Fig 1 - uploaded by Maarten Arnoud Prins
Content may be subject to copyright.
a: Map of eastern Canadian Arctic and western Greenland, showing the positions of Nares Strait, Disko Bugt, Frobisher Bay, and sites of previous studies (*), locations of LSSL2001 long cores (@BULLET) and other samples (x) from Cruise LSSL2001, and arrows showing surface currents (bold black = Arctic Surface Water; gray = mixed Arctic and North Atlantic Water). The rectangle delineates the Nares Strait study area.
Source publication
A sediment-sampling program was carried out in the Nares Strait region during the Nares 2001 Expedition to obtain cores for high-resolution palaeoceanographic studies of late Pleistocene-Holocene climate change. Long cores (>4 m) were obtained from basins near Coburg Island, Jones Sound (Core 6, 75°35' N, 78°41'W), John Richardson Fiord off Kane Ba...
Similar publications
The late Aptian (Early Cretaceous) is a crucial time interval for understanding the paleoceanographic changes in the Southern Hemisphere. Oceanographic changes in the emerging South Atlantic Ocean during this interval are reflected in the stratigraphic distribution of dinoflagellate communities recorded in the Muribeca and Riachuelo formations of t...
Zusammenfassung: Während der Nares-Expedition 2001 wurden die Sedi-mente im Gebiet der Nares Strait beprobt, um Kerne für hochauflösende paläozeanographische Untersuchungen des pleistozänen bis holozänen Klima-wandels zu gewinnen. Kerne mit einer Länge von über 4 m wurden aus Sedi-menten des Jones Sound bei Coburg Island (Kern 6: 75°35' N, 78°41' W...
Analysis of compositional changes in fossil organic-walled dinoflagellate cyst (dinocysts) assemblages is a widely used tool for the quantitative reconstruction of past environmental parameters. This approach assumes that the assemblage composition is significantly and independently related to the reconstructed environmental parameters. Theoretical...
The Fram Strait is one of the largest gateways through which meltwater and sea ice are exported to the subarctic North Atlantic, transiting the North-East Greenland shelf via the southward flowing East Greenland Current. Observations indicate a recent freshening of the East Greenland Current that may have implications for wider oceanic circulation...
Since its existence, paleoceanography has relied on fossilized populations of planktonic foraminifera. Except for some extreme environments, this calcareous protist group composes most of the silty-to-sandy fraction of the marine sediments, i.e., the foraminiferal oozes, and its extraction is probably the simplest among the currently existing set o...
Citations
... 2 of 14 microscopy analyses of fossilized eukaryotes, such as diatoms, foraminifera, dinoflagellate cysts, radiolaria, and coccolithophores (all belonging to the large group of single-celled protists) have been the gold standard to reconstruct paleoenvironments, paleoproductivity and palaeoceanographic conditions (Mudie et al., 2006;O'Brien et al., 2021;Oksman et al., 2019;Weckström et al., 2020;Yasuhara et al., 2020). However, such microfossil-based reconstructions are limited, as only the more robust and fossilized species are preserved in seafloor sediments, meaning that the vast number of soft-bodied organisms that have also thrived in the past ocean are not accounted for (e.g., many flagellates, chlorophytes, haptophytes, ciliates, zooplankton) (Ellegaard et al., 2020;Witkowski et al., 2016). ...
Studies incorporating sedimentary ancient DNA (sedaDNA) analyses to investigate paleo‐environments have increased considerably over the last few years, and the possibility of utilizing archived sediment cores from previous field campaigns could unlock an immense resource of sampling material for such paleo‐investigations. However, sedaDNA research is at a high risk of contamination by modern environmental DNA, as sub‐optimal sediment storage conditions may allow for contaminants (e.g., fungi) to grow and become dominant over preserved sedaDNA in the sample. Here, we test the feasibility of sedaDNA analysis applied to archive sediment material from five sites in the North Atlantic, collected between 1994 and 2013. We analyzed two samples (one younger and one older) per site using a metagenomic shotgun approach and were able to recover eukaryotic sedaDNA from all samples. We characterized the authenticity of each sample through sedaDNA fragment size and damage analyses, which allowed us to disentangle sedaDNA and contaminant DNA. Although we determined that contaminant sequences originated mainly from Ascomycota (fungi), most samples were dominated by Emiliania huxleyi, a haptophyte species that commonly blooms in the study region. We attribute the presence of contaminants to non‐ideal sampling and sample storage conditions of the investigated samples. Therefore, while we demonstrate that sedaDNA analysis of archival North Atlantic seafloor sediment samples are generally achievable, we stress the importance of best‐practice ship‐board sampling techniques and storage conditions to minimize contamination. We highly recommend the application of robust bioinformatic tools that help distinguish ancient genetic signals from modern contaminants, especially when working with archive material.
... The NOW area is highly vulnerable to long-term changes in climate and ocean dynamics (e.g. Tremblay 2002;Mudie et al. 2006;Cormier et al. 2016;Ribeiro et al. 2021;Koerner et al. 2021). Indeed, increases in the northward advection of warm Atlantic-sourced water via the West Greenland Current (WGC) and atmospheric temperature can contribute to enhanced mass loss from the glaciers and ice caps of northern Baffin Bay and the NW Greenland margin (e.g. ...
... Deglacial and Holocene sedimentation rates near the Manson Icefield area range from 0.67 to 0.046 cm a −1 (e.g. Rochon & Vernal 1994;Mudie et al. 2006;Bailey et al. 2013;St-Onge & St-Onge 2014;Cormier et al. 2016;Ribeiro et al. 2021). ...
The physical, sedimentological, mineralogical and elemental geochemical properties of sediment cores AMD1803-02BC and 01PC from the Cape Norton Shaw Inlet were investigated to reconstruct glacial sediment discharges from southeastern Manson Icefield and document the impact of ice–ocean interactions on the sediment dynamics and opening of the North Water Polynya (NOW) in northwestern Baffin Bay since the last deglaciation. Laminated glaciomarine sediments rich in quartz and feldspar are observed prior to 11 cal. ka BP and were probably deposited by hyperpycnal currents triggered by the local retreat of the southern margin of the Innuitian Ice. Detrital proxies suggest that Early Holocene sediment dynamics were mainly influenced by sea ice and iceberg rafting and meltwater discharges related to the deglaciation of eastern Smith (~11 to 10.65 cal. ka BP) and Jones (~10.7 cal. ka BP) sounds. This also provides an upper limit to the timing of formation of the NOW. The high detrital carbonate contents during 8.8 to 6.6 cal. ka BP confirm that enhanced carbonate-rich sediment export from Nares Strait to northern Baffin Bay occurred during and after the deglaciation of Kennedy Channel (8.8 to 8.2 cal. ka BP). Canadian Shield sediment inputs have dominated since 6.6 cal. ka BP, indicating that sedimentation is mainly influenced by Cape Norton Shaw glacier discharges. The lower level of sedimentation recorded in core 01PC during the Middle to Late Holocene suggests an accelerated landward retreat of the Cape Norton Shaw glaciers in response to warmer marine conditions. During the Neoglacial period, higher sedimentation rates and detrital proxies in the cores suggest increased glacial erosional processes, probably associated with the long-term declines in boreal summer insolation and glacier growth. Finally, mineralogical and grain-size data in core 02BC support the idea that increased Arctic atmospheric temperatures have had an important influence on the glacial dynamics during the industrial period.
... Many oceanographic studies have contributed to a better understanding of the mechanisms driving the formation and maintenance of the NOW polynya (e.g., Barber et al., 2001;Yao and Tang, 2003;Kwok et al., 2010;Rasmussen et al., 2010;Moore and McNeil, 2018), and characterizing its water masses (e.g., Melling et al., 2001;Bâcle et al., 2002;Lobb et al., 2003;Tang et al., 2004;Münchow et al., 2015). In addition, marine sediment records from northern Baffin Bay have been studied to investigate past climate variability in the NOW region (e.g., Levac et al., 2001;Cormier et al., 2016;St-Onge and St-Onge, 2014;Knudsen et al., 2008;Mudie et al., 2005Mudie et al., , 2006. However, our understanding of past sea-surface changes in northern Baffin Bay is still incomplete due to the low resolution or hiatuses in these published records. ...
The accelerating sea-ice, ice sheet and glacial melt associated with climate warming have resulted in important changes in the Arctic region over the past decades. In northern Baffin Bay, the formation of the North Open Water (NOW) polynya, which is intrinsically linked to regional sea-ice conditions and ocean circulation, has become more variable in recent years. To understand how climate-driven changes affect sea-surface conditions in the polynya, we analyzed dinoflagellate cyst assemblages from a sediment core record that covers the past ca. 3800 years, and developed an index based on the locations of modern analogues from a large regional reference dataset. Our results suggest a prolonged open-water season characterized by higher summer sea-surface salinity and temperature between ca. 3800 to 2500 years BP, followed by gradual cooling, freshening and increased sea-ice influence from 2500 to 1500 years BP, and continued sea-surface cooling with a shorter open-water season from 1500 to 156 years BP. The modern warming translates into a rapid turnover in the composition of dinoflagellate cyst assemblages during the last 50 years of our record, unprecedented for at least the past 3800 years studied here. For the uppermost part of our core (ca. 2009 to 2015 CE), the dinoflagellate cyst assemblages suggest increased stratification and sea-surface freshening resulting from increased glacial runoff and Arctic sea-ice export into the NOW region. Arctic climate projections indicate accelerated sea-ice thinning and ice sheet melt in the future, pointing to a shorter polynya season and increased polar inflows leading to fundamental changes within the NOW polynya into future years.
... Our central NOW record does not cover this period, but sea-ice-free conditions for 4-5 months per year were inferred from core 91-039-008P nearby our central site 50 . High diatom productivity from ~ 7400 yrs BP was seen as evidence of polynya conditions off Jones Sound 27 and there was an increase in the relative abundance of phototrophic dinoflagellate cyst species at the outlet of Lancaster Sound 51 . An increase in biological productivity, expressed by increasing BSi fluxes, is evident at our peripheral NOW site during this interval. ...
... The rapid increase in the relative abundance of agglutinated taxa at our peripheral NOW site likely reflects the onset of moderate production of corrosive CO 2 -rich brines [23][24][25][26] . A similar shift toward agglutinated assemblages ~ 6500 yrs BP and increasing diatom abundance in the western sector of the NOW were attributed to summer open water polynya production 27 . The appearance of the benthic foraminifera species N. labradorica (Fig. 7) suggests fresh supplies of phytodetritus from enhanced sea-ice related productivity in the area (e.g. ...
... Physical preconditioning for strong NOW formation, namely the harsh sea-ice conditions and the inception of ice arches in Smith Sound, had already begun by ~ 5000 yrs BP 17 , consistent with and likely sustained by a negative phase of the Arctic Oscillation and the regional Neoglacial cooling starting at ~ 4500 yrs BP 17,52,53 . At our peripheral NOW site, a decrease in biological production and significant change in bottom ocean conditions is evident; a combination of minimal Atlantic water influence, dominance of agglutinated foraminifera (> 85%) and decreased sulphur precipitation are consistent with a cold and well-ventilated water column (Fig. 7), also observed after ~ 4000 yrs BP at the western margin of the polynya 27 . Benthic foraminifera species within this assemblage such as C. arctica and T. torquata are typical of Polar/Arctic environments ( Table 2). ...
Baffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.
... The Holocene history of Nares Strait, Northwest Greenland, has remained somewhat cryptic despite investigations during the past four decades (e.g., Blake, 1979;Jennings et al., 2011;Kelly and Bennike, 1992;Mudie et al., 2006). Nares Strait is a key gateway for Arctic seawater and ice toward the Atlantic Ocean, contributing to up to half of the volume of water transported through the Canadian Arctic Archipelago (CAA), which provides fresh water to the Labrador Sea and influences deep water formation (Belkin et al., 1998;McGeehan and Maslowski, 2012;Münchow et al., 2006). ...
... Kennedy Channel). These land-based studies have been complemented by Jennings et al. (2011) and Mudie et al. (2006) investigations of marine sediment cores collected in Hall Basin, northernmost Nares Strait, which record a change in a number of environmental proxies ca. 8.3 14 C ka BP (ca. ...
Nares Strait is one of three channels of the Canadian Arctic Archipelago (CAA) which connect the Arctic Ocean to Baffin Bay. The CAA throughflow is a major component of ocean circulation in western Baffin Bay. Nares Strait borders the CAA to the east, separating Ellesmere Island from Greenland, and is 80% covered in sea ice 11 months of the year. The heavy sea ice cover is constituted of (1) Arctic (multi-year) sea-ice having entered the strait by the north, and (2) locally formed first year sea ice, which consolidates the ice cover. The hydrological history of the area is intimately linked to the formation of land-fast sea ice in the strait, constituting ice arches. The seaice cover in Nares Strait regulates freshwater (liquid and solid) export towards Baffin Bay, and is integral to the formation of an area of open water in northernmost Baffin Bay: The North Water polynya.Nares Strait has been at the heart of major geomorphological changes over the past 10,000 years. Its deglacial and post-glacial history is marked by (1) rapid retreat of the Greenland and Innuitian ice-sheets which coalesced along Nares Strait during the Last Glacial Maximum, (2) post-glacial shoaling associated to isostatic rebound, and (3) variable multi-year and seasonal sea ice conditions. Little is known about the evolution of these three environmental components of the Nares Strait history, and they are poorly constrained in terms of chronology and synchronism with other regional changes. Nares Strait and its eventful Holocene history provide a unique case study of the response of the marine and continental cryosphere to rapid climate change, such as that affecting Arctic regions in modern times.The marine sediment archives that were retrieved during the ANR GreenEdge and ArcticNet (2014 and 2016) cruises of CCGS Amundsen offer a unique opportunity to investigate the Deglacial to Late Holocene history of Nares Strait. Our reconstructions are based on a multi-proxy study of these cores, including sedimentologic (grain size and lithofacies), geochemical (XRF), mineralogical (q-XRD), micropaleontological (planktic and benthic foraminiferal assemblages), and biogeochemical (sea ice biomarkers IP25 and HBI III).Our results include an age for the Deglacial opening of Nares Strait between 9.0 and 8.3 cal. ka BP, with the event likely occurring closer to the later bracket of the timeframe (i.e., ca 8.5-8.3 cal. ka BP). This event established the throughflow from the Arctic Ocean towards northernmost Baffin Bay. Environmental conditions were highly unstable in the Early Holocene, and marine primary productivity was limited. A period of minimum sea-ice cover occurred from ca 8.1 to 7.5 cal. ka BP, during the Holocene Thermal Maximum, when atmospheric temperatures were higher than today in Nares Strait. Sea-ice cover became more stably established as a seasonal feature around 7.5 cal. ka BP and primary productivity related to ice edge blooms increased. Eventually, the duration of the ice arches increased and they were present in spring and into the summer from 5.5 to 3.7 cal. ka BP, which allowed the inception of the North Water polynya. The North Water reached its maximal potential between 4.5 and 3.7 cal. ka BP, when warmer Atlantic-sourced water upwelled in the polynya, providing nutrients for primary productivity. The establishment of a near-perennial ice arch in northern Nares Strait prevented export of multi-year sea ice into Nares Strait and hindered the formation of the southern ice arch, ultimately resulting in a less productive polynya over the past ca 3.0 cal. ka BP.
... We interpret this pattern to reflect a dominance of rainout processes that uniformly draped bedrock/till with up to 15 m of layered sediments unless (i) material was redeposited downslope and into basins or (ii) strong currents in Nares Strait (e.g. Mudie et al., 2006;Münchow et al., 2006) prevented the deposition of fine-grained material on the highest seafloor areas. Iceberg ploughing also probably helped to homogenize sediment layers deposited on the highs (see iceberg plough marks on S2 in Jakobsson et al., 2018). ...
Petermann Fjord is a deep (>1000 m) fjord that incises the coastline of north-west Greenland and was carved by an expanded Petermann Glacier, one of the six largest outlet glaciers draining the modern Greenland Ice Sheet (GrIS). Between 5 and 70 m of unconsolidated glacigenic material infills in the fjord and adjacent Nares Strait, deposited as the Petermann and Nares Strait ice streams retreated through the area after the Last Glacial Maximum. We have investigated the deglacial deposits using seismic stratigraphic techniques and have correlated our results with high-resolution bathymetric data and core lithofacies. We identify six seismo-acoustic facies in more than 3500 line kilometres of sub-bottom and seismic-reflection profiles throughout the fjord, Hall Basin and Kennedy Channel. Seismo-acoustic facies relate to bedrock or till surfaces (Facies I), subglacial deposition (Facies II), deposition from meltwater plumes and icebergs in quiescent glacimarine conditions (Facies III, IV), deposition at grounded ice margins during stillstands in retreat (grounding-zone wedges; Facies V) and the redeposition of material downslope (Facies IV). These sediment units represent the total volume of glacial sediment delivered to the mapped marine environment during retreat. We calculate a glacial sediment flux for the former Petermann ice stream as 1080–1420 m3 a-1 per metre of ice stream width and an average deglacial erosion rate for the basin of 0.29–0.34 mm a-1. Our deglacial erosion rates are consistent with results from Antarctic Peninsula fjord systems but are several times lower than values for other modern GrIS catchments. This difference is attributed to fact that large volumes of surface water do not access the bed in the Petermann system, and we conclude that glacial erosion is limited to areas overridden by streaming ice in this large outlet glacier setting. Erosion rates are also presented for two phases of ice retreat and confirm that there is significant variation in rates over a glacial–deglacial transition. Our new glacial sediment fluxes and erosion rates show that the Petermann ice stream was approximately as efficient as the palaeo-Jakobshavn Isbræ at eroding, transporting and delivering sediment to its margin during early deglaciation.
... Indeed, the establishment of warmer conditions in Baffin Bay is likely to be a response to the reinforcement of the warm and saline component (IC) of the WGC, linked with the final retreat of both the Laurentide ice sheet and the GIS (Lloyd et al., 2005;Ouellet-Bernier et al., 2014;Gibb et al., 2015). In addition, the dominance of the phototrophic species O. centrocarpum and S. elongatus is often associated with the North Atlantic Drift, suggesting surface water temperatures >0°C throughout the year (Rochon et al., 1999;Mudie et al., 2006;Zonneveld et al., 2013). ...
... Glacial geological reconstructions based on terrestrial glacial geology (Bennike et al. 1987;Funder 1990;Blake 1992;Blake et al. 1992Blake et al. , 1996England 1999;Kelly et al. 1999;Bennike 2002;England et al. 2004England et al. , 2006, and marine studies (Levac et al. 2001;Mudie et al. 2004 (Dawes 1997). Green lines south of 014 denote locations of inferred subglacially moulded bedforms (Blake et al. 1996). ...
Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.
... The Holocene history of Nares Strait, Northwest Greenland, has remained somewhat cryptic despite investigations during the past 4 decades (e.g. Blake Jr., 1979;Kelly and Bennike, 1992;Mudie et al., 2004;Jennings et al., 2011.). Nares Strait is a key gateway for Arctic seawater and ice toward the Atlantic Ocean, contributing to up to half of the volume of water transported through the Canadian Arctic Archipelago (CAA), which provides fresh water to the Labrador Sea and influences deep water formation (Belkin et al., 1998;Münchow et al., 2006;McGeehan and Maslowski, 2012). ...
... Kennedy Channel). These land-based studies have been complemented by Jennings et al. (2011) and Mudie et al. (2004) investigations of marine sediment cores collected in Hall Basin, northernmost Nares Strait, which record a change in a number of environmental proxies ca. 8.3 14 C ka BP (∼ 8.5 cal ka BP, R = 240). ...
... The speed of the flow decreases in the wider sections of Nares Strait. A northward current has been shown to enter Kane Basin from northern Baffin Bay (Bailey, 1957;Muench, 1971;Melling et al., 2001;Münchow et al., 2007). Temperature and salinity isolines imply that an anticlockwise circulation takes place in the surface layers of Kane Basin, while the deeper southward flow of Arctic water is channelled by bottom topography and concentrated in the basin's western trough (Muench, 1971;Moynihan, 1972;Münchow et al., 2007). ...
A radiocarbon-dated marine sediment core retrieved in Kane Basin, central Nares Strait, was analysed to constrain the timing of the postglacial opening of this Arctic gateway and its Holocene evolution. This study is based on a set of sedimentological and geochemical proxies of changing sedimentary processes and sources that provide new insight into the evolution of ice sheet configuration in Nares Strait. Proglacial marine sedimentation at the core site initiated ca. 9.0 cal ka BP following the retreat of grounded ice. Varying contributions of sand and clasts suggest unstable sea ice conditions and glacial activity, which subsisted until ca. 7.5 cal ka BP under the combined influence of warm atmospheric temperatures and proglacial cooling induced by the nearby Innuitian (IIS) and Greenland (GIS) ice sheets. An interval rich in ice-rafted debris (IRD) is interpreted as the collapse of the ice saddle in Kennedy Channel ca. 8.3 cal ka BP that marks the complete opening of Nares Strait and the initial connection between the Lincoln Sea and northernmost Baffin Bay. Delivery of sediment by icebergs was strengthened between ca. 8.3 and ca. 7.5 cal ka BP following the collapse of the buttress of glacial ice in Kennedy Channel that triggered the acceleration of GIS and IIS fluxes toward Nares Strait. The destabilisation in glacial ice eventually led to the rapid retreat of the GIS in eastern Kane Basin at about 8.1 cal ka BP as evidenced by a noticeable change in sediment geochemistry in our core. The gradual decrease in carbonate inputs to Kane Basin between ∼8.1 and ∼4.1 cal ka BP reflects the late deglaciation of Washington Land. The shoaling of Kane Basin can be observed in our record by the increased winnowing of lighter particles as the glacio-isostatic rebound brought the seabed closer to subsurface currents. Reduced iceberg delivery from 7.5 to 1.9 cal ka BP inferred by our dataset may be linked to the retreat of the bordering ice sheets on land that decreased their number of marine termini.
... Such studies are somewhat different from those carried out on surface sediments (typically 0-1 cm) or longer timeframe investigations generally conducted on material from gravity/piston cores since, in some cases, at least, they likely result from analysis of material that spans the oxic/anoxic (redox) sediment boundary. However, such boundary layers are not generally identified (reported), even though they are likely found in the upper few centimetres of box cores or multi-cores, which reflect accumulation over decades or recent centuries for many Arctic Shelf regions (e.g., Stein and Fahl, 2000;Darby et al., 2006;Mudie et al., 2006;Maiti et al., 2010;Vare et al., 2010). On the other hand, in the central Arctic Ocean, such a layer may reflect substantially longer-term accumulation due to much lower sedimentation rates (e.g., Stein et al., 1994a,b). ...
The organic geochemical IP25 (Ice Proxy with 25 carbon atoms) has been used as a proxy for Arctic sea ice in recent years. To date, however, the role of degradation of IP25 in Arctic marine sediments and the impact that this may have on palaeo sea ice reconstruction based on this biomarker have not been investigated in any detail. Here, we show that IP25 may be susceptible to autoxidation in near-surface oxic sediments. To arrive at these conclusions, we first subjected a purified sample of IP25 to autoxidation in the laboratory and characterised the oxidation products using high resolution gas chromatography–mass spectrometric methods. Most of these IP25 oxidation products were also detected in near-surface sediments collected from Barrow Strait in the Canadian Arctic, although their proposed secondary oxidation and the relatively lower abundances of IP25 in other sediments probably explain why we were not able to detect them in material from other parts of the region. A rapid decrease in IP25 concentration in some near-surface Arctic marine sediments, including examples presented here, may potentially be attributed to at least partial degradation, especially for sediment cores containing relatively thick oxic layers representing decades or centuries of deposition. An increase in the ratio of two common phytoplanktonic sterols – epi-brassicasterol and 24-methylenecholesterol – provides further evidence for such autoxidation reactions given the known enhanced reactivity of the latter to such processes reported previously. In addition, we provide some evidence that biodegradation processes also act on IP25 in Arctic sediments. The oxidation products identified in the present study will need to be quantified more precisely in downcore records in the future before the effects of degradation processes on IP25-based palaeo sea ice reconstruction can be fully understood. In the meantime, a brief overview of some previous investigations of IP25 in relatively shallow Arctic marine sediments suggests that overlying climate conditions were likely dominant over degradation processes, as evidenced from often increasing IP25 concentration downcore, together with positive relationships to known sea ice conditions.
