend, we find short-term oscillations in open water primary production and terrigenous input, which may be related to the Atlantic Multidecadal Oscillation and solar activity changes as potential climatic trigger mechanisms. A direct sample-to-sample multiproxy comparison of our new biomarker record with microfossil (i.e., benthic foraminifera, dinocysts, and diatoms) and other geochemical records (i.e., alkenone biomarkers) indicates that different proxies are influenced by the complex environmental system with pronounced seasonal changes and strong oceanographic gradients, e.g., freshwater inflow from the Greenland Ice Sheet. Differences in sea ice reconstructions may indicate that the IP25 record reflects only the relatively short sea ice season (spring), whereas other microfossil reconstructions may reflect a longer (spring–autumn) interval.
... During the recent decades, the diatom-inferred quantitative reconstructions of SST and sea ice have increased remarkably (e.g. Koç Karpuz and Schrader, 1990;Jiang et al., 2001Jiang et al., , 2005Andersen et al., 2004a,b;Justwan and Koç, 2008;Miller and Chapman, 2013;Sha et al., 2014;Miettinen et al., 2015;Krawczyk et al., 2016;Oksman et al., 2017a;. ...
... Recently diatom-based quantitative SST reconstructions from the supolar North Atlantic and Arctic have been generated using several data sets consisting of modern diatom assemblages of the surface sediment samples and modern SST data from the North Atlantic (Koç Karpuz and Schrader, 1990;Andersen et al., 2004a,b;Jiang et al., 2005;Miettinen et al., 2015;Krawczyk et al., 2016) and the transfer function methods, such as weighted averaging partial least square (WA-PLS; ter Braak and Juggins, 1993), Imbrie-Kipp (IKM; Imbrie and Kipp, 1971), maximum likelihood (ML), the modern analogue technique (MAT; Hutson, 1980), and the artificial neural network approach (ANN; Malmgren and Nordlund, 1997). The largest and most commonly used diatom SST calibration data set for the North Atlantic/Arctic consists of 183 surface sediment samples with 52 diatom species the North-Atlantic Ocean, Nordic Seas, Svalbard, the Labrador Sea and Baffin Bay ( Fig. 1) (Miettinen et al., 2015). ...
... As some diatom species are associated to sea ice, this link has been used to reconstruct quantitatively past sea ice variability since the 2000s (Justwan and Koç, 2008;Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Miettinen et al., 2015;Krawczyk et al., 2016). For example, a sea-ice calibration data set of Miettinen et al. (2015) for quantitative reconstruction of April sea-ice concentrations comprises of 89 surface sediment samples from the northern North Atlantic, the Nordic Seas, Baffin Bay and northwestern Labrador Sea (Fig. 3). ...
Paleoclimate research define the baselines for the natural climate change and is imperative to help us to set the recent observed changes in the long-term natural climate context. Fossil marine diatoms have proved to be an excellent tools for the paleoclimatic reconstructions, e.g. for the reconstruction of sea surface temperature (SST) and sea ice. A number of studies have been conducted from the northern high latitude region using diatoms as potential proxy. Nevertheless, these studies are scattered and thus there is a need to expand diatom research in the Arctic regions. Due to the possibilities offered by an emerging trend of diatom-based research, it is important to identify both the research themes and geographical areas of highest importance in order to obtain the best possible scientific outcome in the research. Here we review some of up-to-date diatom-based reconstruction methods applicable for paleoceanographic research for the northern North Atlantic and Arctic regions, and discuss the knowledge gaps in the Arctic research, which potentially can be solved by diatom applications. The modern diatom research has progressively concentrated on quantitative reconstruction based on diatoms and statistical transfer function providing the most useful data for the climate research. However, also qualitative reconstruction methods are still needed; the recent studies show that although the quantitative reconstruction method for SST appears to be statistically robust, there are uncertainties in quantitative reconstructions for sea ice, and thus it is still recommended to use the Marginal Ice Zone diatom taxa as a qualitative reconstruction method for the Arctic sea ice. Diatom applications offer highly potential tools for filling the knowledge gaps in the Arctic research.
... Several used benthic foraminifer assemblages to infer bottom water properties and their relationship with the dynamics of the WGC (Andresen et al., 2011;Lloyd, 2006;Lloyd et al., 2005Lloyd et al., , 2007Moros et al., 2016;Perner, Moros, Jennings, et al., 2013). A few other studies referred to diatom assemblages and led to qualitative or quantitative interpretation of the paleo-sea ice cover (Krawczyk et al., 2010(Krawczyk et al., , 2013(Krawczyk et al., , 2017Moros et al., 2006;Sha et al., 2014). Alkenone biomarkers also provided information on surface waters and were interpreted in terms of SST and/or meltwater input (Moros et al., 2016). ...
... This climate optimum was followed by the Neoglacial cooling, between 3.5 to 2 ka BP, marked by cold subsurface waters (Andresen et al., 2011;Lloyd et al., 2007;Moros et al., 2016;Perner, Moros, Jennings, et al., 2013;Perner et al., 2011) and a reduction in meltwater discharge (Andresen et al., 2011;Moros et al., 2016). Then, relatively warm conditions set in from 2 to 1.5 ka BP, followed by another regional cooling (Andresen et al., 2011;Krawczyk et al., 2010Krawczyk et al., , 2013Krawczyk et al., , 2017Lloyd et al., 2007;Moros et al., 2006Moros et al., , 2016Ouellet-Bernier et al., 2014;Perner, Moros, Jennings, et al., 2013;Perner et al., 2011;Ribeiro et al., 2012;Seidenkrantz et al., 2008;Sha et al., 2014). ...
... The major oceanic change at~1.5 ka BP in the Disko Bugt has been reported in other studies (Andresen et al., 2011;Krawczyk et al., 2010Krawczyk et al., , 2013Krawczyk et al., , 2017Lloyd et al., 2007;Moros et al., 2006Moros et al., , 2016Ouellet-Bernier et al., 2014;Perner, Moros, Jennings, et al., 2013;Perner et al., 2011;Ribeiro et al., 2012;Seidenkrantz et al., 2008;Sha et al., 2014) and seems to correspond to a general cooling phase. However, the high-frequency variability in sea surface conditions we have reconstructed for the Disko Bugt area has not been previously reported. ...
Palynological analyses of sediment core MSM343310 from Disko Bugt (68°38’861 N, 53°49’493 W) document decadal- to centennial-scale variability of sea-surface conditions during the last ca. 3600 years. High dinocyst fluxes (>104 cysts/cm2year1) indicate a very high productivity. Dinocyst assemblages dominated by Islandinium minutum, Brigantedinium spp., Islandinium? cezare and the cyst of Pentapharsodinium dalei suggest low surface salinity and marked shifts of summer sea-surface temperature. The application of the modern analogue technique to dinocyst assemblages, using an updated reference dataset with new sites from the West Greenland margin, led to reconstruct decadal-centennial scale variations in sea-surface salinity and temperature, in phase with the δ18O variations in the Camp Century ice core. At ca. 1.5 ka BP, the seasonal sea-ice cover records an important regime change, from winter-only sea ice to more unstable conditions marked by successive cooling pulses with sea-ice cover of up to 8 months/year. The data suggest a close relationship between hydrographic conditions and regional climate over Greenland. Our record shows variations with a mean 200-years periodicity until ~2 ka BP, which supports the hypothesis of climate variations driven by solar variability. After 1.5 ka BP, our data show a variability characterized by a 60-70 year periodicity, which suggests linkages with the Atlantic Multidecadal Oscillation and southwestward migration of the atmospheric polar front. The most recent part of the record, from ~1900 CE to 2007 CE, is characterized by assemblages reflecting warmer surface conditions and reduced sea-ice cover.
... Krawczyk et al. (2013), based on the recorded diatoms from the cores of Disko Bay, Greenland suggest that F. cylindrus to be grouped as sea ice associated species, with strong association with meltwater, flowing from sea ice or ice sheets. In the regional diatom dataset based on surface sediment from West Greenland shelf, Krawczyk et al. (2016) Comparison and remarks: Fragilariopsis oceanica has an apical axis length ranging from 10-41 µm, transapical axis length ranging around 6 µm and 12-15 striae per 10 µm. The specimens from our core show apical axis ranging between 12.2 to 22.9 µm and length of transapical axis ranging from 5 to 5.7 µm (Plate 1, Fig. 5-6). ...
... Map of the major sediment core locations taken into account in this study.Krawczyk et al. (2010;2013) categorized B. bathyomphala resting spore as sea ice assemblage/species based on studies from Disko Bay, Greenland.Sha et al. (2014Sha et al. ( , 2017 categorized B. bathyomphala as a sea ice species based on Western Greenland marine sediment core records. However,Krawczyk et al (2016), categorized B. Bathyomphala as "open marine" diatom from various assembled surface sediment samples and sediment cores from West Greenland shelf.Oksman et al. (2019), based on the large North Atlantic dataset opined that B. bathyomphala, had a generally higher SST optimum (4.6°C), can occur at both high and low sea ice concentrations and it is better suited to be used as a cold-water indicator, rather than sea ice. This inference is shown in diatom abundances and diatom-based reconstructions byGurvayoorappan et al. (2020),Oksman et al. (2017a, b),Orme et al. (2021) andOksman et al (2022) in the sediment cores from Krossfjorden Svalbard, Isvika Bay Svalbard, Disko Bugt in Western Greenland, Trinity Bay in Newfoundland and fjords in Western Greenland.Fragilariopsis cylindrus (Grunow ex Cleve) Kreiger in Helmcke & KreigerBasionym: Fragilaria cylindrus Grunow ex Cleve Synonym: Nitzschia cylindrus (Grunow ex Cleve) Hasle References:Hasle and Syvertsen (1996), pp. ...
Diatoms-the unicellular, eukaryotic, photosynthetic phytoplankton belonging to Class Bacillariophyceae are an excellent tool to understand past ocean surface conditions, especially in high latitude regions. Along with sea surface temperature and sea ice, which they are primarily sensitive to, diatom assemblages could potentially be used to record runoff from melting glaciers and atmospheric teleconnections such as North Atlantic Oscillations (NAO) in Arctic fjords. However, understanding the ecology and geographical distribution of diatoms is extremely important before they can be used for palaeoceanographic reconstructions. In this study, four significant Arctic diatoms namely Bacterosira bathyomphala, Fragilariopsis cylindrus, Fragilaripsis oceanica and Thalassiosira antarctica var. borealis resting spores (R.S.) have been reviewed to understand their current status in their use for palaeoceanographic reconstructions. These four diatoms have been selected as they represent a typical Arctic environment. Numerous studies in the past thirty years had classified these diatoms into different assemblage groups, indicating specific ocean surface conditions. Here, we review the previous studies and to present the up-to-date classification of these species. We also compared the change in abundance of these four species through mid to late Holocene and modern period to their respective sea surface temperature and sea ice reconstructions, to show the robustness of their usage in palaeoceanographic reconstructions. The findings of this study will help to understand the up-to-date ecological characteristics of Arctic diatoms used in palaeoceanographic as well as palaeoecological reconstructions and the gap areas in diatom research such as a requirement for pan Arctic Sea ice diatom dataset.
... Biogenic proxies that commonly underlie marine-based climate and ecosystem reconstructions are mainly produced by planktic, benthic and sympagic primary producers and heterotrophic protists. These include planktic and benthic foraminifera (Jorissen et al., 2007;Kucera, 2007;Aagaard-Sørensen et al., 2010), coccolithophores (Gard, 1989;Giraudeau and Beaufort, 2007), diatoms (Miettinen et al., 2015;Krawczyk et al., 2017;Oksman et al., 2017), radiolarians (Lazarus, 2005;Matul and Mohan, 2017) and dinoflagellate cysts (Dale, 1983;de Vernal and Marret, 2007;Ellegaard et al., 2017). ...
... The resulting inference model is subsequently applied to down-core fossil assemblages, providing quantitative reconstructions of environmental parameters back in time (e.g. Koç et al., 1993;de Vernal et al., 2001;Ledu et al., 2010;Miettinen et al., 2015;Sha et al., 2016;Krawczyk et al., 2017;Falardeau et al., 2018) (Fig. 2). A rapid rise of sea-ice reconstructions based on HBI biomarkers has followed the introduction of IP 25 (Belt et al., 2007), to date the most well-known and most widely used of the HBIs (e.g. ...
Frozen components on land and in the ocean (sea ice, ice sheets, glaciers and permafrost) form the cryosphere, which, together with the ocean, moderates the physical and chemical habitat for life in the Arctic and beyond. Changes in these components, as a response to rapidly warming climate in the Artic, are intensely expressed in the coastal zone. These areas receive increased terrestrial runoff while subject to a changing sea-ice and ocean environment. Proxies derived from marine sediment archives provide long-term data that extend beyond instrumental measurements. They are therefore fundamental in disentangling human-driven versus natural processes, changes and responses. This paper (1) provides an overview of current Arctic cryosphere change, (2) reviews state-of-the-art palaeoecological approaches, (3) identifies methodological and knowledge gaps, and (4) discusses the strengths and future potential of palaeoecology and palaeoceanography to respond to societally-relevant coastal marine ecosystem challenges. We utilize responses to an open survey conducted by the Future Earth Past Global Changes (PAGES) working group Arctic Cryosphere Change and Coastal Marine Ecosystems (ACME). Significant research advancements have taken place in recent decades, including the increasingly common use of multi-proxy (multiple lines of evidence) studies, improved understanding of species-environment relationships, and development of novel proxies. Significant gaps remain, however, in the understanding of proxy sources and behaviour, the use of quantitative techniques, and the availability of reference data from coastal environments. We highlight the need for critical methodological refinement, interdisciplinary collaboration on research approaches, and enhanced communication across the scientific community.
... Diatoms (Bacillariophyta) are unicellular, siliceous organisms that are photoautotrophic and thrive in the euphotic zone of the ocean. Owing to their sensitive responses to environmental conditions, diatoms are frequently used as indicators for paleoenvironmental reconstructions, to assess, for exam-ple, changes in surface water temperatures (Birks and Koç, 2002;Krawczyk et al., 2017;Miettinen et al., 2015), paleoproductivity (Fahl and Stein, 1997;Limoges et al., 2018), and sea-ice distribution (Smirnova et al., 2015;Weckström et al., 2013). Next to microfossil-based reconstructions, the diatom-produced sea-ice proxy IP 25 (a highly branched isoprenoid alkene with 25 carbon atoms; Belt et al., 2007) combined with phytoplankton biomarkers (e.g. ...
... frigida, whereas samples characterised by moderate to high (> 0.8 µg g −1 total organic carbon) concentrations of IP 25 display highly variable proportions without a clear relationship. Nitzschia frigida (Grunow) forms arborescent colonies (Medlin and Hasle, 1990) and is often abundant from late winter in the bottom layer of nearshore first-year ice and in multi-year ice in the Arctic pack-ice zones (Krawczyk et al., 2017;Melnikov et al., 2002;Olsen et al., 2017;Poulin et al., 2011;von Quillfeldt et al., 2003), but it can also be found in the water column during vernal under-ice or ice-edge blooms (Hasle and Heimdal, 1998;Olsen et al., 2017). Recently, De Schepper et al. (2019) used sedaDNA metabarcoding on a core from the East Greenland Sea and identified the Mediophyceae OTU_5051 which was significantly correlated to the IP 25 concentrations. ...
The Fram Strait is an area with a relatively low and irregular distribution of diatom microfossils in surface sediments, and thus microfossil records are scarce, rarely exceed the Holocene, and contain sparse information about past richness and taxonomic composition. These attributes make the Fram Strait an ideal study site to test the utility of sedimentary ancient DNA (sedaDNA) metabarcoding. Amplifying a short, partial rbcL marker from samples of sediment core MSM05/5-712-2 resulted in 95.7 % of our sequences being assigned to diatoms across 18 different families, with 38.6 % of them being resolved to species and 25.8 % to genus level. Independent replicates show a high similarity of PCR products, especially in the oldest samples. Diatom sedaDNA richness is highest in the Late Weichselian and lowest in Mid- and Late Holocene samples. Taxonomic composition is dominated by cold-water and sea-ice-associated diatoms and suggests several reorganisations – after the Last Glacial Maximum, after the Younger Dryas, and after the Early and after the Mid-Holocene. Different sequences assigned to, amongst others, Chaetoceros socialis indicate the detectability of intra-specific diversity using sedaDNA. We detect no clear pattern between our diatom sedaDNA record and the previously published IP25 record of this core, although proportions of pennate diatoms increase with higher IP25 concentrations and proportions of Nitzschia cf. frigida exceeding 2 % of the assemblage point towards past sea-ice presence.
... Received 31 October 2019; Received in revised form 23 March 2020; Accepted 11 April 2020 qualitatively and quantitatively (e.g., Koç et al., 1993;Jiang et al., 2001;Andersen et al., 2004;Justwan and Koç, 2008;Berner et al., 2008Berner et al., , 2011Miettinen et al., 2012Miettinen et al., , 2015. Around Greenland, qualitative and quantitative diatom-based reconstructions indicate a reduction in sea-ice concentrations during warm intervals of the Holocene (Justwan and Koç, 2008;Sha et al., 2014Sha et al., , 2016Sha et al., , 2017Miettinen et al., 2015;Krawczyk et al., 2016). Quantitative approaches are important as they provide essential data for proxy-model comparisons and climate model development, but they come with limitations. ...
... In our data, the SIS group comprises the pennate species Fossula arctica, Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Pauliella taeniata, and the centric under-ice species Melosira arctica (e.g., Melnikov and Bondarchuk, 1987;Snoeijs, 1993;von Quillfeldt, 2000;Limoges et al., 2018;Oksman et al., 2019). The MIZ group includes four species: Actinocyclus curvatulus, Porosira glacialis, Thalassiosira bulbosa and Coscinodiscus oculus-iridis, which are found in the Marginal Ice Zone during and after the spring bloom (e.g., Syvertsen and Hasle, 1984;von Quillfeldt, 2000;Krawczyk et al., 2016;Oksman et al., 2019). The CWS group is a more diverse group than the previous two, comprised of ten species, which prefer cold-water conditions, but are not tightly coupled to sea ice. ...
We recorded diatom species succession over one full year (May 2017–May 2018) using automated sediment traps installed in two contrasting Greenlandic fjords: the seasonally ice-covered Young Sound in high-arctic Northeast Greenland and the nearly sea-ice free Godthåbsfjord in subarctic Southwest Greenland. The traps were positioned at differing water depths (37 m in Young Sound vs. 300 m in Godthåbsfjord). Distinct differences between the study sites were observed in both sediment and diatom fluxes. In Young Sound, total diatom flux was extremely seasonal and as high as 880 × 10⁶ valves m⁻² d⁻¹ in the spring. In Godthåbsfjord, total diatom flux was more stable throughout the year, with a maximum of 320 × 10⁶ valves m⁻² d⁻¹ in the summer. The diatom assemblage in Young Sound was dominated by the sea-ice species Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica, which exhibited pulse-like deposition in the trap during and after the ice melt. In Godthåbsfjord, the fluxes were dominated by Chaetoceros (resting spores), while the remaining assemblage was characterised by the cold-water indicator species Detonula confervacea (resting spores) and Thalassiosira antarctica var. borealis (resting spores) together with Fragilariopsis cylindrus. Our data show that, F. oceanica, F. reginae-jahniae and F. arctica exhibit similar seasonal behaviour and a clear linkage to sea ice. Fragilariopsis cylindrus seems to have a more flexible niche, and based on our study, cannot be considered an unequivocal ice indicator. Taking into account these ecological and seasonal preferences of individual diatom species is crucial when reconstructing past sea-ice conditions both qualitatively and quantitatively.
... 2. The observation equation allows the relationship between the sea ice and the predictor variables to be expressed through their less variable state process versions (e.g., a state variable close to the yearly average of ice core MSA) rather than just the noisy observed value. 3. The model can be thought of a more sophisticated stochastic process version of the canonical correlation analysis currently used in sea ice reconstruction (Krawczyk et al., 2017). 4. The state process model, for example, Equation 2, represents the influence of time lagged effects where the lags can be month-to-month and cross-variable lags (e.g., sea surface temperature in the prior month on sea ice extent this month). ...
Antarctic sea ice, a key component in the complex Antarctic climate system, is an important driver and indicator of the global climate. In the relatively short satellite‐observed period from 1979 to 2022 the sea ice extent has continuously increased (contrasting a major decrease in Arctic sea ice) up to a dramatic decrease between 2014 and 2017. Recent years have seen record sea ice lows in February 2022–February 2023. We use a statistical ensemble reconstruction of Antarctic sea ice to put the observed changes into the historical context of the entire 20th century. We propose a seasonal Vector Auto‐Regressive Moving Average (VARMA) model fit in a Bayesian framework using regularized horseshoe priors on the regression coefficients to create a stochastic ensemble reconstruction of monthly Antarctic Sea ice extent from 1900 to 1979. This novel model produces a set of 2,500 plausible sea ice extent reconstructions for the sea ice by sector that incorporate the autocorrelation structure of sea ice over time as well as the dependence of sea ice between the sectors. These fully observed reconstructions exhibit plausible month‐to‐month changes in reconstructed sea ice as well as plausible interactions between the sectors and the total. We reconstruct an overall higher sea ice extent earlier in the 20th century with a relatively sharp decline in the 1970s. These trends agree well with previous reconstructions of Antarctic sea ice based on ice core data, whaling locations, and climatological data, as well as early satellite observations in the reconstruction period.
... A large number of proxies, including microfossil assemblages, provide indirect information about the presence/ absence of sea ice (Cronin et al., 2013;de Vernal et al., 2001de Vernal et al., , 2013Krawczyk et al., 2017;Seidenkrantz, 2013). However, the only proxy directly produced inside sea ice is a highly branched isoprenoid (HBI) with 25 carbon atoms, namely IP 25 (Belt et al., 2007). ...
The ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP25, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.
... While the commonly used sea-ice proxies Fragilariopsis cylindrus, F. oceanica, F. reginae-jahniae and Fossulaphycus arcticus (e.g. [31][32][33] ) are taxonomically distinct in sediment diatom preparations, there is little comparable knowledge from sea ice, water column and sinking flux. For highly branched isoprenoid lipids (HBIs), biomarkers selectively synthesised by some diatom species, there are field and laboratory studies giving insight into their sources. ...
Despite their wide use in past sea-ice reconstructions, the seasonal, habitat and species-based sources of sedimentary sea-ice proxies are poorly understood. Here, we conduct direct observations of the community composition of diatoms, dinoflagellate cysts and highly branched isoprenoid lipids within the sea ice, water column, sediment traps and sediment surface in the Belcher Islands Archipelago, Hudson Bay throughout spring 2019. We find that Arctic diatom and dinoflagellate cysts species commonly used as sea-ice proxies appear to be only indirectly linked to sea-ice conditions, and that the sediment assemblages of these groups overrepresent summertime pelagic blooms. Species contributing to the diverse sea-ice diatom communities are rare in the sediment. Dinoflagellate cysts form a typical Arctic assemblage in the sediment, although they are virtually absent in the sea ice and water column in spring. We also find that certain highly branched isoprenoid lipids that were previously considered indicators of open water, can be produced in sea-ice. We conclude that contextual knowledge and a multiproxy approach are necessary in reconstruction, encouraging further studies on the sources and controls of sea-ice proxy production in different geographic areas.
... BP (400 -765 CE); Helama et al., 2017), the majority of the marine records by Greenland document a transition towards colder conditions likely in response to a general southward movement of the polar front. Around this time sea ice increased, but also fluctuated in East and South Greenland (Jennings et al., 2002(Jennings et al., , 2011Miettinen et al., 2015;Kolling et al., 2018;Jensen et al., 2004;Roncaglia and Kuijpers, 2004) and in Disko Bugt in West Greenland (Krawczyk et al., 2010(Krawczyk et al., , 2013(Krawczyk et al., , 2017Moros et al., 2006Moros et al., , 2016Andresen et al., 2011;Ribeiro et al., 2012;Seidenkrantz et al., 2008;Sha et al., 2012, Allan et al., 2018Kolling et al., 2018). Concurrently, the occurrence of the Irminger Current offshore South Greenland was relatively intense (Lassen et al., 2004;Møller et al., 2006;Seidenkrantz et al., 2007;Andresen et al., 2013. ...
In the Northern Hemisphere, an insolation driven Early to Middle Holocene Thermal Maximum was followed by a Neoglacial cooling that culminated during the Little Ice Age (LIA). Here, we review the glacier response to this Neoglacial cooling in Greenland. Changes in the ice margins of outlet glaciers from the Greenland Ice Sheet as well as local glaciers and ice caps are synthesized Greenland-wide. In addition, we compare temperature reconstructions from ice cores, elevation changes of the ice sheet across Greenland and oceanographic reconstructions from marine sediment cores over the past 5,000 years. The data are derived from a comprehensive review of the literature supplemented with unpublished reports. Our review provides a synthesis of the sensitivity of the Greenland ice margins and their variability, which is critical to understanding how Neoglacial glacier activity was interrupted by the current anthropogenic warming. We have reconstructed three distinct periods of glacier expansion from our compilation: two older Neoglacial advances at 2,500 – 1,700 yrs. BP (Before Present = 1950 CE, Common Era) and 1,250 – 950 yrs. BP; followed by a general advance during the younger Neoglacial between 700-50 yrs. BP, which represents the LIA. There is still insufficient data to outline the detailed spatio-temporal relationships between these periods of glacier expansion. Many glaciers advanced early in the Neoglacial and persisted in close proximity to their present-day position until the end of the LIA. Thus, the LIA response to Northern Hemisphere cooling must be seen within the wider context of the entire Neoglacial period of the past 5,000 years. Ice expansion appears to be closely linked to changes in ice sheet elevation, accumulation, and temperature as well as surface-water cooling in the surrounding oceans. At least for the two youngest Neoglacial advances, volcanic forcing triggering a sea-ice /ocean feedback, could explain their initiation. There are probably several LIA glacier fluctuations since the first culmination close to 1250 CE (Common Era) and available data suggests ice culminations in the 1400s, early to mid-1700s and early to mid-1800s CE. The last LIA maxima lasted until the present deglaciation commenced around 50 yrs. BP (1900 CE). The constraints provided here on the timing and magnitude of LIA glacier fluctuations delivers a more realistic background validation for modelling future ice sheet stability.
... Here, this decrease in biological (carbonate) productivity could be linked to a decline in the WGC strengths, while the high dinosterol accumulation rates might be due to the increased deposition of fine-grained sediments ( Fig. 8H; Weiser et al. 2021). The declined WGC strength temporally coincides with the onset of Neoglacial cooling, widely reported around Greenland areas (Levac et al. 2001;Long & Roberts 2003;Briner et al. 2010;Müller et al. 2012;Perner et al. 2012;Krawczyk et al. 2017;Schweinsberg et al. 2017). Dinocyst-based reconstructions in the nearby core SA13-ST3 also indicate a slight decrease in summer primary productivity in this interval (Allan et al. 2021), in agreement with our study. ...
Reconstructions of sea-surface conditions during the Holocene were achieved using three sediment cores from northeastern Baffin Bay (GeoB19948-3 and GeoB19927-3) and the Labrador Sea (GeoB19905-1) along a north-south transect based on sea-ice IP 25 and open-water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea-surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice-free in spring/autumn due to the enhanced influx of Atlantic Water (West Greenland Current, WGC) from 11.5 until~9.1 ka BP, succeeded by a period of continued (spring-autumn) ice-free conditions between 9.1 and 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)-like conditions. A transition towards reoccurring ice-edge and significantly reduced SIC conditions in Baffin Bay is evident in the Middle Holocene (~7.6-3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM-like conditions. These HTM-like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring-autumn) ice-free conditions from 5.9-3 ka BP. In the Late Holocene (last~3 ka), our combined proxy records from eastern Baffin Bay indicate low in-situ ice algae production; however, enhanced multi-year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring-autumn) ice-free. Our data from the Baffin Bay-Labrador Sea transect suggest a dominant influence of meltwater influx on sea-ice formation throughout the Holocene, in contrast to sea-ice records from the Fram Strait area, which seem to follow predominantly the summer insolation trend.
... Here, this decrease in biological (carbonate) productivity could be linked to a decline in the WGC strengths, while the high dinosterol accumulation rates might be due to the increased deposition of fine-grained sediments ( Fig. 8H; Weiser et al. 2021). The declined WGC strength temporally coincides with the onset of Neoglacial cooling, widely reported around Greenland areas (Levac et al. 2001;Long & Roberts 2003;Briner et al. 2010;Müller et al. 2012;Perner et al. 2012;Krawczyk et al. 2017;Schweinsberg et al. 2017). Dinocyst-based reconstructions in the nearby core SA13-ST3 also indicate a slight decrease in summer primary productivity in this interval (Allan et al. 2021), in agreement with our study. ...
Reconstructions of sea‐surface conditions during the Holocene were achieved using three sediment cores from northeastern Baffin Bay (GeoB19948‐3 and GeoB19927‐3) and the Labrador Sea (GeoB19905‐1) along a north–south transect based on sea‐ice IP25 and open‐water phytoplankton biomarkers (brassicasterol, dinosterol and HBI III). In Baffin Bay, sea‐surface conditions in the Early Holocene were characterized by extended (early) spring sea ice cover (SIC) prior to 7.6 ka BP. The conditions in the NE Labrador Sea, however, remained predominantly ice‐free in spring/autumn due to the enhanced influx of Atlantic Water (West Greenland Current, WGC) from 11.5 until ~9.1 ka BP, succeeded by a period of continued (spring–autumn) ice‐free conditions between 9.1 and 7.6 ka BP corresponding to the onset of Holocene Thermal Maximum (HTM)‐like conditions. A transition towards reoccurring ice‐edge and significantly reduced SIC conditions in Baffin Bay is evident in the Middle Holocene (~7.6–3 ka BP) probably caused by the variations in the WGC influence associated with the ice melting and can be characterized as HTM‐like conditions. These HTM‐like conditions are predominantly recorded in the NE Labrador Sea area shown by (spring–autumn) ice‐free conditions from 5.9–3 ka BP. In the Late Holocene (last ~3 ka), our combined proxy records from eastern Baffin Bay indicate low in‐situ ice algae production; however, enhanced multi‐year (drifted) sea ice in this area was possibly attributed to the increased influx of Polar Water mass influx and may correlate with the Neoglacial cooling. The conditions in the NE Labrador Sea during the last 3 ka, however, continued to remain (spring–autumn) ice‐free. Our data from the Baffin Bay–Labrador Sea transect suggest a dominant influence of meltwater influx on sea‐ice formation throughout the Holocene, in contrast to sea‐ice records from the Fram Strait area, which seem to follow predominantly the summer insolation trend.
... Ocean conditions during the Holocene have been well documented for selected regions off West Greenland, in particular in the Disko Bay area (Fig. 1), where a number of sedimentological, micropalaeontological and geochemical investigations have been conducted (Moros et al. 2006(Moros et al. , 2016Lloyd et al. 2007;Seidenkrantz et al. 2008;Krawczyk et al. 2010Krawczyk et al. , 2013Krawczyk et al. , 2017Andresen et al. 2011;Perner et al. 2011Perner et al. , 2013Ribeiro et al. 2012;Jennings et al. 2014;Ouellet-Bernier et al. 2014;Sha et al. 2014;Kolling et al. 2017;Allan et al. 2018). The records from the aforementioned studies have shown a relatively late establishment of the Holocene Thermal Maximum (HTM) following the phase of maximum insolation in the Early Holocene in surface waters, and a decoupling between surface and subsurface temperatures during the Middle Holocene, which presumably link to meltwater discharge from the GrIS and the history of the relatively warm WGC (Moros et al. 2016). ...
We address here the specific timing and amplitude of sea‐surface conditions and productivity changes off SW Greenland, northern Labrador Sea, in response to the high deglacial meltwater rates, the Early Holocene maximum insolation and Neoglacial cooling. Dinocyst assemblages from sediment cores collected off Nuuk were used to set up quantitative records of sea ice cover, seasonal sea‐surface temperature (SST), salinity (SSS), and primary productivity, with a centennial to millennial scale resolution. Until ~10 ka BP, ice‐proximal conditions are suggested by the quasi‐exclusive dominance of heterotrophic taxa and low dinocyst concentrations. At about 10 ka BP, an increase in species diversity and abundance of phototrophic taxa marks the onset of interglacial conditions at a regional scale, with summer SST reaching up to 10 °C between 8 and 5 ka BP, thus in phase with the Holocene Thermal Maximum as recorded in the southern Greenlandic areas/northern Labrador Sea. During this interval, low SSS but high productivity prevailed in response to high meltwater discharge and nutrient inputs from the Greenland Ice Sheet. After ~5 ka BP, a decrease in phototrophic taxa marks a two‐step cooling of surface waters. The first started at ~5 ka BP, and the second at ~3 ka BP, with a shift toward colder conditions and higher SSS suggesting reduced meltwater discharge during the Neoglacial. This second step coincides with the disappearance of the Saqqaq culture. The gap in human occupation in west Greenland, between the Dorset and the Norse settlements from 2000 to 1000 years BP, might be linked to high amplitude and high frequency variability of ocean and climate conditions.
... Diatoms are good indicators of past climate and environmental changes in the North Atlantic because of their near ubiquity in the marine environment and their high sensitivity to environmental and ecological conditions (Jiang et al., 2001(Jiang et al., , 2015Koc Karpuz and Schrader, 1990). Diatom-based transfer function for paleo sea-surface temperature reconstructions have been widely applied in the North Atlantic (Jiang et al., 2005(Jiang et al., , 2015Justwan et al., 2008;Krawczyk et al., 2017;Li et al., 2017;Miettinen et al., 2015). ...
We analyzed the biogenic silica (BSi) content and produced a diatom-based summer sea-surface temperature (SST) reconstruction for sediment core GC4 from the Holsteinsborg Dyb, West Greenland. Our aim was to reconstruct marine productivity and climatic fluctuations during the last millennium. Increased BSi content and diatom abundance suggest relatively high marine productively during the interval of AD 1000–1400, corresponding in time to the Medieval Warm Period (MWP). The summer SST reconstruction indicates relatively warm conditions during AD 900–1100, followed by cooling after AD 1100. An extended cooling period during AD 1400–1900 is characterized by prolonged low in reconstructed SST and high sea-ice concentration. The BSi values fluctuated during this period, suggesting varying marine productivity during the Little Ice Age (LIA). There is no significant correlation between the BSi content and SST during the last millennium, suggesting that the summer SST has little influence on marine productively in the Holsteinsborg Dyb. A good correspondence between the BSi content and the element Ti counts in core GC4 suggests that silicate-rich meltwater from the Greenland ice sheet was likely responsible for changes in marine productively in the Holsteinsborg Dyb.
... Bay (Lafond et al., 2019). In surface sediments and sediment traps from Greenland, M. arctica is strongly associated with spring/summer sea ice (Krawczyk et al., 2017;Luostarinen et al., 2020). The drift-ice/pack-ice assemblage also includes A. curvatulus, a coldwater species that is associated with high sea-ice concentrations (Oksman et al., 2019) and heavy pack ice in northern Baffin Bay (Williams, 1986(Williams, , 1990. ...
Climate warming is rapidly reshaping the Arctic cryosphere and ocean conditions, with consequences for sea ice and pelagic productivity patterns affecting the entire marine food web. To predict how ongoing changes will impact Arctic marine ecosystems, concerted effort from various disciplines is required. Here, we contribute multi‐decadal reconstructions of changes in diatom production and sea‐ice conditions in relation to Holocene climate and ocean conditions off northwest Greenland. Our multiproxy study includes diatoms, sea‐ice biomarkers (IP25 and HBI III) and geochemical tracers (TOC [total organic carbon], TOC:TN [total nitrogen], δ¹³C, δ¹⁵N) from a sediment core record spanning the last c. 9,000 years. Our results suggest that the balance between the outflow of polar water from the Arctic, and input of Atlantic water from the Irminger Current into the West Greenland Current is a key factor in controlling sea‐ice conditions, and both diatom phenology and production in northeastern Baffin Bay. Our proxy record notably shows that changes in sea‐surface conditions initially forced by Neoglacial cooling were dynamically amplified by the shift in the dominant phase of the Arctic Oscillation (AO) mode that occurred at c. 3,000 yr BP, and caused drastic changes in community composition and a decline in diatom production at the study site. In the future, with projected dominant‐positive AO conditions favored by Arctic warming, increased water column stratification may counteract the positive effect of a longer open‐water growth season and negatively impact diatom production.
... The summer Sea-Surface Temperature (SST) reconstruction from core MSM343300 of waters entering Disko Bay shows three different periods for surface ocean conditions: a relatively warm period at the Early Holocene with July SST's between 5 and 8 + C, followed by a cooler period at the Mid-Holocene (8e3 ka BP), with July SST's of 4e5 + C, and finally the Late-Holocene or Neoglaciation warming, when the July SST's rose to 4e6 + C (purple line in Fig. 1b). Krawczyk et al. (2017) attribute the Mid-Holocene period of cold surface waters to a large amount of glacial meltwater during the summer season. The timing of the onset of this cold period matches with the period of the retreat of JI inland from the sill, supporting large glacial meltwater fluxes as a reason for the surface water cooling. ...
Marine terminating glaciers evolve on millenial timescales in response to changes in oceanic and atmospheric conditions. However, the relative role of oceanic and atmospheric drivers remains uncertain. The evolution of marine terminating glaciers under the warmer than present Holocene Climate Optimum climate can give important insights into the dynamics of ice streams as the climate evolves. The early Holocene evolution of Jakobshavn Isbræ, from the Last Glacial Maximum extent up to 8.2 ka BP is well constrained by geomorphological studies in the area. However, the Holocene minimum extent of the glacier is unknown. Here, we use a high-resolution regional ice sheet model to study the retreat and readvance of Jakobshavn Isbræ from the Mid-Holocene to the Little Ice Age. This model of Jakobshavn Isbræ accurately tracks the terrestrial ice margin and agrees with available estimates of marine grounding line evolution. We find that the Holocene minimum extent of both the terrestrial ice margin and the grounding line, reached at 6–5 ka BP, is close to the present day extent of the glacier. We also find that the glacier is currently located close to a tipping point, from beyond which readvance would require a longer and more significant cooling than the Little Ice Age. We assess the importance of the ocean forcing in explaining the Holocene evolution of Jakobshavn, and find that cooling within the fjord during the Mid-Holocene is critical for the glacier to readvance. This finding emphasizes the role of ocean forcing when trying to understand the millenial scale evolution of marine terminating glaciers.
... Records that extend earlier into the Holocene exist elsewhere on Greenland, however as mentioned above, it is becoming clear that temperature change around Greenland was not uniform . Marine records off the west coast of Greenland are relatively abundant compared to terrestrial records and many document the Holocene marine evolution of Baffin Bay (Erbs-Hansen et al., 2013;Krawczyk et al., 2017;Moros et al., 2016;Perner et al., 2012;Seidenkrantz, 2013), but many of these studies' results conflict or document highly variable environments. There is a clear need for additional climate records to fill the 700 km gap (from Kangerlussuaq to Qipisarqo, Fig. 1) where no quantitative constraints exist on the timing and magnitude of temperature change that drove Holocene ice sheet and glacier fluctuations there. ...
Terrestrial temperature reconstructions from the ice-free margins of Greenland are critical for constraining the sensitivity of the Greenland ice sheet to past climate change. Numerous investigations have clarified the glacial history of southwest Greenland in recent decades; however, very few local quantitative temperature reconstructions exist as context for changes in the cryosphere. We examine sedimentary records from two lakes south of Nuuk, Greenland (informally named lakes T1 and T2), and investigate millennial scale Holocene climate change using a multi-proxy approach. Changes in X-Ray fluorescence spectroscopy (XRF), δ¹⁵N, δ¹³C and biogenic silica concentrations of bulk lake sediments mark the transition from a marine environment to isolated lakes as relative sea level fell in the early Holocene. δ¹⁸O values of subfossil insects (chironomids) from lakes T1 and T2 decreased by 2–3‰ from c. 8.8 ka BP (minimum limiting age for the onset of lacustrine sediment deposition in lake T2; ka BP = thousands of years before 1950) to 1 ka BP. Existing isotope-independent temperature reconstructions from the west coast of Greenland suggest that these changes in δ¹⁸O values accompanied gradual cooling of 2–4 °C, concomitant with decreasing summer insolation. There is widespread regional evidence that this cooling resulted in progressive regrowth of local glaciers and of the ice sheet. The regional consensus on the magnitude of this temperature change indicates that the local, modern modeled temperature - precipitation δ¹⁸O relationship cannot be used to quantify millennial-scale temperature changes at these sites through the Holocene. This reinforces that studies utilizing δ¹⁸O-based proxies to infer temperature change should carefully assess local isotope-temperature relationships over space and time.
... High resolution, continuous biotic proxy records obtained from marine sediment cores off western Greenland, especially in the Disko Bay region, have been widely used in the past 10-15 years to shed light on the intricate connection between hydrographic conditions and the behavior of the western GIS over the Holocene (Lloyd et al., 2005;Lloyd et al., 2007;Moros et al., 2006;Perner et al., 2012;Perner et al., 2013;Sha et al., 2014;Krawczyk et al., 2016;among others). More recently, mineralogy has been used to assess the provenance of sediment from the various ice-sheets draining into Baffin Bay over the last glacial cycle (Andrews et al., 2012;Simon et al., 2013) by applying a sediment-unmixing program to the bulk mineralogy of marine sediments and taking into account the bedrock geology underlying major ice-streams (Andrews and Eberl, 2011). ...
A better understanding of the past dynamics of local sectors of the Greenland ice sheet (GIS) with regards to ocean circulation and climate changes can be developed from proxy records derived from marine sedimentary archives. Here we investigate the post 9.1 cal. Kyr BP history of the western sector of the GIS from the XRF core scanner-derived geochemistry of a sediment core retrieved from Upernavik Trough, Melville Bay. The elemental signature of material derived from Melville Bay glaciers, Upernavik Isstrom and Rink Isbrae can be inferred from the geology of the bedrocks drained by these major ice streams of the western GIS. Changes in abundance of Fe-rich basaltic material reflect changes in West Greenland Current (WGC) strength. Contributions from Melville Bay glaciers were dominant during the early part of the record as a result of the rapid retreat of this stretch of the NW GIS. Atmospheric warming and strengthened WGC between 7.5 and 5 cal. Kyrs BP promoted contributions from distal southern sources of lithic material to the sedimentation over Upernavik Trough. The Neoglacial shift in climate and ocean circulation led to a general reduction in the delivery of lithic material from western GIS glacier outlets glaciers. The particular geomorphology of the fjord hosting Rink Isbrae as well as the important depth of the Uummannaq Trough likely explain the high relative contribution of this glacier to the lithic sedimentation over Upernavik Trough during the later part of the Holocene despite a weakened WGC.
... Several oceanographic properties can be reconstructed from dinocyst assemblages including sea-surface temperature (SST), salinity (SSS), seasonal sea ice cover (SIC), and primary productivity (de Vernal et al., , 2013aRadi and de Vernal, 2008). Previous studies based on dinocysts, but also diatoms, molluscs, foraminifera and sea ice biomarkers (IP 25 ) have contributed to our knowledge of past sea-surface conditions in Baffin Bay (e.g., Knudsen et al., 2008;Krawczyk et al., 2017). However, information available on the northeastern Baffin Bay (Melville Bay) and Nares Strait sea-surface variability during the Holocene is still incomplete, as studies have mainly focused on the regions of the North Water Polynya (e.g., Levac et al., 2001) and Disko Bay region (e.g., Ribeiro et al., 2012;Allan et al., 2018). ...
... Marine diatoms of the North Atlantic Ocean are very sensitive to changes in e.g., sea surface temperatures and sea-ice cover (e.g., Schrader et al., 1993a;Kohly, 1998;Jiang et al., 2001;Justwan and Koç, 2008;Krawczyk et al., 2017;Oksman et al., 2019), and salinity (Juggins, 1992), and have been used in numerous studies dealing with reconstructions of past palaeoceanographic changes. However, most studies from high-latitude marine sediments have focused on younger sediments from the late glacial and Holocene (e.g., Koç Karpuz and Schrader, 1990;Koç Karpuz and Jansen, 1992;Koç et al., 1993; This has been attributed to differences in living depth in the water column and differences in seasonality (see e.g., Moros et al., 2004;Andersson et al., 2010). ...
Fossil marine diatom assemblages in a sediment core from the central northern Faroe slope in the Norwegian Sea were used to reconstruct palaeoceanographic changes in the surface water mixed layer from the last ~130,000 years (Marine Isotope Stage (MIS) 6/5 transition to MIS 1 (including the Eemian and Holocene interglacials) and to compare the results with previously published results on planktic foraminifera representing the subsurface conditions of the thermocline. Diatom floras from MIS 5 of the Nordic seas have rarely been studied in detail before and never the entire period from pre-Eemian to present. The composition of diatom species together with maxima in absolute abundance of diatoms, indicate two periods of warmer sea surface temperatures correlating with the Eemian and Holocene interglacials, respectively. The Eemian differs from the Holocene in that the Iceland-Faroe Front never developed, suggesting the cold East Icelandic Current (originating from the East Greenland Current) running north of Iceland was reduced or more mixed with Atlantic water than during the Holocene and that the surface temperature and salinity gradients were weaker. The northern Faroe slope was in the early Weichselian of MIS 5d–5a mainly influenced by weaker inflow of Atlantic water and stronger influence of the East Icelandic Current and by seasonal sea-ice cover. During the later part of the Weichselian (MIS 4–MIS 2) cold conditions prevailed with extensive sea-ice cover except during the warmer interstadials. The diatom floras were more sensitive to climate changes than the planktic foraminifera and indicate longer periods with warm surface conditions, and increased influence of the warm Atlantic surface water from the Faroe Current in MIS 5, suggesting a shallower and much steeper thermocline during the transitional periods compared to today. The diatoms are good indicators for Atlantic water inflow and possible convection in the Nordic seas, not merely reflecting orbital variations in insolation as previously suggested.
... From our dataset, it is difficult to determine whether their absence or low representation in the sediments was primarily due to degradation during vertical sinking or caused by a "dilution effect" due to the dominance of the main spring blooming species. Our observations are however consistent with studies from other Arctic regions where these are generally rare or absent (e.g., Moros et al., 2006;Sha et al., 2014;Krawczyk et al., 2017). Similarly, the weakly silicified vegetative cells of Chaetoceros spp., that were important contributors to the phytoplankton community as illustrated by their high abundance in the second set of trap samples, were not reported from the surface sediment sample. ...
The biomarker IP25 and fossil diatom assemblages preserved in seafloor sediments are commonly used as proxies for paleo Arctic sea-ice reconstructions, but how their production varies over the seasons and is exported to the sediment remains unclear. We analyzed IP25 concentrations and diatom assemblages from a 5-week consecutive series of sea-ice cores and compared the results with sediment trap and surface sediment samples collected at the same site in the Young Sound fjord, Northeast Greenland. Our aim was to investigate the dynamics of diatom colonization of the spring sea ice and the in situ production of IP25. Additionally, selected diatom taxa observed in the sea-ice samples were isolated from in-ice assemblages and their lipid composition was analyzed via gas chromatography-mass spectrometry. We confirm that Haslea spicula (and not the closely related species H. crucigeroides) is an IP25-producer. All three known IP25-producing taxa (Haslea spicula, H. kjellmanii, and Pleurosigma stuxbergii var. rhomboides) were present in Young Sound sea-ice and the low IP25 concentrations measured in the sea-ice (0.44–0.72 pg mL−1) were consistent with the low abundance of these source species (0.21–9.66 valves mL−1). Total sympagic diatom production also remained very low (21–985 valves mL−1), suggesting that the fjord's sea ice did not provide an optimal physical-chemical environment for diatoms to thrive. Temporal changes in the sympagic diatom community were also observed, with an early presence of the pelagic Thalassiosira hyperborea and subsequent dominance of pennate taxa, including Nitzschia and Navicula species, Fossula arctica and Stauronella arctica. The assemblages observed during and after the seasonal ice melt consisted primarily of Fossula arctica, Fragilariopsis oceanica, Thalassiosira antarctica var. borealis (resting spores), and Chaetoceros spp. (vegetative cells and resting spores). The seafloor sediment assemblages largely reflected the melt and post-melt planktic production and were dominated by the resting spores of the centric Chaetoceros spp. and Thalassiosira antarctica var. borealis, and the pennate Fragilariopsis oceanica, Fossula arctica, and Fragilariopsis reginae-jahniae. This study documents that IP25 is produced in Young Sound, and that the weak fingerprint of sea ice in the sediment appears to be primarily due to the limited sea-ice diatom biomass.
... From our dataset, it is difficult to determine whether their absence or low representation in the sediments was primarily due to degradation during vertical sinking or caused by a "dilution effect" due to the dominance of the main spring blooming species. Our observations are however consistent with studies from other Arctic regions where these are generally rare or absent (e.g., Moros et al., 2006;Sha et al., 2014;Krawczyk et al., 2017). Similarly, the weakly silicified vegetative cells of Chaetoceros spp., that were important contributors to the phytoplankton community as illustrated by their high abundance in the second set of trap samples, were not reported from the surface sediment sample. ...
The biomarker IP25 and fossil diatom assemblages preserved in seafloor sediments are commonly used as proxies for paleo Arctic sea-ice reconstructions, but how their production varies over the seasons and is exported to the sediment remains unclear. We analyzed IP25 concentrations and diatom assemblages from a 5-week consecutive series of sea-ice cores and compared the results with sediment trap and surface sediment samples collected at the same site in the Young Sound fjord, Northeast Greenland. Our aim was to investigate the dynamics of diatom colonization of the spring sea ice and the in situ production of IP25. Additionally, selected diatom taxa observed in the sea-ice samples were isolated from in-ice assemblages and their lipid composition was analyzed via gas chromatography-mass spectrometry. We confirm that Haslea spicula (and not the closely related species H. crucigeroides) is an IP25-producer. All three known IP25-producing taxa (Haslea spicula, H. kjellmanii, and Pleurosigma stuxbergii var. rhomboides) were present in Young Sound sea-ice and the low IP25 concentrations measured in the sea-ice (0.44–0.72 pg mL⁻¹) were consistent with the low abundance of these source species (0.21–9.66 valves mL⁻¹). Total sympagic diatom production also remained very low (21–985 valves mL⁻¹), suggesting that the fjord's sea ice did not provide an optimal physical-chemical environment for diatoms to thrive. Temporal changes in the sympagic diatom community were also observed, with an early presence of the pelagic Thalassiosira hyperborea and subsequent dominance of pennate taxa, including Nitzschia and Navicula species, Fossula arctica and Stauronella arctica. The assemblages observed during and after the seasonal ice melt consisted primarily of Fossula arctica, Fragilariopsis oceanica, Thalassiosira antarctica var. borealis (resting spores), and Chaetoceros spp. (vegetative cells and resting spores). The seafloor sediment assemblages largely reflected the melt and post-melt planktic production and were dominated by the resting spores of the centric Chaetoceros spp. and Thalassiosira antarctica var. borealis, and the pennate Fragilariopsis oceanica, Fossula arctica, and Fragilariopsis reginae-jahniae. This study documents that IP25 is produced in Young Sound, and that the weak fingerprint of sea ice in the sediment appears to be primarily due to the limited sea-ice diatom biomass.
... A large number of studies dealing with the reconstruction of past sea-ice cover are based on sedimentological, mineralogical, and geochemical data as well as microfossils such as diatoms, dinoflagellates, ostracods, and foraminifers (e.g. [31,32,28,30,58,88]). These are all predominantly indirect sea-ice proxies, with different advantages and disadvantages (see [32]). ...
This study focusses on the last glacial–deglacial–Holocene spatial and temporal variability in sea-ice cover based on organic geochemical analyses of marine sediment cores from the subarctic Pacific and the Bering Sea. By means of the sea-ice proxy “IP25” and phytoplankton-derived biomarkers (specific sterols and alkenones), we reconstruct the spring sea-ice conditions, (summer) sea-surface temperature (SST) and primary productivity, respectively. The large variability of sea ice was explained by a combination of local and global factors, such as solar insolation, global climate anomalies and sea-level changes controlling the oceanographic circulation and water mass exchange between the subarctic Pacific and the Bering Sea. During the Last Glacial Maximum, extensive sea-ice cover prevailed over large part of the subarctic Pacific and the Bering Sea. The following deglaciation is characterized by a rapid sea-ice advance and retreat. During cold periods (Heinrich Stadial 1 and Younger Dryas) seasonal sea-ice cover generally coincided with low alkenone SSTs and low primary productivity. Conversely, during warmer intervals (Bølling/Allerød, Early Holocene) reduced sea-ice or ice-free conditions prevailed in the study area. At the northern Bering Sea continental shelf a late-Early/Mid Holocene shift to marginal sea-ice conditions is in line with the simultaneous wide-spread sea-ice recovery observed in the other Arctic marginal seas and is likely initiated by the lower Northern Hemisphere insolation and surface-water cooling.
... They are also used as a proxy for past sea ice variability (e.g., sea ice concentration and IP25) in both the Northern and Southern Hemispheres (e.g. Belt et al., 2007;Crosta, Pichon, & Burckle, 1998;de Vernal et al., 2013;Krawczyk et al., 2017Krawczyk et al., , 2010Müller et al., 2009;Sha et al., 2014Sha et al., , 2017Sha et al., , 2016. A previous study showed that changes in surface diatom assemblages in the western Pacific marginal seas are due to variations in SST W and summer sea surface salinity (SSS), and thus, they are the two most important environmental factors controlling the regional diatom distribution . ...
The East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SSTW) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SSTW reconstruction for the last millennium based on a diatom record from sediment core MD05-2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SSTW varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SSTW in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SSTW record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.
... The EGC and IC water masses meet off southern Greenland and although becoming increasingly mixed as they travel northwards along the West Greenland coast, remain distinguishable 14 . The polar water component of the WGC loses its strength around the latitude of 64°N and does not penetrate into northern Baffin Bay, allowing Irminger Current water to rise toward the surface 15,16 . The average modern July water temperature of the area is around 5°C 16 . ...
The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more high-resolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0-10.2 kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate.
... Diatom analyses used in this study allow us to examine important environmental variables (e.g., SST, sea-ice cover) that have not been presented before from Isvika Bay. While a number of quantitative diatom-based sea surface condition records exist for the subpolar and polar North Atlantic region [1,5,6,23,24,32,38,39], diatom-based reconstructions (either qualitative or quantitative) from the high Arctic are sparse [28]. Thus, our record is an important addition to knowledge of the past high-Arctic ocean variability. ...
Paleoclimate records are crucial for understanding current changes taking place in the Arctic, e.g., the amplified warming and associated changes in sea-ice cover. However, paleoclimate and -oceanographic reconstructions, especially from the high Arctic, are scarce. Here, we present a reconstruction of sea surface and paleoenvironmental conditions from a Holocene marine sediment core collected from a high-Arctic fjord, Isvika Bay, Nordauslandet, Svalbard (79°N). Our proxies include qualitative diatom assemblage data [focusing on the Marginal Ice Zone (MIZ) taxa], a quantitative diatom-based August sea surface temperature (aSST) reconstruction, sediment grain-size distribution, and ice-rafted debris (IRD) spanning the period from 4200 cal. yr BP to the Little Ice Age (LIA) at ca. 200 cal. yr BP. The results reveal cold and stable, glacier-proximal conditions for the beginning of the late Holocene (from 4200 to 2500 cal. yr BP). Then, at 2500 cal. yr BP, the environment shifted into distinctly more fluctuating conditions, where colder and warmer aSSTs alternated in a glacier-distal environment. During the latter part of the late Holocene, sea-ice cover was extensive, yet variable, negatively co-varying with aSST. Based on our diatom data, we observe a clear increase in the influence of Atlantic water in Isvika Bay during the last ca. 600 years.
Marine microfossils record oceanographic changes that are closely linked to climate variability. We use diatoms, planktic foraminifera, and calcareous nannofossils to reconstruct the paleoceanographic evolution along the western margin of Spitsbergen (Arctic) during the last 10 kyr BP. The data are compared with other records from the western margin of Spitsbergen. We recognize three distinct units corresponding to the late phase of the early Holocene, the middle Holocene, and the late Holocene.
The results indicate warm sea surface conditions along the western margin of Spitsbergen from 10 to 7.5 kyr BP, simultaneous to a maximum of summer insolation. Maximum advection of North Atlantic Water (NAW) occurs between 10 and 9 kyr BP, corresponding to the last part of the Holocene Thermal Maximum (HTM).
The microfossil association evidenced a gradual cooling of the surface water between 7.4 and 3.8 kyr BP. Surface cooling can be explained by increased water mass exchange with the Arctic Ocean and/or reduced solar insolation. From 3.8 kyr BP, we have evidence of strong seasonality, stratified surface waters, and a slight inflow of NAW. The last 2000 years are characterized by an alternation of warm and cold periods associated with a change in NAW inflow.
Diatom assemblages from ARA2B-1A taken in the Chukchi Sea shelf were analyzed to reconstruct paleoenvironmental changes during the last 10 ka BP. The main factors controlling the distribution of diatom in the Chukchi Sea are the relatively warm and nutrient-rich Pacific water inflow after the opening of the Bering Strait. Based on the selected diatoms, three diatom assemblage zones are identified. The diatom assemblage zone I shows a rare or very low abundance, which corresponds to the early Holocene (10–8 ka BP). The diatom assemblage zone II corresponds to the mid-to-late Holocene (8–2 ka BP). It is a seasonal sea-ice environment with relatively abundant diatom valves and Chaetoceors resting spores, as well as sea-ice species, cold-water species, coastal species, and upwelling species. The diatom assemblage zone III corresponds to the late Holocene (2–0 ka BP), and the the sea-ice species generally decreased compared to zone II, while the coastal species Paralia sulcata occurred abundantly. In particular, the Thalassiosira antarctica, a cold-water species, increased distinctly during this time interval. After ∼2 ka BP, T. antarctica rapidly increased while sea-ice species rarely appeared, indicating limited open-marine environments. In particular, after 1 ka BP, T. antarctica decreased while the sea-ice species increased, suggesting that the sea-ice increased again before the recent global warming of the Arctic, the late Holocene.
Knowledge of the marine reservoir age is fundamental for creating reliable chronologies of marine sediment archives based on radiocarbon dating. This age difference between the 14C age of a marine sample and that of its contemporaneous atmosphere is dependent on several factors (among others, ocean circulation, water mass distribution, terrestrial runoff, upwelling, and sea-ice cover) and is therefore spatially heterogeneous. Anthropogenic influence on the global isotopic carbon system, mostly through atmospheric nuclear tests, has complicated the determination of the regional reservoir age correction ΔR, which therefore can only be measured in historic samples of known age. In this study we expand on the few existing measurements of ΔR for the coastal waters around Greenland, by adding 92 new radiocarbon dates on mollusks from museum collections. All studied mollusk samples were collected during historic expeditions of the late 19th and early 20th centuries, and besides coastal sites around Greenland, the new measurements also include localities from the western Labrador Sea, Baffin Bay, and the Iceland Sea. Together with existing measurements, the new results are used to calculate average ΔR values for different regions around Greenland, all in relation to Marine20, the most recent marine radiocarbon calibration curve. To support further discussions and comparison with previous datasets, we use the term ΔR13, where the suffix 13 refers to the previous calibration curve Marine13. Our study explores the links between the marine reservoir age and oceanography, sea-ice cover, water depth, mollusk feeding habits, and the presence of carbonate bedrock. Although we provide regional averages, we encourage people to consult the full catalogue of measurements and determine a suitable ΔR for each case individually, based on the exact location including water depth. Despite this significant expansion of the regional reservoir age database around Greenland, data from the northern coast, directly bordering the Arctic Ocean, remain missing.
Knowledge of the marine reservoir age is fundamental for creating reliable chronologies of marine sediment archives based on radiocarbon dating. This age difference between the 14C age of a marine sample and that of its contemporaneous atmosphere is dependent on several factors, among others ocean circulation, water mass distribution, terrestrial runoff, upwelling, sea-ice cover and is therefore spatially heterogenous. Anthropogenic influence on the global isotopic carbon system, mostly through atmospheric nuclear tests, has complicated the determination of the regional reservoir age correction ΔR, which therefore can only be measured on historic samples of known age. In this study we expand on the few existing measurements of ΔR for the coastal waters around Greenland, by adding 92 new radiocarbon dates on mollusks from museum collections. All studied mollusk samples were collected during historic expeditions of the late 19th and early 20th centuries and besides coastal sites around Greenland, the dataset also includes localities from the western Labrador Sea, Baffin Bay, and the Iceland Sea. Together with existing measurements, the new results are used to calculate average ΔR values for different regions around Greenland, all in relation to Marine20, the most recent radiocarbon calibration curve. To support further discussions and comparison with previous datasets, we introduce the term ΔR13 where the suffix 13 refers to the previous calibration curve Marine13. Our study explores the links between the marine reservoir age and oceanography, sea ice cover, water depth, mollusk feeding habits, and the presence of carbonate bedrock. Although we provide regional averages, we encourage people to consult the full catalogue of measurements and determine a suitable ΔR for each case individually, based on the exact location including water depth. Despite this significant expansion of the regional reservoir age database around Greenland, data from the northern coast, directly bordering the Arctic Ocean remains missing.
In this paper we describe seafloor terrain of nearly the entire Disko Bay region and provide scientific baseline information about surface geology and sedimentary environments that can support the seafloor management plan in Greenland. Our study utilized multiple datasets of multibeam bathymetry and backscatter, seismic profiles and ground-truthing consisting of video footage from drop camera and benthic video sled, as well as sediment samples from grab and corers. Our results revealed that the key geological units in Disko Bay characterize the scale of geomorphic features, which in turn affects the distribution and complexity of habitat zones. The NE sub-region is underlain by Cretaceous sandstone and characterized by large-scale landforms, mainly vast flat areas draped by glacial lineations, bedrock ridges and pockmark fields. This setting promotes less topographically complex habitats, i.e. coarse plain, muddy/sand plain with dropstones and muddy plain. The SW sub-region is characterized by Precambrian Gneiss and Paleoproterozoic metasedimentary rocks with complex system of small-scale geomorphic features, such as cross-cutting channels. This results in topographically complex habitats in the area, such as rocky bank, coarse rugged terrain, and rocky slopes. Two distinctive habitat areas, associated with potential gas seeps, i) southern pockmark field and ii) western zoanthid-sponge wall, were discovered at the geological boundary separating the two sub-regions. Our study highlights the importance of seafloor habitat mapping and analyses by providing fundamental geophysical knowledge necessary to comply with long-term sustainable use of marine resources in Greenland.
Located in northwestern South China Sea (SCS), the Beibu Gulf constitutes an environmentally sensitive region shaped by land-ocean-atmosphere interactions in Asia between the western Pacific and eastern Indian Oceans. This study aims to provide a comprehensive view of the sub-fossil diatom biogeography, distribution pattern and oceanographic environmental controls with support of multivariate methods based on Beibu Gulf core-top samples. Cluster analysis of diatom assemblages divides the distribution pattern into four subclusters. Sea surface salinity (SSS), temperature (SST), trophic state (chlorophyll a concentration in this study) and water depth constrain the diatom distribution pattern through canonical redundancy analysis although only partly support an interpretation of the relationship between these various variables. Chlorophyll a has a strong correlation to diatom distribution, and responds to Paralia sulcata occurrence, while SSS and SST also have significant influence and indicate warm water invasion from the open SCS. Water depth is a subordinate factor in terms of Beibu Gulf diatom distribution. The ca. 25 m water-depth marks the upper extent of Paralia sulcata dominance in the northern Beibu Gulf. A strong mixing area with a complex diatom distribution exists below this water depth in the middle of Beibu Gulf. Coastal currents from north of SCS invade Beibu Gulf through Qiongzhou Strait and south of Hainan Island, as recorded by higher percentages of Paralia sulcata and Cyclotella striata at these sites. Our results provide a selection of evaluation method for a marine ecological red-line definition for sustainable development. This study highlights the perspective relationships between the spatial distribution of sub-fossil diatom assemblages in surface sediments and oceanographic variables, which could serve as a model for paleoenvironmental and paleoclimatic reconstruction in future marginal sea geoscience research for the Beibu Gulf, northwestern SCS.
Palynological analyses of 60 surface sediment samples from West Greenland margin revealed high concentrations of dinoflagellate cysts (dinocysts), particularly in the Disko Bugt area, where they reach >10⁴ cysts g⁻¹. Dinocyst assemblages are characterized by a relatively high species diversity and are dominated by Operculodinium centrocarpum, cysts of Pentapharsodinium dalei, Islandinium minutum, Islandinium? cezare, and Brigantedinium spp. On a regional scale, the overall assemblages show statistical relationships with sea-ice cover duration, primary productivity, salinity and summer-fall temperature. The cysts of Pentapharsodinium dalei, Operculodinium centrocarpum, and Spiniferites elongatus appear linked to high productivity and to characterize the late summer-fall bloom. Although Islandinium minutum and Islandinium? cezare are generally associated with a seasonally sea-ice covered environment, there is no linear relationship between their relative abundance and sea-ice concentration or duration on a regional scale, along the West Greenland margin. The abundance of these taxa primarily reflects cold and low-salinity water in the study area. Radionuclide measurements (²¹⁰Pb and ¹³⁷Cs) allow the distinction between two categories of samples, the “modern” ones likely encompassing the interval younger than 1950 CE, and the others that may be considered “sub-modern”. Statistical analyses indicate that dinocyst assemblages belonging to “modern” and “sub-modern” categories are not significantly different. Hence, the dinocyst assemblages of surface sediment samples, both “modern” and “sub-modern”, represent fluxes homogenized over a relatively long time interval, which illustrates a spatial distribution corresponding to the main gradient in oceanographic conditions. Consequently, dinocyst assemblages in surface sediments can be assumed to represent the average “modern” conditions with a sufficiently high degree of confidence for their use in environmental studies and paleoclimate reconstructions.
To understand the relationship between planktonic diatoms and environmental variables in the lakes on the Songnen Plain, northeast (NE) China, we investigated water quality and planktonic diatoms from 71 sampling points in 27 lakes, based on which Canonical Correspondence Analysis (CCA) was conducted. The result show that planktonic diatoms displayed certain responses to environment gradients, and the total phosphorus (TP) explained the maximum variation of planktonic diatom species among the 15 environmental variables, suggesting that TP was the most important and significant environmental parameter affecting the distribution of diatom species. In addition, we established a diatom-total phosphorus transfer (DTPT) function, of which component 5 of the weighted averaging partial least squares regression (WAPLS) was chosen to and compared with a series of weighted average regression (WA) models and WA-PLS models. According to the jackknifing statistical test, the component 5 of WA-PLS models provided a lower root-mean-square error prediction (RMSEP=0.202) and a higher correlation coefficient between observation and prediction (R²_Jack=0.759). After deletion of three outliers, the root-mean-square error prediction of the DTPT function was reduced (RMSEP=0.169) while the correlation coefficient between observation and prediction was increased (R²_Jack=0.823). Therefore, this DTPT function performed better than other regional TP models in the world. However, it remains demanding for expanding the background dataset to improve the prediction ability of the model.
During the Last Interglacial (LIG; ~130 thousand years BP), part of the Greenland Ice Sheet (GIS) melted under the influence of a warmer than present-day climate. However, the impact of this melting on the LIG climate in the North Atlantic region is unknown. Using the LOVECLIM earth system model of intermediate complexity we have systematically tested the sensitivity of the LIG climate to increased freshwater runoff from the GIS. Moreover, additional experiments have been performed to investigate the impact of an idealized reduction of both altitude and extent of the GIS on the LIG climate. By comparing the simulated deep ocean circulation with proxy-based reconstructions, the most realistic simulated climate could be discerned. The resulting climate is characterized by a shutdown of deep convection in the Labrador Sea and a subsequent cooling here by ~6 °C and ~2 °C over the southern part of Baffin Island and the North Atlantic Ocean between 40° N and 60° N. The reduction of altitude and extent of the GIS results in a local warming of up to 6 °C and a reduction in deep convection and accompanying cooling in the Nordic Seas. Combining model results and proxy-based reconstructions enabled us to constrain the possible melt rate of the GIS to a flux between 0.052 Sv and 0.13 Sv. A further comparison of simulated summer temperatures with both continental and oceanic proxy-records reveals that the partial melting of the GIS during the LIG could have delayed maximum summer temperatures in the western part of the North Atlantic region relative to the insolation maximum.
Diatom inferred 2900-year-long records of August sea surface temperature (aSST) and April sea-ice concentration (aSIC) are generated from a marine sediment core from the SE Greenland shelf with a special focus on the interval ca. 870–1910 Common Era (CE) reconstructed in subdecadal temporal resolution.
The Medieval Climate Anomaly (MCA) between 1000 and 1200 CE represents the warmest ocean surface conditions of the SE Greenland shelf over the late Holocene (880 BCE–1910 CE). It was characterized by abrupt, decadal to multidecadal changes, such as an abrupt warming of ~2.4 °C in 55 years around 1000 CE. Temperature changes of these magnitudes are rare on the North Atlantic proxy data. Compared to regional air temperature reconstructions, our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the Greenland ice sheet or intensified sea-ice export from the Arctic as a response to atmospheric warming at the beginning of the MCA. A cool phase, from 1200–1890 CE, associated with the Little Ice Age (LIA), ends with the rapid warming of aSST and diminished aSIC in the early 20th century. The results show that the periods of warm aSST and aSIC minima are coupled with the solar minima suggesting that solar forcing possibly amplified by atmospheric forcing have been behind the variability of surface conditions on the SE Greenland over the last millennium. The results indicate that the SE Greenland shelf is a climatologically sensitive area where extremely rapid changes are possible and highlights the importance of the area under the present warming conditions.
Assessing changes in sea surface conditions due to the effects of past freshwater outflow through Baffin Bay and Davis Strait to the Labrador Sea, hereafter referred to as the Baffin Bay corridor, is relevant in understanding the variability in Labrador Sea Water (LSW) formation. Here, regional changes in oceanographic circulation and sea surface conditions are reconstructed based on organic-walled dinoflagellate cyst (dinocyst) assemblages from four cores collected from deep, central sites of the Baffin Bay corridor. All cores exhibit a major shift in dinocyst assemblages since the late glacial period. This shift consists of a change from a polar–subpolar heterotrophic species assemblage tolerating cold and near permanent ice-covered conditions, to assemblages
characterized by a higher diversity and the occurrence of phototrophic taxa associated with mild conditions. Sea surface reconstructions from the modern analogue technique display a shift from harsh, quasi-perennial ice cover to warmer summer sea surface temperatures and a seasonal sea ice. South of the Davis Strait sill, this regime shift occurred at ca. 11.9 cal ka BP due to the influence of North Atlantic waters. Baffin Bay, however, remained densely sea ice covered until about 7.4 cal ka BP, when these warmer waters penetrated into Baffin Bay and mixed with the West Greenland Current (WGC). This mixing was facilitated by the retreat of the Greenland and Laurentide Ice Sheet (LIS) margins. A major change in Labrador Sea surface conditions occurred nearly at about the same time (~7.6 cal ka BP) when the strong stratification of surface waters weakened because of the reduction in meltwater supplies from the LIS that allowed winter convection and the inception of LSW formation. All these new records demonstrate large amplitude fluctuations in sea surface conditions tightly controlled by the relative strengths and shifts of the warmer WGC and colder Baffin Island Current.
The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years-a key interval for understanding the present and future climate response to these forcings-global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (ce) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 ce that is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 ce, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 ce is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content.
The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis
of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a
pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient
climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation
as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven
reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades
of our 2000-year-long reconstruction occurring between 1950 and 2000.
Studies of annual successions and inter-annual variations in sub-Arctic and Arctic microplankton assemblages are required in order to understand the structure and function of marine ecosystems. This study depicts the microplankton (>20 μm) structure in a sub-Arctic tidewater glacial fjord system, SW Greenland. The descriptions are based on monthly net hauls collected between January 2006 and December 2010. Two blooms, with distinctive species compositions, were identified across all years: a spring bloom and a summer/autumn bloom. In addition, the winter season—with weak stratification, deep tidal mixing, and dense coastal inflows—was characterised by a separate species composition at much lower abundance. Here, the highest variety of microplankton groups was recorded and represented by diatoms (Chaetoceros spp. and Thalassiosira spp.), silicoflagellates, dinoflagellates, and ciliates. During the spring bloom, species correlated with higher light intensities, i.e. haptophytes and diatoms (Thalassiosira spp. and Fragilariopsis spp.), dominated the microplankton assemblage. Among these, diatoms were also correlated with cooler and fresher waters influenced by springtime melt. During the summer/autumn bloom, the microplankton assemblage was mainly represented by diatoms, such as Chaetoceros spp. ‘Low-saline’ chrysophytes were also present. The latter bloom coincides with elevated temperatures in the fjord and renewal of nutrients due to the onset of glacial meltwater run-off from the Greenland Ice Sheet. Our study shows a yearly recurrent succession of microplankton assemblages and that the annual succession is controlled primarily by ocean-fjord-glacier interactions.
This study describes seasonal patterns and proposes likely drivers of an unusual phytoplankton primary production pattern in the outer-sill region of a tidewater outlet glacierinfluenced fjord (Godthåbsfjord) in SW Greenland. It is based on monthly measurements of pelagic primary production and hydrographic conditions during a 7 yr period. Total annual primary production during 2005 to 2012 was between 84.6 and 139.1 g C m-2 yr-1. Two phytoplankton blooms of similar magnitude reoccur in the fjord every year. A 'classical' spring bloom of up to 1743 mg C m-2 d-1 occurred in late April/early May in a water column almost fully mixed due to tidal forces at the fjord sill. After the spring bloom, primary production decreased in June, after which a summer bloom of up to 1383 mg C m-2 d-1 built up. This bloom coincided with the development of a pycnocline caused by substantial runoff from the Greenland Ice Sheet every year during midsummer. This observation supports a hypothesis that fjord circulation modes and subglacial freshwater discharge, leading to upwelling of nutrient rich water, stimulate primary production in the fjord. Future changes in the timing or magnitude of meltwater runoff from the Greenland Ice Sheet are thus likely to affect phytoplankton dynamics in the fjord. © The authors 2015. Open Access under Creative Commons by Attribution Licence.
Cores from a transect along the Kangerdlugssuaq Trough, southeast Greenland shelf, were analysed. Mass susceptibility, total organic carbon, and grain size change markedly around 8 ka, indicating major changes in sediment source and/or depositional environment and mechanisms. Biogenic and inorganic content of the surface and bottom water show dramatic changes over the past ca. 14 ka. indicated by diatoms and opal variations between ca. 13.5 and 9 ka in the form of cool-warm pulses on the outer shelf. On the inner shelf, surface water warming/cooling pulses occur from ca 9 to 6 ka with a general cooling after ca. 6 ka to present. Dinoflagellates indicate meltwater pulses between 13 and 12 ka on the outer shelf with a warming of surface water around 11 ka. The 6 ka cooling is reflected in Baffin Island shelf flora and fauna. Transport paths of exotic pollen show marked changes during three time periods, 12-10 ka, 10-8 ka, and 8 ka-present. -from Authors
Detailed studies on sub-Arctic and Arctic marine diatom assemblages contribute to the understanding of spatial distribution patterns and their physical drivers. In this study, diatom species were analyzed from water samples collected with a Niskin bottle rosette combined with a CTD along the West Greenland coast (63°58′N–71°08′N and 50°49′W–59°06′W) during summer 2007. Diatom community was represented mainly by three genera Thalassiosira,
Fragilariopsis, and Chaetoceros and linked to observed hydrographic and environmental conditions. Thalassiosira spp. were common in coastal waters (particularly Godthåbsfjord) and linked to increased surface water temperature, typical of summer water stratification in West Greenland. Fragilariopsis spp., along with other dominant species associated with higher geographic latitudes, dominated in Arctic fjords (Uummannaq Fjord-Qaumarujuk Fjord). These species generally characterized coastal waters influenced by melting sea ice and/or glacial ice. Chaetoceros spp. were linked to more saline open marine waters, particularly in the Davis Strait south of 70°N, probably corresponding to weaker water stratification and the influence of the West Greenland Current. The present paper provides new knowledge on diatom assemblages along a south–north climate gradient in West Greenland, which is necessary in order to understand how observed ocean-climate changes influence Arctic marine ecosystems. This study provides a reference for palaeoenvironmental reconstructions using diatom microfossils deposited in the West Greenland marine sediments.
Climate in the Arctic region and northwestern Europe is strongly affected by the North Atlantic Oscillation (NAO), the dominant mode of atmospheric variability at mid-latitudes in the North Atlantic region. The NAO index is an indicator of atmospheric circulation and weather patterns: when the index is positive, Europe and the eastern US are mild and wet, whereas Greenland and northern Canada are cold and dry. A negative index is associated with the reverse pattern. Reconstructions of the NAO have so far been limited to the past 900 years. Here we analyse a 5,200-year-long, high-resolution lake sediment record from southwestern Greenland to reconstruct lake hypolimnic anoxia, and link the results to an existing reconstruction of the NAO index from tree rings and speleothems. Using the relationship between the two records, we find that around 4,500 and 650 years ago--around the end of the Holocene Thermal Maximum and the beginning of the Little Ice Age, respectively--the NAO changed from generally positive to variable, intermittently negative conditions. We suggest that variability in the dominant state of the NAO tend to coincide with large-scale changes in Northern Hemisphere climate. However, the onset of the Medieval Climate Anomaly was not associated with any notable changes in the NAO.
Benthic foraminiferal assemblages from a core southwest of Disko Bugt provide a Holocene perspective (last ~7 ka BP) on ice-sheet/ocean interactions between the West Greenland Current (WGC) and the West Greenland ice sheet. Changes in the fauna reveal significant variations in the water mass properties (temperature and salinity) of the WGC through time. From 7.3 to 6.2 ka BP, a relatively warm/strong WGC influences ice-sheet melt in Disko Bugt and causes enhanced meltwater production, resulting in low surface-water productivity. The most favourable oceanographic conditions occur from 5.5 to 3.5 ka BP, associated with ‘thermal optimum-like’ conditions, encompassing minimum ice sheet extent in the Disko Bugt area. These conditions are attributed to: (1) reduced meltwater influence as the ice sheet is land based and (2) enhanced contribution of warm/saline water masses from the Irminger Current to the WGC. The transition into the late Holocene (last ~3.5 ka BP) is characterized by a cooling of oceanographic conditions, caused by increased advection of cold/low-salinity water masses from the East Greenland Current. A longer-term late-Holocene cooling trend within the WGC is attributed to the onset of Neoglacial cooling within the North Atlantic region. Superimposed on this cooling trend, multicentennial-scale variability within the WGC matches reconstructions from a nearby coring site in Disko Bugt as follows: (1) cooling at ~2.5 ka BP, linked to the 2.7 ka BP ‘cooling event’; (2) a warm phase centred at 1.8 ka BP, associated with the ‘Roman Warm Period’; (3) slight warming between 1.4 and 0.9 ka BP, linked to the ‘Medieval Climate Anomaly’; (4) severe cooling of the WGC after 0.9 ka BP, culminating at 0.3 ka BP during the ‘Little Ice Age’. We show that multicentennial-scale palaeoceanography variability along the West Greenland margin is driven by ocean forcing, i.e. variations in the relative contribution of Atlantic (Irminger Current) and Polar (East Greenland Current) water masses to the WGC during the last ~7 ka BP, influencing ice sheet dynamics.
A reconstruction of oceanographic variability of the past 5800 years on the southeast Greenland shelf was obtained by analysing a combined marine sediment record based on two cores from the same site. Cores Fox04G/05R were retrieved from a side basin to a cross-shelf trough connecting the 900 m deep Sermilik Fjord with the Irminger Sea in the northwestern North Atlantic. The record was analysed in terms of grain size distribution, XRF and benthic and planktonic foraminiferal content and the chronology was obtained on the basis of 210Pb and 14C dating. The late-Holocene paleoceanographic variations in the record were characterised by a marked influence from the Irminger Current (IC) at the onset of the record at 5800 cal. yr BP and the regional Holocene Climatic Optimum between 5200 and 4200 cal. yr BP. After 3600 cal. yr BP Neoglacial cooling with increased influence of polar waters from the East Greenland Current (EGC) diminished the influence from the IC. Between 1500 and 700 cal. yr BP, the environment was highly dominated by cold low-salinity water masses characterised by sea ice forming locally and/or transported with an intensified EGC. At 700 cal. yr BP, concordant with the onset of the ‘Little Ice Age’, inflow of IC water masses intensified, notably during short-lived warming episodes of the North Atlantic Current most likely related to a contracted subpolar gyre. At the same time, the EGC polar water transport also intensified leading to a stratified water column on the shelf and this may have favoured entrainment of warm subsurface IC waters. Alternatively, the relatively warm rim of the eastern subpolar gyre may have promoted intense submarine melting of extended Southeast Greenland outlet glaciers at this time, producing enhanced meltwater outflow which favoured estuarine circulation processes maintaining the inflow of IC water masses.
Diatom analyses have been performed on a 425cm long Holocene marine sediment sequence from the North Atlantic south of Iceland and a 920cm sediment core spanning the last c. 7500 years from Skalafjord, Faeroe Islands. Additional core data include stable isotopes and results from magnetic susceptibility measurements, while chronostratigraphic control has been provided by AMS 14C measurements. The diatom records reveal distinct changes in North Atlantic surface circulation and climate that have been correlated with published terrestrial and marine records. Initial Holocene warming is dated at 9900 14C years BP, and after a Preboreal cold spell enhanced North Atlantic Current activity and warming prevailed from 9600 to 8800 14C years BP. From 8800 to 8000 "4C years BP the advection of warm Atlantic water masses weakened, presumably under atmospheric circulation conditions characterized by a dominating negative NAO. Prior to the Holocene Climatic Optimum (6000-5000 14C years BP) distinct hydrographic gradients existed in the northern North Atlantic that were probably most pronounced during the reported '8200 cal. years BP cold event'. After 5000 "4C years BP both core records indicate increased climate instability and periods of cooling ('Neoglaciation'), with enhanced cyclone activity affecting the northern North Atlantic particularly at around 4700, 4200, 3200, 2000, 1500 and 1000 14C years BP.
The study presents data from a multi-year zooplankton sampling programme with year-round monthly sampling in a sub-Arctic
fjord in Greenland (Godthåbsfjord). A total of 56 zooplankton groups were identified over 5 years, with the copepod Microsetella norvegica dominating the mesozooplankton community. Microsetella norvegica was found to be very abundant (maximum abundance: 408 125 ± 161 387 nauplii m−3 and 91 995 ± 6 864 copepodites m−3) and to make up, on average, 87% of the annual copepod assemblage. There was a seasonal zooplankton succession whereby Cirripedia nauplii dominated the biomass in March and April, and Calanus spp. dominated in May and June, followed by M. norvegica from July to September. The total copepod biomass peaked in August (71 ± 10 mg C m−3), mainly (68% on average) due to biomass of M. norvegica, indicating that small copepods are important in this system. This multi-year study describes inter-annual variation in species
abundance and seasonal succession. Fjord–ocean interactions, tidal mixing and the extensive freshwater run-off from the Greenland
Ice Sheet are characteristic features of fjords in Greenland that could be a principle driver behind the present findings.
Changes in the dynamics of the North Atlantic subpolar gyre are involved in the modulation of the northward salinity and heat transport in the northern North Atlantic via the North Atlantic Current (NAC). Variations in the strength of the East Greenland Current (EGC) can influence the gyre dynamics by impacting deep convection in the Labrador Sea. Oxygen isotope data of three planktonic foraminiferal species (surface water Neogloboquadrina pachyderma dextral coiling and Globigerina bulloides; thermocline recorder Globorotalia inflata) from a site located close to the present Sub-Arctic Front at the Reykjanes Ridge suggest significant strengthening or shifting of the Sub-Arctic Front throughout the late Holocene. The oxygen isotope based inferences are supported by Mg/Ca-derived temperature reconstructions from Neogloboquadrina pachyderma dextral coiling, alkenone-derived sea surface temperature and other paleoclimatic proxy data. The late-Holocene strengthening/shift of the Sub-Arctic Front appears caused by an increasingly more defined and fresher EGC. The proposed subpolar gyre changes may modulate the northward heat transport, and explain the geographically different long-term climatic trends in the North Atlantic during the late Holocene, i.e. a cooling of the EGC-influenced regions and a warming of the NAC-influenced areas from c. 4 to 5 ka. This mechanism cannot, however, explain the simultaneous occurrence of millennial-scale events at c. 5.6, 3.9, 2.7, 1.3 ka and the ‘Little Ice Age’ in both areas. Noteworthy is the steadily increasing amplitude of these cold events at the Reykjanes Ridge, likely induced by drift ice and/or EGC-influence culminating in the ‘Little Ice Age’. A widespread pronounced warming at 2.0 ka seems to represent the ‘Roman Warm Period’ and reflects the warmest period of the late Holocene.
Measurements of sea ice concentration from the Special Sensor Microwave Imager (SSM/I) using seven different algorithms are compared to ship observations, sea ice divergence estimates from the Radarsat Geophysical Processor System, and ice and water surface type classification of 59 wide-swath synthetic aperture radar (SAR) scenes. The analysis is confined to the high-concentration Arctic sea ice, where the ice cover is near 100%. During winter the results indicate that the variability of the SSM/I concentration estimates is larger than the true variability of ice concentration. Results from a trusted subset of the SAR scenes across the central Arctic allow the separation of the ice concentration uncertainty due to emissivity variations and sensor noise from other error sources during the winter of 2003–2004. Depending on the algorithm, error standard deviations from 2.5 to 5.0% are found with sensor noise between 1.3 and 1.8%. This is in accord with variability estimated from analysis of SSM/I time series. Algorithms, which primarily use 85 GHz information, consistently give the best agreement with both SAR ice concentrations and ship observations. Although the 85 GHz information is more sensitive to atmospheric influences, it was found that the atmospheric contribution is secondary to the influence of the surface emissivity variability. Analysis of the entire SSM/I time series shows that there are significant differences in trend between sea ice extent and area, using different algorithms. This indicates that long-term trends in surface and atmospheric properties, unrelated to sea ice concentration, influence the computed trends.
The diatom flora from a high-resolution core collected from Disko Bugt, central West Greenland, records variations in surface water temperature for the late Holocene (1600—300 cal. BP). Our data support the existence of a previously identified anti-phase relationship between the surface water temperature from West Greenland and climate events recorded in the NE Atlantic and between surface and subsurface waters (identified from benthic foraminifera) of the West Greenland Current (WGC). The diatom flora record relatively cool surface water conditions during the end of the ‘Roman Warm Period’ and ‘Medieval Warm Period’ (MWP), and relatively warmer surface water conditions during the ‘Dark Ages Cold Period’ and ‘Little Ice Age’ (LIA). This is particularly pronounced during the MWP, experiencing the coldest conditions, and the LIA experiencing the warmest conditions through the whole sequence studied. The most likely explanation for this anti-phase relationship is linked to the flux of meltwater delivered to the WGC from sea ice and the Greenland ice sheet off the West Greenland margin. The generally warmer conditions of the MWP resulted in increased melting of sea ice and the Greenland ice sheet producing an increased meltwater flux and cooling of the surface waters of the WGC. In contrast, reduced meltwater flux during the relatively cold LIA resulted in reduced meltwater flux to the WGC, producing a relative warming of the surface waters recorded by the diatom flora.
The oxygen-isotope record of palaeotemperature from Greenland ice cores has for many years been the kingpin of climate reconstructions for the North Atlantic region and northern Europe. An air temperature ‘seesaw’ between Greenland and northern Europe, first described in AD 1765, is also well known and is related to the North Atlantic Oscillation (NAO). Whereas the NAO index series is based on instrumental records of air pressure, the North Atlantic climate ‘seesaw’ has conventionally been based on air-temperature records. Here we describe relationships between this ‘seesaw’ mechanism and the Greenland (GISP2) oxygen-isotope chronology of air-temperature variations, as well as relationships between GISP2 Na+ (sea-salt) variations and instrumental records of North Atlantic storminess. The GISP2 proxy air-temperature record is calibrated for the last 130 years with instrumental weather records for West Greenland, while the Na+ series is compared with instrumental records of North Atlantic storminess change. Reconstruction of an annual series of these climate parameters for the last 1000 years shows that during the ‘Mediaeval Warm Period’ there were no years characterized by high Na+ extremes (high North Atlantic storminess) but there were many years when there were extremes of temperature. Remarkably, there were no years of exceptionally low air temperature and high Na+ precipitation at GISP2 between AD 1650 and 1710, a period of time that in northern Europe incorporates the period of maximum ‘Little Ice Age’ cooling. It would appear also that for the last thousand years the most extreme ‘seesaw’ winters when GISP2 temperatures were very low and Na+ concentrations were high occurred in discrete clusters and pairs of years.
Examination of 17 samples collected by a 20 ?m meshed meshed net in Kongsfjorden, Svalbard, 8–19 July 1988, showed a dominance of dinoflagellates and the chrysophyte Dinobryon Balticum in the surface layers, whereas the diatom and the haptophyte Phaecystis pouchetii abundance increased with depth. The diatom Pseudo-nitzschia granii appeared together with P. pouchetii through the whole water column, and Actinocyclus curvatulus was one of the few diatoms present also in the surface samples. Two samples, from 15 and 50 m, respectively, were cleaned of organic material and mounted in Naphrax for a more critical identification of the diatoms. We were able to group the species according to habitats, especially types of ice. The planktonic Thalassiosira antarctica var. borealis, T. hyalina, T. nordenskioeldii, Bacterosira bathyomphaia, Chaetoceros furcellatus, C. socialis and Fragilariopsis oceanica were present mainly as resting stages representing a post-bloom situation. These species and T. gravida appear early in the season and may have started to grow already under the ice. Fragilariopsis cylindrus and F. oceanica seem to have a closer affinity to ice than Thalassiosira and Chaetoceros spp. although they are common in the plankton. Some Nitzschia species which are usually regarded as typical sea-ice diatoms and have thicker and older ice as the main habitat were present only in small cell numbers in the plankton samples. The last component, evidently introduced from Atlantic water in the Norwegian Sea, consisted of diatoms with a more oceanic distribution, e. g. Fragilariopsis pseudonana and a small form of Thalassiosira bioculata.
Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
If radiocarbon measurements are to be used at all for chronological purposes, we have to use statistical methods for calibration. The most widely used method of calibration can be seen as a simple application of Bayesian statistics, which uses both the information from the new measurement and information from the 14 C calibration curve. In most dating applications, however, we have larger numbers of 14 C measurements and we wish to relate those to events in the past. Bayesian statistics provides a coherent framework in which such analysis can be performed and is becoming a core element in many 14 C dating projects. This article gives an overview of the main model components used in chronological analysis, their mathematical formulation, and examples of how such analyses can be performed using the latest version of the OxCal software (v4). Many such models can be put together, in a modular fashion, from simple elements, with defined constraints and groupings. In other cases, the commonly used “uniform phase” models might not be appropriate, and ramped, exponential, or normal distributions of events might be more useful. When considering analyses of these kinds, it is useful to be able run simulations on synthetic data. Methods for performing such tests are discussed here along with other methods of diagnosing possible problems with statistical models of this kind.
Foraminiferal assemblages and the sedimentology of two cores (POR20 and POR21) from eastern Disko Bugt, west Greenland, are used to identify environmental changes in the area over the past c. 2200 years. Changes in the sediment flux supplied to the core sites from Jakobshavn Isbrae are used to assess the relative position of the calving margin. An Atlantic water influence as strong as, or slightly stronger than, present prevailed at c. 2200 cal. yr BP. A trend of increasing Atlantic water influence then culminated in peak warm and saline hydrographic conditions c. 1664-474 cal. yr BP encompassing the 'Medieval Warm Period'. This period was marked by a retreat of the calving front of Jakobshavn Isbrae and was followed by a marked cooling in hydrographic conditions relating to an increase in the influence of the East Greenland Current in the West Greenland Current corresponding to the climatic episode the 'Little Ice Age'. A rise in sedimentation rate over this period relates to the well-documented advance of Jakobshavn Isbrae. The record from Disko Bugt shows good agreement with the temperature record from the Greenland ice cores and other climatic and oceanographic reconstructions in the region.
We present new surface water proxy records of meltwater production (alkenone derived), relative sea surface temperature (diatom, alkenones) and sea ice (diatoms) changes from the Disko Bugt area off central West Greenland. We combine these new surface water reconstructions with published proxy records (benthic foraminifera - bottom water proxy; dinocyst assemblages – surface water proxy), along with atmospheric temperature from Greenland ice core and Greenland lake records. This multi-proxy approach allows us to reconstruct centennial scale middle to late Holocene palaeoenvironmental evolution of Disko Bugt and the Western Greenland coastal region with more detail than previously available.
This chapter provides an introductory biology of marine diatoms, their classification, heteromorphy, evolution, and critical evaluation. It consists of sections on classification as well as generic atlas. A diatom system is based on results from light and electron microscopy and constructed key to the diatom families. Diatoms reproduce vegetatively by binary fission resulting in formation of two new individuals within the parent cell frustule. The probable size range of the diatom cells are species dependent, and the specific variation may be as large as 8–10 times the length of the apical axis or the diameter. Despite the availability of other publications, there is still a need to fill the gap with respect to the global aspect, especially when identifying Marine diatoms at the specific level. The entire discussion aims to meet the morphological need of new diatom information as well as the classical identification literature. This comprehensive volume explores the two Polar Regions and has an ecological interpretation as well as a taxonomic part with the key to the study of marine diatom species. General characteristics of marine diatoms together with their life cycles have also been discussed.
Geophysical ice-sheet models are used to predict future ice-sheet dimensions and, in turn, these projections help estimate the magnitude of eustatic sea-level rise. Before models can confidently predict ice-sheet behavior, they must be validated by being able to duplicate the geological record of ice-sheet change. Here, we review geological records of Greenland Ice Sheet (GrIS) change, with emphasis on the warmer-than-present middle Holocene, and compare these records to published studies that numerically simulate GrIS behavior through the Holocene. Geological records are concentrated in West and Southwest Greenland, which are also the regions where the GrIS margin likely experienced the greatest distance of inland retreat during the middle Holocene. Several records spanning from Melville Bugt to Jakobshavn Isfjord in western Greenland indicate the GrIS achieved its minimum extent between ~5 and 3 ka, and farther south in the Kangerlussuaq region, new data presented here indicate the ice margin reached its minimum extent between ~4.2 and 1.8 ka. In the Narsarsuaq region in southern Greenland, the GrIS likely achieved its minimum configuration between ~7 and 4 ka. We highlight key similarities and discrepancies between these reconstructions and model results, and finally, we suggest that despite some degree of inland retreat, the West and Southwest GrIS margin remained relatively stable and close to its current position through the Holocene thermal maximum.
Records of foraminiferal assemblages combined with lithological properties (grain size, magnetic parameters and XRF data) of marine sediment cores from West Greenland coastal waters and the adjacent Labrador Sea document widespread early Holocene meltwater discharge. This discharge is concluded to originate from large-scale melting of the Greenland Ice Sheet (GIS) having started prior to 8600 cal. yr BP and ended at about 7700–7500 cal. yr BP, when the GIS margin had withdrawn from the fjords and become mainly land-based. The benthic foraminiferal record from one of the coastal sites mainly reflects West Greenland Current (WGC) subsurface water properties and to a minor degree surface productivity. The most significant feature in this record is an abrupt shift to a higher-productivity regime around ~ 7700 cal. yr BP. We suggest that the cessation of a widespread GIS meltwater discharge at that time favoured an increased influence of (sub)surface water of Atlantic origin and initiation of modern subpolar gyre circulation enabling Labrador Sea deep convection. Further offshore, a record of planktonic foraminiferal assemblages shows an oceanographic change at ca. 9500 cal. yr BP, whilst a gradual but marked change in the planktonic foraminiferal assemblage between 8800 and 7000 cal. yr BP may be related to a narrowing of the WGC low-salinity surface water belt. The oceanic regime off West Greenland prior to ~ 7800 cal. yr BP was thus characterised by the presence of a permanent and widespread meltwater surface layer, presumably preventing deep convection in this region. Apart from indications of a slight decrease in meltwater discharge by the benthic foraminiferal fauna data, neither of the records show any clear signal of a regionally important 8.2 ka event.
A multi-sensor bias correction method has been developed using satellite sea surface temperature (SST) products from one microwave and five infrared sensors that cover the Arctic Ocean. The correction method has been used to construct improved single sensor and multi-sensor, merged and interpolated satellite SST products from January to December 2008.
The validation of the satellite products ingested in the level 4 production shows that large biases can persist for months in this region. The SST products from the AATSR sensor on ENVISAT and the NAVOCEANO AVHRR GAC are the most stable and reliable products for the Arctic region. These products have therefore been used to construct the reference product against which the other satellite products have been corrected. The bias correction method has been developed using detailed error characteristics and thorough time-space analysis, and the bias corrected fields are validated against in situ observations from drifting buoys. All the individual satellite products show improvement in both bias and standard deviation after correction. Largest improvements are found for the Modis sensor on the Terra satellite, where biases are improved from −0.46 K to 0.02 K with the correction method. Temporal validation statistics reveal that extended periods with significant biases are also removed by the bias correction method.
A significant improvement is seen when the corrected satellite products are used for the SST analysis. When compared against drifting buoys, not included in the analysis, the corrected level 4 satellite SST product shows a bias of −0.04 K and standard deviation of 0.54 K, compared to an original bias of −0.28 K and standard deviation of 0.61 K. The effect of a missing reference sensor is assessed for the full period. Level 4 test runs using only one reference sensor demonstrates that improvements can be obtained with a single sensor bias correction method, and that the AATSR sensor gives the largest improvements. However, using both reference sensors in the bias calculation gives significantly better performance than using just one.
The ice-loaded Labrador Current (LC) is an important component of the western North Atlantic circulation that influences the position and strength of the northern limb of the North Atlantic Current (NAC). This flow of cold and fresh Polar Waters originating from the Arctic has a marked impact on the North Atlantic climate, yet little is known about its variability beyond the instrumental period. In this study, we present the first sub-decadal alkenone-based 2000-year long sea-surface temperature (SST) records from the western Labrador Sea, a climatically crucial region at the boundary between the LC and the NAC. Our results show a clear link between the LC strength and the Northern Annular Mode (NAM), with a stronger NAM and a more vigorous LC during the Medieval Climate Anomaly (MCA). This suggests enhanced LC activity upon future global warming with implications for the Atlantic meridional overturning circulation (AMOC).
A diatom-based sea-ice concentration (SIC) transfer function was developed by using 72 surface samples from west of Greenland and around Iceland, and validated against associated modern SIC. Canonical correspondence analysis on surface sediment diatoms and monthly average of SIC indicated that April SIC is the most important environmental factor controlling the distribution of diatoms in the area, justifying the development of a diatom-based SIC transfer function. The agreement between reconstructed SIC based on diatoms from West Greenland and the satellite and modelled sea-ice data during the last ~ 75 yr suggests that the diatom-based SIC reconstruction is reliable for studying the palaeoceanography off West Greenland.
Relatively warm conditions with a strong influence of the Irminger Current (IC) were indicated for the early part of the record (~ 5000–3860 cal. yr BP), corresponding in time to the latest part of the Holocene Thermal Maximum. Between 3860 and 1510 cal. yr BP, April SIC oscillated around the mean value (55%) and during the time interval 1510–1120 cal. yr BP and after 650 cal. yr BP was above the mean, indicating more extensive sea-ice cover in Disko Bugt.
Agreement between reconstructed April SIC and changes in the diatom species suggests that the sea-ice condition in Disko Bugt was strongly influenced by variations in the relative strength of two components of the West Greenland Current, i.e. the cold East Greenland Current and the relatively warm IC. Further analysis of the reconstructed SIC record suggests that solar radiation may be an important forcing mechanism behind the historic sea-ice changes.
Paleoenvironments during the late Younger Dryas through early Holocene retreat of the Greenland Ice Sheet from the outer shelf in the Disko Trough system of central West Greenland were investigated via lithofacies, foraminifera, dinocysts and sediment provenance analyses in radiocarbon-dated sediment cores from the upper slope (JR175-VC35) and outer shelf (JR175-VC20 and HU2008029-070CC). Core data show that the ice margin retreated rapidly from the outer shelf by calving, beginning by 12.2k cal a BP under cold paleoceanographic conditions with up to 11 months of sea-ice. Ice retreat into Disko Bugt was well underway by 10.9k cal a BP. Enhanced ice-sheet ablation in Disko Bugt and elsewhere along the West Greenland coast is inferred from cold glacial marine conditions associated with high sedimentation rates between 10.9 and 9.5k cal a BP on the outer shelf. Glacial marine conditions are recorded on the outer shelf until 7.8k cal a BP. Detrital carbonate-bearing sediments rich in >2-mm clasts deposited between 11.6 and 10.6 k cal a BP indicate that icebergs calved from northern Baffin Bay ice margins were melting and releasing sediments along West Greenland while the Greenland Ice Sheet margin was retreating into Disko Bugt.
Sea surface temperature fields of the North Sea and Baltic Sea have been
constructed for the year 2001 using a multiplatform Optimal
Interpolation scheme. The analyzed fields are constructed every 12 h on
a 10 km spatial grid. The product is based upon observations from the
three NOAA satellites 12, 14 and 16 together with a large amount of in
situ observations. Space dependent covariance functions are estimated
from the satellite observations and account for spatial and temporal
lags. Several independent methods have been used to assess the error on
the sea surface temperature product. Compared against independent in
situ observations, the mean RMS difference for the year 2001 is 0.78
°C. The spatial distribution of the errors reveals that the Baltic
Sea in general show higher errors than the North Sea. The error
statistics throughout the year show a temporal variation of the errors
with maximum during summer and winter. Tests with a varying number of
satellite observations show that the accuracy of the satellite
observations is the most important parameter in terms of reducing the
errors on the interpolated sea surface temperature product.
A decadally resolved diatom record from a sediment core collected from
Disko Bay, central West Greenland, reveals variations in hydrological
conditions for the late Holocene. The diatom flora record two clear
trends in surface water temperatures: a pronounced cooling of surface
waters during the Medieval Climate Anomaly (MCA) and a progressive
warming in surface waters during the Little Ice Age (LIA), previously
identified in North Atlantic studies. Our data support the existence of
a previously identified anti-phase relationship between surface water
temperatures off West Greenland and climate events recorded in the
north-east Atlantic. The diatom assemblages show relatively cool surface
water conditions during warmer climatic intervals, e.g.
3.6-2.7 cal. ka BP, the MCA, while relatively warm
surface water conditions during colder climatic periods, e.g. the Dark
Ages (DA) and the LIA. The exception to this is the Roman Warm Period
(RWP), which in West Greenland shows warmer surface waters and climatic
conditions. Our data also show the existence of anti-phase relationship
between surface and sub-surface water temperatures in Disko Bay during
the interval 3.6-2.7 cal. ka BP (cooler surface with
warmer subsurface waters) and towards the end of the LIA (warmer surface
and cooler sub-surface waters). These anti-phases patterns are possibly
linked to: 1) the local spring-summer hydrological conditions (e.g.
warmer climatic intervals), such as meltwater flux from sea
ice/continental ice and water stratification, and 2) large-scale
ocean-climate interactions (e.g. cooler climatic intervals) within the
North Atlantic Oscillation (NAO)-type climate see-saw between West
Greenland and north-west Europe associated with variability in the
Atlantic Meridional Overturning Circulation (AMOC).
This paper presents new evidence regarding relative sea-level (RSL) changes and vertical land motions at three sites in Greenland since 1300 A.D., a time interval that spans the later part of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We observe RSL rise at two sites in central west Greenland from c. − 0.80 ± 0.20 m at c. 1300 A.D. to c. − 0.20 m ± 0.25 m at c. 1600 A.D., after which RSL slowed and then stabilised. At a third site in south Greenland, we observe RSL rise from c. − 1.40 ± 0.20 m at c. 1400 A.D. until c. 1750 A.D., after which RSL slowed and was stable during at least the latter part of the 20th century. The c. 1600 A.D. RSL slow-down seen at the two former sites is surprising because it occurs during the LIA when one might expect the ice sheet to be gaining mass and causing RSL to rise. We interpret this RSL slowdown to indicate a period of enhanced regional mass loss from central west Greenland since c. 1600 A.D. and propose two hypotheses for this loss: first, a reduction in precipitation during cold and dry conditions and second, higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards. The latter hypothesis is compatible with a well-established temperature seesaw between western Greenland and northern Europe and, potentially, a previously identified shift from a positive to generally more negative NAO conditions around 1400 to 1600 A.D. Our study shows how RSL data from Greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern Europe the ice sheet in west Greenland gained mass.
Diatom assemblages from Holsteinsborg Dyb on the West Greenland shelf were analysed with high temporal resolution for the last 1200 years. A high degree of consistency between changes in frequency of selected diatom species and instrumental data from the same area during the last 70 years confirms the reliability of diatoms (particularly sea-ice species and warm-water species) for the study of palaeoceanographic changes in this area. A general cooling trend with some fluctuations is marked by an increase in sea-ice species throughout the last 1200 years. A relatively warm period with increased influence of Atlantic water masses of the Irminger Current (IC) is found at ad 750–1330, although with some oceanographic variability after ad 1000. A pronounced oceanographic shift occurred at ad 1330, corresponding in time to the transition from the so-called ‘Medieval Warm Period’ (MWP) to the ‘Little Ice Age’ (LIA). The LIA cold episode is characterized by three intervals with particularly cold sea-surface conditions at ad 1330–1350, ad 1400–1575 and ad 1660–1710 as a result of variable influence of Polar waters in the area. During the last 70 years, two relatively warm periods and one cold period (the early 1960s to mid-1990s) are indicated by changes in the diatom components. Our study demonstrates that sedimentary records on the West Greenland shelf provide valuable palaeoenvironment data that confirm a linkage between local and large-scale North Atlantic oceanographic and atmospheric oscillations.
Global warming signals are expected to be amplified in the polar regions
because of ice-atmosphere feedbacks associated with the high
reflectivity of the ice and snow that blankets much of the region.
Analysis of infrared satellite data reveals that the Arctic region has
been warming at the rate of 0.5 ºC per decade since 1981 but large
spatial variability in the trends are apparent with the most positive
occurring in North America and the Western Arctic and with some negative
trends occurring in parts of Russia. During approximately the same
period, the Arctic perennial ice cover declined at a rapid rate of 9.2 %
per decade. While large interannual variability in the perennial ice
area was observed in the 1980s and early 1990s, the perennial ice areas
from 1998 to 2004 have been abnormally low compared to the average
perennial ice area during the previous 20 years. Moreover, the length
of melt temperatures has also been increasing by 13 days per decade over
sea ice covered areas, suggesting concurrent thinning in the ice cover.
In other regions, the length of melt has increased by 5 days per decade
over Greenland, showing consistency with the observed thinning in the
ice sheets and increasing extent of melt areas. The length of thawing
at the permafrost areas of North America has also been increasing at 7
days per decade, which can be a major concern in inhabited regions.
Furthermore, the areal extent of the snow cover in the entire Northern
Hemisphere has been decreasing by about 2.6 % per decade while most
glaciers in the Arctic region have been declining. The locations of
most rapid changes are in same general areas as where the surface
temperature data show considerable warming. The overall impact of
aforementioned changes in the Arctic region can be profound, especially
if the current trends continue.
We present a new coefficient-based retrieval scheme for estimation of sea surface temperature (SST) from the Along Track Scanning Radiometer (ATSR) instruments. The new coefficients are banded by total column water vapour (TCWV), obtained from numerical weather prediction analyses. TCWV banding reduces simulated regional retrieval biases to <0.1 K compared to biases similar to 0.2 K for global coefficients. Further, detailed treatment of the instrumental viewing geometry reduces simulated view-angle related biases from similar to 0.1 K down to <0.005 K for dual-view retrievals using channels at 11 and 12 mu m. A novel analysis of trade-offs related to the assumed noise level when defining coefficients is undertaken, and we conclude that adding a small nominal level of noise (0.01 K) is optimal for our purposes. When applied to ATSR observations, some inter-algorithm biases appear as TCWV-related differences in SSTs estimated from different channel combinations. The final step in coefficient determination is to adjust the offset coefficient in each TCWV band to match results from a reference algorithm. This reference uses the dual-view observations of 3.7 and 11 mu m. The adjustment is independent of in situ measurements, preserving independence of the retrievals. The choice of reference is partly motivated by uncertainty in the calibration of the 12 mu m of Advanced ATSR. Lastly, we model the sensitivities of the new retrievals to changes to TCWV and changes in true SST, confirming that dual-view SSTs are most appropriate for climatological applications.
Among the most common diatoms in arctic spring blooms are Fossula arctica Hasle, Syvertsen et von Quillfeldt, Fragilariopsis cylindrus (Grunow) Krieger in Helmcke et Krieger, F. oceanica (Cleve) Hasle, Thalassiosira antarctica var. borealis Fryxell, Doucette et Hubbard, T. hyalina (Grunow) Gran and Chaetoceros socialis Lauder. Although Fossula arctica was described as late as 1996, the others have been recorded for more than 100 years. Despite this, the different Fragilariopsis species are often confused with each other and with other ribbon-shaped species. This is also true of Thalassiosira spp. The need to clarify the differences between some of these common arctic diatoms is clear. Identifying species in water mounts may be particularly difficult. Descriptions in the literature of species in water mounts are also rather few. A study was conducted in order to facilitate the identification of those species most often confused. Distinctive features for each species are described and illustrated and possible misidentifications discussed to ease the identification. The results are based on the author's samples collected from different Arctic areas as well as on information from the literature.