Nares Strait, a marine gateway connecting the Arctic Ocean with northern Baffin Bay, is characterised by the formation of seasonal ice bridges between Canada and Greenland that prevent the southward export of multiyear sea ice. Recent observations indicate increasing instability in sea-ice formation particularly evident in Kane Basin, which either freezes over or remains open during winter and spring, depending on ice-bridge dynamics. Kane Basin is influenced by contrasting ocean currents in its eastern and western sides, as well as by the Humboldt Glacier, Greenland's widest marine-terminating glacier. Kane Basin is a critical region due to its pronounced sensitivity to cryospheric and oceanic changes. However, its long-term environmental history, particularly in the eastern sector, remains poorly constrained prior to the satellite era. Here, we present two multi-proxy sediment core records from opposite sides of Kane Basin, spanning the 18th century to the present, that we compare with Humboldt Glacier solid ice discharge and retreat since 1965 CE. Clear spatial differences are evident across the basin in terms of sediment delivery, primary productivity, and organic matter sources. Both records also reveal temporal changes, transitioning from cold sea-surface conditions with extensive sea-ice cover during the Little Ice Age (peaking around 1900 CE), towards more open and stratified waters, accompanied by a shift towards higher primary production from approximately 1950 CE to the present.

Diatom frustules and dinoflagellate cysts preserved in sedimentary archives are routinely utilized as indicators of past climate and environmental change. However, fragile or lightly silicified diatom frustules can be prone to fragmentation and dissolution, and indicator species are often rare or not preserved at all. For dinoflagellates, only a fraction of species are known to form fossilizable organic-walled cysts, thus the large majority remains unaccounted for in the microfossil record. Sedimentary ancient DNA (sedaDNA) can potentially fill this gap due to its ability to trace biota even in the absence of physical remains, yet direct comparisons of microfossil records with marine sedaDNA are still limited. Here, we present a comparative analysis of marine sedaDNA metabarcoding with microfossil records of diatoms and dinoflagellates in a marine sediment core taken off North-West Greenland spanning the past similar to 8300 years. Our results show that the microfossil and sedaDNA records are complementary, both with regard to uncovering past diversity and describing temporal changes. Incongruencies between data types were due to database incompleteness, primer biases, and marker resolution for sedaDNA, while the microfossil records were affected by low abundance or differential preservation potentials. For dinoflagellates, unknown cyst-theca relationships and differential preservation potentials additionally limited comparability. Community efforts are needed to generate reference DNA sequences through culturing and to determine cyst-theca relationships via life-cycle studies. Our study highlights the importance of combining sedaDNA with classical approaches to gain a better understanding of long-term climate and marine ecosystem changes in the Arctic and for marine biodiversity assessments and monitoring.

Abstract Resting stages of protists act as biological time capsules when buried in marine sediments, preserving viable cells that enable the study of ecological and evolutionary processes across timescales. Recent studies have extended the known viability in diatoms to several millennia and in dinoflagellates to over a century, while also identifying molecular and physiological mechanisms, such as selective gene activity and hormonal regulation, that sustain long‐term dormancy. These advances emphasize the role of marine seed banks in population renewal and ecosystem resilience. However, research has so far concentrated on temperate regions and has focused primarily on a few diatom and dinoflagellate taxa, leaving most other protist groups and biogeographic areas largely unexplored. In this review, we synthesize recent developments, identify critical taxonomic and geographic gaps, and emphasize the potential of resurrection ecology as a tool to investigate adaptation and evolutionary dynamics in a rapidly changing global ocean.

Functional traits are central to species fitness and ecosystem resilience, yet our understanding of climate change impacts on functional diversity is limited by a paucity of long-term data. Here, we apply a trait framework to a marine sedimentary ancient DNA record from the high Arctic spanning the past ~8300 years. This period includes warm and cold oscillations, including a phase when regional summer temperatures were higher than today. Our framework uncovers heterogenous responses to climate variability among functional groups, and millennial-scale diversity pulses synchronous with swings in the dominant mode of the Arctic Oscillation. Furthermore, protists show a temperature-size relationship with trade-offs under different temperature and sea ice regimes. By extending trait-based approaches into the paleogenetic realm, our study provides biodiversity reconstructions at unprecedented resolution, captures diversity components inaccessible from the fossil record alone, and opens new avenues for understanding how marine ecosystems respond to climate forcing across millennial timescales.

Decreasing sea-ice extent and retreating and thinning of Greenland’s glaciers are rapidly changing Arctic coastal environments by warming and freshening the sea surface and impacting light availability. In Arctic fjords, productivity is significantly influenced by the position of glacier termini, and the present retreat of the Greenland Ice Sheet will increase the number of fjords surrounded only by land-terminating glaciers in the future. This will most likely affect the productivity and ecosystem structure of coastal marine areas. To predict future cryosphere change and its impacts, it is essential to understand climate and ecosystem variability beyond the instrumental era. Here we present a high-resolution reconstruction of coastal marine ecosystem change and its linkages to terrestrial freshwater and organic matter inputs in Young Sound fjord, Northeast Greenland, over the Holocene. The reconstructions are based on marine sediment-core proxies: organic-walled palynomorphs (including e.g. dinoflagellate cysts and pollen), sympagic and pelagic biomarkers (highly branched isoprenoids and sterols) and a set of geochemical indicators (sediment organic carbon, nitrogen, their stable isotopes, and biogenic silica). The results suggest a relatively cold early Holocene with extensive sea-ice cover and low productivity. Warmer and more variable conditions take hold after approximately 9 kyr with increasing productivity, species richness and terrestrial freshwater inputs, with colder conditions seen after approximately 3.5 kyr with high productivity coupled with higher ice-algae contribution. The results also indicate that this near-shore marine ecosystem is clearly influenced by local forcings, such as terrestrial freshwater and organic matter inputs, suggesting that the continuous melting of the Greenland Ice Sheet will affect marine productivity and ecosystem structure in Greenland’s fjord systems, with potential impacts on biodiversity and sustainability of fisheries.

Greenland’s west coast is highly vulnerable to the impacts of climate change, with profound implications for marine ecosystems and their services. Projections suggest significant restructuring of Arctic marine ecosystems due to ongoing sea ice decline, yet uncertainties remain regarding the biosphere-specific responses of these ecosystems. The Arctic cryosphere has undergone significant changes throughout the Holocene, with the Holocene Thermal Maximum (HTM) representing a key period of reduced sea ice and warmer conditions. These past environmental shifts provide a valuable analogue for understanding the ongoing impacts of climate warming on Arctic marine ecosystems. Understanding past climate impacts on marine species is essential for predicting future changes and informing policy decisions.While traditional microfossil records have advanced our knowledge of past ecosystems, they are biased toward species with hard body parts and are insufficiently covered in time and space. To address these limitations, we use sedimentary ancient DNA (sedaDNA) to track HTM marine biodiversity dynamics. This method allows for the detection of a broad range of organisms, including soft-bodied species such as ciliates and jellyfish, which are not preserved in the fossil record. To enhance the taxonomic resolution of marine eukaryotes across all trophic levels, from primary producers to marine mammals, we developed custom hybridization capture probes targeting barcoding regions. This approach enables the retrieval of short DNA fragments and the assessment of postmortem damage to validate the sedaDNA signal. We employed a two-step methodology: (1) compiling databases such as GBIF and WoRMS to identify knowledge gaps in Arctic marine biodiversity, and (2) evaluating various barcoding genes (e.g., 18S, rbcL, ITS2, COI) for taxonomic resolution and reference availability. Using the SILVA-NR99 database, we focused on the V7 region of the small subunit ribosomal RNA gene as a universal marker, while applying alternative markers for groups lacking sufficient resolution. We generated 46,804 80bp-long probes targeting 11,389 species, which we tested both in silico and on marine surface sediment samples collected from 25 sites around Greenland before their application to Holocene sediment cores from western Greenland.This approach holds great potential for identifying key marine Arctic species across trophic levels and optimizing their taxonomic resolution during the HTM, revealing ecosystem responses to warming. By providing new insights into Arctic marine ecosystem dynamics and their long-term responses to climate change, we aim to offer valuable information for developing adaptive management strategies aimed at ensuring the ecological sustainability of the region.

Arctic marine ecosystems have undergone notable reconfigurations in response to Holocene climate and environmental changes. Yet our understanding of how marine mammal occurrence was impacted remains limited, due to their relative scarcity in the fossil record. We reconstruct the occurrence of marine mammals across the past 12,000 years through detections based on sedimentary ancient DNA from four marine sediment cores collected around Northern Greenland, and integrate the findings with local and regional environmental proxy records. Our findings indicate a close association between marine mammals at densities detectable in marine sediments and the deglaciation of high Arctic marine environments at the onset of the Holocene. Further, we identify air temperature and changes in sea ice cover as significant drivers of community change across time. Several marine mammals are detected in the sediments earlier than in the fossil record, for some species by several thousand years. During the Early-to-Mid Holocene, a period of warmer climate, we record northward distribution shifts of temperate and low-arctic marine mammal species. Our findings provide unique, long-term baseline data on the occurrence of marine mammals around Northern Greenland, enabling insights into past community dynamics and the effects of Holocene climatic shifts on the region's marine ecosystems.

The Holocene Thermal Maximum has been considered an analog for near-future climate. Terrestrial records show that this period culminated in Southwest Greenland with the Greenland Ice Sheet retreating behind its present-day position. However, there is a paucity of Holocene coastal marine records proximal to the ice sheet from which to infer marine conditions. Here we present a multi-proxy record from Nuup Kangerlua covering the past similar to 10,500 years, supported by a one-year sediment trap time-series. We infer modern sea-surface conditions comparable to those following the fjord's deglaciation from 10,000 to 8000 calibrated years before present. Warmer temperatures led to a period of pronounced meltwater discharge and peak marine productivity by 7500 calibrated years before present. We detect an exceptional oceanographic regime with no recent analog from similar to 7000 to 3000 calibrated years before present, when reduced ice-sheet extent was coeval with entrainment of subpolar mode water (of Atlantic origin) into the fjord.

AbstractMarine protists are globally distributed and sensitive to environmental conditions, which makes them a focal group when studying the effects of climate change on biodiversity and ocean health. However, they are a highly diverse group with varying evolutionary histories and morphologies and widely variable preservation potential in the fossil record. Thus, their past diversity and composition are poorly known. Paleogenetics, which relies, among other approaches, on DNA metabarcoding of sedimentary ancient DNA (sedaDNA), provides a promising avenue to explore the past history and responses of marine protists to global change. Choosing the right marker for sedaDNA studies is critical, striking a balance between marker length and taxonomic resolution. While marker guides exist for modern environmental DNA surveys, a thorough assessment of existing short markers for sedaDNA studies targeting protists is lacking. In this study, we report on a comparison of in silico PCR for eight short 18S rDNA markers, including one from the Tara Oceans initiative and a longer marker commonly used in modern marine eDNA studies. We analyze their taxonomic coverage and resolution, taxonomic overlap and uniqueness between markers, co‐amplification of non‐protist taxa, and amplicon size differences across taxonomic groups. Additionally, we provide a detailed analysis of diatoms, dinoflagellates, haptophytes, and chlorophytes. Our study is aimed at supporting project‐specific marker choices for characterizing protist composition and diversity. While we focus on marine protists, our results are applicable to other aquatic and terrestrial environments.

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.

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected‐light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land‐derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that >70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land‐derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies.

The Arctic is among the most climatically sensitive environments on Earth, and the disappearance of multiyear sea ice in the Arctic Ocean is predicted within decades. As apex predators, polar bears are sentinel species for addressing the impact of environmental variability on Arctic marine ecosystems. By integrating genomics, isotopic analysis, morphometrics, and ecological modeling, we investigate how Holocene environmental changes affected polar bears around Greenland. We uncover reductions in effective population size coinciding with increases in annual mean sea surface temperature, reduction in sea ice cover, declines in suitable habitat, and shifts in suitable habitat northward. Furthermore, we show that west and east Greenlandic polar bears are morphologically, and ecologically distinct, putatively driven by regional biotic and genetic differences. Together, we provide insights into the vulnerability of polar bears to environmental change and how the Arctic marine ecosystem plays a vital role in shaping the evolutionary and ecological trajectories of its inhabitants.

Abstract 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 ancient DNA from Polarella glacialis, a sea-ice microalga, for tracing past sea-ice conditions. Our observations confirm that this cyst-forming species is common in first-year sea ice and sinking particulate matter following sea-ice melt. Using species-specific primers targeting the nuclear ribosomal ITS1 region, we quantified Polarella glacialis DNA (Pgla-DNA) by digital PCR in marine and fjord surface sediments. Inferred Pgla-DNA gene copy numbers in sediments reflect the spatial variability of recent sea-ice cover, they increase for sites with 20-80% sea-ice concentration and decrease for sites with concentrations > 80%. Furthermore, Pgla-DNA was detected in a sediment core from northern Baffin Bay spanning ca. 12,000 years. Its detection is more efficient following a molecular approach than standard micropaleontological methods. Given that the species inhabits coastal and marine environments in the Arctic and Antarctic, Pgla-DNA has the potential to become a useful tool for circum-polar sea-ice reconstructions both in marine and glaciated fjord environments, where biomarker and microfossil approaches are limited.

The Pikialasorsuaq (North Water polynya) is an area of local and global cultural and ecological significance. However, over the last decades, the region has been subject to rapid warming, and in some recent years, the seasonal ice arch that has historically defined the polynya's northern boundary has failed to form. Both factors are deemed to alter the polynya's ecosystem functioning. To understand how climate-induced changes to the Pikialasorsuaq impact the basis of the marine food web, we explored diatom community-level responses to changing conditions, from a sediment core spanning the last 3800 years. Four metrics were used: total diatom concentrations, taxonomic composition, mean size, and diversity. Generalized additive model statistics highlight significant changes at ca. 2400, 2050, 1550, 1200, and 130 cal years BP, all coeval with known transitions between colder and warmer intervals of the Late Holocene, and regime shifts in the Pikialasorsuaq. Notably, a weaker/contracted polynya during the Roman Warm Period and Medieval Climate Anomaly caused the diatom community to reorganize via shifts in species composition, with the presence of larger taxa but lower diversity, and significantly reduced export production. This study underlines the high sensitivity of primary producers to changes in the polynya dynamics and illustrates that the strong pulse of early spring cryopelagic diatoms that makes the Pikialasorsuaq exceptionally productive may be jeopardized by rapid warming and associated Nares Strait ice arch destabilization. Future alterations to the phenology of primary producers may disproportionately impact higher trophic levels and keystone species in this region, with implications for Indigenous Peoples and global diversity. The Pikialasorsuaq is a site of outstanding global value located in northern Baffin Bay. The biological productivity of this ecosystem largely relies on diatoms, that is, siliceous phytoplankton at the basis of the marine food web. This study investigates diatom community-level responses to environmental and climate forcing over the last 3800 years to assess future trends under continued warming. We show that diatoms are sentinels for climate-induced changes in the Pikialasorsuaq and that the strong spring pulse of small fast-growing diatoms that makes the polynya exceptionally productive is threatened by the destabilization of the ice arch that sharply defines its northern boundary.image

Spiny brown dinoflagellate cysts are commonly used as sea-ice indicators in the Arctic, but their biological affinities are not well known. We present the first indication of hitherto temperate Protoperidinium tricingulatum in the Arctic based on single-cell LSU rDNA sequencing from sediments of the Disko Bay-Vaigat Sound, West Greenland. The morphological similarity of the sequenced cyst morphotype to the sea-ice indicator Islandinium? cezare morphotype 1 is striking. The morphology of the isolated cysts, as well as those observed in the total cyst assemblage following standard palynological preparation, both resemble either I.? cezare morphotype 1 or P. tricingulatum, suggesting that the specimens may in fact be close morphological variants of the same species. In addition, nine LSU rDNA sequences were obtained from morphological variants assigned to Islandinium minutum s.l.: including both subspecies minutum and subspecies barbatum. The two subspecies could not be differentiated based on partial LSU rDNA sequencing. Overall, Arctic spiny brown dinoflagellate cyst species may be morphologically more diverse and taxonomically more complex than shown earlier and further genetic and morphological studies are needed. Importantly, the value of cysts as palaeoecological indicators depends on a sound understanding of their biological affinity and taxonomy.

The Ancylonema genus includes the most-documented microalgae on glaciers and ice sheets worldwide. There is significant interest in these microalgae in the context of climate change, considering their role in lowering surface ice albedo and acceleration of ice melt. However, currently, no cultures of the two closely related species A. nordenskioldii or A. alaskanum have been established, restricting our ability to study these globally important species under laboratory conditions. We established and kept cultures of Ancylonema sp. alive for up to 2 years, by testing and optimizing different growth media and parameters. Maximum growth was achieved when using 1:100 diluted media with soil extract and low light intensity (300 & mu;mol m-2s-1). However, as a consequence of incubation in lab conditions, some of the cultures lost their purpurogallin pigmentation and appeared green. Sanger sequencing of the ribulose-1,5 bisphosphate carboxylase/oxygenase large subunit (rbcL) marker gene revealed a large genetic diversity (possibly cryptic) and confirmed the cultures as falling within the same clade as A. nordenskioldii and A. alaskanum. Growth experiments allowed us to estimate a division rate of between 15 & PLUSMN; 5.2 and 21.9 & PLUSMN; 4.8 days. This is up to 4 times slower than current field-based estimates (3.75-5.5 days) and indicates that, despite the successful growth and long-term maintenance of the cultures, laboratory settings can be further improved to achieve optimal growth conditions.

At the Pingorsuit Glacier in North‐West Greenland, an organic‐rich deposit that had recently emerged from the retreating ice cap was discovered at an elevation of 480 m above sea level. This paper reports on macrofossil analyses of a coarse detritus gyttja and peaty soil, which occurred beneath a thin cover of till and glacifluvial deposits. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates. The flora includes black spruce, tree birch, boreal shrubs and wetland and aquatic taxa, which shows that mires, lakes and ponds were present in the area. We describe a new extinct waterwort species Elatine odgaardii . The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present. The fossil assemblages show strong similarities with others from Greenland that have been assigned an Early Pleistocene age, and we suggest a similar age for the sediments found at the margin of the Pingorsuit Glacier. At the Pingorsuit Glacier in North‐West Greenland, an organic‐rich deposit was discovered at an elevation of 480 m above sea level. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates. The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present.

Polysaccharides constitute an important carbon pool in marine systems, but much is still unknown about the fate and degradation of these compounds. They are derived partly from production in situ, and in coastal areas, they are partly terrestrially derived, originating from freshwater runoff from land. The aim of this study was to test the applicability of high-throughput polysaccharide profiling for plant and algal cell-wall compounds in dated sediment cores from a coastal marine environment, to examine the preservation of cell-wall polysaccharides and explore their potential as proxies for temporal environmental changes. Preserved compounds and remains of organisms are routinely used as paleoenvironmental proxies as the amount and composition of different compounds that can provide insight into past environmental conditions, and novel means for reporting environmental changes are highly sought.

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 regimes. The North-East Greenland shelf is an opportune region to assess these changes back through time. Paleoceanographic reconstructions from the North-East Greenland shelf are sparse and their temporal coverage is limited to the Holocene, limiting our ability to assess the impact of rapid climatic variations on marine conditions, such as during the Younger Dryas/Holocene transition. Here, we present data from a well-dated marine sediment core retrieved from the North-East Greenland shelf (74°N; east of Young Sound-Tyrolerfjord system) that captures the late Younger Dryas Stadial through to the Mid-Holocene at sub-centennial resolution. We apply a multi-proxy approach to reconstruct changes in productivity, surface and bottom ocean conditions. We show that at 74° N the presence of warm Atlantic waters on the inner North-East Greenland shelf was limited to the late Younger Dryas, as the Greenland Ice Sheet retreated landward and isostatic rebound caused the area to uplift. A unique dimension to this record is its location within one of the few biological hotspots on the East Greenland shelf today; the Sirius Water polynya. Archaeological studies indicate the polynya was forming as early as 4500 years ago, but nothing is known about its evolution from a marine perspective. Cooling of bottom waters, increasing sea-surface productivity and more frequent open water conditions indicate an Early Holocene onset of the Sirius Water (ca. 10–8.7 ka BP).

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 Arctic, 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 utilise 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.