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This paper describes the first finding of authigenic carbonates on the southern flank of Gakkel Ridge in its junction with the continental margin of the Laptev Sea of the Russian Federation. The samples are represented by compact magnesian calcites and aragonites, including rounded and angular fragments of terrigenous material, as well as microphytoplankton and spores and pollen of terrestrial and aquatic plants of various ages. The elemental and organochemical characteristics are indicative of the predominant oxidation conditions or those intermediate between oxidation and reduction conditions of carbonate crystallization likely due to the fact that carbonates were formed near the bottom surface. The O, C, and Sr isotopic compositions make it possible to conclude that diagenetic carbonates of Gakkel Ridge were deposited mainly in isotopic equilibrium with bottom water at a temperature of about 0°C, corresponding to measurements from the research vessel. A wide range of δ13С (from –23.5 to –37.3) is indicative of the fact that methane was an important, but not the sole source of carbon in carbonates. Based on wide variations in 87Sr/86Sr (0.70906–0.70933) correlated with δ13С values, the carbonate-forming fluid was not only modern seawater, but also diagenetic solutions coming from the sedimentary cover together with methane and methane and organic matter oxidation products. The active discharge of heterogeneous methane-bearing fluids can be related to the high modern tectonic activity of the study region. [ABSTRACT FROM AUTHOR]

Arctic Ocean freshwater storage increased since the mid‐1990s, but the cause was unknown. Jahn and Laiho (2020, https://doi.org/10.1029/2020GL088854) use ensemble runs of a coupled climate model to suggest that the observed increase is anthropogenic. The paper quantifies when the anthropogenic signals should emerge from the noise of natural variability. This result contextualizes research on the Arctic Ocean freshwater system and sketches an unprecedented opportunity. Future work should elucidate mechanisms, seek to observe the anthropogenic freshwater changes, and investigate the impacts on biogeochemistry and the North Atlantic Ocean circulation. Plain Language Summary: The Arctic is a region of clear man‐made climate change. Changes in the Arctic Ocean salinity and currents have been seen, but the cause was unknown. A new paper shows that the changes are probably due to man‐made climate change. The reason is they only occur in a climate model with man‐made climate forcing. This is an important result because it helps scientists focus their research into how the changes work. It also points to a valuable opportunity to watch the Arctic Ocean respond to man‐made climate change. There might be important future impacts on North Atlantic oceanography and North Atlantic climate that scientists can now look for. Key Points: A recent paper shows that observed increases in Arctic Ocean freshwater storage are anthropogenicThe paper anticipates future anthropogenic changes, which are testable predictions for observersThere are widespread impacts of anthropogenic freshwater change, both within the Arctic and the North Atlantic Oceans [ABSTRACT FROM AUTHOR]

Polar-orbiting satellite observations are of fundamental importance to explore the main scientific challenges in the Arctic Ocean, as they provide information on bio-geo-physical variables with a denser spatial and temporal coverage than in-situ instruments in such a harsh and inaccessible environment. However, they are limited by the lack of coverage near the North Pole (Polar gap), the polar night, and frequent cloud cover or haze over the ocean and sea ice, which prevent the use of optical satellite instruments, as well as by the limited availability of external validation data. The satellite sensors' coverage and repeat cycles may also have limitations in properly identifying and resolving the dominant spatial and temporal scales of atmospheric, ocean, cryosphere and land variability and their interactive processes and feedback mechanisms. In this paper, we provide a state of the art of contribution of satellite observations to the understanding of the polar environment and climate scientific challenges tackled within the Arktalas Hoavva project funded by the European Space Agency. We identify the current limitations to the wider use of polar orbiting remote sensing data, as well as the observational gaps of the existing satellite missions. A comprehensive overview of all satellite missions and applications is given provided with a primary focus on the European satellites. Finally, we assess the expected capability of the approved future satellite missions to answer today's scientific challenges in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

Since the mid-1990s, there has been a marked decrease in the sea ice extent (SIE) in the Arctic Ocean. After reaching an absolute minimum in September 2012, the seasonal variations in the SIE have settled at a new level, which is almost one-quarter lower than the average climatic norm of 1979–2022. Increased melting and accelerated ice export from marginal seas ensure an increase in the open water area, which affects the lower atmosphere and the surface layer of the ocean. Scientists are cautiously predicting a transition to a seasonally ice-free Arctic Ocean as early as the middle of this century, which is about 50 years earlier than was predicted just a few years ago. Such predictions are based on the fact that the decrease in sea ice extent and ice thinning that occurred at the beginning of this century, initially caused by an increase in air temperature, triggered an increase in the thermal and dynamic contribution of the ocean to the further reduction in the ice cover. This paper reviews published evidence of such changes and discusses possible mechanisms behind the observed regional anomalies of the Arctic Sea ice cover parameters in the last decade. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is undergoing rapid change: sea ice is being lost, waters are warming, coastlines are eroding, species are moving into new areas, and more. This paper explores the many ways that a changing Arctic Ocean affects societies in the Arctic and around the world. In the Arctic, Indigenous Peoples are again seeing their food security threatened and cultural continuity in danger of disruption. Resource development is increasing as is interest in tourism and possibilities for trans-Arctic maritime trade, creating new opportunities and also new stresses. Beyond the Arctic, changes in sea ice affect mid-latitude weather, and Arctic economic opportunities may re-shape commodities and transportation markets. Rising interest in the Arctic is also raising geopolitical tensions about the region. What happens next depends in large part on the choices made within and beyond the Arctic concerning global climate change and industrial policies and Arctic ecosystems and cultures. [ABSTRACT FROM AUTHOR]

This paper reports new data on the composition of hydrocarbon gases in bottom sediments of the Laptev–East Siberian marginal shelf transition zone, the continental slope of the Lomonosov Ridge, and Podvodnikov Basin of the Arctic Ocean. Anomalous concentrations of methane and hydrocarbon gases (up to C5 inclusive) have been established. Gas-geochemical indicators of eight genetic groups of hydrocarbon gases have been determined. The oil-and-gas content of the study area has been predicted based on the data obtained. [ABSTRACT FROM AUTHOR]

Substantial changes have occurred in the Arctic Ocean in the last decades. Not only sea ice has retreated significantly, but also the ocean at middepth showed a warming tendency. By using simulations we identified a mechanism that intensifies the upward trend in ocean heat supply to the Arctic Ocean through Fram Strait. The reduction in sea ice export through Fram Strait induced by Arctic sea ice decline increases the salinity in the Greenland Sea, which lowers the sea surface height and strengthens the cyclonic gyre circulation in the Nordic Seas. The Atlantic Water volume transport to the Nordic Seas and Arctic Ocean is consequently strengthened. This enhances the warming trend of the Arctic Atlantic Water layer, potentially contributing to the Arctic "Atlantification." Our study suggests that the Nordic Seas can play the role of a switchyard to influence the heat budget of the Arctic Ocean. Plain Language Summary: The Arctic sea ice decline is among the key indications of climate change, which has strong impacts on the environment, human beings, and biodiversity. In this paper we found that the Arctic sea ice decline at the surface can even cause Arctic Ocean warming at middepth by intensifying the upward trend of ocean heat supply to the Arctic Ocean through Fram Strait. The Nordic Seas play the role of a switchyard for the involved processes: The sea ice decline reduces the sea ice export through Fram Strait, which further increases the salinity in the Greenland Sea. Consequently, in the Nordic Seas the sea surface height decreases and the gyre circulation strengthens. These changes then increase the Atlantic Water inflow to the Nordic Seas and the Arctic Ocean, causing significant warming in the Atlantic Water layer of the Arctic Ocean. The changes in the ocean heat budget have strong implications on potential feedbacks to sea ice decline through basal melting in a future warming climate. The intensification of the Atlantic Water volume transport through Fram Strait can impact not only the Arctic heat budget but also potentially the nutrient budget and the primary production. Key Points: The decline of Arctic sea ice reduces its export, thus increasing the salinity in Greenland SeaThis reduces the sea surface height and speeds up the gyre circulation in Greenland and Nordic SeasThe consequently enhanced Atlantic Water transport intensifies the warming at Fram Strait and in the Arctic Ocean [ABSTRACT FROM AUTHOR]

In addition to the traditional so-called Arctic states, non-Artic states and some other international organisations are now showing a growing interest in this area. China, for example, has achieved some progress, since becoming an Arctic Council permanent observer, through participation in resource development in the region and strengthening its bilateral relations with the Arctic states. The present study examines China's Arctic policy and its implications for the governance of the Arctic Ocean. It also provides an insight into the existing relevant international legal instruments and examines China's interest in the participation, governance, and resource protection activities in the Arctic Ocean region, to successfully implement Chinese Arctic policy. To this end, the study examines the connection between the "white paper" and "China's Arctic Policy", in the context of executing the "Belt and Road Initiative", in particular the "Arctic Silk Road". The study concludes that China intends to perform a dynamic role in governing the Arctic Ocean, as a less challenging but cooperative partner in this region. [ABSTRACT FROM AUTHOR]

In the summer Arctic, bump-like vertical temperature profiles of the upper layer in the Canada Basin suggest a near-surface temperature maximum (NSTM) beneath the mixed layer. This paper concentrates on describing the decadal variance of these NSTMs. Essentially, the temporal evolution of the summer NSTM revealed three decadal phases. The first period is before 2003, when the summer NSTM could rarely be observed except around the marginal of the Canada Basin. The second period is between 2003 and 2015, when the summer NSTM nearly occurred over the whole basin as accelerated decline of summer sea ice. The third period is from 2016 to 2017, when the summer NSTM almost disappeared due to prevailing warm surface water. Furthermore, for the background behind the decadal variance of summer NSTM, linear trends of the September minimum sea ice extent and surface water heat content in the Canada Basin from 2003 to 2017 were –2.75 ± 1.08 × 104 km2yr−1 and 2.29 ± 1.36 MJ m−2yr−1, respectively. According to a previous theory, if we assume that the trend of the summer surface water heat content was only contributed by NSTM, it would cause a decrease in sea ice thickness of approximately 13 cm. The analysis partially explains the reason for sea ice decline in recent years. [ABSTRACT FROM AUTHOR]

Polar sea surface height observation by radar altimeters requires missions with high-latitude orbit and specific processing to observe the sea-ice-covered region within fractures in the ice. Here, we combine sea surface height estimates from different radar satellites over the ice-free and ice-covered polar oceans to create cross-calibrated along-tracks and gridded products over the Arctic Ocean (2011-2021) and the Southern Ocean (2013-2021). The sea surface height from our regional polar products is in great agreement with tide gauges and bottom pressure recorders at monthly timescales in seasonally to year-round icecovered regions. Thanks to the use of several missions and the mapping strategy, our multi-mission products have a greater resolution than monomission products. Part of the sea level variability of the Arctic Ocean product is related to the Arctic Oscillation atmospheric circulation. At long term, the Arctic altimetry sea level is coherent with in-situ steric height evolution in the Beaufort gyre, and negative sea level trends over the 10-year period are observed in the East Siberian slope region, which may be related to the local freshwater decrease observed by other studies. Our regional polar sea level products are limited by current understanding of the sea-ice lead measurements, and homogenization of these polar products with global sea level products needs to be tackled. [ABSTRACT FROM AUTHOR]

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]

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Over the Arctic regions, current conventional altimetry products suffer from a lack of coverage or from degraded performance due to the inadequacy of the standard processing applied in the ground segments. This paper presents a set of dedicated algorithms able to process consistently returns from open ocean and from sea-ice leads in the Arctic Ocean (detection of water surfaces and derivation of water levels using returns from these surfaces). This processing extends the area over which a precise sea level can be computed. In the frame of the European Space Agency Sea Level Climate Change Initiative (http://cci.esa.int), we have first developed a new surface identification method combining two complementary solutions, one using a multiple-criteria approach (in particular the backscattering coefficient and the peakiness coefficient of the waveforms) and one based on a supervised neural network approach. Then, a new physical model has been developed (modified from the Brown model to include anisotropy in the scattering from calm protected water surfaces) and has been implemented in a maximum likelihood estimation retracker. This allows us to process both sea-ice lead waveforms (characterized by their peaky shapes) and ocean waveforms (more diffuse returns), guaranteeing, by construction, continuity between open ocean and ice-covered regions. This new processing has been used to produce maps of Arctic sea level anomaly from 18-Hz ENVIronment SATellite/RA-2 data. [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]

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]

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 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]

Inhomogenities in the sea ice motion field cause deformation zones, such as leads, cracks and pressure ridges. Due to their long and often narrow shape, those structures are referred to as Linear Kinematic Features (LKFs). In this paper we specifically address the identification and characterization of variations and discontinuities in the spatial distribution of the total deformation, which appear as LKFs. The distribution of LKFs in the ice cover of the polar oceans is an important factor influencing the exchange of heat and matter at the ocean-atmosphere interface. Current analyses of the sea ice deformation field often ignore the spatial/geographical context of individual structures, e.g., their orientation relative to adjacent deformation zones. In this study, we adapt image processing techniques to develop a method for LKF detection which is able to resolve individual features. The data are vectorized to obtain results on an object-based level. We then apply a semantic postprocessing step to determine the angle of junctions and between crossing structures. The proposed object detection method is carefully validated. We found a localization uncertainty of 0.75 pixel and a length error of 12% in the identified LKFs. The detected features can be individually traced to their geographical position. Thus, a wide variety of new metrics for ice deformation can be easily derived, including spatial parameters as well as the temporal stability of individual features. [ABSTRACT FROM AUTHOR]

Wide areas of the Siberian Arctic shelf are covered by freshened surface water layers, which are among the largest in the World Ocean. River discharge is the main freshwater source for formation of these layers; therefore, they are commonly referred to as river plumes (the Ob-Yenisei plume in the Kara Sea and the Lena plume in the Laptev and East Siberian seas). The contribution of sea ice meltwater (SIM) to the Ob-Yenisei and Lena plumes is pointed out to be small, albeit its actual volume remains unknown. In this study, we use a novel dataset of satellite-derived sea ice thickness in the Arctic Ocean during the melt period to quantify the annual volume of SIM, which was received by the Ob-Yenisei and Lena plumes during 2012-2020. We reveal that SIM is a significant source for the Lena plume providing, on average, 20% of total annual freshwater content. Moreover, the share of SIM in the Lena plume shows large inter-annual (14%-29%) variability, i.e., during certain years, SIM provides almost one-third of freshwater volume of the Lena plume. This variability is governed by interannual variability of ice thickness, as well as seasonal variability of sea ice melting conditions. Conversely, the contribution of SIM to the Ob-Yenisei plume is relatively low (8% on average), and its total annual share varies from 6% to 11% during the study period. This difference is mainly caused by significantly smaller area of the Ob-Yenisei plume as compared with the Lena plume. The forecasted earlier onset of ice melting in the Arctic Ocean in future decades due to climate change could decrease the contribution of SIM to the Ob-Yenisei plume, whereas its influence on the Lena plume remains unclear. [ABSTRACT FROM AUTHOR]

The East Siberian Sea (ESS) is one of the least studied seas in terms of ostracod fauna. Ostracods are sensitive organisms to environmental changes, and detailed information on their ecology is still required. To fill this knowledge gap, we studied 33 meiobenthic dredge samples collected from the western part of the ESS and the Chaun Bay together with 17 grab samples taken from the eastern part of the sea. Quantitative analyses of the ostracod assemblages demonstrate that the river-influenced western part of the ESS is inhabited by low diverse and impoverished fauna consisting of the taxa which are able to adapt to different environmental conditions. In the isolated Chaun Bay sheltered from significant riverine influence, the ostracod assemblages contain species that prefer more stable conditions. The predominance of living specimens over dead ones and individual valves points to strong carbonate dissolution that is more pronounced in the western ESS than in the Chaun Bay. The formation of such conditions might be related to the high content of dissolved carbon dioxide resulting from bacterial remineralization of in situ produced and land-derived organic matter in the bottom sediments and low pH near the seabed. Numerous ferromanganese crusts were found on the ostracod valve surfaces and inside the shells from the Chaun Bay. [ABSTRACT FROM AUTHOR]

As sea ice disappears, the emergence of open ocean deep convection in the Arctic, which would enhance ice loss, has been suggested. Here, using 36 state‐of‐the‐art climate models and up to 50 ensemble members per model, we show that Arctic deep convection is rare under the strongest warming scenario. Only five models have convection by 2100, while 11 have had convection by the middle of the run. For all, the deepest mixed layers are in the eastern Eurasian basin. When that region undergoes a salinification and increasing wind speeds, the models convect; yet most models are freshening. The models that do not convect have the strongest halocline and most stable sea ice, but those that lose their ice earliest ‐because of their strongly warming Atlantic Water‐ do not have a persistent deep convection: it shuts down mid‐century. Halocline and Atlantic Water changes urgently need to be better constrained in models. Plain Language Summary: Both observations and modeling simulations suggest that deep vertical mixing (or deep convection) in winter may become the new normal in the Arctic as sea ice disappears, which further accelerates that disappearance. These simulations are often done using only one model, so here we used all models available that participated in the Climate Model Intercomparison Project Phase 6 (CMIP6), for the strongest warming scenario. We show that after removing those that are already inaccurate in the present, and even with a restrictive threshold, most models have no deep convection in the Arctic, or extremely rarely. Only five still had deep convection by the time the run finishes in 2100. We found that deep convection regions and periods are associated with a saltier, windier surface, while the rest of the Arctic and/or run freshens. The subsurface properties were crucial too: a deep halocline, that is, strongly stratified model, leads to less ice loss and no deep convection. In contrast, models with a shallow halocline and strongly warming Atlantic Water lose their ice and convect earliest, although it does not persist. As water mass properties are poorly represented in CMIP6 models, these need improving to better constrain Arctic deep convection and sea ice projections. Key Points: Oceanic deep convection does not emerge and persist in the Arctic in the majority of Climate Model Intercomparison Project Phase 6 models, despite a drop in the Nordic SeasArctic deep convection occurs only when both surface salinity and winds are increasing, year round, yet most models are fresheningA deep halocline and stable ice cover hinder deep convection, while early ice loss due to warmer Atlantific water can also stop it rapidly [ABSTRACT FROM AUTHOR]

Marine plastic pollution is currently one of the most serious environmental threats. In this study, based on scenario calculations for a five-year period, we analyzed the possible spread of microplastics carried by Siberian rivers to the Kara Sea shelf. The Lagrangian particle model used daily data from 3D numerical modeling to simulate microplastic transport by ocean currents and sea ice drift. The results of a series of scenario calculations show how the distribution of particles and their subsequent deposition depend on their type (density), size, processes of freezing into the ice, and biofouling (accumulation of microorganisms). The crucial influence of the effects of microplastic embedding in sea ice and particle biofouling on the trajectories of floating particles and their deposition on the seafloor is highlighted. The transport of light particles of microplastics from Siberian rivers by ice can contribute to the pollution of the Barents Sea, in addition to their more active outflow through the Fram Strait. Biofouling is a driver of microplastic deposition on the shelf bottom or transport along the continental slope in a cyclonic direction following the trajectory of the Atlantic waters. [ABSTRACT FROM AUTHOR]

The Arctic is gaining the position of an important strategic and geopolitical area and the extension of the legal continental shelf cannot be considered only as a "race for resources" in terms of economic benefits, but in the end it brings with it both political and socio-economic benefits. The article presents a comprehensive analysis of the current status of submissions to the Commission for the Limits of the Continental Shelf regarding the Arctic Ocean and the stage in which they currently are. It also approaches a legal definition of the continental shelf, the work of the Commission and compares the view of the Arctic states on particular seafloor highs. [ABSTRACT FROM AUTHOR]

We present multi-sensor measurements from satellites, unmanned aerial vehicle, marine radar, thermal profilers, and repeated conductivity–temperature–depth casts made in the Kara Gates strait connecting the Barents and the Kara Seas during spring tide in August 2021. Analysis of the field data during an 18-h period from four stations provides evidence that a complex sill in the Kara Gates is the site of regular production of intense large-amplitude nonlinear internal waves. Satellite data show a presence of a relatively warm northeastward surface current from the Barents Sea toward the Kara Sea attaining 0.8–0.9 m/s. Triangle-shaped measurements using three thermal profilers revealed pronounced vertical thermocline oscillations up to 40 m associated with propagation of short-period nonlinear internal waves of depression generated by stratified flow passing a system of shallow sills in the strait. The most intense waves were recorded during the ebb tide slackening and reversal when the background flow was predominantly supercritical. Observed internal waves had wavelengths of ~100 m and traveled northeastward with phase speeds of 0.8–0.9 m/s. The total internal wave energy per unit crest length for the largest waves was estimated to be equal to 1.0–1.8 MJ/m. [ABSTRACT FROM AUTHOR]

The interannual features of the salinity in the Chukchi Sea during the ice-free period of a year are investigated on the base of Soil Moisture Active Passive (SMAP) satellite measurements and GLORYS12v1 reanalysis data. Analysis of salinity measurements revealed two types of Bering Summer Waters (BSW) propagation: "western" and "eastern". The first is characterized by the penetration of Pacific waters into the northwest part of the sea, as well as the propagation of BSW to 180°W and 72.5°N. During the "eastern" type, salty waters are pressed to the eastern part of the shelf. Their area decreases and the northern boundary of the BSW area shifts to 174–176°W. Areas with low salinity, ~29 psu, are observed in the western part of the sea. Our study reveals that the formation of these types is affected not only by the inflow of Pacific waters through the Bering Strait but also by the East Siberian Current (ESC). Both factors are related and lead to correlated changes in the salinity of the Chukchi Sea waters. ESC carries Arctic freshwaters from west to east and leads to a decrease in salinity in the western part of the sea. At the same time, southward ESC caused the blockage of the northward currents in the Bering Strait and a decrease in the influx of saline Pacific waters in the southern part of the Chukchi Sea. The intensification of ESC occurred in 1994, 2002, 2012, and 2016, when the volume transport of ESC increased by approximately 0.2 Sv, while the influx through the Bering Strait decreased. As a result, in the years with intense ESC, the spatial structure of the salinity of the Chukchi Sea changed significantly and the shelf-averaged salinity decreased by 0.3–0.5 psu. [ABSTRACT FROM AUTHOR]

The Arctic has experienced rapid change associated with warming since the 1970s. The rapid retreat of the terrestrial cryosphere can release a large amount greenhouse gas from the permafrost regions into the air, and the sea ice decline will affect the CO2 and CH4 balance in the ocean. Changes in the Arctic provide feedback mechanisms that can also impinge on the global ocean's thermohaline circulation. During the past years, the overall natural processes in the Arctic have been studied although the magnitude and timing of carbon release from the cryosphere changes require further investigation. However, few studies have been conducted to link the natural and social systems in the Arctic. Scientists and policymakers must consider the coupled Arctic land, ocean, and social systems in their decisions for coping with climate change. Plain Language Summary: The Arctic is warming more than twice the global average. The Arctic is connected to the rest of the world through the climate system, it appears to be the first domino to fall, with the other dominoes pointing south. The Arctic science community and the people who live in the Arctic have known the rapid Arctic changes for a long time. It has been recognized that the cryosphere components are declining, and the carbon cycle in both the land and ocean will be affected by the cryosphere shrinkage. Despite some scientific breakthroughs, there are still major knowledge gaps in the Arctic carbon cycle. The policymakers at this stage are not only asking for more data about the Arctic changes, they also need scientific suggestions to cope with Arctic changes. The science community should work together to draw a full picture of the Arctic changes that include both natural and social systems. Key Points: The changing Arctic carbon cycle can affect global climateMore field observation should be carried out in the Arctic land and oceanThe Arctic land, ocean, and social domain should be considered as a system [ABSTRACT FROM AUTHOR]

The age of magmatic rocks of basic composition sampled at the Alpha–Mendeleev Rise in the Arctic Ocean by a research submarine was studied based on the measurement of the U/Pb age of zircons separated from them. Early Cretaceous rocks of the moderately alkaline series, which had been formed at the turn of 112 million years, are most common on the Rise. These rocks contain a large number of ancient xenogenic zircons the age analysis of which shows that the subalkaline melts interacted with the crust at two levels including the horizon of Early Cretaceous sandstones and with rocks of the Late Archean crystalline basement aged 2675.1 ± 11.6 Ma. They also contain a small number of younger zircons aged 83 to 87 Ma, which probably arose during the recrystallization of Early Cretaceous zircons under the influence of Late Cretaceous magmatism. [ABSTRACT FROM AUTHOR]

Marine environments are a rich source of Actinobacteria and have the potential to produce a wide variety of biologically active secondary metabolites. In this study, we used four selective isolation media to culture Actinobacteria from the sediments collected from the Chukchi Shelf in the Arctic Ocean. A total of 73 actinobacterial strains were isolated. Based on repetitive DNA fingerprinting analysis, we selected 30 representatives for partial characterization according to their phylogenetic diversity, antimicrobial activities and secondary-metabolite biosynthesis genes. Results from the 16S rRNA gene sequence analysis indicated that the 30 strains could be sorted into 18 phylotypes belonging to 14 different genera: Agrococcus, Arsenicicoccus, Arthrobacter, Brevibacterium, Citricoccus, Janibacter, Kocuria, Microbacterium, Microlunatus, Nocardioides, Nocardiopsis, Saccharopolyspora, Salinibacterium and Streptomyces. To our knowledge, this paper is the first report on the isolation of Microlunatus genus members from marine habitats. Of the 30 isolates, 11 strains exhibited antibacterial and/or antifungal activity, seven of which have activities against Bacillus subtilis and Candida albicans. All 30 strains have at least two biosynthetic genes, one-third of which possess more than four biosynthetic genes. This study demonstrates the significant diversity of Actinobacteria in the Chukchi Shelf sediment and their potential for producing biologically active compounds and novel material for genetic manipulation or combinatorial biosynthesis. [ABSTRACT FROM AUTHOR]

In recent decades, the reduction in the area of Arctic ice and its thickness has accelerated. These phenomena are associated with global warming. But the ice cover is destroyed not only under the influence of external causes, but also under the influence of the deep fluid-dynamic factor of the lithosphere. The authors analyzed the satellite observations of ice thickness together with the interpretation of the anomalies of the geomagnetic field and the gravity field. The studies made it possible to put forward an assumption about the influence of thermofluid channels of faults on the formation of the ice cover due to a decrease in the thickness of the ice. The paper presents the results of studying the structure of the lithosphere of the Arctic Ocean in the zones of accelerated ice melting above the outlets of thermofluid channels to the bottom surface. The mechanism of influence of the endogenous factor on the processes of ice destruction is considered. It is noted that the nature of the horizontal layering of the earth's crust affects the process of ice formation. Taking into account the fluid dynamic factor and the layering of the earth's crust on the formation of the ice regime can be useful in determining the optimal transport and logistics routes for year-round navigation along the Northern Sea Route and safe navigation.

Abstract The extension of oil and gas exploration in High Arctic offshore locations will likely require floating drilling capability in the presence of high-concentration sea ice (pack ice) at the beginning and end of the open water season. The detection and drift forecasting of potentially unmanageable ice features (PUIF) will be key components of an ice management system designed to manage risk while drilling during pack ice intrusions. In September 2015 during the Oden Arctic Technology Research Cruise 2015 (OATRC 2015), an ExxonMobil Upstream Research Company (EMURC) free drift tactical ice forecast model designed to forecast the drift of individual ice floes in low concentration ice conditions was applied in near real-time to high concentration pack ice with predominant thicknesses of medium first-year ice in the Arctic Ocean. The description and application of the proposed ice drift forecast model is presented in this paper. In addition, forecast results are compared to drift data collected during OATRC 2015. It is shown that the free drift forecasting tool produces reasonably accurate and useful forecasts in the high concentration ice observed. Highlights • The EMURC free drift tactical ice forecast model was applied in near real-time to a pack ice environment. • The EMURC tactical ice forecast model produced accurate ice drift forecasts in high concentration pack ice. • The additional post-cruise model tuning increased the forecast accuracy. [ABSTRACT FROM AUTHOR]

Large areas of the seafloor in the Laptev Sea consist of submarine permafrost, which has experienced intense degradation over the last decades and centuries. Thermal abrasion of the submarine permafrost results in upward advection of suspended matter, which could reach the surface layer in shallow areas. This process is visually manifested through increased turbidity of the sea surface layer, which is regularly detected in optical satellite imagery of the study areas. In this study, satellite data, wind and wave reanalysis, as well as in situ measurements are analyzed in order to reveal the main mechanisms of seafloor erosion in shallow areas of the Laptev Sea. We describe the synoptic variability in erosion at the Vasilyevskaya and Semenovskaya shoals in response to wind and wave conditions. Finally, using reanalysis data, daily suspended matter flux from this area was evaluated during ice-free periods in 1979–2021, and its seasonal and inter-annual variabilities were described. The obtained results contribute to our understanding of subsea permafrost degradation, the sediment budget, and carbon and nutrient cycles in the Laptev Sea. [ABSTRACT FROM AUTHOR]

The Arctic is experiencing the greatest increase in air temperature on Earth. This significant climatic change is leading to a significant positive trend of increasing wave heights and greater coastal erosion. This in turn effects local economies and ecosystems. Increasing wave energy is one of the main drivers of this alarming trend. However, the data on spatial and temporal patterns of wave heights in the Arctic are either coarse, interpolated or limited to point measurements. The aim of this study is to overcome this shortcoming by using remote sensing data. In this study, the Synthetic Aperture Radar (SAR) satellite TerraSAR-X (TS-X) and TanDEM-X (TD-X) imagery are used to obtain sea state information with a high spatial resolution in Arctic nearshore waters in the Canadian Beaufort Sea. From the entire archive of the TS-X/TD-X StripMap mode with coverage around 30 km × 50 km acquired between 2009 and 2020 around Herschel Island, Qikiqtaruk (HIQ), all the ice-free scenes were processed. The resulting dataset of 175 collocated scenes was used to map the significant wave height ( H s ) and to link spatial and temporal patterns to local coastal processes. Sea state parameters are estimated in raster format with a 600 m step using the empirical algorithm CWAVE_EX. The statistics of the H s were aggregated according to spatial variability, seasonality and wind conditions. The results show that the spatial wave climate is clearly related to the dominant wind regime and seasonality. For instance, the aggregation of all the scenes recorded in July between 2009 and 2020 results in an average of 0.82 m H s , while in October the average H s is almost 0.40 m higher. The analysis by wind direction shows that fetch length and wind speed are likely the most important variables influencing the spatial variability. A larger fetch under NW conditions results in a mean wave height of 0.92 m, while waves generated under ESE conditions are lower at 0.81 m on average. [ABSTRACT FROM AUTHOR]

Freshwater content (FWC), generally characterized in the Arctic Ocean by salinities lower than 34.8 psu, has shifted in both quantity and distribution in recent decades in the Arctic Ocean. This has been largely driven by changes in the volume and salinity of freshwater sources and the direction and magnitude of major currents. In this study, we analyze the variability in FWC and other physical oceanographic variables from 1993 to 2021 in the Arctic Ocean and Beaufort Gyre (BG) using in situ and remote sensing observations and five ocean models and reanalysis products. Generally, ocean models and reanalysis products underestimate FWC in the BG when compared with observations. Modeled FWC and sea surface height (SSH) in the BG are well correlated during the time period and are similar to correlations of the observational data of these variables. ORAS5 compares best to EN4 salinity over the entire study period, although GLORYS12 agrees well pre-2007 and SODA post-2007. Outside the BG, consistency between modeled SSH, FWC, and limited observations varies between models. These comparisons help identify discrepancies in ocean model and reanalysis products while highlighting areas where future improvements are necessary to further our understanding of Arctic FWC. As observations are scarce in the Arctic, these products and their accuracy are important to studying this dynamic and vulnerable ocean. [ABSTRACT FROM AUTHOR]

As climate change progresses, the Arctic Ocean creates opportunities for new resource development and navigation routes. Such economic opportunities are attractive, but carry with them an increased risk of accidents and oil spills. Existing methods of emergency response face enormous challenges in the Arctic because of its lack of transportation infrastructure and support services. Cargo airships offer a practical solution. Many airship designs are proposed that can carry over 30 tons, travel long distances at 150 km per hour, and land close to the emergency site. However, it is difficult to justify the economics of having enough capacity waiting and available to be marshaled in response to infrequent events. One solution is to develop a synergy with a new civilian cargo airship industry that can serve the regular transport needs of remote communities and mining operations. Through contingency contracts with these civilian operations, the Government of Canada could stretch its budgets and have access to the latest airship models and trained crews at locations across the Arctic. This paper gives valuable insight into the development of cargo airships. Advances in technology that make cargo airships a practical option in the 21st century are reviewed, and five competing airship designs are discussed. A case study of an existing rare earth mine proposal is used to illustrate the cost comparison of roads versus airships that could provide contingency services. [ABSTRACT FROM AUTHOR]

The Arctic Ocean is a challenging region for tidal modelling. The accuracy of the global tidal models decreases by several centimeters in the Polar Regions, which has a large impact on the quality of the satellite altimeter sea surface heights and the altimetry-derived products. NOVELTIS, DTU Space and LEGOS have developed Arctide2017, a regional, high-resolution tidal atlas in the Arctic Ocean, in the framework of an extension of the CryoSat Plus for Ocean (CP4O) ESA STSE (Support to Science Element) project. In particular, this atlas benefits from the assimilation of the most complete satellite altimetry dataset ever used in this region, including Envisat data up to 82°N and CryoSat-2 data between 82°N and 88°N. The combination of these satellite altimetry missions gives the best possible coverage of altimetry-derived tidal constituents. The available tide gauge data were also used for data assimilation and validation. This paper presents the implementation methodology and the performance of this new regional tidal model in the Arctic Ocean, compared to the existing global and regional tidal models. [ABSTRACT FROM AUTHOR]

In this paper, the first version of a new Arctic Ocean circulation and thermodynamic sea-ice model is presented by the authors based on the framework of a twenty-layer World Oceanic general circulation model developed by Zhang et al. in 1994. The model's domain covers the Arctic Ocean and Greenland-Norwegian Seas with the horizontal resolution of 200 km × 200 km on a stereographic projection plane. In vertical, the model uses the Eta-coordinate (Sigma modified to have quasi-horizontal coordinate surfaces) and has ien unevenly-spaced layers to cover the deepest water column of 3000 m. Two 150-year integrations of coupling the ocean circulation model with the sea-ice model have been performed with seasonally cyclic surface boundary conditions. The only difference between the two experiments is in the model's geography. Some preliminary analyses of the experimental results have been done focused on the following aspects: (1) surface layer temperature, salinity and current; (2) the 'Atlantic Layer'; (3) sea-ice cover and its seasonal variation. In comparison with the available observational data, these results are acceptable with reasonable accuracy. [ABSTRACT FROM AUTHOR]