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The Ising model, initially proposed about 100 years ago to explain ferromagnetism and phase transitions, has become a central pillar of statistical physics and a powerful tool for diverse applications in other fields including environmental studies. In this paper, we introduce continuous spin values between −1 and +1 to a two-dimensional Ising model and utilize the generalized Ising lattice to simulate the dynamics of sea ice/water transition for a large area of 1500 km by 1500 km in the Arctic region. The simulation process follows the Metropolis-Hastings algorithm and incorporates an innovative factor to account for the inertia of spin value changes. Using the sea ice concentration data collected by the National Snow and Ice Data Center, our results exhibit striking similarity between the simulated and the observed ice melting and freezing dynamics, and two numerical measures from the simulation—the ice coverage percentage and the ice extent—match closely with the data statistics. Moreover, the model's best-fit parameters demonstrate the substantial impact of the external forces, which can be further enriched and linked to the environmental factors in other climate change research. [ABSTRACT FROM AUTHOR]

Freezing temperature parameterization significantly impacts the heat balance at sea‐ice bottom and, consequently, the simulated sea‐ice thickness. Here, the single‐column model ICEPACK was used to investigate the impact of the freezing temperature parameterization on the simulated sea‐ice thermodynamic growth during the MOSAiC expedition from October 2019 to September 2020. It is shown that large model errors exist with the standard parameterization and that different formulations for calculating the freezing temperature impact the simulated sea‐ice thickness significantly. Considering the winter mixed layer temperature, a modified parameterization of the freezing point temperature based on Mushy scheme was developed. The mean absolute error (ratio) of simulating sea‐ice thickness for all buoys reduces from 7.4 cm (4.9%) with the "Millero" scheme, which performs the best among the existing schemes in the ICEPACK model, to 4.2 cm (2.9%) with the new developed scheme. Plain Language Summary: The heat transferred from the ocean to the sea‐ice influences the growth and melting of the sea‐ice. Freezing temperature is an essential parameter for calculating the heat transfer. Nevertheless, few studies have attempted to evaluate the impact of different freezing temperature parameterizations on the simulated sea‐ice thermodynamic growth. This study uses observed atmosphere and ocean data to force a single‐column model. Using different methods to calculate the freezing temperature significantly impacts the simulated sea‐ice thickness. After a series of testing and comparisons, we have developed a modified parameterization of freezing temperature that significantly reduces the simulation deviation from the observations. Key Points: Different parameterizations of the freezing temperature significantly influence the simulated sea‐ice thicknessA modified‐Mushy parameterization method is developed for the freezing temperature, significantly improving ice thickness simulation [ABSTRACT FROM AUTHOR]

In March and April 2021, buoys were deployed in the Beaufort Sea, Arctic Ocean, to measure sea‐ice horizontal deformation over spatial scales that had not been previously achieved. Geodetic‐quality position measurements allowed measurements of strain‐rate over lengths from about 200 m to 2 km. Conventional ice‐drifters extended spatial coverage up to about 100 km. Past studies find there is multi‐fractal behavior for horizontal sea‐ice deformation from 10 to 1,000 km. Our results demonstrate that such behavior does not hold when including spatial scales below 10 km. We find that sea‐ice deformation is not scale invariant between the scale of individual sea‐ice floes and aggregates of floes. Therefore, we cannot expect the same physical laws or forcing to describe sea‐ice kinematics over these regimes, nor can we assume log‐log linear behavior for mean deformation. Using this scaling behavior as a metric to validate models that resolve sea ice floes and their interactions is hence not recommended. Plain Language Summary: In March and April of 2021, a nested array of buoys was deployed around a drifting camp on sea ice 50 km off‐shore in the Beaufort Sea, Arctic Ocean. The inner buoys of the array measured their position with centimeter‐level accuracy allowing for measurements of sea ice deformation at a wide range of spatial scales. Sea ice deformation includes the opening and closing of the ice and shearing motion that occurs along cracks in the ice known as leads and ridges. This experiment was the first time that sea‐ice deformation has been analyzed over scales from 100s of meters to 100s of kilometers. Past studies over areas spanning more than 10 km suggest that the sea‐ice deformation has fractal behavior, a mathematical relationship where the rates of deformation increase as you measure over increasingly smaller regions. Past measurements of deformation over smaller areas found a different fractal behavior. In this study, we find that the mathematical relationship does not fit observations across any region larger than a kilometer square. We conclude that sea‐ice deformation is not fractal and caution against assuming that this relationship exists for climate and forecast modeling. Key Points: Results from the first field experiment measuring sea‐ice deformation across spatial scales ranging from 200 m to over 100 km are presentedPrevious studies indicate sea‐ice deformation is multi‐fractal for scales above 10 km, and we find this does not holdOver spatial scales from 1 to ∼100 km, deformation does not scale log‐log linearly with separation distance, and is not fractal [ABSTRACT FROM AUTHOR]

The last glacial inception (LGI) marks the transition from the interglacial warm climate to the glacial period with extensive Northern Hemisphere ice sheets and colder climate. This transition is initiated by decreasing boreal summer insolation but requires positive feedbacks to stimulate the appearance of perennial snow. We perform simulations of LGI with climate model AWI‐ESM‐2.1, forced by the astronomical and greenhouse gas forcing of 115,000 years before present. To compare with the preindustrial (PI) simulation, we use a consistent definition of the seasons during the LGI and the PI and evaluate model output on an angular astronomical calendar. Our study reveals a prominent role of the sea‐ice albedo feedback to amplify the delayed climate signal at polar latitudes. Through a radiative budget analysis, we examine that the ice‐albedo feedback exceeds the shortwave radiative forcing, contributing to the cooling and high latitude snow built‐up during LGI. Plain Language Summary: The onset of the last ice age marks the transition from the interglacial warm climate to the ice age with extensive Northern Hemisphere (NH) ice sheets and colder climate. This transition is initiated by decreasing boreal summer irradiance and reinforced by positive feedbacks. We perform climate simulations under the astronomical and greenhouse gas forcing, and use a consistent definition of seasons. Our study shows that a delayed ice‐albedo feedback plays an important role in generating a cold NH climate. Key Points: Climate simulations reveal year‐round cooling in the Northern Hemisphere high latitudes during the last glacial inceptionA refined angular calendar provides a tool to analyze the seasonal dynamicsWe identify the crucial role of the albedo feedback on the high‐latitude radiative budget [ABSTRACT FROM AUTHOR]

Summertime Greenland blocking (GB) can drive melting of the Greenland ice sheet, which has global implications. A strongly increasing trend in GB in the early twenty‐first century was observed but is missing in climate model simulations. Here, we analyze the temporal evolution of GB in nearly 500 members from the CMIP6 archive. The recent period of increased GB is not present in the members considered. The maximum 10‐year trend in GB in the reanalysis, associated with the recent increase, lies almost outside the distributions of trends for any 10‐year period in the climate models. GB is shown to be partly driven by the sea surface temperatures and/or sea ice concentrations, as well as by anthropogenic aerosols. Further work is required to understand why climate models cannot represent a period of increased GB, and appear to underestimate its decadal variability, and what implications this may have. Plain Language Summary: An increasing trend in summertime atmospheric blocking over Greenland was observed during the early twenty‐first century. However, this trend is not reproduced in climate models. This may have important implication for climate change projections, as summertime Greenland blocking drives the melting of its ice sheet which is a major contributing factor to global sea level rise. Here, recent trends in Greenland blocking are assessed in nearly 500 ensemble members from a large archive of state‐of‐the‐art climate models. We find that a recent increasing trend like that observed is absent in all of the ensemble members, and a trend of such magnitude is very unlikely to be simulated in them, which suggests a deficiency in the climate model simulation of Greenland blocking. The model simulations do however suggest that Greenland blocking is partly forced by sea surface temperatures/sea ice concentrations and/or anthropogenic aerosols, but the response of the models to these forcings may be too weak. These results provide new understanding on drivers of Greenland blocking in climate models and offer avenues for model development designed to improve simulations of Greenland climate. Key Points: The observed rapid increase in summertime Greenland blocking during the first decade of the twenty‐first century has not continuedA period of increased summer Greenland blocking of similar magnitude to observed is rarely reproduced in a large ensemble of climate modelsDecadal variability in Greenland blocking in climate models is partly driven by SST/sea ice and/or anthropogenic aerosols [ABSTRACT FROM AUTHOR]

The role of internal variability in generating an apparent link between autumn Barents‐Kara sea (BKS) ice and the winter North Atlantic Oscillation (NAO) has been intensely debated. In particular, the robustness and causality of the link has been questioned by showing that BKS‐NAO correlations exhibit nonstationarity in both reanalysis and climate model simulations. We show that the lack of ice observations means nonstationarity cannot be confidently assessed using reanalysis prior to 1961. Model simulations are used to corroborate an argument that forced nonstationarity could result from ice edge changes due to global warming. Consequently, the observed change in BKS‐NAO correlations since 1960 might not be purely a result of internal variability and may also reflect that the ice edge has moved. The change could also reflect the availability of more accurate ice observations. We discuss potential implications for analysis based on coupled climate models, which exhibit large ice edge biases. Plain Language Summary: Does the amount of ice in the Barents‐Kara Sea influence European air pressure or are the patterns we see caused by random changes in the weather? In climate models and in estimates of the atmosphere's history these patterns change depending on which years we look at. This has been interpreted as evidence that the patterns are random. However, there are very few measurements of ice in this region before 1961, so we argue that looking at these years is not helpful. Since 1961, where we have more measurements, the winter sea ice edge has been moving Northwards because of global warming. When the ice in a particular region disappears, it changes the expected relationship with the atmosphere because heat can now quickly leave the ocean. We therefore hypothesize that some of the changes seen in the patterns may therefore not be random, but a result of ice edge changes. We also observe that different climate models put the ice edge in different places, and the same hypothesis therefore implies that models might not get potential ice‐air pressure relationships in specific regions correct. Key Points: A lack of observations means that ice‐NAO links cannot be confidently assessed with reanalysis prior to 1961Nonstationarity since 1961 may reflect forced changes to the ice edge, due to the dependence of heatflux anomalies on ice edge variabilityThe magnitude of this potential forced nonstationarity in the real world is currently unclear [ABSTRACT FROM AUTHOR]

The response to Antarctic sea ice loss within a coupled modeling framework is examined in comparison to the response to Arctic sea ice loss and within the context of general greenhouse warming. Sea ice loss responses are found to be linear (particularly in response to Antarctic or global sea ice loss) with respect to the degree of imposed perturbation and additive when perturbations are applied in hemispheres separately and concurrently. Globally, and in the tropical Pacific in particular, Antarctic sea ice loss plays a relatively larger role than Arctic sea ice loss in both the atmosphere and the ocean, within the parameters of our experiments. The pattern of response to Antarctic sea ice loss is also found to more closely resemble that of greenhouse warming, again particularly in the tropics. An extension to multiparameter pattern scaling is developed to include a scaling factor for Antarctic change in addition to those for tropical warming and Arctic sea ice loss. The decomposition is applied to the modeled response to Antarctic sea ice loss to break it down into component partial responses that scale with Antarctic, tropical, and Arctic changes. This reveals the aspects of the response that are directly related to Antarctic change, such as an equatorward intensification of tropical precipitation in the Northern Hemisphere, and those that are modified via the induced changes in the tropics and Arctic, such as Northern Hemisphere temperature change. With this, we hope to gain a deeper understanding of the role of each of these changes for the development of physical mechanisms of the response. [ABSTRACT FROM AUTHOR]

Among nine La Niña events since 1980, there are seven double-peaked La Niña events that typically persist for 2 years and peak twice in the two consecutive boreal winters. In the study, the individual impacts of the first and second peak episodes of such La Niña on the Antarctic sea ice in austral spring (September–November) were compared. The results suggest a difference. The first episode induces a tripolar distribution of sea ice concentration (SIC) with a negative anomaly in the Bellingshausen Sea sandwiched with positive anomalies in the Ross Sea and the northeastern Weddell Sea. The second causes an SIC reduction in most parts of the Southern Ocean except for the eastern Ross–western Amundsen Seas where an increase is observed. Mechanistically, the first episode forces one single Rossby wave train to propagate southeastward, causing a strong cyclone anomaly over the eastern Ross–Amundsen–Bellingshausen Seas along with a weak anticyclone over the Weddell Sea. In comparison, the second La Niña excites two branches of Rossby wave trains emanating from the southeastern tropical Indian Ocean and the central equatorial Pacific, respectively, which induce three anomalous anticyclones and two anomalous cyclones over the Southern Ocean. These different atmospheric circulation anomalies shape their different sea ice distributions between the two La Niña episodes through both dynamic and thermodynamic processes. The modeling results from CAM5 verify these differences. Significance Statement: Under global warming, the double-peaked La Niña occurs more frequently. The first and second La Niña episodes in such double-peaked La Niña are distinct from each other not only in their onset and developing mechanisms but also in their climate impacts. Based on observational analyses and model experiments, the study investigated the distinctive impacts of the first and second episodes on the austral spring Antarctic sea ice. The results reveal that the first episode excites one single southeastward-propagated Rossby wave train, while the second episode forces two branches of Rossby wave trains. These different atmospheric responses in the Southern Hemisphere shape the distinct sea ice distributions both dynamically and thermodynamically. The study also indicates the diversity of tropical–Antarctic teleconnections. [ABSTRACT FROM AUTHOR]

Climate change is anticipated to have long-term and pervasive effects on marine ecosystems, with cascading consequences to many ocean-reliant sectors. For the marine fisheries sector, these impacts can be further influenced by future socio-economic and political factors. This raises the need for robust projections to capture the range of potential biological and economic risks and opportunities posed by climate change to marine fisheries. Here, we project future changes in the abundance of eight commercially important fish and crab species in the eastern Bering Sea and Chukchi Sea under different CMIP6 Shared Socioeconomic Pathways (SSPs) leading to contrasting future (2021–2100) scenarios of warming, sea ice concentration, and net primary production. Our results revealed contrasting patterns of abundance and distribution changes across species, time periods and climate scenarios, highlighting potential winners and losers under future climate change. In particular, the least changes in future species abundance and distribution were observed under SSP126. However, under the extreme scenario (SSP585), projected Pacific cod and snow crab abundances increased and decreased, respectively, with concurrent zonal and meridional future shifts in their centers of gravity. Importantly, projected changes in species abundance suggest that fishing at the same distance from the current major port in the Bering Sea (i.e., Dutch Harbor) could yield declining catches for highly valuable fisheries (e.g., Pacific cod and snow crab) under SSP585. This is driven by strong decreases in future catches of highly valuable species despite minimal declines in maximum catch potential, which are dominated by less valuable taxa. Hence, our findings show that projected changes in abundance and shifting distributions could have important biological and economic impacts on the productivity of commercial and subsistence fisheries in the eastern Bering and Chukchi seas, with potential implications for the effective management of transboundary resources. [ABSTRACT FROM AUTHOR]

The new permanent seismic station SVZ started working in Arctic (Severnaya Zemlya archipelago, Bolshevik Island), we discuss the first results of the local seismicity study. We have processed 46 local seismic events for 2017–2022. Data processing using a single seismic sensor is difficult, but using waveforms and spectral-temporal analysis of P, S, and surface waves, it is possible to separate shallow earthquakes from glacial events. We distinguish two types of icequakes—glacier-related events and pulses. An increase in seismic background noise is related to processes of glacial nature in summertime. Data processing allows to obtain the main peculiarities of local seismicity, i.e., mutual connection of glacial processes and crustal seismicity. We show the presence of icequakes induced by local crustal events; their epicenters confined to the ice domes edges. Spatio-temporal sequence and the rate of events migration show that the glacial events are a result of the defusing deformations process in the glaciers caused by the impact of shallow tectonic earthquakes. Thousands of pulsed and high-frequency micro-oscillations associate with the sea ice sheet or lake ice. The temporal variation of events' number and energy per day correlates with air temperature temporal variations. Moreover, there is a sharp increase in the number of pulses with sharp temperature changes. The greatest activity of this pulsed events is in winter and especially in March, connected with ice surface destruction. In case a network deployment is not feasible, even a single seismic station allows to get a useful information about the glacial and seismic processes. [ABSTRACT FROM AUTHOR]

There is a heightened risk of an oil spill occurring in the Arctic, as climate change driven sea ice loss permits an increase in Arctic marine transportation. The ability to detect an oil spill and monitor its progression is key to enacting an effective response. Microwave scatterometer systems may be used detect changes in sea ice thermodynamic and physical properties, so we examined the potential of C-band polarimetric radar for detecting diesel fuel beneath a thin sea ice layer. Sea ice physical properties, including thickness, temperature, and salinity, were measured before and after diesel addition beneath the ice. Time-series polarimetric C-band scatterometer measurements monitored the sea ice evolution and diesel migration to the sea ice surface. We characterized the temporal evolution of the diesel-contaminated seawater and sea ice by monitoring the normalized radar cross section (NRCS) and polarimetric parameters (conformity coefficient (μ), copolarization correlation coefficient (ρco)) at 20° and 25° incidence angles. We delineated three stages, with distinct NRCS and polarimetric results, which could be connected to the thermophysical state and the presence of diesel on the surface. Stage 1 described the initial formation of sea ice, while in Stage 2, we injected 20L of diesel beneath the sea ice. No immediate response was noted in the radar measurements. With the emergence of diesel on the sea ice surface, denoted by Stage 3, the NRCS dropped substantially. The largest response was for VV and HH polarizations at 20° incidence angle. Physical sampling indicated that diesel emerged to the surface of the sea ice and trended towards the tub edge and the polarimetric scatterometer was sensitive to these physical changes. This study contributes to a greater understanding of how C-band frequencies can be used to monitor oil products in the Arctic and act as a baseline for the interpretation of satellite data. Additionally, these findings will assist in the development of standards for oil and diesel fuel detection in the Canadian Arctic in association with the Canadian Standards Association Group. [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 Arctic Beaufort Gyre plays a critical role in climate and marine ecosystems. This study investigates the response of the liquid freshwater in the Beaufort Gyre to various wind perturbations using numerical simulations. A new diagnostic called "freshwater renewal" is introduced, which quantifies the amount of freshwater that has entered the Beaufort Gyre since a specific point in time. The findings reveal that the process of freshwater renewal is persistently efficient in the Beaufort Gyre region, occurring irrespective of the gyre's status. The spatial distribution of freshwater renewal varies, influenced by factors such as wind forcing and gyre circulation patterns. Cyclonic wind perturbation associated with a negative Beaufort high sea level pressure anomaly triggers freshwater release from the Beaufort Gyre, with freshwater export and renewal dependent on wind-perturbation locations and time scales. While some released Beaufort Gyre freshwater exits the Arctic Ocean through the Davis and Fram Straits, a considerable portion could remain within the Arctic Ocean for many years under specific conditions. Wind perturbation associated with the positive Arctic Oscillation enhances the Arctic export of Beaufort Gyre freshwater, mainly through the Fram Strait. The Arctic export of total freshwater and the Arctic export of the portion originating from the Beaufort Gyre have different time scales and magnitudes. Hence, it is essential to collectively examine different freshwater components in order to assess the role of Arctic export in the climate system. [ABSTRACT FROM AUTHOR]

Many previous studies have examined the influence of Arctic sea ice on the weather/climate of the Northern Hemisphere. However, the precursor signals of Arctic sea ice regarding East Asian winter low temperatures, which are important for climate prediction, have received little attention. This study identified an out‐of‐phase relationship between the autumn sea ice area of the Kara Sea (SICK) and subsequent winter minimum temperature in Northeast China (NEC) during 1979–2019, that is, diminished SICK facilitates cooling anomalies at NEC. Further results showed that the Arctic Oscillation (AO) acts as a bridge in the linkage between the autumn SICK and minimum temperature in NEC. Diminished autumn SICK leads to a weakened polar vortex in both the troposphere and the stratosphere in the subsequent winter through vertical propagation of planetary waves, contributing to a negative phase of the AO. Accordingly, the SICK is followed by anomalous Rossby wave train that originates from Mediterranean Sea and propagates eastward to Northeast Asia. Thus, the SICK has substantially influences on the Mongolia cyclone and minimum temperature in NEC by modulation of the AO. Moreover, the shrinking SICK could lead to the upper‐level decelerated westerly anomalies at East Asia through altering the equator‐to‐pole temperature gradient and induce negative minimum temperature anomalies at NEC. The results of this study have importance regarding the prediction of low temperature anomalies over NEC. [ABSTRACT FROM AUTHOR]

Bacterial strains isolated from root nodules of the legume plant Hedysarum arcticum B. Fedtsch growing on Samoylov Island in the Lena River delta (Arctic zone of Yakutia) were assigned to the genera Rhizobium (family Rhizobiaceae) and Mesorhizobium (Phyllobacteriaceae) of the order Hyphomicrobiales (class Alphaproteobacteria) according to the rrs gene sequencing data. According to phylogenetic analysis of concatemers of the atpD, dnaK, gyrB, and rpoB genes, the strains belonged to the species Rhizobium giardinii and Mesorhizobium norvegicum. The strains were shown to be facultative psychrotrophs growing at 5 and 28°C. These microsymbionts are promising for further study of their symbiotic efficiency regarding other forage legume species, with an aim to establish highly productive agrophytocenoses in the Far North. [ABSTRACT FROM AUTHOR]

The abundance and diversity of filamentous fungi in the bottom sediments of the Arctic Ocean seas (the Greenland, Barents, and Kara seas) were studied. Samples of the surface bottom sediments were collected during the 84th (July–August 2021) and 86th (October–November 2021) cruises of RV Akademik Mstislav Keldysh. The taxonomic affiliation of the isolated fungi was determined using polyphasic taxonomy. The isolated fungi belonged to 16 genera of different classes of ascomycetous, basidiomycetous, and zygomycetous fungi. The effect of cultivation temperature and different NaCl concentrations on fungal growth was determined, as well as the effect of cultivation conditions on the fatty acid profile for the strains capable of growth on media with increased osmotic potential. While fatty acid composition was shown to be affected by changes in environmental conditions, the response to osmotic stress differed among the studied cultures from deep-sea sediments. [ABSTRACT FROM AUTHOR]

This study presents a systematic literature review of ice load measurements on dams. Several hypotheses about the relationship between the maximum ice load and external variables are tested using regression analysis on the data collected from the literature. The performed tests show that ice thickness, water level change category, and dam height are factors that have a significant and relevant relationship with the magnitude of all measured ice loads. The ice thickness is the only tested variable that also shows a significant and relevant relationship with differences in ice load between winters at one dam. The variation in recorded ice load from several sensor positions at one dam during the same winter is considerable. Generally, the difference between the sensor area and the structure–ice interaction area is large, resulting in extensive extrapolation and uncertainties regarding the representativeness of the measured results. [ABSTRACT FROM AUTHOR]

The ice-associated nematode Theristus melnikovi has a long-distance dispersal throughout the Arctic. However, this species' taxonomic position and phylogenetic relationships remain unresolved. We used an integrative approach of single-specimen barcoding of morphologically identified specimens of T. melnikovi with note on the phylogeny of two new ice-associated species of the family Xyalidae. DNA barcodes (18S and 28S gene markers) were obtained from 13 specimens of T. melnikovi collected from sea ice in the White and Kara Seas. Analysis of the D2D3 region found three genetically distinct lineages of T. melnikovi from the White Sea ice, suggesting that T. melnikovi specimens belong to the cryptic species, with genetic differentiation attributed to limited ice exchange between remote semi-isolated areas and open Arctic seas. The Kara Sea specimens belong to a single species. Our results highlight that using 18S rDNA data alone underestimates species diversity within sympagic nematodes. The barcoded specimens of T. melnikovi could not be distinguished morphologically, as the majority of the sequenced specimens were juveniles (92.3%). Additional comparative analysis of morphological traits was performed on 34 specimens from sea ice in the Barents, White, Kara, and East Siberian Seas, and from sediment in the East Siberian Sea. Our specimens differed from previous descriptions of T. melnikovi by variable body size, amphidial fovea shape, and absence of precloacal supplements and pigment spots. This study contributes to the understanding of the diversity, variability in habitat, and ecology of sympagic nematodes, confirming the need to put together the integration of molecular and morphological methodologies. [ABSTRACT FROM AUTHOR]

Rapid changes in sea ice extent and changes in freshwater inputs from land are rapidly changing the nature of Arctic estuarine ecosystems. In the Beaufort Sea, these nearshore habitats are known for their high productivity and mix of marine resident and diadromous fishes that have great subsistence value for Indigenous communities. There is, however, a lack of information on the spatial variation among Arctic nearshore fish communities as related to environmental drivers. In summers of 2017–2019, we sampled fishes in four estuarine ecosystems to assess community composition and relate fish abundance to temperature, salinity, and wind conditions. We found fish communities were heterogeneous over larger spatial extents with rivers forming fresh estuarine plumes that supported diadromous species (e.g., broad whitefish Coregonus nasus), while lagoons with reduced freshwater input and higher salinities were associated with marine species (e.g., saffron cod Eleginus gracilis). West–East directional winds accounted for up to 66% of the community variation, indicating importance of the wind-driven balance between fresh and marine water masses. Salinity and temperature accounted for up to 54% and 37% of the variation among lagoon communities, respectively. Recent sea ice declines provide more opportunity for wind to influence oceanographic conditions and biological communities. Current subsistence practices, future commercial fishing opportunities, and on-going oil and gas activities benefit from a better understanding of current fish community distributions. This work provides important data on fish spatial distributions and community composition, providing a basis for fish community response to changing climatic conditions and anthropogenic use. [ABSTRACT FROM AUTHOR]

Although trends toward earlier ice‐out have been documented globally, the links between ice‐out timing and lake thermal and biogeochemical structure vary spatially. In high‐latitude lakes where ice‐out occurs close to peak intensity of solar radiation, these links remain unclear. Using a long‐term dataset from 13 lakes in West Greenland, we investigated how changing ice‐out and weather conditions affect lake thermal structure and oxygen concentrations. In early ice‐out years, lakes reach higher temperatures across the water column and have deeper epilimnia. Summer hypolimnia are the warmest (~ 11°C) in years when cooler air temperatures follow early ice‐out, allowing full lake turnover. Due to the higher potential for substantive spring mixing in early ice‐out years, a warmer hypolimnion is associated with higher dissolved oxygen concentrations. By affecting variability in spring mixing, the consequences of shifts in ice phenology for lakes at high latitudes differ from expectations based on temperate regions. [ABSTRACT FROM AUTHOR]

Among polar bears (Ursus maritimus), only parturient females den for extended periods, emerging from maternal dens in spring after having substantially depleted their energy reserves during a fast that can exceed 8 months. Although den emergence coincides with a period of increasing prey availability, polar bears typically do not depart immediately to hunt, but instead remain at the den for up to a month. This delay suggests that there are likely adaptive advantages to remaining at the den between emergence and departure, but the influence of the timing and duration of this post-emergence period on cub survival has not been evaluated previously. We used temperature and location data from 70 denning bears collared within the Southern Beaufort Sea and Chukchi Sea subpopulations to estimate the phenology of the post-emergence period. We evaluated the influence of various spatial and temporal features on duration of the post-emergence period and evaluated the potential influence of post-emergence duration on litter survival early in the spring following denning. For dens that likely contained viable cubs at emergence (n = 56), mean den emergence occurred on 16 March (SE = 1.4 days) and mean departure on 24 March (SE = 1.6 days), with dates typically occurring later in the Chukchi Sea relative to Southern Beaufort Sea and on land relative to sea ice. Mean duration of the post-emergence period was 7.9 days (SE = 1.4) for bears that were observed with cubs later in the spring, which was over 4 times longer than duration of those observed without cubs (1.9 days). Litter survival in the spring following denning (n = 31 dens) increased from 0.5 to 0.9 when duration of the post-emergence period increased by ~4 days and other variables were held at mean values. Our limited sample size and inability to verify cub presence at emergence suggests that future research is merited to improve our understanding of this relationship. Nonetheless, our results highlight the importance of the post-emergence period in contributing to reproductive success and can assist managers in developing conservation and mitigation strategies in denning areas, which will be increasingly important as human activities expand in the Arctic. [ABSTRACT FROM AUTHOR]

Studying Arctic ice formation stays in the focus of research groups over the past decades in the context of ice cover changes, thermal budget and climate agenda in general. Nevertheless, the phenomenon's underlying mechanisms are still not completely understood and described. The main reason for the lack in understanding is the limited experimental access to the field data when it comes to the processes that occur below the ice floe. Thus, there is a need to build competent analogies between the natural (ocean water–ice) and laboratory (here: binary alloy) conditions of the experiment as a step of data preparation for the verification of the mathematical model. In the current paper, the existing qualitative models describing the process of melting and crystallization were expanded and the experimental method was developed copying the layering of the natural ocean water–ice mixture. The experimental set‐up for studying the solidification within the intermediate zone was designed for Al–Cu alloys being the system with appropriate solidus line for creating a sufficient concentration gradient and by that temperature dependent phase fraction under isothermal conditions. The gained experimental data were used for validating a binary phase‐field model for solidification considering moving boundaries. The model includes the description of the free energy of both phases and their respective diffusion coefficients. It allows modeling a binary system at a mesoscopic spatial level by including the concentration‐driven phase transition and resolidification in the two‐phase region. The novel results will help the quantitative understanding of solidification phenomena and are highly‐evaluated from interdisciplinary point of view, including glaciology and geosciences, being ultimately significant for the understanding the global climate change landscape. [ABSTRACT FROM AUTHOR]

The Arctic sea ice cover has decreased rapidly over the last few decades both in extent and thickness. Here we present multi‐year (2013–2022) observations of sea ice thickness in the northwestern Barents Sea based on Upward Looking Sonar measurements and show that the winter sea ice has become thicker over the last decade. Sea ice thickness from the Pan‐Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) reproduces both the observed variability and recent 10‐year trend and shows that this thickening (0.24 m decade−1) has not been seen since the 1990s. Using PIOMAS we find that the recent increase in sea ice thickness can be explained by increased sea ice freezing as a result of lower temperatures in the ocean and in the atmosphere. The recent thickening is set in the context of a long‐term thinning trend, with PIOMAS showing much thinner ice now than in the 1980s. Plain Language Summary: The Arctic sea ice cover is becoming smaller and thinner due to global warming. We have measured sea ice thickness in the Barents Sea since 2013, and find that the ice thickness has increased since the measurements were initiated, contrary to what we would expect in a warming world. The Arctic sea ice cover can, however, increase for periods typically up to a decade due to natural climate variability. We find that increased sea ice formation due to lower ocean and air temperatures has caused the recent thickening of the ice cover. We also find that the Barents Sea ice thickness has decreased since the 1980s, and despite the recent thickening, the ice cover is much thinner now than it used to be. Key Points: Upward Looking Sonar measurements in the Barents Sea show increased sea ice thickness during the last decadeIn an ice‐ocean reanalysis (PIOMAS) the recent thickening is due to increased ice freezing, associated with lower ocean and air temperaturesThe long‐term thickness trend is negative, meaning that despite recent thickening, ice is now much thinner than in the 1980s [ABSTRACT FROM AUTHOR]

Antarctic Bottom Water (AABW) transports surface nutrients deep into the ocean, sequestering them for centuries. Enhancing its biological carbon fixation could augment carbon sinks and reduce atmospheric CO2. Yet, it is uncertain if AABW receives enough light for significant photosynthesis before subducting. Using Lagrangian particle tracking in an ocean sea‐ice model, we found: (a) 70% (66%–73%, depending on euphotic zone (Zeu) criteria) nutrient rich circumpolar deep water never enters the Zeu before becoming AABW. This percentage varies from 70% to 91%, depending on the mixed layer (ML) parameterization adjustments; (b) The remaining particles in the euphotic zone have 39 (34–49, depending on Zeu criteria) days average residence time. The time is not sensitive to ML parameterization strength but turning it off doubles the time; and (c) AABW is mainly exposed to enough light on the Antarctic continental shelf during spring and summer. We conclude that the potential of biotic carbon sequestration in AABW is highly limited by light energy. Plain Language Summary: Antarctic Bottom Water (AABW) originates primarily from nutrient‐rich deep waters upwelled around Antarctica. AABW spends a relatively brief time at the sea surface, thus being exposed to comparatively little light energy and leaving a considerable amount of nutrients unused by photosynthetic carbon fixation. If more of these nutrients were utilized through photosynthesis, for example, stimulated by ocean iron fertilization, more atmospheric CO2 could be sequestered in the oceans. Understanding how long AABW stays in the euphotic zone is therefore critical to assess the potential for biologically based CO2 sequestration in the Southern Ocean. To constrain this residence time, we released virtual particles in a high‐resolution ocean model and tracked their trajectories through the Southern Ocean. We found that more than half of the particles are never exposed to sufficient light to enable carbon fixation while the remaining particles are only exposed to relevant light energy for less than 2 months in spring and summer near Antarctica. Our results indicate that the capacity for increasing atmospheric CO2 sequestration in the Southern Ocean near Antarctica is limited by sunlight. Key Points: 30% (27%–34%) of circumpolar deep water (CDW) transforming into Antarctic Bottom Water (AABW) enters the euphotic zone (Zeu), with uncertainty in parentheses based on adjusted Zeu thresholds4.1% (2.8%–6.2%) of the seawater that upwells as CDW and transforms into AABW has ≥4 consecutive weeks in the euphotic zoneThe euphotic zone residence occurred predominantly in spring and summer near Antarctica, with an average duration of 39 (34–49) days [ABSTRACT FROM AUTHOR]

Antarctic ice shelves are losing mass at drastically different rates, primarily due to differing rates of oceanic heat supply to their bases. However, a generalized theory for the inflow of relatively warm water into ice shelf cavities is lacking. This study proposes such a theory based on a geostrophically constrained inflow, combined with a threshold bathymetric elevation, the Highest Unconnected isoBath (HUB), that obstructs warm water access to ice shelf grounding lines. This theory captures ∼ 90% of the variance in melt rates across a suite of idealized process‐oriented ocean/ice shelf simulations with quasi‐randomized geometries. Applied to observations of ice shelf geometries and offshore hydrography, the theory captures ∼80% of the variance in measured ice shelf melt rates. These findings provide a generalized theoretical framework for melt resulting from buoyancy‐driven warm water access to geometrically complex Antarctic ice shelf cavities. Plain Language Summary: The floating extensions of Antarctic glaciers ("ice shelves") are losing ice at drastically different rates. A large component of this ice loss is due to melting from below by relatively warm ocean waters, which typically lie hundreds of meters below the surface. Previous studies have attempted to predict ice shelf melt rates using knowledge of the interface between the ice and the ocean. However, these relationships struggle to capture the variations in melt rates around Antarctica, in part because they do not account for obstruction of warm water access by variations in the shae of the seafloor. In this study we introduce a theory for the rate at which warm waters access Antarctica's ice shelves, which indirectly predicts how much the ice shelf melts. This theory is grounded in the assumption that the ocean flow beneath cavities is dominated by the rotation of the earth, and utilizes a novel quantification of seafloor obstruction of warm water inflows. We show that this theory is successful at predicting melt in simulations of ice shelves of different shapes, and in observations of real ice shelves. This work provides a theoretical grounding for melt resulting from warm subsurface waters flowing underneath Antarctic ice shelves. Key Points: We introduce a new theoretical framework for inflow of warm water into ice shelf cavities based on geostrophically‐constrained circulationA new metric, the Highest Unconnected Isobath (HUB), quantifies bathymetric barriers to warm water access in complex geometriesOur HUB‐informed theoretical framework is able to accurately predict melt rates across a suite of idealized models and observational data [ABSTRACT FROM AUTHOR]

In 2023, Antarctic sea‐ice extent (SIE) reached record lows, with winter SIE falling to 2.5Mkm2 below the satellite era average. With this multi‐model study, we investigate the occurrence of anomalies of this magnitude in latest‐generation global climate models. When these anomalies occur, SIE takes decades to recover: this indicates that SIE may transition to a new, lower, state over the next few decades. Under internal variability alone, models are extremely unlikely to simulate these anomalies, with return period >1000 years for most models. The only models with return period <1000 years for these anomalies have likely unrealistically large interannual variability. Based on extreme value theory, the return period is reduced from 2650 years under internal variability to 580 years under a strong climate change forcing scenario. Plain Language Summary: In 2023, the area of winter Antarctic sea ice fell to the lowest measured since satellite records began in late 1978. It is still under debate how far this low can be explained by natural variations, and how much can be explained by climate change. Global climate models are tools used to study past and predict future global change. We show that, without climate change, the latest generation of these models are extremely unlikely to simulate a sea‐ice reduction from the mean as large as observed in winter 2023. Including strong climate change quadruples the chance of such a reduction, but the chance is still very low. When these rare reductions are simulated, sea ice takes around 10 years to recover to a new, lower, area: this indicates that Antarctic sea ice may transition to a new, lower, state over the next few decades. Key Points: The latest generation of global climate models rarely simulate an Antarctic sea‐ice extent anomaly as negative as observed in winter 2023The return period for such an anomaly is 2650 years under internal variability, decreasing to 580 years under strong climate change forcingAfter the anomaly occurs, sea‐ice extent recovers within a decade to a new, lower state [ABSTRACT FROM AUTHOR]

The cloud feedback may result in amplification or damping of Arctic warming. Two common techniques used to diagnose the top‐of‐the‐atmosphere cloud feedback are the Adjusted Cloud Radiative Effect (AdjCRE) method and the Cloud Radiative Kernel (CRK) method. We apply both to CMIP5 and CMIP6 model data, finding that the AdjCRE calculated Arctic shortwave cloud feedback is twice as correlated with sea ice loss in CMIP5, and four times in CMIP6, as the CRK method. We find that the CRK method produces Arctic all‐sky residual percentages exceeding 20% in 15 of 18 models. We use the CRK method to decompose the feedback in CMIP5 and CMIP6 finding that its median value changed from negative to positive driven by a less‐negative cloud optical depth feedback. Despite its lack of closure, we conclude that the CRK method is better suited for Arctic SW feedbacks as it is less impacted by surface albedo changes. Plain Language Summary: The cloud feedback is the process by which cloud property changes in a warming climate can either further enhance warming or damp it. The Arctic is warming faster than the rest of the globe, and one of the largest sources of uncertainty in its climate projections is the cloud feedback. There are two popular methods to calculate the cloud feedback: the Adjusted Cloud Radiative Effect technique, and the Cloud Radiative Kernel technique. In this paper we compare the two methods in a suite of climate models by considering the extent to which changes in Arctic sea ice impact the cloud feedbacks. From this analysis we conclude that the Cloud Radiative Kernel method is less affected by sea ice loss. We then apply the Cloud Radiative Kernel technique to data from the two most recent generations of global climate models to investigate how polar day Arctic cloud feedbacks have changed between these generations. We find that the median value of these Arctic feedbacks is slightly positive in the newest generation of models, a change from slightly negative in the previous generation that is largely fueled by a weakening of the feedback associated with changes in cloud optical depth. Key Points: The Cloud Radiative Kernel method is less sensitive to surface albedo changes than the Adjusted Cloud Radiative Effect techniqueThe Cloud Radiative Kernel method provides poor radiative closure in a suite of global climate modelsThe median shortwave Arctic cloud feedback in recent climate models is slightly positive due to a weakened cloud optical depth feedback [ABSTRACT FROM AUTHOR]

Global warming is causing rapid changes to the cryosphere. Predicting the future trajectory of the cryosphere requires quantitative reconstruction of its past variations. A recently identified sea-ice-associated haptophyte, known as Group 2i Isochrysidales, has given rise to a new sea-ice proxy with its characteristic alkenone distributions. However, apart from the occurrence of Group 2i Isochrysidales in regions with sea ice, and the empirical relationship between C37:4 alkenone abundance and sea-ice concentration, little is known about the ecology of these haptophyte species. Here, we systematically mapped the spatial and temporal occurrence of known Group 2i Isochrysidales based on environmental DNA in both marine and lacustrine environments. Our results indicate Group 2i is widely distributed in icy marine and lacustrine environments in both Northern and Southern Hemisphere, but is absent in warm environments. Temporally, Group 2i is part of the sea-ice algae bloom during the cold seasons, in contrast to other Isochrysidales that bloom in open waters during warm seasons. Our results indicate that ice is a prerequisite for the occurrence of the psychrophilic Group 2i haptophytes in marine and lacustrine ecosystems and further affirms its value for past ice reconstructions. [ABSTRACT FROM AUTHOR]

The present study investigates the interdecadal change in the interannual relationship between winter sea surface temperature (SST) in the tropical central‐eastern Pacific and the subsequent summer Arctic sea ice concentration (SIC) and its possible mechanism using 1979–2023 monthly SST and SIC data from Hadley Center and atmospheric reanalysis data from NCEP/NCAR. It is found that the relationship between the winter tropical Pacific SST and the subsequent summer SIC of Beaufort Sea experienced an obvious interdecadal change from a significant negative correlation to a weak and insignificant correlation before and after the early 2000s, respectively. Before the early 2000s, when winter SST warming (cooling) anomalies occurred in the central and eastern tropical Pacific, it could sustain into summer and enhance a Rossby wave propagating from Tropic to high latitude, forming negative (positive) pressure anomalies in the North Pacific. Influenced by such anomalies, it is conducive to maintaining negative (positive) SST anomalies in the North Pacific from winter to subsequent summer. The summer SST cooling (warming) in the North Pacific could form a favourable atmospheric circulation anomaly for less (more) SIC. In contrast, after the early 21st century, the strong SST anomalies in winter over the eastern tropical Pacific would weaken with time and subsequently diminish in spring, leading to the SST anomalies in the North Pacific persist to spring, which can hardly affect summer SIC anomaly in the Beaufort Sea. Therefore, the relationship collapses after the the early 2000s due to the weakened persistence of the eastern tropical Pacific SST anomaly. [ABSTRACT FROM AUTHOR]

Commercial GNSS RO products are being touted for their coverage in polar regions where COSMIC-2 observations don't reach. This study seeks to explore their value for Arctic PBL investigations where sufficient lower atmospheric penetration of GNSS RO is vital for representing the persistently shallow PBL. Both NASA purchased commercial RO products, Spire and GeoOptics, have improved lower tropospheric penetration probability over the Arctic Ocean compared to MetOp observations, with Spire having greater volume of observations (nearly two orders of magnitude) compared to GeoOptics. A seasonal cycle is evident in the RO penetration probability (except for Spire) that is found to be related to the water vapor pressure. For winter months, at the 500 m level, which is the standard cut-off threshold used for GNSS RO PBL studies, both products yield a penetration probability of ~80 % of total observations over the Arctic Ocean and up to ~100 % over the frozen sea ice region. As a result, both products are able to sufficiently represent the shallow Arctic PBLH (less than 300 m depth) which is comparable to the PBLH from MERRA-2 reanalysis, unlike MetOp observations which fails to capture PBL heights below 400 m. [ABSTRACT FROM AUTHOR]

The Greenland Ice Sheet is losing mass at increasing rates. Substantial amounts of this mass loss occur by ice discharge which is influenced by ocean thermal forcing. The ice sheet is surrounded by thousands of peripheral, dynamically decoupled glaciers. The mass loss from these glaciers is disproportionately high considering their negligible share in Greenland' overall ice mass. We study the relevance of ocean thermal forcing for ice discharge evolution in the context of this contrasting behaviour. Our estimate of ice discharge from the peripheral tidewater glaciers yields a rather stable Greenland-wide mean of 5.40 ± 3.54 Gt a−1 over 2000–2021. The evolutions of ice discharge and ocean thermal forcing are heterogeneous around Greenland. We observe a significant sector-wide increase of ice discharge in the East and a significant sector-wide decrease in the Northeast. Ocean thermal forcing shows significant increases along the northern/eastern coast, while otherwise unchanged conditions or decreases prevail. For East Greenland, this implies a clear influence of ocean thermal forcing on ice discharge. Similarly, we find clear influences at peripheral tidewater glaciers with thick termini that are similar to ice sheet outlet glaciers. At the peripheral glaciers in Northeast Greenland ice discharge evolution opposes ocean thermal forcing for unknown reasons. [ABSTRACT FROM AUTHOR]

The majority of ice mass loss from Antarctica flows through narrow, fast sliding regions of ice. The lateral boundaries of these regions, termed shear margins, are characterized by lateral shear strains in excess of ∼10−3 yr−1. Shear heating within these margins could warm ice significantly–even to the melting point–but other processes such as lateral advection of cold ice and fabric development compete with this effect. Radar observations can help constrain where temperate ice exists because englacial temperature increases electric conductivity which increases radar attenuation. We utilize the temperature‐dependent attenuation of ice to develop a novel method for constraining englacial temperature in shear margins by combining existing thermal models with very high frequency radar depth‐sounding data. We find evidence supporting temperate shear margins in 18 locations and find evidence for non‐temperate margins in 37 locations, notably in the Amundsen Sea Embayment. Plain Language Summary: Most of the ice lost from Antarctica to the ocean goes through narrow areas of fast sliding ice. At the sides of these fast sliding areas the fast ice abuts slow ice and heavily deforms. Deformation warms the ice–potentially to its melting temperature. This warming should be noticeable in radar data because ice at or near the melting point reduces the power of radar waves. We develop a method for using airborne radar measurements to look for the presence of this warm ice, and apply our method across the Antarctic continent. We find evidence supportive of warm ice in many locations, but we notably find little evidence of warm ice in the Amundsen Sea Embayment where the inflow of cold ice may offset warming. Key Points: We develop a novel method for identifying evidence for temperate ice in Antarctic shear margins using existing airborne radar data setsWe find evidence for temperate ice in 18, and evidence contrary in 37, of 106 radar lines over shear margins we consider across AntarcticaNeglecting heats sinks like advective cooling overpredicts the size of temperate zones, particularly in the Amundsen Sea Embayment [ABSTRACT FROM AUTHOR]

The ice streams flowing into the Amundsen Sea, West Antarctica, are losing mass due to changes in oceanic basal melting of their floating ice shelves. Rapid ice‐shelf melting is sustained by the delivery of warm Circumpolar Deep Water to the ice‐shelf cavities, which is first supplied to the continental shelf by an undercurrent that flows eastward along the shelf break. Temporal variability of this undercurrent controls ice‐shelf basal melt variability. Recent work shows that on decadal timescales the undercurrent variability opposes surface wind variability. Using a regional model, we show that undercurrent variability is induced by sea‐ice freshwater fluxes, particularly those north of the shelf break, which affect the cross‐shelf break density gradient. This sea‐ice variability is linked to tropical Pacific variability impacting atmospheric conditions over the Amundsen Sea. Ice‐shelf melting also feeds back onto the undercurrent by affecting the on‐shelf density, thereby influencing shelf‐break density gradient anomalies. Plain Language Summary: The glaciers that flow toward the Amundsen Sea, West Antarctica, are losing ice faster than most others about the continent. Once these glaciers reach the coast, they extend out onto the ocean surface, forming ice shelves. The rapid loss of ice is caused by changes in melting by relatively warm ocean waters beneath the floating ice shelves. In the Amundsen Sea, a deep ocean current is responsible for delivering warm water from the deep ocean to the ice shelves. We present model results that show that this deep current varies on decadal timescales as a consequence of systematic sea‐ice melt and formation patterns. A faster current drives more rapid ice shelf melting which, via a feedback process, further accelerates the current. Climate variability originating in the tropical Pacific Ocean is responsible for the variability in the sea‐ice, and is therefore also responsible for the effects on melting of the ice shelves. Key Points: In the Amundsen Sea decadal variability of an undercurrent flowing along the shelf break drives decadal variability in ice‐shelf basal meltSea‐ice freshwater fluxes and positive feedbacks from ice‐shelf basal melt drive the undercurrent variabilityTropical Pacific teleconnections induce atmospheric anomalies over the Amundsen Sea which drive the sea‐ice freshwater flux variability [ABSTRACT FROM AUTHOR]

The sea ice albedo can amplify global climate change and affect the surface energy in the Arctic. In this paper, the data from Visible and Infra-Red Radiometer (VIRR) onboard Fengyun-3C satellite are applied to derive the Arctic sea ice albedo. Two radiative transfer models, namely, 6S and FluxNet, are used to simulate the reflectance and albedo in the shortwave band. Clear sky sea ice albedo in the Arctic region (60°~90°N) from 2016 to 2019 is derived through the physical process, including data preprocessing, narrowband to broadband conversion, anisotropy correction, and atmospheric correction. The results are compared with aircraft measurements and AVHRR Polar Pathfinder-Extended (APP-x) albedo product and OLCI MPF product. The bias and standard deviation of the difference between VIRR albedo and aircraft measurements are −0.040 and 0.071, respectively. Compared with APP-x product and OLCI MPF product, a good consistency of albedo is shown. And analyzed together with melt pond fraction, an obvious negative relationship can be seen. After processing the 4-year data, an obvious annual trend can be observed. Due to the influence of snow on the ice surface, the average surface albedo of the Arctic in March and April can reach more than 0.8. Starting in May, with the ice and snow melting and melt ponds forming, the albedo drops rapidly to 0.5–0.6. Into August, the melt ponds begin to freeze and the surface albedo increases. [ABSTRACT FROM AUTHOR]

Present study focuses on the utilization of Earth observation satellite-04 (EOS-04) synthetic aperture radar (SAR) data for maintaining the continuity of the first Indian radar imaging satellite (RISAT)-1 SAR derived products along with exploring the potential of capability of the improved sensor over mountain and polar cryospheric region. Backscattering coefficient (σ0) of various snow and ice features over mountain and polar cryosphere have been analysed to understand the interaction mechanism using C-band SAR data. EOS-04 is able to pick up the spatio-temporal variability of SAR backscatters over accumulation and ablation zone of the glacier due to melt-freeze cycles, and observations were in accordance with variation in elevations over the glacier surface. When analysed for Drang-Drung glacier, wet snow zone was found to be prominently centered around 5500 m elevation zone, having sigmanaught backscatter lower than –10 dB in the ablation months, whereas percolation zone was observed at more than 6000 m elevation with higher sigma-naught backscatter of around –4 dB and above as winter started setting in. EOS-04 also showed the potential to classify various polar ice features based on backscattering signature using HH (H, horizontal) (σ0), HV (V, vertical) (σ0) and normalized difference polarization ratio index (NDPRI) respectively. EOS-04 data have been used to implement approaches to retrieve wet snow cover and set up of Weather Research and Forecasting Model Hydrological Modelling System (WRF hydro) model for snow melt runoff studies, interaction mechanism of snow and ice, snow/ice facies extraction, ice shelf monitoring, sea ice properties and sea ice advisory for Indian scientific expedition to Antarctica. Enrichment of EOS-04 data, suitable for cryosphere studies, will be employed to retrieve parameters such as snowpack properties, elevation, ice surface velocities over mountain and polar region, and to further improve comprehensive understanding on regional and global frozen ice dynamics. [ABSTRACT FROM AUTHOR]

Open-ocean polynyas formed over the Maud Rise, in the Weddell Sea, during the winters of 2016-2017. Such polynyas are rare events in the Southern Ocean and are associated with deep convection, affecting regional carbon and heat budgets. Using an ocean state estimate, we found that during 2017, early sea ice melting occurred in response to enhanced vertical mixing of heat, which was accompanied by mixing of salt. The melting sea ice compensated for the vertically mixed salt, resulting in a net buoyancy gain. An additional salt input was then necessary to destabilize the upper ocean. This came from a hitherto unexplored polynya-formation mechanism: an Ekman transport of salt across a jet girdling the northern flank of the Maud Rise. Such transport was driven by intensified eastward surface stresses during 2015-2018. Our results illustrate how highly localized interactions between wind, ocean flow and topography can trigger polynya formation in the open Southern Ocean. [ABSTRACT FROM AUTHOR]

In the Western Arctic Ocean lies the largest freshwater reservoir in the Arctic Ocean, the Beaufort Gyre. Long-term changes in freshwater reservoirs are critical for understanding the Arctic Ocean, and data from various sources, particularly measured or reanalyzed data, must be used to the greatest extent possible. Over the past two decades, a large number of intensive field observations and ship surveys have been conducted in the western Arctic Ocean to obtain a large amount of CTD data. Multiple machine learning methods were evaluated and merged to reconstruct annual salinity product in the western Arctic Ocean over the period 2003–2022. Data mining-based machine learning methods make use of variables determined by physical processes, such as sea level pressure, sea ice concentration, and drift. Our objective is to effectively manage the mean root mean square error (RMSE) of sea surface salinity, which exhibits greater susceptibility to atmospheric, sea ice, and oceanic changes. Considering the higher susceptibility of sea surface salinity to atmospheric, sea ice, and oceanic changes, which leads to greater variability, we ensured that the average root mean square error of CTD and EN4 sea surface salinity field during the machine learning training process was constrained within 0.25 psu. The machine learning process reveals that the uncertainty in predicting sea surface salinity, as constrained by CTD data, is 0.24 %, whereas when constrained by EN4 data it reduces to 0.02 %. During data merging and post-calibrating, the weight coefficients are constrained by imposing limitations on the uncertainty value. Compared with commonly used EN4 and ORAS5 salinity in the Arctic Ocean, our salinity product provide more accurate descriptions of freshwater content in the Beaufort Gyre and depth variations at its halocline base. The application potential of this multi-machine learning results approach for evaluating and integrating extends beyond the salinity field, encompassing hydrometeorology, sea ice thickness, polar biogeochemistry, and other related fields. The datasets are available at https://zenodo.org/records/10990138 (Tao and Du, 2024). [ABSTRACT FROM AUTHOR]

Mysids, besides krill, play a significant role in energy transfer and carbon sequestration. The ecology of coastal species is better understood than that of deep dwelling species such as Boreomysis arctica. The objectives of this study were to quantify spatiotemporal variations in body condition and the trophic level of B. arctica in autumn and winter, under sea-ice conditions in the St. Lawrence system, using a multimarker approach. We sampled along a 1000 km transect. Mean abundances in winter were higher in the estuary compared to the Gulf of St. Lawrence. Body condition, measured as total lipid content, was higher in winter than in autumn. Lipids of B. arctica were mainly composed of wax esters, thereby B. arctica is richer in energetic lipids compared to the three dominant krill species. We also observed seasonal differences in the trophic level of B. arctica, revealing carnivorous behavior in autumn compared to omnivory in winter. High intra-specific variability in both energetic strategy and feeding behavior was found that is potentially due to opportunistic feeding. Energy rich reserves suggest that B. arctica could act as a valuable prey for both benthic and pelagic consumers and thus playing a key role in bentho-pelagic energy transfer. [ABSTRACT FROM AUTHOR]

Numerical climate model simulations suggest that global warming is enhanced or hampered by the spatial pattern of the warming itself. This phenomenon is known as the "pattern effect" and has in recent years become the most promising explanation for the change over time of climate sensitivity in climate models. Under historical global warming, different patterns of surface-temperature change have emerged, notably a yet unexplained cooling in the Southern Ocean and the East Pacific. Historical climate model simulations notoriously fail to reproduce this cooling, which may contribute to the deviation of the simulated global-mean warming from the observed record. Here we qualitatively investigate the potential impact of historical and other surface-temperature pattern changes by changing the ocean heat transport convergence (Q-flux) in a slab-ocean model. The Q-flux changes are always implemented such that in the global mean they impose no net forcing. Consistent with earlier studies we find that the impact of a negative Q-flux change in the Southern Ocean has a stronger effect than in other regions because of a feedback loop between sea-surface temperatures (SSTs) and clouds in the Southern Ocean and the stably stratified regions in the tropics. The SST-cloud feedback loop facilitates the expansion of the Antarctic sea ice, indeed taking the model into a Snowball-Earth state. The intensity of this effect is found to be model dependent, especially due to differences in the cloud parametrisation. In experiments with deactivated sea ice the impact of the negative Q-flux change is much weaker. [ABSTRACT FROM AUTHOR]

We investigate historical simulations of relevant components of the Arctic energy and water budgets for 39 Coupled Model Intercomparison Project Phase 6 (CMIP6) models and validate them against observation-based estimates. We look at simulated seasonal cycles, long-term averages and trends of lateral transports and storage rates in atmosphere and ocean as well as vertical fluxes at top-of-atmosphere and the surface. We find large inter-model spreads and systematic biases in the representation of annual cycles and long-term averages. Surface freshwater fluxes associated with precipitation and evaporation as well as runoff from Arctic lands tend to be overestimated by most CMIP6 models and about two thirds of the analysed models feature an early timing bias of one month in the runoff cycle phase, related to an early snow melt bias and the lack of realistic river routing schemes. Further, large biases are found for oceanic volume transports, partly because data required for accurate oceanic transport computations has not been archived. Biases are also present in the simulated energy budget components. The net vertical energy flux out of the ocean at the Arctic surface as well as poleward oceanic heat transports are systematically underestimated by all models. We find strong anti-correlation between average oceanic heat transports and mean sea ice cover, atmospheric heat transports, and also the long-term ocean warming rate. The latter strongly suggests that accurate depiction of the mean state is a prerequisite for realistic projections of future warming of the Arctic. Our diagnostics also provide useful process-based metrics for model selection to constrain projections. [ABSTRACT FROM AUTHOR]

The East Asian jet stream is an important component of mid-high latitude circulation systems, and its intraseasonal oscillation plays a crucial role in the formation and development of persistent climate anomalies and extreme events over East Asia–Pacific region. This study examines the decadal changes in the intraseasonal variability (ISV) of the East Asian jet stream and investigates the possible reasons with reanalysis and observational datasets. It is found that the zonal winds over East Asia show notable ISV with a significant period of 10–25 days. The variance of 10–25-day filtered East Asian zonal winds exhibits a significant decrease around 2000, which is mainly contributed by the weakened ISV of westerlies within the key region of East Asian polar front jet (EAPJ). Further analysis reveals that the EAPJ experienced remarkable ISV changes in both intensity and location. The ISV of EAPJ intensity was weakened around 2000 due to decreased frequencies of both the extremely strong and weak cases, whereas the ISV of EAPJ location was evidently enhanced, with the southward shifts increased more than the northward ones. Along with the ISV increase (decrease) of EAPJ intensity (location), the dominant mode of EAPJ intraseasonal variation has changed from its intensity change to position shift since the year 2000. The decadal ISV changes and mode transition of EAPJ are closely associated with the modulation of lower-level large-scale circulation over Eurasia. The weakened ISV of meridional winds over Ural region after 2000 is favorable for an intraseasonal circulation pattern change from a continental-scale cyclonic anomalous pattern to a meridional dipole structure across the Eurasia in lower troposphere, resulting in regime shifts of East Asian temperature and its meridional gradient through temperature advection. The intraseasonal temperature gradient patterns display ISV changes parallel to those of EAPJ around 2000, indicating that the thermal anomalies are effective in leading to corresponding intensity and location variations of EAPJ via thermal wind relationship. Furthermore, the modulation of lower-level circulation is closely related to strengthened Arctic warming and weakened temperature variability over Barents sector after 2000, which may further be linked to sea ice reduction in the Barents Sea. [ABSTRACT FROM AUTHOR]

Differential penetration of green laser light into snow and ice has long been considered a possible cause of range and thus elevation bias in laser altimeters. Over snow, ice, and water, green photons can penetrate the surface and experience multiple scattering events in the subsurface volume before being scattered back to the surface and subsequently the instrument's detector, therefore biasing the range of the measurement. Newly formed sea ice adjacent to open-water leads provides an opportunity to identify differential penetration without the need for an absolute reference surface or dual-color lidar data. We use co-located, coincident high-resolution natural-color imagery and airborne lidar data to identify surface and ice types and evaluate elevation differences between those surfaces. The lidar data reveals that apparent elevations of thin ice and finger-rafted thin ice can be several tens of centimeters below the water surface of surrounding leads, but not over dry snow. These lower elevations coincide with broadening of the laser pulse, suggesting that subsurface volume scattering is causing the pulse broadening and elevation shift. To complement our analysis of pulse shapes and help interpret the physical mechanism behind the observed elevation biases, we match the waveform shapes with a model of scattering of light in snow and ice that predicts the shape of lidar waveforms reflecting from snow and ice surfaces based on the shape of the transmitted pulse, the surface roughness, and the optical scattering properties of the medium. We parameterize the scattering in our model based on the scattering length Lscat , the mean distance a photon travels between isotropic scattering events. The largest scattering lengths are found for thin ice that exhibits the largest negative elevation biases, where scattering lengths of several centimeters allow photons to build up considerable range biases over multiple scattering events, indicating that biased elevations exist in lower-level Airborne Topographic Mapper (ATM) data products. Preliminary analysis of ICESat-2 ATL10 data shows that a similar relationship between subsurface elevations (restored negative freeboard) and "pulse width" is present in ICESat-2 data over sea ice, suggesting that biased elevations caused by differential penetration likely also exist in lower-level ICESat-2 data products. The spatial correlation of observed differential penetration in ATM data with surface and ice type suggests that elevation biases could also have a seasonal component, increasing the challenge of applying a simple bias correction. [ABSTRACT FROM AUTHOR]

The net Arctic sea-ice area (SIA) can be estimated from the sea-ice concentration (SIC) by passive microwave measurements from satellites. To be a truly useful metric, for example of the sensitivity of the Arctic sea-ice cover to global warming, we need, however, reliable estimates of its uncertainty. Here we retrieve this uncertainty by taking into account the spatial and temporal error correlations of the underlying local sea-ice concentration products. As 1 example year, we find that in 2015 the average observational uncertainties of the SIA are 306 000 km 2 for daily estimates, 275 000 km 2 for weekly estimates, and 164 000 km 2 for monthly estimates. The sea-ice extent (SIE) uncertainty for that year is slightly smaller, with 296 000 km 2 for daily estimates, 261 000 km 2 for weekly estimates, and 156 000 km 2 for monthly estimates. These daily uncertainties correspond to about 7 % of the 2015 sea-ice minimum and are about half of the spread in estimated SIA and SIE from different passive microwave SIC products. This shows that random SIC errors play a role in SIA uncertainties comparable to inter-SIC-product biases. We further show that the September SIA, which is traditionally the month with the least amount of Arctic sea ice, declined by 105000±9000 km 2 a -1 for the period from 2002 to 2017. This is the first estimate of a SIA trend with an explicit representation of temporal error correlations. [ABSTRACT FROM AUTHOR]

Forecasts of sea-ice motion and fragmentation are of vital importance for all human interactions with sea ice, ranging from those involving indigenous hunters to shipping in polar regions. Sea-ice models are also important for simulating long-term changes in a warming climate. Here, we apply the Helsinki Discrete Element Model (HiDEM), originally developed for glacier calving, to sea-ice breakup and dynamics. The code is highly optimized to utilize high-end supercomputers to achieve an extreme time and space resolution. Simulated fracture patterns and ice motion are compared with satellite images of the Kvarken region of the Baltic Sea from March 2018. A second application of HiDEM involves ice ridge formation in the Gulf of Riga. With a few tens of graphics processing units (GPUs), the code is capable of reproducing observed ice patterns that in nature may take a few days to form; this is done over an area of ∼100km×100km , with an 8 m resolution, in computations lasting ∼10 h. The simulations largely reproduce observed fracture patterns, ice motion, fast-ice regions, floe size distributions, and ridge patterns. The similarities and differences between observed and computed ice dynamics and their relation to initial conditions, boundary conditions, and applied driving forces are discussed in detail. The results reported here indicate that the HiDEM has the potential to be developed into a detailed high-resolution model for sea-ice dynamics at short timescales, which, when combined with large-scale and long-term continuum models, may form an efficient framework for forecasts of sea-ice dynamics. [ABSTRACT FROM AUTHOR]

In recent decades, the Arctic Ocean has undergone changes associated with enhanced poleward inflow of Atlantic and Pacific waters and increased heat flux exchange with the atmosphere in seasonally ice-free regions. The associated changes in upper-ocean heat content can alter the exchange of energy at the ocean–ice interface. Yet, the role of ocean heat content in modulating Arctic sea ice variability at sub-seasonal timescales is still poorly documented. We analyze ocean heat transports and surface heat fluxes between 1980–2021 using two eddy-permitting global ocean reanalyses, C-GLORSv5 and ORAS5, to assess the surface energy budget of the Arctic Ocean and its regional seas. We then assess the role of upper-ocean heat content, computed in the surface mixed layer (Qml) and in the 0–300 m layer (Q300), as a sub-seasonal precursor of sea ice variability by means of lag correlations. Our results reveal that in the Pacific Arctic regions, sea ice variability in autumn is linked with Qml anomalies leading by 1 to 3 months, and this relationship has strengthened in the Laptev and East Siberian seas during 2001–2021 relative to 1980–2000, primarily due to reduced surface heat loss since the mid-2000s. Q300 anomalies act as a precursor for wintertime sea ice variability in the Barents and Kara seas, with considerable strengthening and expansion of this link from 1980–2000 and 2001–2021 in both reanalyses. Our results highlight the role played by upper-ocean heat content in modulating the interannual variability of Arctic sea ice at sub-seasonal timescales. Heat stored in the ocean has important implications for the predictability of sea ice, calling for improvements in forecast initialization and a focus upon regional predictions in the Arctic region. [ABSTRACT FROM AUTHOR]

The Canadian Arctic Archipelago (CAA) serves as both a source and a sink for sea ice from the Arctic Ocean, while also exporting sea ice into Baffin Bay. We use observations from Sentinel-1, RADARSAT-2, the RADARSAT Constellation Mission (RCM), and CryoSat-2, together with the Canadian Ice Service ice charts, to quantify sea ice transport and replenishment across and within the CAA from 2016 to 2022. We also provide the first estimates of the ice area and volume flux within the CAA from the Queen Elizabeth Islands to Parry Channel, which spans the central region of the Northwest Passage shipping route. Results indicate that the CAA primarily exports ice to the Arctic Ocean and Baffin Bay, with an average annual (October to September) ice area flux of 137 ± 72 × 10 3 km 2 and a volume flux of 58 ± 68 km 3. The CAA contributes a larger area but smaller volume of ice downstream to the North Atlantic than what is delivered via Nares Strait. The average annual ice area flux from the Queen Elizabeth Islands to Parry Channel was 27 ± 10 × 10 3 km 2 and the volume flux was 34 ± 12 km 3 , with a majority occurring through Byam Martin Channel, which is directly above the central region of Northwest Passage. Over our study period, annual multi-year ice (MYI) replenishment within the CAA was resilient, with an average of 14 ± 38 × 10 3 km 2 imported from the Arctic Ocean and an average of 56 ± 36 × 10 3 km 2 of first-year ice (FYI) retained following the melt season. The considerable ice flux to Parry Channel, together with sustained MYI replenishment, emphasizes the continued risk that sea ice poses to practical utilization of key shipping routes in the CAA, including the Northwest Passage. [ABSTRACT FROM AUTHOR]

Silt-rich meltwater plume deposits (MPDs) analyzed from marine sediment cores have elucidated relationships that are clearly connected, yet difficult to constrain, between subglacial hydrology, ice-marginal landforms, and grounding-zone retreat patterns for several glacial catchments. Few attempts have been made to infer details of subglacial hydrology, such as flow regime, geometry of drainage pathways, and mode(s) of sediment transport through time, from grain-scale characteristics of MPDs. Using sediment samples from MPD, till, and grounding-zone proximal diamicton collected offshore of six modern and relict glacial catchments in both hemispheres, we examine grain shape distributions and microtextures (collectively, grain micromorphology) of the silt fraction to explore whether grains are measurably altered from their subglacial sources via meltwater action. We find that 75 % of all imaged grains (n = 9400) can be described by 25 % of the full range of measured shape morphometrics, indicating grain shape homogenization through widespread and efficient abrasive processes in subglacial environments. Although silt grains from MPDs exhibit edge rounding more often than silt grains from tills, grain surface textures indicative of fluvial transport (e.g., v-shaped percussions) occur in only a modest number of grains. Furthermore, MPD grain surfaces retain several textures consistent with transport beneath glacial ice (e.g., straight or arcuate steps, (sub)linear fractures) in comparable abundances to till grains. Significant grain shape alteration in MPDs compared to their till sources is observed in sediments from glacial regions where (1) high-magnitude, potentially catastrophic meltwater drainage events are inferred from marine sediment records and (2) submarine landforms suggest supraglacial melt contributed to the subglacial hydrological budget. This implies that quantifiable grain shape alteration in MPDs could reflect a combination of high-energy flow of subglacial meltwater, persistent sediment entrainment, and/or long sediment transport distances through subglacial drainage pathways. Integrating grain micromorphology into analysis of MPDs in site-specific studies could therefore aid in distinguishing periods of persistent, well-connected subglacial discharge from periods of sluggish or disorganized drainage. In the wider context of deglacial marine sedimentary and bathymetric records, a grain micromorphological approach may bolster our ability to characterize ice response to subglacial meltwater transmission through time. This work additionally demonstrates that glacial and fluvial surface textures are retained on silt-sized quartz grains in adequate amounts for microtexture analysis, which has heretofore been conducted exclusively on the sand fraction. Therefore, grain microtextures can be examined on silt-rich glaciogenic deposits that contain little to no sand as a means to evaluate sediment transport processes. [ABSTRACT FROM AUTHOR]

We present laboratory experiments on the growth of a tubular ice structure surrounding a plume of cold brine that descends under gravity into water with a higher freezing point. Brinicles are geological analogues of these structures found under sea ice in the polar regions on Earth. Brinicles are hypothesized to exist in the oceans of other celestial bodies, and being environments rich in minerals, serve a potentially analogous role as an ecosystem on icy-ocean worlds to that of submarine hydrothermal vents on Earth. [ABSTRACT FROM AUTHOR]

Automated sea ice charting from synthetic aperture radar (SAR) has been researched for more than a decade, and we are still not close to unlocking the full potential of automated solutions in terms of resolution and accuracy. The central complications arise from ground truth data not being readily available in the polar regions. In this paper, we build a data set from 20 near-coincident x-band SAR acquisitions and as many airborne laser scanner (ALS) measurements from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), between October and May. This data set is then used to assess the accuracy and robustness of five machine-learning-based approaches by deriving classes from the freeboard, surface roughness (standard deviation at 0.5 m correlation length) and reflectance. It is shown that there is only a weak correlation between the radar backscatter and the sea ice topography. Accuracies between 44 % and 66 % and robustness between 71 % and 83 % give a realistic insight into the performance of modern convolutional neural network architectures across a range of ice conditions over 8 months. It also marks the first time algorithms have been trained entirely with labels from coincident measurements, allowing for a probabilistic class retrieval. The results show that segmentation models able to learn from the class distribution perform significantly better than pixel-wise classification approaches by nearly 20 % accuracy on average. [ABSTRACT FROM AUTHOR]

The study of transient acoustic wave propagation across the Arctic Ocean ice layer provides theoretical guidance for the design of trans-ice acoustic communication systems. In this study, the Arctic Ocean was modeled as an ice–water composite structure, where the ice and water are regarded as an elastic solid and liquid, respectively. An analytical transient solution for acoustic wave propagation in this structure was derived using the eigenfunction expansion method. Further, the numerical procedures were presented and used to analyze the acoustic wave propagation characteristics across the ice layer. The results show that waveforms corresponding to the radial displacements are more severely distorted than the axial displacements. The amplitudes of the radial and axial displacements decreased rapidly with increasing propagation distance. The ice thickness had a greater impact on the radial displacement than axial displacement; the thicker the ice, the greater the distortion for both radial and axial displacements. [ABSTRACT FROM AUTHOR]