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Arctic warming has been substantially greater than that in the rest of the world and has had an important influence on the global climate. This study first explores the temporal and spatial evolutionary characteristics of marine heatwaves (MHWs) over the Arctic Ocean in multiyear ice (MYI), first‐year ice (FYI), and open‐water (OPW) regions from 1982 to 2020. MHWs in the Arctic Ocean show obvious spatial and seasonal variations, mainly occurring over the FYI region in the JAS (July–August–September, JAS), and their occurrences have a significant increasing trend in recent decades, accompanied by an abrupt increase since 2010. Furthermore, a multivariable network‐based method is adopted to delineate the relationship between different climatic factors and MHWs in the Arctic Ocean and the climatic impacts of MHWs. The results show that the correlations between different climatic factors and MHWs in JAS in 2010–2020 are generally stronger than those in 1982–2009, and the main influencing factors of MHWs in different ice covers are different. MHWs in the MYI region are mainly affected by freshwater dilution processes, such as sea‐ice concentrations (SIC), precipitation, and mixed‐layer salinity. For the FYI region, the 2‐m air temperature and total heat flux mainly affect MHWs by thermodynamic processes, and the 500‐hPa geopotential height affects MHWs mainly by large‐scale atmospheric circulation. The MHWs in the OPW region are mainly related to the SIC, 850‐hPa geopotential height, and 10‐m v‐wind, indicating that they are correlated with atmospheric processes and wind fields. MHWs in JAS are also revealed to reduce or delay the formation of sea ice in OND (October–November–December, OND) by storing more abnormal heat, indicating that unfrozen ocean surfaces may lead to enhanced Arctic amplification in the following seasons. [ABSTRACT FROM AUTHOR]

Previous studies have reported an accumulation of nitrous oxide (N2O) on shallow continental shelves of the western Arctic Ocean. In this study, we sampled seawater profiles for N2O measurements in the eastern Arctic shelves, in the North Kara Sea, in the context of the Arctic Century Expedition. Despite some variability in the vertical distribution, we typically observe an accumulation of N2O in shelf bottom waters, which correlates with a fixed nitrogen (N) deficit. Longer residence times on the shelf promote greater N2O enrichment and a larger fixed N deficit. These observations point towards N2O production at depth, linked to benthic denitrification processes that are intensified on productive shelve areas. However, in surface waters, physical processes – i.e. temperature-dependent solubility and air-sea exchange – emerge as the main factor controlling N2O concentrations. We observe low saturations of 80% at the surface of open ocean stations influenced by water that has previously flowed beneath sea ice. Arctic surface water becomes undersaturated due to cooling and remains undersaturated due to limited air-sea exchange. River supply does not exert a discernable influence on N2O concentrations of the studied area. This study reveals the potential of the Arctic Siberian shelves as a sink of atmospheric N2O during the summer. [ABSTRACT FROM AUTHOR]

A statistical summary of chemical composition of atmospheric aerosol is presented based on the long-term research results obtained in the Eurasian sector of the Arctic Ocean: concentrations of 8 ions, 22 trace elements, organic and elemental carbon (OC, EC), as well as total carbon isotopic composition δ13C. The average aerosol characteristics were obtained: 5.14 μg/m3 for the total ion concentration with a predominant contribution (72%) of Na+ and Cl– ions; 175 ng/m3 for the total concentration of trace elements with a main contribution (70%) of terrigenous elements Fe and Al; 700 ng/m3 for the OC concentration; 32 ng/m3 for the ЕC concentration; and δ13C = –27.9‰ VPDB. High enrichment factors of Cr, Ni, Se, Mo, Sn, Pb, Cu, Zn, As, Ag, and Sb (relative to the composition of the continental crust) are due to their anthropogenic origin. The spatial distribution of concentrations of all ions is characterized by a decrease (3.5 times, on average) from the Norwegian Sea to the Chukchi Sea. The spatial distribution of trace element concentrations was divided into three groups with maxima over the Norwegian, Barents, or Kara seas and a minimum over the Chukchi Sea. Characteristic features of carbon-containing aerosol also tend to change eastward: a decrease in OC and EC and heavier carbon isotopic composition. [ABSTRACT FROM AUTHOR]

The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the Laptev Sea shelf leads to the development of a thick alluvial fan at the continental rise, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western flank of which is complicated by terraces. The presence of fault structures, bottom subsidence, extensive sediment supply, and the widespread development of subaqueous slump processes indicate the high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate rocks have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. The palynological and micropaleontological analysis of the carbonate rocks indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and oxidation products of gases and organic matter. The authigenic carbonates were precipitated mainly in an isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between 87Sr/86Sr and δ13C indicates the presence of at least two different sources of carbonate-forming solutions. [ABSTRACT FROM AUTHOR]

Gelatinous zooplankton (GZ), play a crucial role in marine food webs, nutrient cycling, and carbon sequestration, however, quantifying their abundances remains challenging due to their delicate body structure, complex life cycles and variable population dynamics. Their tendency to form sporadic, large-scale aggregations further complicate the differentiation between true ecosystem alterations and stochastic variations in their abundance. In the Arctic Ocean, our understanding of GZ aggregations remains generally incomplete. Using in-situ observations from a towed pelagic camera system, we assessed the diversity and vertical distributions of GZ in fjord and offshore environments in northern Norway and the Svalbard archipelago. We found that Atlantic water masses harbored the highest GZ abundance, while intermediate waters showed the highest diversity. We documented dense aggregations of Beroe spp. in Van Mijenfjorden in Svalbard (observed during ascent of the camera system, not quantified in ind. m−3) and Bolinopsis infundibulum in the open Barents Sea (> 2.67 ind. m−3 at 100 m). Other observed taxa included the hydrozoans Aglantha digitale, Melicertum octocostatum, Solmundella bitentaculata, Pandeidae sp. and Physonectae spp., the scyphozoan Cyanea capillata and the ctenophores Mertensia ovum and Euplokamis sp. By linking the vertical distribution and observations of local aggregations with physical and biotic factors, we described the potential drivers of the distributional patterns observed. Towed camera surveys contribute to accurate in-situ observations, thereby improving our understanding of GZ aggregations and distributions in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

In recent years, the Arctic Ocean has been experiencing the impacts of climate change. Global warming has led to the melting of ice caps and a significant reduction in ice coverage. As a result, the Arctic Ocean has indirectly opened up two new shipping routes known as the "Northeast Passage" and the "Northwest Passage." The opening of these new routes has the potential to transform Northeast Asia into a major transshipment hub, linking the Indo-Pacific and Europe regions. Novel business models are also generated and investigated within the maritime industry. This study involved conducting semi-structured interviews with potential stakeholders from industry, government, and academia. Additionally, qualitative analysis software- NVivo11 was utilized along with grounded theory for data analysis. The rationale supporting this view includes the advantages of Taiwan's shipping industry, its strategic geographic location, and the potential for shorter shipping routes through the Arctic. Additionally, Taiwan can establish conducive conditions to enhance its international standing and diplomatic relationships concerning Arctic Ocean matters. This initiative will facilitate the sustainable development of Taiwan's maritime industry in the Arctic region. • The evolving perspectives of Taiwan's maritime and transportation industry in balancing economic and environmental considerations. • Incorporating stakeholders' feedback into policy formulation: Perspectives and insights. • Positioning and reflections on Taiwan's development strategy for the Arctic sea routes. [ABSTRACT FROM AUTHOR]

Early Eocene (∼56–48 Ma) climates are useful to investigate polar climate dynamics in the absence of ice. We explore early Eocene orbital variability of Arctic climate using sediments recovered by the Arctic Coring Expedition (ACEX). High resolution records of lipid biomarkers (GDGTs; 2‐kyr) and palynological assemblages (5‐kyr) in the ∼4 m interval below Eocene Thermal Maximum 2 (∼54 Ma) show cyclic signals related to ∼20‐kyr precession, ∼40‐kyr obliquity, and ∼100‐kyr eccentricity. Biomarkers indicate obliquity and precession variability representative of sea surface temperature (SST) variations up to ∼1.4 and ∼0.5°C, respectively. Peak SSTs coincide with an elevated supply of pollen and spores and increased marine productivity. This implies an orbital control on precipitation and terrestrial nutrient supply to the Arctic Basin. Assuming that SST maxima correspond to Arctic insolation maxima (precession minima/obliquity maxima), precipitation maxima also correspond to insolation maxima, implying regional hydrological processes as a forcing rather than variations in meridional water transport, contrasting Pleistocene Arctic hydrology. The relative amplitudes of precession and obliquity in the SST record match that of local insolation between spring and fall, corroborating a seasonal GDGT bias. The reconstructed complete orbital imprint refutes a bias to one end of the orbital variability. Eccentricity‐related SST variability was ∼0.8°C, ∼2–3 times higher than synchronous variability in the deep ocean, and 3–4 times higher than similar variations in the tropics. This confirms eccentricity‐forced global temperature variability and that this had pronounced polar amplification, despite the absence of ice‐albedo feedbacks. Plain Language Summary: During the early Eocene (56–48 million years ago), an ancient period of global high atmospheric CO2 concentrations and temperatures, the Arctic Ocean was an ice‐free (sub)tropical, semi‐enclosed basin. Our understanding of this unfamiliar Arctic situation relies largely on analysis of sediments retrieved by the single academic drilling expedition that recovered sediments from this period. However, the available temperature reconstructions are insufficient to capture the climate variations caused by Earth's orbit (often termed "Milankovitch cycles"), which are also responsible for the repeating occurrence of ice ages over the past million years. Here, we reconstruct past Arctic temperatures using temperature‐sensitive molecular fossils in a 4‐m thick sediment interval deposited during the early Eocene on a 1‐cm (∼2,000‐year) resolution. Our results show that Arctic surface temperatures varied more than those at lower latitudes during global variations, and display 2°C variability corresponding to the local insolation changes resulting from precession and the tilt of Earth's axis, with respective periods of 21,000 and 41,000 years. Changes in microfossil content show that the warmer periods coincided with increased rainfall, indicating that moisture availability at the poles was similarly forced on these timescales. Key Points: TEX86‐based early Eocene Arctic surface water temperatures (SSTs) show obliquity and precession imprints matching a spring‐to‐fall forcingEccentricity forcing caused ∼0.8°C Arctic SST variability, depicting strong Arctic amplification despite absent albedo feedbacksPrecipitation maxima were in‐phase with implied insolation maxima, suggesting a strong orbital imprint on local hydrological processes [ABSTRACT FROM AUTHOR]

Starting from the governing equations for a viscous, incompressible fluid, written in a rotating, spherical coordinate system that is valid at the North Pole, the thin-shell approximation is invoked. No further approximations are needed in the derivation of the system of asymptotic equations used here. Suitable stress conditions on the upper and lower surfaces of the ice are described, leading to the construction of a solution for the Transpolar Drift current. This involves the specification of a suitable geostrophic flow, combined with an Ekman component. Then, via the stress conditions across the ice at the surface, a solution for the motion of the ice, and for the associated wind blowing over it, are obtained. In addition, the model adopted here provides a prediction for the reduction in ice thickness along the Transpolar Drift current as it passes through the Fram Strait. The formulation that we present allows considerable freedom in the choices of the various elements of the flow; the model chosen for the physical properties of the ice is particularly significant. All these aspects are discussed critically, and it is shown that many avenues for future investigation have been opened. [ABSTRACT FROM AUTHOR]

In this contribution, we present tritium‐3He (3H‐3He) apparent ages and hydrographic data from 21 expeditions spanning 27 years of Arctic Ocean section work (1987–2013) to estimate flow paths and spreading velocities of the Atlantic Waters (AW) circulation on a pan‐Arctic scale. Tracer data not only corroborate the well‐organized cyclonic flow along the continental slope but also introduce a temporal dimension to these observations. Additionally, they provide insights into other circulation branches of the Atlantic layer, which are hypothesized to be influenced by deep submarine ridges. Tracer measurements indicate that mean spreading rates vary across different branches of the circulation pattern. Along the boundary current, spreading velocities range from approximately 0.7 to 1.5 cm s−1, with no significant difference observed between the waters of the two vertically stacked Atlantic branches. Within the limits of our method, tracer data support the hypothesis originally proposed by Rudels et al. (1994), https://doi.org/10.1029/gm085p0033—of stable pathways in the Atlantic Layer, influenced by topographic constraints. Plain Language Summary: In this study, we analyze tritium and helium‐3 (3He) data from 21 oceanographic expeditions conducted over 27 years to track the movement and speed of the Atlantic Layer—waters originating from the North Atlantic, found in the Arctic Ocean. The combined measurement of tritium and 3He acts as a "natural clock," allowing us to estimate the water age and understand its movement through various oceanic pathways. Our findings confirm that the Atlantic Layer circulates in a consistent counterclockwise pattern along the continental slope, functioning as a boundary current. This circulation is influenced by underwater mountain ridges, which generate northbound flows where they intersect with the continental slope. We noted that the speed of the Atlantic Layer varies horizontally depending on the route it follows, but there is no significant speed difference between the upper and lower parts of the layer. Our research supports the hypothesis originally proposed by Rudels et al. (1994), https://doi.org/10.1029/gm085p0033, suggesting that the pathways of Atlantic water are stable and shaped by the ocean's underwater topography. This study provides new insights into the intricate patterns of ocean circulation in the Arctic. Key Points: Tracer data independently reveal Arctic Ocean's Atlantic Water circulation pathTracer‐derived velocities vary across circulation branches27‐year study shows stable circulation and spreading rates in Arctic Ocean [ABSTRACT FROM AUTHOR]

Parasitological investigations of anadromous Dolly Varden (Salvelinus malma) (Walbaum, 1792) harvested along the Canadian Beaufort Sea coast in summer 2021 and 2022 revealed infections by the parasitic cestode Nybelinia surmenicola (Okada in Dollfus, 1929) (2% and 0.8% prevalence, respectively) whose only documented final host is salmon shark (Lamna ditropis) (Hubbs and Follett, 1947), which to date has been documented only once in the Arctic. Infection rates were low as only two fish, captured in consecutive years, were infected with a single worm at the plerocercoid stage in their stomach. These infections are the first record of the parasite in the Arctic Ocean and for Dolly Varden in North America. The source of infection in both fishes was likely from consuming a euphausiid, presumably Thysanoessa raschii (M. Sars, 1863), which is an infrequent prey of Dolly Varden and a known first host of the parasite, that became infected by consuming N. surmenicola eggs expelled by salmon shark. The euphausiids presumably originated from the Bering Sea and were actively transported by currents into the Arctic Ocean yet it is unknown where their infection occurred. Given the amount of time for exogenous feeding to begin, the presumed rate of transport and time spent feeding in Arctic waters (i.e., Chukchi and Beaufort seas), we infer the infection of euphausiids most likely occurred in the Arctic, which suggests the presence of salmon shark. Additionally, the findings provide evidence that salmon shark may becoming increasingly prevalent in Arctic waters in recent years due to climate change. Our observation underscores the utility of parasitological information for surveillance for detecting climate-related change in Arctic marine biodiversity.

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.

In the Arctic Ocean (AO), net community production (NCP $NCP$) has displayed spatially heterogeneous responses to sea ice reduction and associated environmental changes. Using a random forest machine learning model trained with >42,000 in situ measurements and concurrent, collocated environmental predictors, we reconstructed 19 years of 8‐day, 6‐km NCP $NCP$ maps. During 2015–2021, the integrated NCP $NCP$ between late‐May and early‐September (NCPint ${}_{\mathit{int}}NCP$) over the western AO was 10.95±3.30TgC $10.95\pm 3.30\,\text{Tg}\,\mathrm{C}$ per year, with interannual variations positively tracking open water area. While the relationship between NCPint ${}_{\mathit{int}}NCP$ and open water area was quasi‐linear at high latitudes, strong nonlinearity was detected on the inflow shelf. The nonlinearity highlights that the NCPint ${}_{\mathit{int}}NCP$ increase resulted from area gain could be compounded by sea‐ice loss induced ecosystem adjustments. Additional retrospective analysis for 2003–2014 suggests a potential long‐term increase of export production and efficiency in the western AO with sea ice loss. Plain Language Summary: Net community production (NCP $NCP$) refers to the portion of phytoplankton production that remains unused by consumers and can be exported to the deeper part of the ocean. In the western Arctic Ocean (AO), NCP $NCP$ patterns are uneven due to complex interactions between the physical environment and the ecosystem. In this study, we developed a machine learning model of NCP $NCP$ in the western AO. The model used publicly available underway measurements and the associated environmental variables to create long‐term, high‐resolution maps of NCP $NCP$. For the period of 2015–2021, we found that the integrated NCP $NCP$ between late‐May and early‐September (NCPint ${}_{\mathit{int}}NCP$) was 10.95±3.30TgC $10.95\pm 3.30\,\text{Tg}\,\mathrm{C}$ per year in the western AO. NCPint ${}_{\mathit{int}}NCP$ varied from year to year and was higher when the open water area was larger. Notably, on the inflow shelf, NCPint ${}_{\mathit{int}}NCP$ increased at a faster rate than a linear relationship would suggest, due to both area expansion and ecosystem adjustments induced by sea ice loss. Our findings indicate that with long‐term sea ice loss, the western AO is likely to export more phytoplankton production to deeper ocean waters. Key Points: A multiyear, gap‐free net community production (NCP $NCP$) product was constructed using a machine learning model for the western Arctic OceanSeasonally and regionally integrated NCP $NCP$ responded to sea ice loss quasi‐linearly at high latitudes but nonlinearly on the inflow shelfCompared with the 2010s, carbon export production has increased in recent years, accompanying sea ice loss in the western Arctic Ocean [ABSTRACT FROM AUTHOR]

The rapid warming of the Arctic-Boreal region has led to the concern that large amounts of methane may be released to the atmosphere from its carbon-rich soils, as well as subsea permafrost, amplifying climate change. In this review, we assess the various sources and sinks of methane from northern high latitudes, in particular those that may be enhanced by permafrost thaw. The largest terrestrial sources of the Arctic-Boreal region are its numerous wetlands, lakes, rivers and streams. However, fires, geological seeps and glacial margins can be locally strong emitters. In addition, dry upland soils are an important sink of atmospheric methane. We estimate that the net emission of all these landforms and point sources may be as much as 48.7 [13.3–86.9] Tg CH4 yr−1. The Arctic Ocean is also a net source of methane to the atmosphere, in particular its shallow shelves, but we assess that the marine environment emits a fraction of what is released from the terrestrial domain: 4.9 [0.4–19.4] Tg CH4 yr−1. While it appears unlikely that emissions from the ocean surface to the atmosphere are increasing, now or in the foreseeable future, evidence points towards a modest increase from terrestrial sources over the past decades, in particular wetlands and possibly lakes. The influence of permafrost thaw on future methane emissions may be strongest through associated changes in the hydrology of the landscape rather than the availability of previously frozen carbon. Although high latitude methane sources are not yet acting as a strong climate feedback, they might play an increasingly important role in the net greenhouse gas balance of the Arctic-Boreal region with continued climate change. [ABSTRACT FROM AUTHOR]

Little is known about the role of remote and sparsely populated Arctic coastal zones in the microplastic cycle. Distribution of microplastics was studied in the Svalbard fjords in June – July 2022 with the main goal of assessing rivers' role in the fate of microplastic in Arctic coastal waters. Surface microplastics (0 – 20 cm depth, 500 – 5000 µm size) were sampled with a neuston net in triplicate per study site in parallel with sampling of subsurface microplastics with a pump system (1.5 m depth, 100 – 5000 µm size). The central part of Isfjorden and its several branches covering populated and unpopulated fjords were studied; the sampling was conducted during an intense riverine discharge in all studied sites. Maximum abundance of surface microplastics (71,400 items/km2 or 0.19 iterms/m3, 0.19 mg/m3) was found along the river plume border in the middle of populated Adventfjorden indicating importance of both local sources and surface hydrodynamics in the formation of microplastics accumulation hotspots. All other unpopulated fjords were free of the floating on the sea surface microplastics as river discharge prevented transport of microplastics inside the fjords. The highest concentration of subsurface microplastics was found in the central part of Isfjorden and the lowest – in river plume waters, which also indicates the removal of microplastics from the inner part of fjords during an intensive river discharge. Our results may suggest that Arctic rivers flowing through unpopulated areas bring clean water and thereby reduce level of microplastic pollution in the coastal waters. In contrast to the rest of the world's ocean, rivers are not the main source of microplastic pollution in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

The present study analyzes the potential propagation trajectories and fate of floating microplastic particles released on the Kara Sea shelf. The transport of microplastics is described using a Lagrangian model based on daily 2016–2020 data obtained from numerical modeling of Arctic Ocean dynamics. A particle biofouling model is used to simulate the submergence of floating microplastic particles in the water column. The model includes a parameterization of the processes of biofilm accumulation (via collision with algae in surrounding water, algae growth) and degradation (via respiration, mortality). The behavior of microplastic particles of different sizes (0.5 and 0.01 mm) during the sinking process and subsequent rising due to biofilm degradation is examined. The simulation results reveal that particles of 0.01 mm in size display a tendency to sink immediately during the process of biofouling. However, when the biofilm degraded, the particles exhibited a rising velocity, comparable to the current vertical velocity, and the particles remained submerged in the water for long periods. In contrast, the 0.5 mm particles remained at the surface for a longer period before sinking, accumulating biofilm. Subsequently, their behavior was oscillatory in response to changes in the biofilm, rising rapidly when the biofilm decayed and sinking rapidly again as a result of biomass accumulation. In winter, the 0.5 mm particles were mostly frozen into the ice. The phenomenon of biofouling, whereby microplastic particles of various sizes sink at different depths, results in considerable variation in the subsequent pathways of these particles in the Arctic Ocean. [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]

Rocks dredged from water depths of 1,605, 2,500, 3,300, and 3,400 m in the Arctic Ocean included Paleozoic continental rocks pervasively mineralized during the Neogene by hydrothermal Fe and Mn oxides. Samples were recovered in three dredge hauls from the Chukchi Borderland and one from Mendeleev Ridge north of Alaska and eastern Siberia, respectively. Many of the rocks were so pervasively altered that the protolith could not be identified, while others had volcanic, plutonic, and metamorphic protoliths. The mineralized rocks were cemented and partly to wholly replaced by the hydrothermal oxides. The Amerasia Basin, where the Chukchi Borderland and Mendeleev Ridge occur, supports a series of faults and fractures that serve as major zones of crustal weakness. We propose that the stratabound hydrothermal deposits formed through the flux of hydrothermal fluids along Paleozoic and Mesozoic faults related to block faulting along a rifted margin during minor episodes of Neogene tectonism and were later exposed at the seafloor through slumping or other gravity processes. Tectonically driven hydrothermal circulation most likely facilitated the pervasive mineralization along fault surfaces via frictional heating, hydrofracturing brecciation, and low‐ to moderate temperature Fe‐ and Mn‐rich hydrothermal fluids, which mineralized the crushed, altered, and brecciated rocks. Plain Language Summary: In this paper, we describe a previously unknown style of marine mineral formation in the Arctic Ocean. We found that these minerals formed in the recent geologic past, approximately 8–4 million years ago, which was a surprise since no hydrothermal activity was known to occur in this region of the Arctic Ocean during this time period. Hydrothermal activity is the heating of seawater through various interactions within the earth. Here we propose that these minerals formed along seafloor faults and were later variably exposed at the seafloor. The unique style of formation for these minerals is also reflected in their mineralogy and element composition relative to other types of marine minerals found in this region. This work increases our understanding of the ways in which marine minerals may be formed, as well as the geologic processes occurring in the Arctic Ocean in the recent geological past. Key Points: First description of unique stratabound hydrothermal Fe‐ and Mn‐oxide deposits in the Amerasia Basin in the Arctic OceanThe Amerasia Basin is not known to have had a Cenozoic magmatic heat sourceWe propose that hydrothermal circulation was driven by tectonism; deposits formed along faults and exposed at the seafloor using gravity processes [ABSTRACT FROM AUTHOR]

The Atlantic Water plays a major and increasing role in the heat budget of the Arctic Ocean (Atlantification). The pathways of Atlantic Water within the Arctic Ocean, and in particular their sensitivities to large‐scale atmospheric patterns such as the Arctic Oscillation, remain unclear. In this study, we used the trace gases CFC‐12 and SF6 ${\text{SF}}_{6}$ to investigate the Atlantic Water pathways during different phases of the Arctic Oscillation. We calculated tracer ages for the temperature maximum of the Atlantic Water, focusing on repeated transects (1994, 2005, 2015) in the Amerasian Basin of the Arctic Ocean. During a positive phase of the Arctic Oscillation in 1994, tracer ages were low along the Chukchi shelf due to a strong coherent boundary current. In contrast, the ages were up to 10 years higher in 2015 without this coherent current during a mixed phase of the Arctic Oscillation. Further, we identified a discontinuity in the inflow between the Makarov Basin and the Canada Basin during this phase. Tracer ages were 10 years higher in the Canada Basin, suggesting a closed circulation without direct inflow in this region. Our tracer ages generally align with previously proposed circulation schemes and water ages, with major exceptions in 2015. We have shown that the tracer ages are applicable to identify decadal changes in the Atlantic Water core pathways in the central Arctic Ocean. Plain Language Summary: The warm Atlantic Water transports heat into the Arctic Ocean, potentially melting the sea ice. The pathways of Atlantic Water within the Arctic Ocean are essential to understand in a changing climate and under changing atmospheric conditions. Our aim here is to analyze repeated transects in the Arctic Ocean to find decadal changes in the Atlantic Water core pathways. We used the anthropogenic trace gases CFC‐12 and SF6 ${\text{SF}}_{6}$ to calculate tracer ages, that is, the time since the water left the surface. We found low ages along the Chukchi slope in 1994, indicating a strong boundary current. After a change in atmospheric conditions, the ages along the slope increased, indicating a different pathway of the Atlantic Water in 2015. Also in 2015, the Canada Basin and the Makarov Basin were disconnected. Our tracer ages agree well with ages derived using different methods and tracers. However, we only require one tracer for the tracer age, enlarging the available data coverage. As climate change continues, it will affect atmospheric conditions and, in turn, the movement of Atlantic Water in the Arctic Ocean. We show that tracer ages can identify these changes in the Atlantic Water pathways. Key Points: Atlantic Water tracer ages under positive Arctic Oscillation are very low near Chukchi Shelf due to coherent boundary currentSF6 tracer ages show a discontinuity in Atlantic Water inflow between the Makarov and Canada Basin during mixed Arctic OscillationTracer ages are applicable to identify pathway changes in the advective Arctic Ocean [ABSTRACT FROM AUTHOR]

In order to quantify pelagic‐benthic coupling on high‐latitude shelves, it is imperative to identify the different physical mechanisms by which phytoplankton are exported to the sediments. In June–July 2023, a field program documented the evolution of an under‐ice phytoplankton bloom on the northeast Chukchi shelf. Here, we use in situ data from the cruise, a simple numerical model, historical water column data, and ocean reanalysis fields to characterize the physical setting and describe the dynamically driven vertical export of chlorophyll associated with the bloom. A water mass front separating cold, high‐nutrient winter water in the north and warmer summer waters to the south—roughly coincident with the ice edge—supported a baroclinic jet which is part of the Central Channel flow branch that veers eastward toward Barrow Canyon. A plume of high chlorophyll fluorescence extending from the near‐surface bloom in the winter water downwards along the front was measured throughout the cruise. Using a passive tracer to represent phytoplankton in the model, it was demonstrated that the plume is the result of subduction due to baroclinic instability of the frontal jet. This process, in concert with the gravitational sinking, pumps the chlorophyll downwards an order of magnitude faster than gravitational sinking alone. Particle tracking using the ocean reanalysis fields reveals that a substantial portion of the chlorophyll away from the front is advected off of the northeast Chukchi shelf before reaching the bottom. This highlights the importance of the frontal subduction process for delivering carbon to the sea floor. Plain Language Summary: The Chukchi Sea shelf north of Bering Strait is known to experience some of the largest phytoplankton blooms in the Arctic Ocean. In 2023, a field program was carried out to quantify aspects of the early summer bloom, with an emphasis on characterizing how the phytoplankton biomass from the bloom is exported to the sea floor. A large bloom was measured under the pack ice in very cold, high‐nutrient water, just north of warmer, ice‐free waters. The front separating the warm and cold waters supported a current flowing eastward, which is one of the main flow pathways on the Chukchi shelf. A plume of high chlorophyll fluorescence extending from the near‐surface bloom downwards along the front was measured throughout the cruise. We demonstrate that this vertical pumping was due to a dynamical process associated with the current which resulted in much faster downward export of phytoplankton than gravitational sinking alone. Tracking the fate of particles on the northeast Chukchi shelf using an ocean simulation revealed that much of the phytoplankton biomass away from the front is carried off the shelf before reaching the bottom. This highlights the importance of the frontal process for delivering chlorophyll to the sea floor. Key Points: An under‐ice phytoplankton bloom developed during June–July in the northeast Chukchi Sea within the Central Channel flow branchA plume of chlorophyll fluorescence extending downwards from the bloom along the current's water mass front was continually presentA simple numerical model demonstrates that the plume is the result of baroclinic instability of the frontal jet [ABSTRACT FROM AUTHOR]

Introduction: Rapid reductions in Arctic sea ice in response to warming have led to increased interest in using the Arctic Ocean for commercial shipping. As the world warms, however, different strategies are being considered to stabilize or reduce surface temperatures in order to prevent critical climate change impacts. One such strategy is stratospheric aerosol injection (SAI), a form of solar climate intervention. Projected changes to Arctic sea ice under SAI with specific regards to shipping have not yet been assessed. Methods: We compare output from two SAI simulations that have different global mean temperature targets with a non-SAI control simulation to provide the first assessment of Arctic Ocean navigability under potential SAI scenarios. Results: We find that sea ice concentration and thickness quickly stabilize or increase after SAI deployment. When sea ice thickness stabilizes in response to SAI, the number of days when the Arctic Ocean is navigable remains fairly constant, but increasing sea ice thickness leads to reduced navigability compared to the non-SAI simulation. From 2035-2069, both the Northwest Passage and Northern Sea Route are accessible from July-November in all three simulations, but there are no navigable routes under either SAI scenario from April-June. When the Arctic is navigable, it can take 2-12 days longer to cross the Arctic Ocean in the SAI simulations than in the non-SAI control simulation, and there are large year-to-year variations in travel time. Discussion: Overall, Arctic shipping may take longer and be more difficult in an SAI vs a non-SAI world because of relatively thicker sea ice, but the degree to which Arctic shipping may change in response to SAI is dependent on the particular climate intervention strategy. [ABSTRACT FROM AUTHOR]

The main source of summer heating of the upper layer of Siberian Arctic shelf seas is shortwave solar radiation. The radiation flux attenuates as it passes through the water depth, and the attenuation rate is determined by the optical properties of water, which mainly depend on the concentration of suspended matter in the water. In numerical models of the ocean and sea ice, the process of shortwave solar radiation absorption is described by different parameterizations. In this work, the sensitivity of the numerical 3D regional ocean and sea ice model SibCIOM to two parameterizations of the penetrating radiation is studied: (1) two-component parameterization with constant attenuation coefficients for the infrared and visible spectral regions depending on one of ten ocean water transparency classes; (2) three-component parameterization with different absorption coefficients for the red, green, and blue parts of the visible spectrum, which is based on satellite data on chlorophyll concentration. The analysis of the results of numerical experiments for the water area of Siberian shelf seas has shown that if the seasonal distribution of chlorophyll concentration is taken into account when simulating a penetrating shortwave radiation flux with the RGB parameterization, then regions of water warming are formed in the surface or bottom layer, which differ from a basic experiment with the two-component parameterization. The comparison between the simulation results with observations shows the RGB parameterization to be preferable for the numerical simulation of Arctic shelf seas. [ABSTRACT FROM AUTHOR]

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]

As the Arctic warms at an increased rate compared to the rest of the globe, freshwater runoff has been shown to be increasing into the Arctic Ocean. The effects of this contemporary increase in riverine freshwater into the Arctic Ocean are estimated from ocean model simulations, using two runoff data sets. One runoff data set is based on older climatological data, which has no inter‐annual variability after 2007 and as such does not represent the observed increases in river runoff into the Arctic. The other data set comes from a hydrological model developed for the Arctic drainage basin, which includes contemporary changes in the climate. At the Pan‐Arctic scale this new data set represents an approximately 11% increase in runoff, compared with the older climatological data. Comparing two ocean model runs forced with the different runoff data sets, overall changes in different freshwater markers across the basin were found to be between 5% and 10%, depending on the regions. The strongest increases were seen from the Siberian rivers, which in turn caused the strongest freshening in the Eastern Arctic. As the surface waters of the Arctic Ocean are sensitive to runoff, incorporating hydrological model data can help to better understand current changes and potential future impacts from increased runoff with climate change. Plain Language Summary: Climate change increases freshwater supply to the Arctic. This study looks at understanding the impacts of this increased riverine water into the Arctic Ocean using a state of the art regional ocean model. Two runoff forcing data sets are used, one data set which only extends to 2007 and thus does not include the recently observed runoff increases due to climate change, and a newer data set which extends up to present day and as such represents contemporary increases in the river runoff into the Arctic. Comparing two simulations forced by the two runoff datasets highlights the effects of river runoff changes on the Arctic Ocean. We find the Arctic surface waters freshen by 5%–10% over 2007–2018, depending on the metric and region considered. Much of this increased freshwater found is driven by the major Siberian rivers. This primarily affects the Eastern Arctic. Our work shows that recently observed increases in Arctic river runoff are likely impacting surface Arctic waters as well as waters transported to lower latitudes. Key Points: Pan‐Arctic river runoff increased by 11% over 2002–2019 according to hydrological model outputIn ocean model simulations this dataset gave a subsequent surface freshening of 5%–10%, as compared with classical runoff climatologySiberian rivers dominate runoff and are the main source of differences, enhancing export through Fram and Davis Straits, as observed [ABSTRACT FROM AUTHOR]

The Arctic Ocean is characterized by substantial seasonal and inter‐annual variability, of which the sources and impacts are not yet fully understood. Here, we analyze how much of the variability found in in situ observations of biogeochemical and ecological variables collected at the Long‐Term Ecological Research Observatory HAUSGARTEN can be explained by differences in the physical conditions in the water masses passing through the Fram Strait (FS). Employing a size‐based plankton ecosystem model with nine distinct size classes of protist phyto‐ and zooplankton, we simulate standing stocks and fluxes within the nutrient, phytoplankton, zooplankton, and detritus pools in water parcels that follow trajectories tracing the opposing East‐Greenland and West‐Spitsbergen currents through the FS. Our model results agree with in situ observations of biogeochemical tracers, plankton size measurements, climatological data, and remote sensing observations. They show distinct temporal developments in plankton size composition, growth, and export in trajectory ensembles, highlighting how variable physical conditions affect the communities' specific growth histories. Our study indicates that 10%–72% of the variability in upper water column tracer concentrations observed in the FS can be attributed to differences in water parcel trajectories. The maxima of net primary production and vertical export along the trajectories occurred in some (spatial and temporal) distance upstream of the sites of in situ sampling. This study shows that Lagrangian modeling helps clarify complex biogeochemical‐ecological relationships in highly dynamic systems such as the FS, which is urgently needed to understand the role of climate change in the Arctic carbon cycle. Plain Language Summary: To study sources of biological and chemical variability in the Fram Strait (FS) (Arctic Ocean), this study uses a model that follows water parcels as they move along the currents and simulates the growth of plankton populations, their influence on nutrient concentrations and the production of dead, dissolved, and decaying organic matter. By simulating many different pathways, the model estimates how variability in the environmental conditions along those pathways contributes to the variability of the plankton ecosystem in the upper water column. When compared to real data measured from ships and observed by satellites, we find that the model successfully reproduces changes in the plankton size structure and estimates productivity and export close to observations from the region. Our study finds that a substantial portion (10%–72%) of the observed variability in biogeochemical tracers can be explained by differences in the origins and pathways of water parcels. Nonetheless, a large amount of variability remains unexplained, indicating the need for further research to better understand essential processes. This research helps us understand the sources of variability in the FS and make better predictions about elemental cycling, productivity and export, which is especially important in the face of climate change. Key Points: Local variability in tracer concentrations in Fram Strait (FS)'s upper 100 m is linked to differences in water parcel trajectoriesTrajectories differ in their origin and timing of passage, leading to differences in plankton size structure, growth, and exportAt the time of in situ observations in the FS, the maxima in net primary production and vertical export have already occurred [ABSTRACT FROM AUTHOR]

Despite its extreme remoteness, the geographic North Pole is attracting more tourists than ever before, bringing increasing numbers of people and ships to the Arctic Ocean. This growth is regarded as potentially damaging to the Arctic environment, especially combined with the effects of climate change on the sea ice. Yet, to understand and anticipate future changes related to increasing tourism at the North Pole (and the Arctic Ocean), it is critical to both assess the current situation of tourism and to anticipate the future of tourism in the region in light of climate change projections. Therefore, this article explores the dimensions and geographies of tourism development at the North Pole, and more generally in the Arctic Ocean, in terms of modes of tourism, itineraries, and estimated numbers of tourists. To do so, we examine three main forms of tourism taking place in the region, namely icebreaker cruises, frontier travelers venturing on the sea ice, and ice camps. The article also aims to discuss the future of tourism in the region in light of estimated climate change impacts on the sea ice, in order to better plan and adapt to a future seasonally ice-free Arctic Ocean. [ABSTRACT FROM AUTHOR]

Sediment-laden sea ice plays an important role in Arctic sediment transport and biogeochemical cycles, as well as the shortwave radiation budget and melt onset of ice surface. However, at present, there is a lack of efficient observation approach from both space and in situ for the coverage of Arctic sediment-laden sea ice. Thus, both spatial distribution and long-term changes in area fraction of such ice floes are still unclear. This study proposes a new classification method to extract Arctic sediment-laden sea ice on the basic of the difference in spectral characteristics between sediment-laden sea ice and clean sea ice in the visible band using the MOD09A1 data with the resolution of 500 m, and obtains its area fraction over the pan Arctic Ocean during 2000–2021. Compared with Landsat-8 true color verification images with a resolution of 30 m, the overall accuracy of our classification method is 92.3%, and the Kappa coefficient is 0.84. The impact of clouds on the results of recognition and spatiotemporal changes of sediment-laden sea ice is relatively small from June to July, compared to that in May or August. Spatially, sediment-laden sea ice mostly appears over the marginal seas of the Arctic Ocean, especially the continental shelf of Chukchi Sea and the Siberian seas. Associated with the retreat of Arctic sea ice extent, the total area of sediment-laden sea ice in June–July also shows a significant decreasing trend of 8.99 × 104 km2 per year. The occurrence of sediment-laden sea ice over the Arctic Ocean in June–July leads to the reduce of surface albedo over the ice-covered ocean by 14.1%. This study will help thoroughly understanding of the role of sediment-laden sea ice in the evolution of Arctic climate system and marine ecological environment, as well as the heat budget and mass balance of sea ice itself. [ABSTRACT FROM AUTHOR]

The North Atlantic and Arctic Oceans are unquestionably major players in the climatic evolution of the Northern Hemisphere and in the history of the meridional overturning circulation of the Atlantic Ocean. The establishment of the modern North Atlantic Water (NAW) transporting heat, salt, and moisture to the Northern Hemisphere has been indicated as one of the main forcing mechanisms for the onset of Northern Hemisphere glaciation. NAW controls the extent and dynamics of circum-Arctic and circum-North Atlantic ice sheets and sea ice in addition to deep water and brine production. How the ocean system and cryosphere worked during past warmer intervals of high insulation and/or high atmospheric CO2 content is still largely unknown and debated. The required information can only be attained by offshore scientific drilling in highresolution continuous expanded sedimentary sequences identified on the western continental margin of Svalbard (and eastern side of the Fram Strait) along the main pathway and northern penetration of the NAW flowing into the Arctic Ocean. The area around Svalbard is very sensitive to climatic variability and can be considered a sentinel of climate change. Furthermore, the reconstruction of the dynamic history of the marine-based paleo-Svalbard-Barents Sea Ice Sheet is important because it is considered the best available analog to the modern, marine-based West Antarctic Ice Sheet, for which the loss of stability is presently the major uncertainty in projecting future global sea level rise in response to the present global climate warming. [ABSTRACT FROM AUTHOR]

Global mean sea level has been rising at a rate of 3.25 ± 0.4 mm yr−1 over 1993–2018. Yet several regions are increasing at a much faster rate, such as the Beaufort Gyre in the Arctic Ocean at a rate of 9.3 ± 7.0 mm yr−1 over 2003–2014. At interannual to decadal time scales, the Beaufort Gyre sea level is controlled by salinity changes due to sea ice melt and wind‐driven lateral Ekman convergence–divergence of freshwater. This study uses recent Greenland discharge and river runoff estimates to isolate and quantify the sea level response to freshwater fluxes variability over the period 1980–2018. It relies on sensitivity experiments based on a global ocean model including sea‐ice and icebergs. These sensitivity experiments only differ by the freshwater fluxes temporal variability of Greenland and global rivers which are either seasonal climatologies or fully time varying, revealing the individual and combined impact of these freshwater sources fluctuations. Fully varying Greenland discharge and river runoff produce an opposite impact on sea level trends over 2005–2018 in the Beaufort Gyre region, the former driving an increase, while the latter, a decrease. Their combined impact leads to a fairly weak sea level trend. The sea level response is primarily driven by salinity variations in the upper 300 m, which are mainly caused by salinity advection involving complex compensations between passive, active, and nonlinear advection. This study shows that including the temporal variability of freshwater fluxes in forced global ocean models results in a better representation of regional sea level change. Plain Language Summary: Sea level is rising globally but not at the same rate everywhere. In the Arctic Ocean, the Beaufort Gyre sea level has been increasing at a fast rate of 9.3 ± 7.0 mm yr−1 over 2003–2014. At long time scales, the Beaufort Gyre sea level change is controlled by salinity, which depends mainly on continental freshwater runoff—particularly high in this region—and sea ice melt. This study uses recent estimates of Greenland discharge and river runoff in a global ocean model. The aim is to isolate and quantify the sea level response of the Beaufort Gyre to freshwater fluxes variability. We compare numerical simulations where Greenland discharge and river runoff are fully varying or set to a repeated seasonal cycle to reveal the individual and combined impacts of the variability of these freshwater sources on regional sea level. Both Greenland discharge and global river runoff impact remotely the Beaufort Gyre sea level. They induce salinity variations in the upper 300 m of the gyre through salinity advection. This study highlights the importance of the variability of continental freshwater fluxes in models in order to better represent regional sea level variability. Key Points: Greenland discharge and river runoff variability contribute to sea level rise and fall in the Beaufort GyreThe positive impact of Greenland is greater than the negative impact of rivers in the 0–78‐m range, and vice versa in the 78–300‐m rangeSea level change in the sensitivity experiments is mostly halosteric with salinity changes mainly controlled by advection [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.

Differences in the composition and spatial distribution of Fluorescent Dissolved Organic Matter (FDOM) between western and eastern Greenland shelf waters reflect the interplay of distinct regional environmental drivers-such as glacial meltwater inputs and stratification effects – which shape local DOM processing and biogeochemical cycles. These contrasts provide unique opportunity to understand how Arctic coastal system responds to climatic changes. To investigate these dynamics, we assessed FDOM by an application of multivariate statistical method - Parallel Factor Analysis (PARAFAC) on samples collected in July 2021 and August 2022. The PARAFAC enabled the distinction of five components representing both humic-like (C1 (λEx/λEm 318/392), C2 (λEx/λEm 363(261)/445), C5 (λEx/λEm 399/513)) and protein-like (C3 (tyrosine) − λEx/λEm 267/305, (C4 (tryptophan) − λEx/λEm 285/345)) substances, showing variations between western and eastern shelves and across different water layers (surface, deep chlorophyll a maximum depth – DCM, and below it (i.e., in the West Slope Greenland Core water – WSGC, and in the core Polar Water - PW). The analysis showed that western DOM is almost equally composed of humic-like (51%) and protein-like (49%) substances, while the eastern shelf is dominated by protein-like FDOM (56%), indicating a stronger influence of autochthonous production in the east. The highest fluorescence intensity was measured of the protein-like component C3 in both eastern (PW layer) and western (DCM layer) shelves. In the surface waters of the western Greenland shelf we found a statistically significant (p

Studying primary biological aerosol particles in the Arctic is crucial to understanding their role in cloud formation and climate regulation at high latitudes. During the Arctic Ocean 2018 expedition, fluorescent primary biological aerosol particles (fPBAPs) were observed, using a multiparameter bioaerosol spectrometer, near the North Pole during the transition from summer to early fall. The fPBAPs showed a strong correlation with the occurrence of ice nucleating particles (INPs) and had similar concentration levels during the first half of the expedition. This relationship highlights the potential importance of biological sources of INPs in the formation of mixed-phase clouds during the central Arctic’s summer and early fall seasons. Our analysis shows that the observed fPBAPs were independent of local wind speed and the co-occurrence of other coarse mode particles, suggesting sources other than local sea spray from leads, melt ponds, re-suspension of particles from the surface, or other wind-driven processes within the pack ice. In contrast, other fluorescent particles were correlated with wind speed and coarse mode particle concentration. A multi-day event of high concentrations of fPBAPs was observed at the North Pole, during which the contribution of fPBAPs to the total concentration of coarse mode aerosol increased dramatically from less than 0.1% up to 55%. Analysis of chemical composition and particle size suggested a marine origin for these fPBAPs, a hypothesis further supported by additional evidence. Air parcel trajectory analysis coupled with ocean productivity reanalysis data, as well as analysis of large-scale meteorological conditions, all linked the high concentrations of fPBAPs to biologically active, ice-free areas of the Arctic Ocean.

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.

Breaks (ruptures) and cracks is the distinguishing feature of any ice cover in the Arctic seas during the cold season and in the whole Arctic Basin throughout a year. The formation of them is a consequence of macro-deformation of the ice thickness. Investigating of the ice breaking in the Arctic begins with single visual observations during the ice aerial surveys in the 1940s and continues till nowadays using regular information from artificial Earth satellites. Processing of big volumes of satellite data and creating climatological datasets on breaks became possible owing to the development of algorithms for automatic identification of the ice breaks in images. Interpretation of the satellite images is based on the fundamental difference between physical properties of breaks and the surrounding consolidated ice. Algorithms for automatic recognition of ruptures using satellite data obtained in different wavelength ranges, including the use of artificial intelligence, are currently being developed. The main characteristics of breaks which are usually analyzed are as follows: the summarized area of them and its ratio to the total area of the ice field, the mean and maximum widths as well as the total length. The temporal and spatial variability of these characteristics is also considered. Such information is needed for solving problems of improving models of ice cover dynamics and modeling the interaction between the ocean and the atmosphere at high latitudes. A specific feature of publications of the Russian authors on this topic is the practical use of the results obtained for hydrometeorological support of navigation in ice. For the navigation purposes, the dominant orientation of the ruptures on the way of ships is of greatest importance. Operational and prognostic information about the orientation and extent of ruptures, including distribution of them in an ice field are the key data for choosing the optimal sailing route in the Arctic.

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.

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.

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 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 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]