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Quantitative reconstructions of past aSST and aSIC from core AMD15-CASQ1-BC located in the NOW. Solid line = Species separated, dashed line = species grouped.
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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 asse...
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... of species having a well-defined relationship with sea-ice concentrations in this training set (e.g., Oksman et al., 2019). However, the separation of the species had an effect on the down-core reconstruction of both environmental variables in core AMD15-CASQ1-BC (77°16.746′ N, 74°21.428′ W, 702 m water depth), especially in the case of aSIC (Fig. 6). While the difference between the aSST reconstructions was only marginal using this training set (the "separated" transfer function & core assemblages resulting in lower aSST estimates), the aSIC reconstruction showed 5-10% higher sea-ice concentrations when the species were separated. It should be noted that some previous aSST ...
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... Belt et al., 2010;Detlef et al., 2021). Past sea-ice reconstructions based on microfossils rely on the presence and abundance of species associated with the presence of seasonal sea ice, typically diatoms or resting stages (cysts) of dinoflagellates (de Vernal et al., 2013;Weckström et al., 2020). Highly branched isoprenoid (HBI) lipids linked with sea-ice environments are increasingly common in sea-ice reconstructions, in particular IP 25 ("ice proxy with 25 carbon atoms"). ...
Sea ice is crucial in regulating the heat balance between the ocean and atmosphere and quintessential for supporting the prevailing Arctic food web. Due to limited and often local data availability back in time, the sensitivity of sea-ice proxies to long-term climate changes is not well constrained, which renders any comparison with palaeoclimate model simulations difficult. Here we compiled a set of marine sea-ice proxy records with a relatively high temporal resolution of at least 100 years, covering the Common Era (past 2k years) in the Greenland–North Atlantic sector of the Arctic to explore the presence of coherent long-term trends and common low-frequency variability, and we compared those data with transient climate model simulations. We used cluster analysis and empirical orthogonal functions to extract leading modes of sea-ice variability, which efficiently filtered out local variations and improved comparison between proxy records and model simulations. We find that a compilation of multiple proxy-based sea-ice reconstructions accurately reflects general long-term changes in sea-ice history, consistent with simulations from two transient climate models. Although sea-ice proxies have varying mechanistic relationships to sea-ice cover, typically differing in habitat or seasonal representation, the long-term trend recorded by proxy-based reconstructions showed a good agreement with summer minimum sea-ice area from the model simulations. The short-term variability was not as coherent between proxy-based reconstructions and model simulations. The leading mode of simulated sea ice associated with the multidecadal to centennial timescale presented a relatively low explained variance and might be explained by changes in solar radiation and/or inflow of warm Atlantic waters to the Arctic Ocean. Short variations in proxy-based reconstructions, however, are mainly associated with local factors and the ecological nature of the proxies. Therefore, a regional or large-scale view of sea-ice trends necessitates multiple spatially spread sea-ice proxy-based reconstructions, avoiding confusion between long-term regional trends and short-term local variability. Local-scale sea-ice studies, in turn, benefit from reconstructions from well-understood individual research sites.
... The summer-bloom species group consists mainly of large centric diatoms that prefer relatively cold waters and typically bloom in the late summer Luostarinen et al., 2020;Oksman et al., 2019). Early-spring bloom species consist of pennate species that prefer cold and fresher waters that occur in the spring during and right after the sea-ice breaks up and melts (von Quillfeldt, 2000(von Quillfeldt, , 2004Weckström et al., 2020). Sea-ice associated species are numerous in high sea-ice concentrations or are known to produce seaice related biomarkers (Belt et al., 2017;Oksman et al., 2019;Weckström et al., 2020). ...
... Early-spring bloom species consist of pennate species that prefer cold and fresher waters that occur in the spring during and right after the sea-ice breaks up and melts (von Quillfeldt, 2000(von Quillfeldt, , 2004Weckström et al., 2020). Sea-ice associated species are numerous in high sea-ice concentrations or are known to produce seaice related biomarkers (Belt et al., 2017;Oksman et al., 2019;Weckström et al., 2020). Benthic species live in the coastal region on the sea floor or attached to substrates (Cremer, 1998;Foged, 1973;Pearce et al., 2014). ...
Greenlandic fjords, located between the ice sheet and the ocean, are dynamic systems that can sustain highly variable levels of primary productivity and are sensitive to climate change. In our current climate trajectory, meltwater discharge is expected to significantly increase but its long‐term effects on fjord productivity are still poorly constrained. Paleo‐archives can offer valuable insights into long‐term effects. Here, we present two marine sediment core records from Nuup Kangerlua, Southwest Greenland. Our goal is to better understand to what extent, and on what time‐scales, climate fluctuations and associated glacier dynamic changes have impacted fjord productivity over the past ca. 3300 years. Our multiproxy records include diatom fluxes and assemblage composition, sediment biogeochemistry, and grain‐size distribution. Our study reveals that fjord productivity is tightly linked to regional climate variability; relatively higher productivity levels coincided with mild climate periods whereas the climate cooling of the last millennium led to a decrease in productivity. The diatom records suggest that lower productivity is associated with shorter or less intense summer blooms, increased sea‐ice cover and/or a stratified water column. Diatom assemblages demonstrate cold sea‐surface conditions around 1600 CE that might be linked to local advance of glaciers. Cold conditions and decreasing productivity culminated at 1850 CE, when glaciers in the fjord retreated and high glacial meltwater discharge would have altered the fjord hydrography, likely leading to limited nutrient availability. Our long‐term records support the idea that changing climate and cryosphere conditions have a non‐linear impact on the productivity of Greenlandic fjords.
... However, the reliability of these inference methods is limited by incomplete information on specific habitats and seasonal niches of sea-ice-associated species, limited knowledge of life cycles (e.g., unknown resting-vegetative stage relationships), and microfossil preservation biases 4 . In addition, the most widely used Arctic sea-ice indicators in microfossil records (such as the dinoflagellate cyst taxon Islandinium minutum and diatom Fragilariopsis oceanica) are not specifically sea ice-dependent and often bloom in cold and stratified waters that can be related to sea ice or glacial meltwater 11 . Frustules of sympagic diatoms are rarely preserved in the sedimentary record. ...
Sea ice is a critical component of the Earth’s Climate System and a unique habitat. Sea-ice changes prior to the satellite era are poorly documented, and proxy methods are needed to constrain its past variability. Here, we demonstrate the potential of sedimentary DNA from Polarella glacialis, a sea-ice microalga, for tracing past sea-ice conditions. We quantified P. glacialis DNA (targeting the nuclear ribosomal ITS1 region) in Arctic marine and fjord surface sediments and a sediment core from northern Baffin Bay spanning 12,000 years. Sea ice and sediment trap samples confirmed that cysts of P. glacialis are common in first-year sea ice and sinking particulate matter following sea-ice melt. Its detection is more efficient with our molecular approach than standard micropaleontological methods. Given that the species inhabits coastal and marine environments in the Arctic and Antarctic, P. glacialis DNA has the potential to become a useful tool for circum-polar sea-ice reconstructions.
... Despite the importance of sea ice for ecosystems and climate, reconstructing its history remains challenging (Heikkilä et al., 2022). While the development of palaeoceanographic sea-ice proxies has 40 progressed in recent decades (de Vernal et al., 2013;Belt, 2019;Weckström et al., 2020), they often exhibit strong local and regional dependencies, limiting their use for large-scale extrapolation (Brennan and Hakim, 2022). In contrast, longer transient paleoclimate simulations of large-scale sea-ice changes using numerical models have only recently become available (Zhong et al., 2018;Mauritsen et al., 2019). ...
... Belt et al., 2010;Cabedo-Sanz et al., 2016;Detlef et al., 2021). Past sea-ice reconstructions based on microfossils rely on the presence and abundance of species associated with the presence of seasonal sea ice, typically diatoms or resting stages 75 (cysts) of dinoflagellates (de Vernal et al., 2013;Weckström et al., 2020). Highly branched isoprenoid lipids (HBIs) linked with sea-ice environments are increasingly common in sea-ice reconstructions, in particular IP25 ("Ice Proxy with 25 carbon atoms"). ...
... Fossulaphycus arcticus, F. reginae-jahniae and F. oceanica present a significant relationship with high April sea-ice concentrations in the Atlantic Arctic (Weckström et al., 120 2020). On the other hand, although F. cylindrus has been frequently used as a sea-ice indicator, it is also commonly found in cold-water ice-free regions and/or periods (Luostarinen et al., 2020;Weckström et al., 2020). Nevertheless, F. cylindrus regularly occurs in the marginal ice zone and dominates exported material to the sediments during the melt season (Oksman et al., 2019;Luostarinen et al., 2023). ...
Sea ice is crucial in regulating the heat balance between the ocean and atmosphere and quintessential for supporting the prevailing Arctic food web. Due to limited and often local data availability back in time, the sensitivity of sea- ice proxies to long-term climate changes is not well constrained, which renders any comparison with palaeoclimate model simulations difficult. Here we compiled a set of marine sea-ice proxy records with a relatively high temporal resolution of at least 100 years covering the Common Era (past 2 k) in the Greenland-North-Atlantic sector of the Arctic to explore the presence of coherent long-term trends and common low-frequent variability and compared those with transient climate model simulations. We used cluster analysis and empirical orthogonal functions to extract leading modes of sea-ice variability, which efficiently filtered out local variations and improved comparison between proxy records and model simulations. We find that a compilation of multiple proxy-based sea-ice reconstructions accurately reflects general long-term changes in sea-ice history, consistent with simulations from two transient climate models. Although sea-ice proxies have varying mechanistic relationships to sea-ice cover, typically differing in habitat or seasonal representation, the long-term trend recorded by proxy-based reconstructions showed a good agreement with summer minimum sea-ice extent from the model simulations. The short-term variability was not as coherent between proxy-based reconstructions and model simulations. The leading mode of simulated sea-ice associated with the multidecadal to centennial timescale presented a relatively low explained variance and might be explained by changes in solar radiation and/or inflow of warm Atlantic waters to the Arctic Ocean. Short variations in proxy-based reconstructions, however, are mainly associated with local factors and the ecological nature of the proxies. Therefore, regional or large-scale view of sea-ice trend necessitates multiple spatially spread sea-ice proxy-based reconstructions, avoiding confusion between long-term regional trends and short-term local variability. Local-scale sea-ice studies, in turn, benefit from reconstructions from well-understood individual research sites.
... 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. ...
... The water column communities showed a clearly larger portion of the sea-ice associated spring blooming species Fragilariopsis oceanica, F. cylindrus, F. reginae-jahniae and Fossulaphycus arcticus, which inhabit the marginal ice zone (Weckström et al. 33 and references therein). Centric Thalassiosira taxa were present at moderate abundances (up to ca. 10%), most notably T. antarctica var. ...
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.
... While diatoms are widely distributed and abundant as a group, many species have narrow ecological preferences in terms of hydrographic conditions (e.g. salinity, temperature, and light availability), which makes them an excellent tool for reconstructing past environmental and productivity changes (Hasle and Syvertsen, 1996;von Quillfeldt, 2000von Quillfeldt, , 2004Krawczyk et al., 2018;Oksman et al., 2019;Weckström et al., 2020). In Nuup Kangerlua, diatom assemblages have been shown to respond mainly to physical conditions in the water column (temperature and salinity) rather than to biogeochemical properties (e.g. ...
Climate warming and the resulting acceleration of freshwater discharge from the Greenland Ice Sheet are impacting Arctic marine coastal ecosystems, with implications for their biological productivity. To accurately project the future of coastal ecosystems and place recent trends into perspective, palaeo-records are essential. Here, we show runoff estimates from the late 19th century to the present day for a large sub-Arctic fjord system (Nuup Kangerlua, southwest Greenland) influenced by both marine- and land-terminating glaciers. We followed a multiproxy approach to reconstruct spatial and temporal trends in primary production from four sediment core records, including diatom fluxes and assemblage composition changes and biogeochemical and sedimentological proxies (total organic carbon, nitrogen, C/N ratio, biogenic silica, δ13C, δ15N, and grain-size distribution). We show that an abrupt increase in freshwater runoff in the mid-1990s was reflected by a 3-fold increase in biogenic silica fluxes in the glacier-proximal area of the fjord. In addition to increased productivity, freshwater runoff modulates the diatom assemblages and drives the dynamics and magnitude of the diatom spring bloom. Our records indicate that marine productivity is higher today than it has been at any point since the late 19th century and suggest that increased mass loss of the Greenland Ice Sheet may continue promoting high productivity levels at sites proximal to marine-terminating glaciers. We highlight the importance of palaeo-records in offering a unique temporal perspective on ice–ocean–ecosystem responses to climate forcing beyond existing remote sensing or monitoring time series.
... 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.
... In general, TOC and BSi values point to a relatively high productivity in Nuup Kangerlua throughout the 20 th century, when compared to modern values from other coastal Arctic sites (e.g., Ribeiro et al., 2017;Limoges et al., 2018a;Kumar et al., 2016, Detlef et al., 2021. Similarly, high values have been observed on the northwest Greenland shelf during the Holocene when climate conditions were favorable for high primary production (Limoges et al., 2020;Saini et al., 2020;Ribeiro et al., 2021). The modern fjord hydrography in Nuup Kangerlua has been shown to maintain productivity also in 345 the outer fjord, as biomass and nutrients are partly advected from the inner fjord by currents, wind and tidal mixing which together with the warm, nutrient-rich waters carried by the WGC, can increase the seasonal productivity (Juul-Pedersen et al., 2015). ...
Climate warming and the resulting acceleration of freshwater discharge from the Greenland Ice Sheet are impacting Arctic marine coastal ecosystems, with implications for their biological productivity. To accurately project the future of coastal ecosystems, and place recent trends into perspective, paleo-records are essential. Here, we present late 20 19 th century to present runoff estimates for a large sub-Arctic fjord system (Nuup Kangerlua, southwest Greenland) influenced by both marine-and land-terminating glaciers. We followed a multiproxy approach to reconstruct spatial and temporal trends in primary production from four sediment cores, including diatom fluxes and assemblage composition changes, biogeochemical and sedimentological proxies (total organic carbon, nitrogen, C/N-ratio, biogenic silica, δ 13 C, δ 15 N, grain size distribution). We show that an abrupt increase in freshwater runoff in the mid-1990's is reflected by a 3-25 fold increase in biogenic silica fluxes in the glacier-proximal area of the fjord. In addition to increased productivity, freshwater runoff modulates the diatom assemblages and drives the dynamics and magnitude of the diatom spring bloom. Our records indicate that marine productivity is higher today than it has been at any point since the late 19 th century and suggest that increased mass loss of the Greenland Ice Sheet is likely to continue promoting high productivity levels at sites proximal to marine-terminating glaciers. We highlight the importance of paleo-records in offering a unique temporal 30 perspective on ice-ocean-ecosystem responses to climate forcing beyond existing remote sensing or monitoring time-series.
... While the knowledge of marine proxies applied at high latitudes has rapidly evolved in the past decades (de Vernal et al., 2013a; Goñi et al., 2013;Belt, 2018), we still do not know the habitat characteristics, seasonal bloom windows, preservation through the sea-ice-water column-sediment continuum, or even biomarker and resting stage producers for many biogenic proxies we readily apply in reconstructions. Investigating the responses of species and biomarker production to environmental variables Limoges et al., 2018a;Oksman et al., 2019;Brown et al., 2020;Weckström et al., 2020), as well as seasonal and population dynamics (Pospelova et al., 2010;Fahl and Stein, 2012;Heikkilä et al., 2016;Limoges et al., 2018a;Bai et al., 2019;Park et al., 2019;Luostarinen et al., 2020) is key to improving the interpretation of proxy records. For a more in-depth understanding of how species and populations may respond to environmental change, laboratory experiments and resurrection ecology approaches based on e.g. ...
... The benefit of the multi-proxy approach stems from the often indirect relationship between the individual proxies and their environment. As an example, the most commonly used sea-ice indicator diatom species reflect the marginal ice zone environment where they bloom as the ice melts (Oksman et al., 2019;Weckström et al., 2020). These marginal ice zone or MIZ conditions, defined by a strongly stratified water column due to a cold and fresh meltwater layer on top of ambient seawater, can also occur under different settings, such as when cold glacial meltwater enters an Arctic fjord (Oksman et al., 2017;Weckström et al., 2020). ...
... As an example, the most commonly used sea-ice indicator diatom species reflect the marginal ice zone environment where they bloom as the ice melts (Oksman et al., 2019;Weckström et al., 2020). These marginal ice zone or MIZ conditions, defined by a strongly stratified water column due to a cold and fresh meltwater layer on top of ambient seawater, can also occur under different settings, such as when cold glacial meltwater enters an Arctic fjord (Oksman et al., 2017;Weckström et al., 2020). Here, combining the diatom record with 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.
... As a result of this imbalance in reference sequences across eukaryotes, some groups are better represented than others in genetic databases, which in turn will impact a study's taxonomic resolution. Crucially, low taxonomic resolution can inhibit paleoenvironmental reconstruction efforts, where species-level identification is often pivotal in order to estimate key environmental or oceanographic conditions in a region of interest (Weckström et al., 2020). ...
Sedimentary ancient DNA (sedaDNA) offers a novel approach to investigating past marine ecosystems—from the smallest bacteria to phytoplankton and their predators— over geological timescales. Knowledge about such paleo-food webs can provide broad-scale biological context to paleoceanographic and environmental reconstructions. However, the field of marine sedaDNA research is still in its infancy; community reconstructions are com-plicated by the minuscule amounts of ancient DNA preserved in the sediments. Consequently, the identification of most prokaryotes and eukaryotes in sedaDNA is difficult, and sedaDNA sampling, extraction, and analysis require optimized procedures and rigorous contami-nation control to ensure that the sedaDNA signal is authentic and not overridden by modern environmental DNA. This article describes some of the latest developments in marine sedaDNA research, including the use of metagenomics to study past marine food webs, and new experimental and computational techniques to maximize taxonomic resolution, partic-ularly that of eukaryotes. An example of bioinformatic techniques designed to increase taxonomic insight is presented, demonstrating the breadth of paleogenetic signals that could be extracted from marine sediments. With ongoing improvements in genetic reference databases, sedaDNA extraction techniques, species-specific enrichment approaches, and computational tools, marine sedaDNA will continue to improve our understanding of how marine ecosystems evolved in concert with changing environmental conditions.
