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There now exists two decades of basin-wide coverage of Arctic sea ice from three dedicated polar-orbiting altimetry missions (ICESat, CryoSat-2, and ICESat-2) launched by NASA and ESA. Here, we review our retrieval approaches and discuss the composite record of Arctic ice thickness (2003–2023) after appending two more years (2022–2023) to our earlier records. The present availability of five years of snow depth estimates—from differencing lidar (ICESat-2) and radar (CryoSat-2) freeboards—have benefited from the concurrent operation of two altimetry missions. Broadly, the dramatic volume loss (5500 km3) and Arctic-wide thinning (0.6 m) captured by ICESat (2003–2009), primarily due to the decline in old ice coverage between 2003 and 2007, has slowed. In the central Arctic, away from the coasts, the CryoSat-2 and shorter ICESat-2 records show near-negligible thickness trends since 2007, where the winter and fall ice thicknesses now hover around 2 m and 1.3 m, from a peak of 3.6 m and 2.7 m in 1980. Ice volume production has doubled between the fall and winter with the faster-growing seasonal ice cover occupying more than half of the Arctic Ocean at the end of summer. Seasonal ice behavior dominates the Arctic Sea ice's interannual thickness and volume signatures. [ABSTRACT FROM AUTHOR]

ABSTRACT The Greenland–Scotland Ridge is a submarine mountain that rises up to 500 m below the sea surface and extends from the east coast of Greenland to the continental shelf of Iceland and across the Faroe Islands to Scotland. The ridge not only separates deeper ocean basins on either side, that is, the North Atlantic and Arctic oceans, but also forms a geomorphological barrier between the cold arctic water masses of the Nordic Seas and the comparably contrastingly warmer water of the North Atlantic Ocean. It is therefore situated at a strategic geographical position in relation to the effect of climate change in the Arctic region. Both the Arctic and the Atlantic subpolar ecosystems are facing each other at the ridge, creating oceanic fronts in the Denmark Strait and in the Iceland–Faroe ridge alike. This ridge in the subarctic area forms the southern boundary of the North Atlantic Gateway to the Arctic Ocean, affecting exchanges of oceanic currents and of marine organisms between the two main ecosystems in the Nordic polar region. For example, the appearance of natural invasive species such as the Atlantic mackerel in this region mainly occurred along the ridge, with arrival through the Scotland–Faroe Islands mount with subsequent waves of colonization which eventually reached the southern tip of Greenland. With the increasing impacts of climate change, such natural colonization through the ridge is likely to happen more frequently and affect regional ecosystems. Yet, the human resources and the economy of the local nations on the ridge are rather limited compared to neighboring countries. With a total of less than half a million people inhabiting the area and a total ocean surface of circa 3 million km2 of continental shelf, Greenland, Iceland, the Faroe Islands, and Scotland will face critical challenges in the coming years with respect to biodiversity conservation and sustainable management of marine resources. Here is a summary of what we know, what we might expect, and an opening to potential discussions for the future of research in this region. The main objective of this paper is calling attention to much needed additional research effort on the marine environment around the Greenland–Scotland Ridge, instead of presenting a comprehensive overview of research in this area. [ABSTRACT FROM AUTHOR]

The results of studying the quantitative, material, and morphometric composition of rock debris in sediments sampled by a box-corer on Lomonosov Ridge (83° N), Arctic Ocean, during the Severnyi Polyus 41 expedition of the Arctic and Antarctic Research Institute are presented. Clasts ≥ 1 cm in size were sampled from each distinguished layer according to the lithological description. The age model was created by the lithostratigraphic correlation with previously dated cores. The content of clasts on the eastern slope and summit is significantly higher than on the western slope, which is explained by the higher sedimentation rate on the western slope after the deglaciation peak. The change in the rock composition from carbonate to igneous and the increase in roundness with time indicate a higher input of Eurasian material in MIS 1. [ABSTRACT FROM AUTHOR]

This article focuses on the study of the distribution of 137Cs in the bottom sediments of Arctic rivers of the Barents Sea basin (using the example of the Nenets Autonomous Okrug, Russian Arctic). This research is relevant due to the poorly studied region and the significant number of radiation-hazardous facilities in the Arctic zone of Russia, both those currently in operation and those that are "nuclear heritage sites". The study of 137Cs specific activity in bottom sediments was carried out in the period from 2020 to 2023 in the rivers Chizha, Nes, Vizhas, Oma, Pechora (river delta), as well as the rivers Kolva and Usa (first and second order tributaries, respectively, of the Pechora River). A total of 199 samples were collected. In addition to 137Cs specific activity, the samples were analysed for sediment particle size distribution, organic matter content, carbonate content and ash content. The 137Cs specific activity mainly ranged from the minimum detectable specific activity to 5.4 ± 0.8 Bq·kg−1. In the Nes River basin (Kaninskaya tundra), the 137Cs content in bottom sediments reached 36.0 ± 3.2 Bq·kg−1 (in the case of lake sediments) and 22.9 ± 3.7 Bq·kg−1 (in the case of river sediments), values that are higher than those of the North-West of Russia. Considering the large area of the study area (Kaninskaya tundra, Pechora river delta, southern part of Bolshezemelskaya tundra) and the similarity of physical and chemical parameters of the studied rivers, it is possible to assume the existence of a zone of increased radionuclide content in the Nes river basin. This may be due to the runoff from the Nes River catchment area, its hydrological features, and the accumulation of 137Cs in the small fractions of bottom sediments. The results confirm the conclusions of previous soil studies in the Nes river basin. The main sources of elevated 137Cs content are global atmospheric deposition and the Chernobyl Nuclear Power Plant accident. [ABSTRACT FROM AUTHOR]

The Chukchi Borderland, connecting the Chukchi continental shelf and the Canada Basin, has become a hotspot for studying how ecosystems respond to rapid environmental changes in the Arctic Ocean. Based on a long‐term hindcast simulation during 1998–2015 using a coupled ocean‐sea ice‐biogeochemical model, this study investigates the responses of phytoplankton assemblage and the biological carbon pump efficiency within the upper layers (0–100 m) of the Chukchi Borderland. The nitrate concentration is found to be a crucial factor controlling the total phytoplankton biomass and determining the spatiotemporal variations in the evolution pattern of phytoplankton assemblage. In the shelf break adjacent region, nitrate concentration increased after 2009, boosting phytoplankton biomass with diatoms persistently dominating. In the Canada Basin adjacent region, the westward expansion of the Beaufort Gyre after 2009 extended the influence of oligotrophic water, leading to phytoplankton miniaturization and a shift in phytoplankton assemblage evolution, from a pre‐2009 pattern that non‐diatoms at start were succeeded by diatoms, to a post‐2009 scenario that non‐diatoms dominated throughout the growing season. The biological pump efficiency evidently increased in the shelf break region after 2009, due to heightened biomass and intensified horizontal advection‐induced particulate organic carbon (POC) supply. The western Canada Basin adjacent region presented the reduced primary production and vertical POC flux. However, the deeper nitracline deepened the phytoplankton habitat, shortening POC residence time in the upper layers and enhancing the biological pump efficiency. Plain Language Summary: The responses of marine phytoplankton and the biological carbon pump efficiency to rapid changes in the Chukchi Borderland are studied through analyzing a numerical model simulation spanning 1998–2015. In the upper ocean (0–100 m depth), the nitrate concentration is found to be a crucial factor for space‐time variations of the total biomass and the dominance of phytoplankton groups. Over the continental shelf and shelf break, nitrate increased after 2009, promoting the growth of larger‐size phytoplankton (diatoms) and sustaining their dominance throughout most of the growing season. In the region near western Canada Basin, the westward expansion of the Beaufort Gyre (nitrate‐low water) favored the smaller‐size phytoplankton growth. This shift is expected to reduce the quality of ecosystem production. The biological carbon pump efficiency generally increased after 2009, indicating a faster transfer of biologically fixed carbon into deep water. In the shelf break region, this efficiency increase was due to heightened local primary production and increased horizontal transport of particulate organic carbon supply. Near the western Canada Basin, it was due to a deeper phytoplankton habitat. These results provide new perspectives for the evaluation of carbon sinks in the western Arctic Ocean. Key Points: Nitrate levels shape regional differences in annual evolution of phytoplankton assemblageOligotrophic Canada Basin water leads to phytoplankton miniaturization and assemblage evolution shifts in its expanded regionBio‐pump efficiency is promoted by increased productivity and advected particulate organic carbon over shelf break, while by deeper habitat near Canada Basin [ABSTRACT FROM AUTHOR]

Fram Strait is one of the main gateways for fresh water leaving the Arctic Ocean toward the deep‐water formation regions of the North Atlantic. Monitoring transport through Fram Strait is important to quantify the impact of Arctic amplification on the hydrography in lower latitudes. We update existing time series from the moorings in the western Fram Strait and investigate the monthly and interannual variability of the liquid freshwater transport (FWT, reference salinity 34.9), volume transport and freshwater content between 2003 and 2020. We examine composites and correlations of sea‐level pressure (SLP) reanalysis, and remote‐sensing dynamic‐ocean topography (DOT) in the Arctic Ocean. We identify two remote forcing mechanisms of FWT: (a) North Pole convergence freshens the region north of Fram Strait 13–24 months before high FWT events. (b) Beaufort Gyre weakening allows spreading of fresh water to the margins of the Arctic Basin zero to 9 months before high FWT events. In addition a third mechanism occurs locally, (b) Fram Strait northerly winds confine freshwater to the Greenland shelf and drive stronger southward FWT. Additionally, we find a decreasing trend in the total volume transport, concurrent with weakening northerly winds and reducing north‐south DOT gradient across the strait. We also examined correlations between the Fram Strait time series and the Arctic Oscillation and Arctic Ocean Oscillation. Both are found to correlate positively with the total volume transport, while the Arctic Oscillation correlates negatively with FWT with 1‐year lag. Plain Language Summary: The East Greenland Current brings fresh water from the central Arctic Ocean to lower latitudes. The exported fresh water affects stratification, and can contribute to variations of the global meridional overturning circulation. In Fram Strait, between Greenland and Svalbard, the properties of this current have been systematically monitored using moored instruments. We present updated time series of freshwater transport from the moorings in the Fram Strait, and analyze their variability between 2003 and 2020. We identify three mechanisms that contribute to high freshwater transport in the Strait. (a) 13–24 months before, clockwise wind anomalies in the Eurasian Arctic drive converging current anomalies and freshen the area preconditioning fresh outflow events. (b) 0–9 months before, anticlockwise wind anomalies in the Canadian Arctic drive diverging current anomalies directing fresh water to the periphery and Fram Strait. (c) Northerly winds over the strait drive southward transport instantly. We find additionally that total volume transport in the Fram Strait decreases in relation to weakening northerlies that could be a result of a warming Greenland. Key Points: Fram Strait local northerly winds force instant southward volume and freshwater transportArctic Ocean large‐scale wind variability forces two distinguished lagged responses of freshwater content and transport in Fram StraitBetween 2004 and 2019 freshwater transport shows no trend but total volume transport of the East Greenland Current decreases by ∼0.1 SV/year [ABSTRACT FROM AUTHOR]

The chirp sub-bottom profiler, for its high resolution, easy accessibility and cost-effectiveness, has been widely used in acoustic detection. In this paper, the acoustic impedance and grain size compositions were obtained based on the chirp sub-bottom profiler data collected in the Chukchi Plateau area during the 11th Arctic Expedition of China. The time-domain adaptive search matching algorithm was used and validated on our established theoretical model. The misfit between the inversion result and the theoretical model is less than 0.067%. The grain size was calculated according to the empirical relationship between the acoustic impedance and the grain size of the sediment. The average acoustic impedance of sub-seafloor strata is 2.5026 × 106 kg (s m2)−1 and the average grain size (θ value) of the seafloor surface sediment is 7.1498, indicating the predominant occurrence of very fine silt sediment in the study area. Comparison of the inversion results and the laboratory measurements of nearby borehole samples shows that they are in general agreement. [ABSTRACT FROM AUTHOR]

The Arctic Ocean and adjacent seas are undergoing increased freshwater influx due to enhanced glacial and sea ice melt, precipitation, and runoff. Accurate delineation of these freshwater sources is vital as they critically modulate ocean composition and circulation with widespread and varied impacts. Despite this, the delineation of freshwater sources using physical oceanographic measurements (e.g., temperature, salinity) alone is challenging and there is a requirement to improve the partitioning of ocean water masses and their mixing relationships. Here, we complement traditional oceanographic measurements with continuous surface seawater isotopic analysis (δ18O and deuterium excess) across a transect extending from coastal Alaska to Baffin Bay and the Labrador Sea conducted from the US Coast Guard Cutter Healy in Autumn 2021. We find that the diverse isotopic signatures of Arctic freshwater sources, coupled with the high freshwater proportion in these marine systems, facilitates detailed fingerprinting and partitioning. We observe the highest freshwater composition in the Beaufort Sea and Amundsen Gulf regions, with heightened freshwater content in eastern Baffin Bay adjacent to West Greenland. We apply isotopic analysis to delineate freshwater sources, revealing that in the Western Arctic freshwater inputs are dominated by meteoric water inputs—specifically the Mackenzie River—with a smaller sea ice meltwater component and in Baffin Bay the primary sources are local precipitation and glacial meltwater discharge. We demonstrate that such freshwater partitioning cannot be achieved using temperature‐salinity relationships alone, and highlight the potential of seawater isotopic tracers to assess the roles and importance of these evolving freshwater sources. Plain Language Summary: Freshwater inputs to the Arctic seas, including glacial and sea ice meltwater, precipitation, and river runoff, are increasing as the Arctic warms. The impacts of these changing freshwater influxes are varied depending on the type of freshwater source, and thus it is important to delineate and trace these different freshwater sources, which represents a significant challenge using only traditional physical oceanographic measurements (e.g., temperature, salinity). In this study, we utilize a new approach to identify and trace freshwater sources using continuous seawater isotopic measurements during a cruise extending from coastal Alaska, through the Canadian Archipelago, and across Baffin Bay and the Labrador Sea. We show that these isotopic measurements, which have been commonly used in other media (e.g., precipitation, water vapor, ice cores), hold important and distinct information about the source and mixing of different freshwater sources. We use these measurements to identify the freshwater sources (e.g., Mackenzie vs. Yukon River) contributing to ocean surface waters across the Arctic region. Key Points: Seawater isotopic measurements (δ18O, δ2H, deuterium excess) show heightened freshwater content in the Beaufort Sea and Baffin BayIsotopic observations enable freshwater source delineation not feasible from traditional physical oceanographic methodsFreshwater source delineation includes the Mackenzie and Yukon Rivers around coastal Alaska and glacial meltwater in Baffin Bay [ABSTRACT FROM AUTHOR]

Analysis of dissolved oxygen (O2) in the Arctic's surface ocean provides insights into gas transfer between the atmosphere‐ice‐ocean system, water mass dynamics, and biogeochemical processes. In the Arctic Ocean's Canada Basin mixed layer, higher O2 concentrations are generally observed under sea ice compared to open water regions. Annual cycles of O2 and O2 saturation, increasing from summer through spring and then sharply declining to late summer, are tightly linked to sea ice cover. The primary fluxes that influence seasonal variability of O2 are modeled and compared to Ice‐Tethered Profiler O2 observations to understand the relative role of each flux in the annual cycle. Findings suggest that sea ice melt/growth dominates seasonal variations in mixed layer O2, with minor contributions from vertical entrainment and atmospheric exchange. While the influence of biological activity on O2 variability cannot be directly assessed, indirect evidence suggests relatively minor contributions, although with significant uncertainty. Past studies show that O2 molecules are expelled from sea ice during brine rejection; sea ice cover can then inhibit air‐sea gas exchange resulting in winter mixed layers that are super‐saturated. Decreasing mixed layer O2 concentrations and saturation levels are observed during winter months between 2007 and 2019 in the Canada Basin. Only a minor portion of the decreasing trend in wintertime O2 can be attributed to decreased solubility. This suggests the O2 decline may be linked to more efficient air‐sea exchange associated with increased open water areas in the winter sea ice pack that are not necessarily detectable via satellite observations. Plain Language Summary: Dissolved oxygen (O2) is a valuable ocean property that allows us to better understand the exchange of gases between the different ocean layers, sea ice, and atmosphere, and the physical and biological processes that control its variability. Understanding how and why O2 concentrations in the Arctic Ocean mixed layer vary spatially and seasonally is crucial for interpreting its evolution over timescales of years to decades that are influenced by global warming. We use physical and thermodynamical relationships to model the main factors that influence O2 concentrations in the mixed layer of the Arctic Ocean's Canada Basin, which we compare to observations made by Ice‐Tethered Profilers. Model results indicate that seasonal variations in O2 concentrations are dominated by the effects of sea ice growth and melt. Other processes that modulate mixed layer O2, including air‐sea exchange and ocean mixing, have a lesser influence. Between 2007 and 2019, mixed‐layer O2 has decreased in winter months, which we attribute to more openings in the sea‐ice pack during wintertime in the Canada Basin. Key Points: Spatial and seasonal distributions of O2 concentrations in the Canada Basin mixed layer are linked to the seasonal evolution of sea iceModeled fluxes suggest brine rejection and meltwater dilution during sea ice melt/formation dominate seasonal variability of mixed layer O2Decreases in mixed‐layer O2 during winter (over 2007–2019) suggest outgassing, likely driven by changes in the wintertime sea ice pack [ABSTRACT FROM AUTHOR]

The Arctic Ocean plays an important role in the regulation of the earth's climate system, for instance by storing large amounts of carbon dioxide within its interior. It also plays a critical role in the global thermohaline circulation, transporting water entering from the Atlantic Ocean to the interior and initializing the southward transport of deep waters. Currently, the Arctic Ocean is undergoing rapid changes due to climate warming. The resulting consequences on ventilation patterns, however, are scarce. In this study we present transient tracer (CFC‐12 and SF6) measurements, in conjunction with dissolved oxygen concentrations, to asses ventilation and circulation changes in the Eurasian Arctic Ocean over three decades (1991–2021). We constrained transit time distributions of water masses in different areas and quantified temporal variability in ventilation. Specifically, mean ages of intermediate water layers in the Eurasian Arctic Ocean were evaluated, revealing a decrease in ventilation in each of the designated areas from 2005 to 2021. This intermediate layer (250–1,500 m) is dominated by Atlantic Water entering from the Nordic Seas. We also identify a variability in ventilation during the observation period in most regions, as the data from 1991 shows mean ages comparable to those from 2021. Only in the northern Amundsen Basin, where the Arctic Ocean Boundary Current is present at intermediate depths, the ventilation in 1991 is congruent to the one in 2005, increasing thereafter until 2021. This suggests a reduced ventilation and decrease in the strength of the Boundary Current during the last 16 years. Plain Language Summary: The Eurasian Arctic Ocean, the region of the Arctic Ocean connected to the European and Asian continents, is an important pathway for recently ventilated water from the Nordic Seas. These waters are exported back to the North Atlantic following their travel through the Arctic Ocean. Ventilation describes the process of surface waters being transported into the interior ocean due to increasing density, which affects the underlying water masses. In this study we investigate how the ventilation patterns have evolved in the Eurasian Arctic Ocean over the past three decades, using transient tracer (CFC‐12 and SF6) measurements. We observed a significant change in the intermediate layer (250–1,500 m) with older waters found in measurements in 1991 and 2021 compared to 2005 and 2015. Moreover, our data suggest a slowdown in ventilation throughout the three decades in the northern Amundsen Basin, implying a decrease in the circulation time‐scale of the Arctic Ocean Boundary Current over the past 16 years. This has potentially important implications for the transport of, for example, heat, salt or oxygen from the Atlantic Ocean around the Arctic Ocean, and back. Key Points: Temporal variability of ventilation in the Eurasian Arctic Ocean during the past 30 years is estimated by observations of transient tracersWe found a slow down of the ventilation between 2005 and 2021 in the intermediate watersEvidence of multidecadal variability of ventilation in the intermediate waters of the Eurasian Arctic Ocean is present [ABSTRACT FROM AUTHOR]

Eclipse Sound, in the northeastern Canadian Arctic, has experienced a substantial increase in ship traffic due to growing tourism and industrial development in the region. This study aims to describe the natural soundscape as well as to assess the noise levels associated with shipping. Underwater sound recordings were collected at two locations: Eastern Eclipse Sound (72° 43.730 N, 76° 13.519 W, 670 m) leading to Baffin Bay, and Milne Inlet (72° 15.260 N, 80° 34.205 W, 313 m) situated near the southwest end of Eclipse Sound. To capture the dynamic nature of the soundscape, the data from these two locations were divided into three seasons: late spring, summer, and early fall. These periods were selected to account for the changing contribution of sea ice to the soundscape during the sea ice break-up, two months of open water, and the sea ice freeze-up. By analyzing ship tracks and underwater acoustic recordings, we identified patterns of ship traffic and estimated underwater noise levels due to ships. Noise emitted by ships is quantified by vessel type, including three cargo ship types, passenger ships, pleasure craft, and icebreakers. Individual ship transits through the region introduce transient noise at frequencies from 20 kHz, with durations lasting from a few minutes to >6 h. The impact of ship noise on the soundscape is significant, resulting in increases in sound levels by 15 to >30 dB when ships are within 10 km and measurable ship noise below 200 Hz at distances of >50 km.

The North Water Polynya is one of the most productive Arctic regions on Earth, sustaining the world's northernmost Inuit communities for millennia. The polynya is a large and persistent region of open water surrounded by sea ice and exhibits high primary productivity, is a biodiversity hotspot, and is a key habitat and migration corridor for Arctic species. Many aspects of the ecosystem structure and the role of resident species in the North Water Polynya remain uncertain. To shed light on these, we developed the first representation of the North Water Polynya food web using the Ecopath modelling framework. Modelled trophic flows indicated that pelagic and benthic communities were primarily connected by Age 1+ Arctic cod (Boreogadus saida), walrus (Odobenus rosmarus), and ringed seal (Pusa hispida). Large copepods, Age 1+ Arctic cod, and bivalves were key prey species. Overall productivity in the North Water Polynya was higher compared to Western Baffin Bay and Western Greenland, corroborating expectations of relatively high productivity within the polynya. This model provides a baseline description of the North Water Polynya ecosystem structure and function prior to future climate-driven food web changes and the emergence of large-scale commercial fisheries.

The aim of our study was to examine the contribution of surface waves from WAVEWATCH-III (WW3) to the variation in sea surface temperature (SST) in the Arctic Ocean. The simulated significant wave height (SWH) were validated against the products from Haiyang-2B (HY-2B) in 2021, obtaining a root mean squared error (RMSE) of 0.45 with a correlation of 0.96 and scatter index of 0.18. The wave-induced effects, i.e., wave breaking and mixing induced by nonbearing waves resulting in changes in radiation stress and Stokes drift, were calculated from WW3, ERA-5 wind, SST, and salinity data from the National Centers for Environmental Prediction and were taken as forcing fields in the Stony Brook Parallel Ocean Model. The results showed that an RMSE of 0.81 °C with wave-induced effects was less than the RMSE of 1.11 °C achieved without the wave term compared with the simulated SST with the measurements from Argos. Considering the four wave effects and sea ice freezing, the SST in the Arctic Ocean decreased by up to 1 °C in winter. Regression analysis revealed that the SWH was linear in SST (values without subtraction of waves) in summer and autumn, but this behavior was not observed in spring or winter due to the presence of sea ice. The interannual variation also presented a negative relationship between the difference in SST and SWH. [ABSTRACT FROM AUTHOR]

This study investigated methylmercury (MeHg) concentrations in Arctic benthic invertebrates from two shelf sites in the Canadian Beaufort Sea. Carbon, nitrogen, and sulfur stable isotopes and fatty acids were measured to examine diet influences on MeHg concentrations in 476 individuals from 53 taxa of benthic invertebrates representing three different feeding guilds. Taxonomic identifications were based on DNA-barcoding and traditional taxonomy. MeHg concentrations ranged from 3 to 421 ng/g dry weight and increased over three trophic levels (δ15N range = 4.4–14.2‰). Organic matter sources had small but significant influences on MeHg bioaccumulation in the benthic food web. Carbon stable isotope ratios (δ13C, range = −25.5 to −19.8‰) were positively correlated with MeHg concentrations, suggesting greater reliance on benthic carbon contributed to higher concentrations. Sulfur stable isotopes were unrelated to MeHg concentrations. Fatty acids suggested feeding on diatoms versus dinoflagellates, and reliance on benthic resources influenced MeHg concentrations. Higher MeHg concentrations were observed at the site closer to the Mackenzie River mouth than the Cape Bathurst site. This study generated the most taxonomically rich dataset of MeHg concentrations in invertebrates from the Arctic marine benthos to date and provides a basis for future research on food web MeHg dynamics in the Canadian Beaufort Sea.

Microbial assemblages under the sea ice of the Dease Strait, Canadian Arctic, were sequenced for metagenomes of a small size fraction (0.2–3 μm). The community from early March was typical for this season, with Alpha‐ and Gammaproteobacteria as the dominant taxa, followed by Thaumarchaeota and Bacteroidetes. Toward summer, Bacteroidetes, and particularly the genus Polaribacter, became increasingly dominant, followed by the Gammaproteobacteria. Analysis of genes responsible for microbial acquisition of iron showed an abundance of ABC transporters for divalent cations and ferrous iron. The most abundant transporters, however, were the outer membrane TonB‐dependent transporters of iron‐siderophore complexes. The abundance of iron acquisition genes suggested this element was essential for the microbial assemblage. Interestingly, Gammaproteobacteria were responsible for most of the siderophore synthesis genes. On the contrary, Bacteroidetes did not synthesize siderophores but accounted for most of the transporters, suggesting a role as cheaters in the competition for siderophores as public goods. This cheating ability of the Bacteroidetes may have contributed to their dominance in the summer. [ABSTRACT FROM AUTHOR]

Understanding the oceanic carbon cycle, particularly in the Arctic regions, is crucial for addressing climate change. However, significant research gaps persist, especially regarding climate effects on the oceanic carbon cycle in these regions. This review systematically explores Arctic-related research, focusing on mechanisms, regulatory frameworks, and modelling approaches in the oceanic carbon cycle, carbon sink, climate change impact, and maritime shipping. The findings highlight the Arctic's limited observer presence and high operational costs, hindering the data availability and studies on carbon-cycle changes. This underscores the need to integrate real-time Arctic Ocean monitoring data. Carbon sink research urgently requires direct methods to measure anthropogenic carbon uptake and address uncertainties in air–ocean carbon fluxes due to sea ice melting. Unlike terrestrial carbon cycling research, carbon-cycle studies in the oceans, which are essential for absorbing anthropogenic emissions, receive insufficient attention, especially in the Arctic regions. Numerous policies often fall short in achieving effective mitigation, frequently depending on voluntary or market-based approaches. Analyzing carbon-cycle and sink models has uncovered limitations, primarily due to their global perspective, hampering in-depth assessments of climate change effects on the Arctic regions. To pave the way for future research, enhancing Arctic Ocean climate data availability is recommended, as well as fostering international cooperation in carbon-cycle research, enforcing carbon policies, and improving regional modelling in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

The duration of ice-free periods in different parts of the Arctic Ocean plays a great role in processes in the climate system and defines the most comfortable sea ice conditions for economic activity. Based on satellite-derived sea ice concentration data acquired by passive microwave instruments, we identified the spatial distribution of the dates of sea ice retreat (DOR), dates of sea ice advance (DOA), and the resulting ice-free period duration (IFP) between these days for the Kara and Laptev seas during 1979–2022. The monthly decline in sea ice extent was detected from June to October in both seas, i.e., during the whole ice-free period. The annual mean sea ice extent during 2011–2021 decreased by 19.0% and 12.8% relative to the long-term average during 1981–2010 in the Kara and Laptev seas, respectively. The statistically significant (95% confidence level) positive IFP trends were detected for the majority of areas of the Kara and Laptev seas. Averaged IFP trends were estimated equal to +20.2 day/decade and +16.2 day/decade, respectively. The observed DOR tendency to earlier sea ice melting plays a greater role in the total IFP extension, as compared to later sea ice formation related to the DOA tendency. We reveal that regions of inflow of warm Atlantic waters to the Kara Sea demonstrate the largest long-term trends in DOA, DOR, and IFP associated with the decrease in ice coverage, that highlights the process of atlantification. Also, the Great Siberian Polynya in the Laptev Sea is the area of the largest long-term decreasing trend in DOR. [ABSTRACT FROM AUTHOR]

The governing equations for a viscous, incompressible fluid, in the thin-shell approximation, written in a coordinate frame which ensures validity at the North Pole, is simplified by invoking the f-plane approximation. Together with suitable stress conditions at the surface, describing the interaction of wind over ice and ice over water, a solution is developed for the Transpolar Drift current. This involves prescribing the near-surface geostrophic ocean flow and also, for ease of calculation, a simple version of the Ekman flow. Then, via the stress conditions at the surface, the near-surface wind consistent with these flows is obtained. An example, which exhibits the reduction in ice thickness as the flow moves over the North Pole towards the Fram Strait, and also describes the relative directions and speeds of the wind, ice and water, is presented in graphical form; this solution recovers what is observed. The considerable freedom available in this approach, allowing choices to be made for the geostrophic flow and the wind (both variable), and the ice profile at some initial position, is explained, opening the way to further, extensive investigations. [ABSTRACT FROM AUTHOR]

Anthropogenic radionuclides 129I and 236U are used to investigate pathways of the Atlantic Water flow in the Canada Basin, estimate transport timescales, and investigate mixing dynamics within the Atlantic Water layer and the overlying Pacific Water. Transit Time Distribution (TTD) model mean ages indicate water takes 25–35 years to reach the Canada Basin from the entrance of the Arctic, with limited lateral and vertical mixing along the core of the Arctic Ocean Boundary Current. Mode ages obtained from the model yield shorter transport times of 20–32 years. These age estimates agree with previous studies using these radionuclides and ventilation tracers in this region, indicating a steady‐state flow of Atlantic Water for the last 15 years. The distribution of the isotopes in the Atlantic layer indicates two pathways Atlantic Water may take into the basin, supported by the distribution of ages in the TTD model. End‐member mixing models indicate that the Pacific Winter water acquires a 20%–40% Atlantic Water signal of the radionuclides, upwelled over short periods, most likely along the shelf and Barrow Canyon region. Plain Language Summary: Man‐made nuclear products are used to trace the path of Atlantic water from the Atlantic Ocean to the Canada Basin in the Arctic, determine its transit time, and how it interacts with itself and Pacific Water that enters through the Bering Strait. The model suggests water takes 25–35 years to flow from the entrance of the Arctic to the Canada Basin, while a second estimate of age suggests slightly shorter transit times. The results of this study show that Atlantic Water flow has not changed significantly in the last 15 years. The distribution of the isotopes and ages also indicates two possible pathways water may take to the basin. An additional finding is that Pacific Winter Water carries a tracer concentration of 20%–40% of Atlantic Water, probably from Atlantic Water upwelling along the shelf, and in the Barrow Canyon region. Key Points: 129I and 236U trace Atlantic sourced water in the Canada BasinUpwelling of tracer labeled Atlantic Water into the Pacific Winter Water distinguishes the layer from Pacific Summer WaterTransit time distributions yield ages of 25–35 years for the core Atlantic Water [ABSTRACT FROM AUTHOR]

To quantitatively assess seasonal variations in the partial pressure of carbon dioxide (pCO2) in the Pacific sector of the Arctic Ocean (Canada Basin and Chukchi Sea) in 2021, water temperature, salinity, chlorophyll‐a, pCO2, dissolved inorganic carbon (DIC), total alkalinity (TA), and nutrients were measured. During summer 2021, surface water pCO2 in our study area (315 ± 41 μatm) was undersaturated with respect to the atmosphere (404 ± 4 μatm), and the ocean was a sink for atmospheric CO2 (−10.5 ± 11.0 mmol C m−2 day−1). Using DIC, TA, and nutrients in the temperature minimum layer, we estimated the under‐ice pCO2 in the water during the previous winter and calculated changes in pCO2 (δpCO2) due to temperature changes, freshwater inflow, biological activity, and other factors (gas exchange and advection) from winter to summer. In the Chukchi Sea, biological activity and temperature changes had significant impacts on pCO2, whereas in the Canada Basin, the influx of freshwater caused a significant decrease in pCO2. Our results suggested that different types of freshwaters had different effects on pCO2, with sea ice meltwater having a greater effect on reducing pCO2 than river water or snowmelt water. We therefore emphasize the importance of freshwater type and proportion, as well as freshwater supply, for prediction of future pCO2 changes. Plain Language Summary: Assessment of the factors that cause ocean CO2 to vary is important in the Arctic Ocean, which acts as an atmospheric CO2 sink that will change significantly because of global warming. Seawater and sea ice samples were collected in the Pacific sector of the Arctic Ocean to investigate the carbonate chemistry. The partial pressure of carbon dioxide (pCO2) was lower on the sea surface than in the atmosphere during summer, and the ocean absorbed atmospheric CO2. The decreases of pCO2 from winter to summer were driven primarily by biological activity in the Chukchi Sea (partially offset by temperature increases) and by freshwater additions in the Canada Basin. Sea ice meltwater, snow meltwater, and river water had different effects on pCO2, even though all of them diluted the carbonate concentrations of surface water, because of differences in the alkalinity and carbonate chemistry among these freshwater sources. Key Points: The Pacific sector of the Arctic Ocean absorbed atmospheric CO2 in summerIn the Chukchi Sea, biological activity and temperature changed pCO2, while in the Canada Basin, the freshwater caused a decrease in pCO2Sea ice meltwater had a greater effect on reducing pCO2 than river water or snow meltwater [ABSTRACT FROM AUTHOR]

The fluorescence characteristics of dissolved organic matter (DOM) were measured to determine the distribution and drivers of DOM in the dark Canada Basin waters. We studied the relationship between fluorescent DOM (FDOM) and apparent oxygen utilization (AOU) in the whole water column as well as in the main water masses (Pacific Winter Water, Atlantic halocline (AH), Atlantic water—Fram Strait and Barents Sea branches, Deep Temperature Minimum, and Canada Basin deep water). The relative water mass fractions of different water masses were estimated using a five end‐members mixing model. The distribution of water mass fractions was found to be in good agreement with the distribution based on the traditional temperature‐salinity diagram. The fractions of AH waters were linked with AOU, highlighting the significant role played by mineralization in shaping AH humic‐like levels. The slope of the relationship between in situ FDOM—AOU was greater than those reported in the other oceans worldwide. This suggests that the AH is a hot spot for microbial mineralization of humic‐like DOM. On the other hand, the relationships with the humic‐like intensities differed among the four humic‐like components in the >125 m waters, indicating distinct environmental dynamics and biogeochemical roles for each humic‐like component. Plain Language Summary: Fluorescent marine dissolved organic matter in the dark ocean is primarily produced by the microbial decomposition of organic material. In this study, we examine the relationship between fluorescent dissolved organic matter (FDOM) and remineralization‐related variables such as apparent oxygen utilization in the main six water masses in the dark Canada Basin waters. Our study reveals a strong influence of in situ microbial processes on the humic‐like FDOM levels measured by the in situ sensor in the Atlantic halocline waters. We identified four more humic‐like and protein‐like FDOM components in samples collected by the CTD‐rosette that behaved differently. To better understand their sensitivity to in situ mineralization in the dark ocean, future studies should concentrate on in situ monitoring of the blue‐shifted humic‐like and protein‐like FDOM. Key Points: The high in situ fluorescent dissolved organic matter (FDOM) levels were linked to the high Pacific winter water mass fractionsThe slopes of the apparent oxygen utilization–FDOM correlations varied for the four humic‐like componentsThe Atlantic halocline serves as a hot spot for microbial formation of humic‐like FDOM [ABSTRACT FROM AUTHOR]

A large proportion of algal production and carbon export occurs after snowmelt and before ice melt in the Arctic Ocean. To determine the magnitude of under-ice export fluxes over the Chukchi Plateau (CP), a total of 25 sediment trap deployments were completed at two ice camps during the annual field survey of the Korean IBRV Araon in 2018: a first ice camp (CP1) conducted from August 17 to 19 and a second ice camp (CP2) conducted from August 20 to 22. Chlorophyll a (chl a) and particulate organic carbon (POC) fluxes were measured at 2, 5, 10 and 30 m under ice, and zooplankton collected in the sediment traps were enumerated and identified. Both chl a and POC fluxes were the highest at 5 m under ice at CP2, likely due to enhanced fluxes of the sea ice algae Melosira arctica and to a potential higher release of particulate matter from a thinner sea ice cover. Whereas Calanus glacialis/marshallae were dominant at all depths and both sites, the large numbers of individuals observed at 10 m at CP1 likely enhanced zooplankton grazing pressure at that site, further contributing to the high spatial variability in under-ice export fluxes. Overall, under-ice fluxes obtained in August 2018 highlighted the importance of M. arctica aggregates as a source of carbon for pelagic consumers and for carbon export during summer over the Chukchi Plateau. [ABSTRACT FROM AUTHOR]

The problem of differences in the rate of evolution among different animal or plant species has been intensely discussed in recent years, so the question of the validity of a so-called molecular clock hypothesis is very relevant. We have performed a search for publications describing median networks, which include haplotypes of mitochondrial genes for closely related boreal and arctic fish species (or those who settled through the Arctic). In all seven cases included into our analysis, the rate of nucleotide substitutions in Arctic taxa or taxa that settled through the Arctic during their evolutionary history was higher, and this difference was statistically significant. Therefore, the formation of new fish taxa in polar latitudes is accompanied by a rapid evolution of mitochondrial DNA that apparently reflects their adaptation to the new environment. In addition, speciation in Arctic fishes is usually accompanied by multiple chromosome fusions. Therefore, both our data and the data of other researchers provide solid reasons to doubt in the validity of the molecular clock hypothesis. [ABSTRACT FROM AUTHOR]

The ocean circulation is typically constrained in operational analysis and forecasting systems through the assimilation of sea level anomaly (SLA) retrievals from satellite altimetry. This approach has limited benefits in the Arctic Ocean and surrounding seas due to data gaps caused by sea ice coverage. Moreover, assimilation of SLA in seasonally ice-free regions may be negatively affected by the quality of the Mean Sea Surface (MSS) used to derive the SLA. Here, we use the Regional Ice Ocean Prediction System (RIOPS) to investigate the impact of assimilating Absolute Dynamic Topography (ADT) fields on the circulation in the Arctic Ocean. This approach avoids the use of a MSS and additionally provides information on sea level in ice covered regions using measurements across leads (openings) in the sea ice. RIOPS uses a coupled ice-ocean model on a 3-4 km grid-resolution pan-Arctic domain together with a multi-variate reduced-order Kalman Filter. The system assimilates satellite altimetry and sea surface temperature together with in situ profile observations. The background error is modified to match the spectral characteristics of the ADT fields, which contain less energy at small scales than traditional SLA due to filtering applied to reduce noise originating in the geoid product used. A series of four-year reanalyses demonstrate significant reductions in innovation statistics with important impacts across the Arctic Ocean. Results suggest that the assimilation of ADT can improve circulation and sea ice drift in the Arctic Ocean, and intensify volume transports through key Arctic gateways and resulting exchanges with the Atlantic Ocean. A reanalysis with a modified Mean Dynamic Topography (MDT) is able to reproduce many of the benefits of the ADT but does not capture the enhanced transports. Assimilation of SLA observations from leads in the sea ice appears to degrade several circulation features; however, these results may be sensitive to errors in MDT. This study highlights the large uncertainties that exist in present operational ocean forecasting systems for the Arctic Ocean due to the relative paucity and reduced quality of observations compared to icefree areas of the Global Ocean. Moreover, this underscores the need for dedicated and focused efforts to address this critical gap in the Global Ocean Observing System. [ABSTRACT FROM AUTHOR]

This study examines the annual cycle of the Surface Energy Budget (SEB) in the Beaufort‐Chukchi seas, focusing on the autumn transition. Shipboard measurements from NASA's Salinity and Stratification at the Sea Ice Edge (SASSIE) experiment (8 September–2 October 2022) and satellite flux analysis for the entire 2022 were utilized to provide a comprehensive perspective of the SEB's seasonal dynamics. An important finding is the alignment of SEB's autumnal transition with the September 22 equinox, marking the onset of prolonged Arctic darkness. This transition involved a shift from the summertime radiative heating to cooling conditions, characterized by outgoing longwave radiation surpassing incoming solar radiation and a notable increase in synoptic turbulent latent and sensible heat flux variability. The increased turbulent heat fluxes after the equinox were associated with increased occurrences of short‐duration cold air outbreaks. These outbreaks seem to originate from cold mesoscale surface winds transitioning from cooling landmasses or ice caps to the warmer seas, driven by differential cooling rates between land/ice and ocean as solar irradiance declined. Turbulent heat losses, outpacing longwave emission by more than fivefold, accelerated ocean surface cooling in the subsequent 2 months, leading to the complete freeze‐up of the Beaufort‐Chukchi seas by late November. These findings underscore the substantial influence of astronomical seasons on the SEB, emphasizing their crucial role in Arctic climate dynamics. Plain Language Summary: This study is to enhance understanding of Arctic Surface Energy Budget (SEB) patterns, focusing on energy exchanges at the open sea surface over the year. It examines autumn energy transition in the Beaufort‐Chukchi seas, using shipboard measurements from NASA's SASSIE experiment (8 September–2 October 2022) and satellite heat flux analyses for the entire year of 2022. These data sources offer insights into the energy flows and patterns in the region. An important finding is the alignment of the autumn energy transition with the September 22 equinox, marking the onset of the extended Arctic darkness and the transition from oceanic heat gain to loss. Cold air outbreaks from surrounding landmasses and ice caps increased, intensifying heat transfer from the ocean to the atmosphere through evaporation, conduction, and convection. Turbulent heat loss exceeded longwave emission by over fivefold, expediting ocean surface cooling over the subsequent 2 months, culminating in complete freezing of the Beaufort‐Chukchi seas by late November. Understanding the influence of astronomical seasons on the SEB is crucial for comprehending and predicting the Arctic climate changes. Key Points: Autumnal Equinox pivotal in ocean surface energy budget: heat loss began to surpass solar radiation gain per shipboard and satellite dataPost‐equinox, synoptic turbulent heat flux variability surged, linked to frequent cold, dry air outbreaks with a duration of a few daysTurbulent heat fluxes, five times longwave emission, accelerated ocean heat release, causing the Beaufort‐Chukchi seas freeze in November [ABSTRACT FROM AUTHOR]

Salinity is among the key climate characteristics of the World Ocean. During the last 15 years, sea surface salinity (SSS) ismeasured using satellite passive microwave sensors. Standard retrieving SSS algorithms from remote sensing data were developed and verified for the most typical temperature and salinity values of the World Ocean. However, they have far lower accuracy for the Arctic Ocean, especially its shelf areas, which are influenced by large river runoff and have low typical temperature and salinity values. In this study, an improved algorithm has been developed to retrieve SSS in the Arctic Ocean during ice-free season, based on Soil Moisture Active Passive (SMAP) mission data, and using machine learning approaches. Extensive database of in situ salinity measurements in the Russian Arctic seas collected duringmultiple field surveys is applied to train and validate the machine learning models. The error in SSS retrieval of the developed algorithm compared to the standard algorithm reduced from 3.15 to 2.15 psu, and the correlation with in situ data increased from 0.82 to 0.90. The obtained daily SSS fields are important to improve accurate assessment of spatial and temporal variability of large river plumes in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

This article discusses Katja Kettu's novel The Midwife in the context of the cultural memory of the World War II in the high north. The Midwife is a Finnish historical novel which depicts events during the war in Pechenga, situated on the shores of the Arctic Ocean. The article primarily analyses the role of the Arctic Ocean and the rich water imagery in the novel. The major claim of the article is that the arctic perspective and the symbolism of water are crucial elements in constructing the critical narrative of war. Additionally, it contends that the novel breaks away from the prevailing national perspective of Finnish war literature and introduces a fresh narrative on the Arctic War. The analysis will show that in The Midwife , the tropes of arctic waters serve as instruments to depict the silenced themes of the war. The theoretical tools of the analysis are based on interdisciplinary memory culture studies, and on research of the representations of water. The article aims to provide tools to understand the role of literature in the construction and deconstruction processes of national discourses and memories concerning the traces of the war in the multicultural arctic areas. [ABSTRACT FROM AUTHOR]

The ultraslow‐spreading Mohns Ridge is a key supersegment of the Arctic Mid‐Ocean system, where it represents a boundary between the Jan Mayen hotspot in the south and the highly anomalous Knipovich Ridge to the north. Understanding the timing and mode of Plio‐Pleistocene seafloor spreading along this ridge segment is critical for establishing the recent geodynamic evolution of the Norwegian‐Greenland Sea. To investigate magmatic accretion at this ultraslow spreading ridge, we collected samples from the Schulz Massif, which is located off‐axis at 73.4°N and exposes gabbroic intrusives and mantle peridotite. The petrology and petrography of these samples indicate that the exposed crustal section underwent multiple episodes of magmatism, which are characterized by distinct crystal sizes and geochemistry. To calibrate the age of the seafloor, we combined high‐resolution and high‐precision single zircon U‐Pb geochronology. Our data suggest that seafloor spreading has been nearly symmetrical for the last ∼4.6 Myr with a time‐averaged half‐spreading rate of ∼7.4 mm yr−1. Crystal size analysis of olivine in porphyric intrusions suggests that the crustal section was fed crystal‐laden melts with recurrence rates predicted to stabilize fault‐dominated seafloor spreading. Our combined geochronological and crystal size approach gives a critical perspective on the mode of seafloor spreading in the Mohns Ridge and allows insights into accretionary mechanisms and crustal structures during symmetric seafloor spreading. Key Points: We investigated a unique suite of lower crustal rocks recovered from a tectonic window off‐axis of the ultraslow‐spreading Mohns RidgeZircon U‐Pb geochronology suggests 4.6 Myr of nearly symmetrical seafloor spreading at a time‐averaged half‐spreading rate of ∼7.4 mm yr−1Small‐scale magmatic injections were important for crustal construction [ABSTRACT FROM AUTHOR]

In 2018 and 2021, the Drift-Towing Ocean Profilers (DTOP) provided extensive temperature and salinity data on the upper 120 m ocean through their drifts over the Alpha Ridge north of the Canada Basin. The thickness and temperature maximum of Alaska Coastal Water (ACW) ranged from 20 m to 40 m and −1.5°C to −0.8°C, respectively, and the salinity generally maintained from 30.2 to 32.5. Comparison with World Ocean Atlas 2018's climatology manifested a 40m-thick and warm ACW roughly exceeding the temperature maximum by 0.4–0.5°C in June–August 2021. This anomalously warm ACW was highly related to the expansion of the Beaufort Gyre in the negative Arctic Oscillation phase. During summer, the under-ice oceanic heat flux FwOHF was elevated, with a maximum value of above 25 W m−2. FwOHF was typically low in the freezing season, with an average value of 1.2 W m−2. The estimates of upward heat flux contributed by ACW to the sea ice bottom FwOHF were in the range of 3–4 W m−2 in June–August 2021, when ACW contained a heat content of more than 80 MJ m−2. The heat loss over this period was driven by a weak stratification upon the ACW layer associated with a surface mixed layer (SML) approaching the ACW core. After autumn, FwOHF was reduced (< 2 W m−2) except during rare events when it elevated FwOHF slightly. In addition, the intensive and widespread Ekman suction, which created a violent upwelling north of the Canada Basin, was largely responsible for the substantial cooling and thinning of the ACW layer in the summer of 2021. [ABSTRACT FROM AUTHOR]

Warming of the ocean waters surrounding Greenland plays a major role in driving glacier retreat and the contribution of glaciers to sea level rise. The melt rate at the junction of the ocean with grounded ice-or grounding line-is, however, not well known. Here, we employ a time series of satellite radar interferometry data from the German TanDEM-X mission, the Italian COSMO-SkyMed constellation, and the Finnish ICEYE constellation to document the grounding line migration and basal melt rates of Petermann Glacier, a major marine-based glacier of Northwest Greenland. We find that the grounding line migrates at tidal frequencies over a kilometer-wide (2 to 6 km) grounding zone, which is one order of magnitude larger than expected for grounding lines on a rigid bed. The highest ice shelf melt rates are recorded within the grounding zone with values from 60 ± 13 to 80 ± 15 m/y along laterally confined channels. As the grounding line retreated by 3.8 km in 2016 to 2022, it carved a cavity about 204 m in height where melt rates increased from 40 ± 11 m/y in 2016 to 2019 to 60 ± 15 m/y in 2020 to 2021. In 2022, the cavity remained open during the entire tidal cycle. Such high melt rates concentrated in kilometer-wide grounding zones contrast with the traditional plume model of grounding line melt which predicts zero melt. High rates of simulated basal melting in grounded glacier ice in numerical models will increase the glacier sensitivity to ocean warming and potentially double projections of sea level rise.

Ice-binding proteins (IBPs) are a group of ecologically and biotechnologically relevant enzymes produced by psychrophilic organisms. Although putative IBPs containing the domain of unknown function (DUF) 3494 have been identified in many taxa of polar microbes, our knowledge of their genetic and structural diversity in natural microbial communities is limited. Here, we used samples from sea ice and sea water collected in the central Arctic Ocean as part of the MOSAiC expedition for metagenome sequencing and the subsequent analyses of metagenome-assembled genomes (MAGs). By linking structurally diverse IBPs to particular environments and potential functions, we reveal that IBP sequences are enriched in interior ice, have diverse genomic contexts and cluster taxonomically. Their diverse protein structures may be a consequence of domain shuffling, leading to variable combinations of protein domains in IBPs and probably reflecting the functional versatility required to thrive in the extreme and variable environment of the central Arctic Ocean.

CHRIS TANNER KNEW IT WAS GOING TO BE A BAD YEAR. Only a fraction of the usual spring rains had fallen on his farm in northwestern Kansas and the summer [...]

Landfast sea ice (LFSI) is sensitive to local climate change, making it an important component of the cryosphere system. In this study, the LFSI around the pan-Arctic domain was simulated from 1979 to 2021 using a well-validated snow and ice thermodynamic model (HIGHTSI) under the framework of the Fast Ice Prediction System (FIPS), forced by the ERA5 reanalysis. The simulation results agree well with the in-situ observations in the Canadian Arctic, with a mean error of −0.06 ± 0.29 m for ice thickness and −0.04 ± 0.12 m for snow depth. A decrease of −2.8 ± 0.4 cm/10a in thickness and −16.2 ± 1.5 km3/a in volume for the Arctic LFSI was modeled during this period. There was significant spatial variability among the different domains, with the fastest decline found in the Vilkitsky Strait. The modeled snow depth shows large interannual and spatial variations, which was confirmed by other modeling results. The spatiotemporal variations in both air temperature and precipitation are the driving factors for the multi-decadal variations in LFSI thickness. The decreasing air temperature during the 2010s aligned with a slower thickness decrease and a slight volume increase for LFSI, which agreed with the pan-Arctic sea ice pattern.