The Arctic Coring Expedition (ACEX) remains the only scientific ocean drilling project conducted in the central Arctic Ocean by IODP and its predecessors. Despite its success, substantial uncertainty persists regarding Neogene and Quaternary sea-ice extent. A major challenge to resolving this is the ongoing debate about the age of sediments in the upper 5–15 m below the seafloor. Classical interpretations of apparent paleomagnetic reversals as chron and subchron boundaries result in ultra-low sedimentation rates across the central Arctic. When applied to the ACEX record this yields sedimentation rates of mm/kyr back to at least the Late Miocene – predicting ages that are incompatible with the observed decay of ¹⁰Be and the dinocyst biostratigraphy. It is conceivable that the Quaternary expansion of the perennial sea-ice zone and development of ice shelves may have reduced sedimentation across parts of the Arctic Ocean, but establishing the existence, timing and extent of this transition requires improved resolution on the age of Pleistocene Arctic sediments. Critically, older age constraints from ACEX indicate that cm/kyr sedimentation rates existed through the Neogene, possibly due to a less extensive perennial ice pack. Future efforts are needed to acquire the spatial sampling necessary to constrain the position of the marginal ice zone, which should have exhibited large variability between the end-member states of a seasonally and perennially sea-ice covered ocean.

Radiocarbon chronologies for Arctic Ocean sediments are argued to be extremely uncertain due to low sedimentation rates, bioturbation and authigenic calcite growth on microfossils. Mixing of sediments may result in under- or overestimation of the true age of sediments and authigenic calcite growth can yield either anomalously old or, even younger radiocarbon ages. Ascertaining the extent of these processes is necessary to determine the fidelity of late Pleistocene and Holocene Arctic paleoceanographic time-series. A key question is the age of microfossil-bearing sediments overlying a widespread diamict in the central Arctic Ocean, particularly whether it was deposited during Marine Isotope Stage (MIS) 3 between 40 and 50 ka, or during an earlier stadial of the last glacial cycle. Here we use two key calcareous nannofossil bioevents: the abundance peak of Coccolithus pelagicus and the transition from a high abundance of Gephyrocapsa spp. to a dominance of Gephyrocapsa huxleyi to identify Holocene and MIS 3 sediments from the central Arctic Ocean. We show that the timing of these events can be correlated to lower latitude records, providing an important stratigraphic framework to assess Arctic radiocarbon chronologies. Bayesian age–depth models constructed for three carbonate-rich cores yield stratigraphically consistent, monotonic age–depth relationships with acceptable agreement indices and reduced uncertainties relative to unmodelled calibrations. The models reveal variable sedimentation rates and localized hiatuses, but confirm that radiocarbon chronologies remain internally coherent when statistically constrained. Similar to many ocean basins, radiocarbon ages in Arctic sediments are influenced by mixing and diagenesis. However the agreement between nannofossil bioevents and Bayesian-modelled radiocarbon-based age estimates in multiple cores suggests that the radiocarbon chronologies retain substantial utility when interpreted alongside biostratigraphic markers. This highlights the potential for combining independent dating methods to improve confidence in Arctic sediment chronologies.

The Beaufort Sea region in the Canadian Arctic has undergone substantial sea ice loss in recent decades, primarily driven by anthropogenic climate warming. To place these changes within the context of natural climate variability, Holocene sea ice evolution and environmental conditions (sea surface temperature, salinity, terrestrial input) were reconstructed using lipid biomarkers (HBIs including IP₂₅, OH-GDGT, brGDGT, C_16:0 fatty acid, phytosterols) from two marine sediment cores collected from the Beaufort Shelf and slope, spanning the past 9.1 ka and 13.3 cal. kyr BP, respectively. The Early Holocene (11.7–8.2 ka) is characterized by relatively higher sea surface temperature, lower salinity and no spring/summer sea ice until 8.5 ka on the Beaufort Sea slope. Around 8.5 ka, a peak in organic matter content is linked to both increased terrestrial input and primary production and may indicate increased riverine input from the Mackenzie River and terrestrial matter input from coastal erosion. Following this period, terrestrial inputs decreased throughout the Mid-Holocene in both cores. A gradual increase in IP₂₅ and HBI-II concentrations aligns with relatively higher salinity, lower sea surface temperature and rising sea levels, and indicate the establishment of seasonal (spring) sea ice on the outer shelf around 7 ka and on the shelf around 5 ka. These patterns suggest an expansion of the sea ice cover beginning in the Mid-Holocene, influenced by decreasing summer insolation. During the Late Holocene (4.2–1 ka), permanent sea ice conditions are inferred on the slope with a peak during the Little Ice Age. After 1 ka, seasonal sea ice conditions on the slope are observed again, alongside an increase in salinity and terrestrial input, and variable primary productivity. Similar patterns of Holocene sea ice variability have been observed across other Arctic marginal seas, highlighting a consistent response to external climate forcing. Continued warming may drive the Beaufort Sea toward predominantly ice-free conditions, resembling those inferred for the Early Holocene.

To investigate the Arctic Ocean response to Quaternary climate change (past ∼1.9 Ma), sediment transport and deposition was investigated in two sediment cores from the Canada and Makarov Basins using end-member modelling of grain size spectra. Four end-members were identified and interpreted as proxies for sea ice transport of sediments entrained by suspension freezing (clayey EM1) and anchor ice (coarse-silty EM3), near-bottom current transport (fine-silty EM2) and iceberg rafting (sandy EM4). Sea ice deposition from suspension freezing and anchor ice transport exhibit opposing long-term trends, with an overall decline in anchor ice. We infer that perennial sea ice expansion suppressed anchor ice but not suspended sediment transport. Interglacial conditions (enhanced ventilation, broader continental shelves) promoted anchor ice formation, whereas glacial environments limited overall sea ice sediment release. Near-bottom currents and iceberg transport are inversely correlated, with coarse ice rafted debris (IRD) peaking during glacial/deglacial periods. Iceberg transport proxies and sediment provenance indicate persistent circum-Arctic ice sheet expansion during the last ∼600–700 ka, after the Mid-Pleistocene Transition (MPT). These results are consistent with geological and modelling data for the Eurasian and North American ice sheet history. Iceberg transport also varied with changes in surface circulation. Anticorrelation with bottom currents indicates that periods of iceberg discharge suppressed deep-water convection, thus weakening bottom currents. These changes are linked to the overall intensification of the Pleistocene Northern Hemisphere glaciation. Massive glacial meltwater fluxes into the North Atlantic weakened the formation of the North Atlantic Deep Water (NADW), and thus the Atlantic Meridional Overturning Circulation (AMOC). The reduced northward heat transport enhanced perennial sea ice expansion and diminished near bottom current activity, as reflected in the Arctic Ocean sediment records.

The Mid-Pleistocene Transition between ~ 1.25 and 0.7 million years ago is a critical interval in Quaternary climate history, marked by a shift in glacial-interglacial cyclicity from ~ 41,000 to ~ 100,000 years, yet its cause remains debated. Here we present authigenic neodymium isotope records from marine sediments to reconstruct past changes in Arctic Ocean circulation during this period. Our results indicate a notable increase in Arctic-Atlantic exchange across the Mid-Pleistocene Transition, likely driven by the opening of the Barents Seaway following extensive glacial erosion. We propose that increased Arctic-Atlantic connectivity at that time contributed to the reorganization of global ocean circulation, enhancing deep-ocean carbon storage and increasing moisture supply to Northern Hemisphere ice sheets. These changes likely accounted for the long-term decline in glacial pCO₂ levels and wetter conditions in surrounding Arctic regions, allowing ice sheets to persist through insolation maxima and ultimately establishing the 100,000-year glacial cyclicity.

The Arctic Ocean is changing rapidly due to global warming, but how this will impact marine Arctic ecosystems remains uncertain. Several Pleistocene interglacials, like Marine Isotope Stages (MIS) 5e, 9 and 11 form potential analogues to a future warmer Arctic and can give important insights on how Arctic ecosystems may respond to climate warming. However, micro- and nannofossils are scarce in many Pleistocene marine sediment cores, and are often not in agreement with biomarker data. Sedimentary ancient DNA (sedaDNA) is an emerging method that does not require the preservation of fossils and can therefore be used to detect taxa without any hard body parts, like most protist groups and zooplankton. Thanks to this method, it is now possible to detect organisms from all trophic layers of marine ecosystems. SedaDNA provides us with new opportunities to reconstruct past sea ice conditions, changes to ocean currents, and borealisation of the Arctic Ocean. Developments in bioinformatics software and new techniques like shotgun metagenomics and hybridisation capture, now enable the study of ancient DNA from Middle and even Early Pleistocene sediments. Moreover, the marine sedaDNA field is working towards detecting within-species genetic variation, which can provide information on population bottlenecks, recolonisation histories, and may lead to important insights for marine conservation. Combined with traditional proxies, sedaDNA is a powerful tool for Arctic Ocean palaeo-environmental reconstructions and can help provide critical proxy data to facilitate climate model calibrations and ultimately improve climate and environmental predictions for the Arctic.

Boreal forest fires are an important component of the vegetation and carbon dynamics in the Arctic. Increased temperature triggered by anthropogenic climate change is intensifying the number and scale of spring and summer boreal fires. High resolution sedimentary archives hold the key to reconstruct reliable records of past biomass burning. We studied a 3 m-long piston core, and its corresponding multicore, located in the Beaufort Sea, in front of the Mackenzie River mouth (Arctic Canada). The core captures a 3000-yrs history of discharge from the Mackenzie River catchment and eolian input. Biomass-burning biomarkers (benzene polycarboxylic acids, BPCA, and levoglucosan, created during low-temperature biomass-burning) as well as microscopic charcoal (larger than 10 µm) were quantified to reconstruct past variation in boreal fires. They are linked to changes in vegetation reconstructed using pollen and biomarkers (lignin phenols). The combined information from multiple biomass burning proxies provide a unique late Holocene record of boreal fire activity in Arctic Canada, recording climatic events such as the Little Ice Age.

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 Greenland Ice Sheet's negative mass balance is driven by a sensitivity to a warming atmosphere and ocean. The fidelity of ice-sheet models in accounting for ice–ocean interaction is inherently uncertain and often constrained against recent fluctuations in the ice-sheet margin from the previous decades. The geological record can be used to contextualise ice-sheet mass loss and understand the drivers of changes at the marine margin across climatic shifts and previous extended warm periods, aiding our understanding of future ice-sheet behaviour. Here, we use the Ice-sheet and Sea-level System Model (ISSM) to explore the Holocene evolution of Ryder Glacier draining into Sherard Osborn Fjord, North Greenland. Our modelling results are constrained with terrestrial reconstructions of the paleo-ice-sheet margin and an extensive marine sediment record from Sherard Osborn Fjord that details ice dynamics over the past 12.5 ka years. By employing a consistent mesh resolution of <1 km at the ice–ocean boundary, we assess the importance of atmospheric and oceanic changes to Ryder Glacier's Holocene behaviour. Our simulations show that the initial retreat of the ice margin after the Younger Dryas cold period was driven by a warming climate and the resulting fluctuations in surface mass balance. Changing atmospheric conditions remain the first-order control in the timing of ice retreat during the Holocene. We find ice–ocean interactions become increasingly fundamental to Ryder's retreat in the mid-Holocene, with higher-than-contemporary melt rates required to force grounding line retreat and capture the collapse of the ice tongue during the Holocene Thermal Maximum. Regrowth of the tongue during the neoglacial cooling of the late Holocene is necessary to advance the terrestrial and marine margins of the glacier. Our results stress the importance of accurately resolving the ice–ocean interface in modelling efforts over centennial and millennial timescales, in particular the role of floating ice tongues and submarine melt, and provide vital analogies for the future evolution of Ryder in a warming climate.