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The Arctic is subjected to all-encompassing disruptions in marine ecosystems caused by anthropogenic warming. To provide reliable estimates of how future changes will affect the ecosystems, knowledge of Arctic marine ecosystem responses to past environmental variability beyond the instrumental era is essential. Here, we present a novel approach on how to evaluate the state of benthic marine biotic conditions during the deglacial and Holocene period on the Northeast Greenland shelf. Benthic foraminiferal species were assigned traits (e.g., oxygen tolerance, food preferences) aiming to identify past faunal changes as a response to external forcing mechanisms. This approach was applied on sediment cores from offshore Northeast Greenland. We performed numerical rate-of-change detection to determine significant changes in the benthic foraminiferal traits. That way, the significant abrupt trait changes can be assessed across sites, providing a better understanding of the impact of climate drivers on the traits. Our results demonstrate that during the last ~ 14,000 years, bottom water oxygen is the main factor affecting the variability in the benthic foraminiferal faunas in this area. Our results show that significant changes in the traits correspond to drastic climate perturbations. Specifically, the deglacial-Holocene transition and mid-Holocene warm period exhibited significant change, with several trait turnovers.

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. Arctic marine ecosystems have experienced significant change through the Holocene. Here, the authors used seda DNA from Northern Greenland to reconstruct marine mammal occurrence, demonstrating the impact of air temperature and sea ice cover over the past 12000 years.

Submarine glacial landforms in fjords are imprints of the dynamic behaviour of marine-terminating glaciers and are informative about their most recent retreat phase. Here we use detailed multibeam bathymetry to map glacial landforms in Petermann Fjord and Nares Strait, northwestern Greenland. A large grounding-zone wedge (GZW) demonstrates that Petermann Glacier stabilised at the fjord mouth for a considerable time, likely buttressed by an ice shelf. This stability was followed by successive backstepping of the ice margin down the GZW’s retrograde backslope forming small retreat ridges to 680 m current depth (∼730–800 m palaeodepth). Iceberg ploughmarks occurring somewhat deeper show that thick, grounded ice persisted to these water depths before final breakup occurred. The palaeodepth limit of the recessional moraines is consistent with final collapse driven by marine ice cliff instability (MICI) with retreat to the next stable position located underneath the present Petermann ice tongue, where the seafloor is unmapped. Submarine glacial landforms are used to reconstruct the Holocene retreat dynamics and stability of Petermann Glacier in northwest Greenland. Here, a large grounding-zone wedge at the mouth of Petermann fjord indicates a period of glacier stability, with final retreat likely driven by marine ice cliff instability.

The geomagnetic field behavior in polar regions remains poorly understood and documented. Although a number of Late Holocene paleomagnetic secular variation (PSV) records exist from marginal settings of the Amerasian Basin in the Arctic Ocean, their age control often relies on a handful of radiocarbon dates to constrain ages over the past 4,200 years. Here we present well‐dated Late Holocene PSV records from two sediment cores recovered from the Chukchi Sea, Arctic Ocean. The records are dated using 26 14C measurements, with local marine reservoir corrections calibrated using tephra layers from the 3.6 cal ka BP Aniakchak eruption in Northern Alaska. These 14C‐based chronologies are extended into the post‐bomb era using caesium‐137 dating, and mercury isochrons. Paleomagnetic measurements and rock magnetic analyses reveal stable characteristic remanent magnetization directions, and a magnetic mineralogy dominated by low‐coercivity minerals. The PSV records conform well to global spherical harmonic field model outputs. Centennial to millennial scale directional features are synchronous between the cores and other Western Arctic records from the area. Due to the robust chronology, these new high‐resolution PSV records provide a valuable contribution to the characterization of geomagnetic field behavior in the Arctic over the past few thousand years, and can aid in developing age models for suitable sediments found in this region. Plain Language Summary Investigating past changes in Earth's magnetic field is important to understand how the field is generated and varies through time. Marine sediments can record geomagnetic field changes, and can be used to reconstruct past field behavior as long as they are well dated. There are few such records from the Arctic, particularly ones that have a robust chronology covering the past few thousand years. This study provides two new sedimentary paleomagnetic records from the Chukchi Sea of the Arctic Ocean, which were dated using radiocarbon and caesium‐137. Behavior of the geomagnetic field over the past 4,200 years as preserved in the studied sediments matches the predictions of geomagnetic field models, and is also similar to other regional sedimentary records. Features that current models do not capture provide new information on variations of the geomagnetic field, and can be used to improve the models, and to date sediments from the region. Key Points Geomagnetic field directions are reconstructed for two sediment cores from the Chukchi Sea for the past 4,200 years The geochronology is based on 26 radiocarbon dates, 137Cs and tephra from the Aniakchak CFE II eruption The records capture paleomagnetic features recognized in the western Arctic and could aid future geochronology

The study of active microbial populations in deep, energy-limited marine sediments has extended our knowledge of the limits of life on Earth. Typically, microbial activity in the deep biosphere is calculated by transport-reaction modelling of pore water solutes or from experimental measurements involving radiotracers. Here we modelled microbial activity from the degree of D:L-aspartic acid racemization in microbial necromass (remains of dead microbial biomass) in sediments up to ten million years old. This recently developed approach (D:L-amino acid modelling) does not require incubation experiments and is highly sensitive in stable, low-activity environments. We applied for the first time newly established constraints on several important input parameters of the D:L-amino acid model, such as a higher aspartic acid racemization rate constant and a lower cell-specific carbon content of sub-seafloor microorganisms. Our model results show that the pool of necromass amino acids is turned over by microbial activity every few thousand years, while the turnover times of vegetative cells are in the order of years to decades. Notably, microbial turnover times in million-year-old sediment from the Peru Margin are up to 100-fold shorter than previous estimates, highlighting the influence of microbial activities on element cycling over geologic time scales.

Shallow coastal embayments are typical features of former glacial landscapes in parts of Scandinavia and North America. An increasing concern over the impact of accelerating sea‐level rise, calls for a better understanding of how coasts respond to sea‐level changes. Studying the response of coastal environments, such as submerged embayments, to sea‐level changes in the past, can provide important insights into the response of present‐day coastlines to future sea‐level rise. Kalø Bay is an embayment situated in south‐western Kattegat, north of the Aarhus Bay, Denmark. This shallow embayment was influenced by sea‐level changes governed by global sea‐level rise and glacio‐isostatic rebound from the Scandinavian Ice Sheet during the latest Pleistocene and Holocene. In this study, we analyse the palaeolandscape in the bay to identify the depositional succession preserved in the bay and understand the dominant geological processes occurring after the last glaciation in response to sea‐level changes. Four major depositional units reflect the variable environment in the bay as it changed from a glacial to proglacial setting through coastal and lagoonal infill stages, and gradually developed into a shallow marine environment as the area was inundated approximately 9–6 cal. ka BP. During a relative sea‐level fall in the Mid‐ and Late Holocene, the deposits in the bay reversed to more coastal facies. Our study highlights the sensitivity of coastal embayments and their dynamic response to sea‐level changes. Our results show how the bay changed from a wave‐dominated setting in the Early Holocene to a current‐dominated setting in the Late Holocene, and how the former glacial landscape and coastal deposits were affected differently by the sea‐level rise and associated erosion and redeposition. These results are important for understanding the impacts of future accelerating sea‐level rise. We analyse the geological processes of a coastal embayment in the Kattegat. Using high‐resolution seismic data and sediment cores, we describe a geological evolution from glacial to shallow marine stages with a variety of preserved facies from different depositional settings, including glacio‐lacustrine, telmatic, limnic and coastal environments. We examine the main agents responsible for the observed deposition and erosion in the bay and find that waves and storm‐surge induced bottom currents are the predominant agents in the bay during the Holocene sea‐level rise.

The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow ( ∼  53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9–11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic–Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, which is later than in several previous studies. Our key evidence is based on a well-dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting at around 11 cal ka BP is observed. The shift corresponds to meltwater pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and the submergence of the large Bering Land Bridge. Although the precise rates of sea level rise cannot be quantified, our new results suggest that the late deglacial sea level rise was rapid and occurred after the end of the Younger Dryas stadial.

The Last Glacial Maximum (LGM, 23–19,000 year BP) designates a period of extensive glacial extent and very cold conditions on the Northern Hemisphere. The strength of ocean circulation during this period has been highly debated. Based on investigations of two marine sediment cores from the Davis Strait (1033 m water depth) and the northern Labrador Sea (2381 m), we demonstrate a significant influx of Atlantic-sourced water at both subsurface and intermediate depths during the LGM. Although surface-water conditions were cold and sea-ice loaded, the lower strata of the (proto) West Greenland Current carried a significant Atlantic (Irminger Sea-derived) Water signal, while at the deeper site the sea floor was swept by a water mass comparable with present Northeast Atlantic Deep Water. The persistent influx of these Atlantic-sourced waters entrained by boundary currents off SW Greenland demonstrates an active Atlantic Meridional Overturning Circulation during the LGM. Immediately after the LGM, deglaciation was characterized by a prominent deep-water ventilation event and potentially Labrador Sea Water formation, presumably related to brine formation and/or hyperpycnal meltwater flows. This was followed by a major re-arrangement of deep-water masses most likely linked to increased overflow at the Greenland-Scotland Ridge after ca 15 kyr BP.

According to climate models, the Lincoln Sea, bordering northern Greenland and Canada, will be the final stronghold of perennial Arctic sea-ice in a warming climate. However, recent observations of prolonged periods of open water raise concerns regarding its long-term stability. Modelling studies suggest a transition from perennial to seasonal sea-ice during the Early Holocene, a period of elevated global temperatures around 10,000 years ago. Here we show marine proxy evidence for the disappearance of perennial sea-ice in the southern Lincoln Sea during the Early Holocene, which suggests a widespread transition to seasonal sea-ice in the Arctic Ocean. Seasonal sea-ice conditions were tightly coupled to regional atmospheric temperatures. In light of anthropogenic warming and Arctic amplification our results suggest an imminent transition to seasonal sea-ice in the southern Lincoln Sea, even if the global temperature rise is kept below a threshold of 2 °C compared to pre-industrial (1850–1900).

The Younger Dryas (YD) cold interval is one of the most abrupt climate events of Earth’s recent history. The origin of this rapid, severe cooling episode is still widely debated, but it was probably triggered by a large freshwater influx to the North Atlantic resulting in disruption of the Atlantic Meridional Overturning Circulation. The YD termination, despite having been even more abrupt than the onset has, however, received significantly less attention. Here using multi-proxy data from a high-resolution marine sediment record, we present evidence for a gradual decrease of the Labrador Current influence, northward migration of the Gulf Stream oceanic front and a rapid decline of sea-ice cover at the YD termination. Our data indicate a stepwise sequence of events with changes in ocean circulation clearly preceding those in atmospheric conditions, in contrast to the hitherto commonly assumed single-event rapid climatic shift at the YD–Holocene transition. The abrupt ending of the Younger Dryas cooling episode marked the onset of the present interglacial and was the most prominent climate change in the Earth’s recent history. This study shows evidence for a sequence of events with a leading role of the ocean at the transition into the present day warm Holocene epoch.