Icebergs drifting within sea ice represent a serious hazard to Arctic maritime activities, yet predicting their drift remains highly uncertain. We show that sea ice governs the drift of five icebergs in the Greenland Sea (IB-I to III) and Barents Sea (IB-IV, V) between 2012 and 2025. Those icebergs were either locked in the sea ice drift or were dragged by a combination of sea ice, water and wind. We investigate the simulation error by ocean and sea ice input data and the model formulation of the used Lagrangian iceberg drift model. The error is quantified as the difference between simulated and observed drift distance and direction, and it varies across cases and environmental conditions, with low errors for IB-I and IB-IV and high errors for IB-II and IB-III. A new sea ice drag formulation substantially reduces these large errors, particularly for trajectories in regions with high sea ice concentration. This formulation enables the small Arctic icebergs to follow the sea ice motion more realistically, either through a lowered lock-in concentration threshold of 0.7 or by applying a sea ice concentration dependent drag coefficient. Contributing to the overall simulation error, differences in the ocean and sea ice input led to substantial simulation spread of 0 . 2 to 1 . 5 × the observed drift distance and 13 to 8 5 ∘ drift direction. Parts of this error originate from the input sea ice concentration fields, which, though consistent with operational sea ice charts, show a slight positive bias from local observations. • Sea ice drags or locks in iceberg and is thus essential in iceberg drift simulations. • The drag by sea ice accounts for large parts of the iceberg drift distance. • Uncertain ocean and sea ice input cause large spread in the iceberg simulations. • The simulation error is decreased by a modified sea-ice-drag-equation.

Hidden diversity of marine zooplankton under sea ice in the Okhotsk Sea: Insights from community and population analyses based on DNA metabarcoding.

Recent studies report high carbon export efficiencies in Arctic regions with seasonal sea ice compared to ice-free regions, yet the mechanisms behind this enhanced export remain unclear. In the marginal ice zone (MIZ), where pack ice meets open ocean, eddies and filaments frequently form. To investigate carbon export mechanisms in such frontal systems, we combined direct in situ observations of export processes and physical oceanography using free-drifting sediment traps, Marine Snow Catchers, and in situ optics during a Fram Strait expedition in July 2020. Dense Atlantic Water (AW) subducted beneath lighter surface meltwater and Polar Water (PW), structuring biogeochemical and biological processes, including chlorophyll distribution, primary production, zooplankton abundance, microbial respiration, and aggregate formation. We observed three main mechanisms supporting carbon export; (i) deep aggregate formation driven by the subduction of chlorophyll-rich AW, (ii) diatom ballasting of aggregates, including slow-sinking Phaeocystis colonies, and (iii) cryogenic mineral ballasting in PW aggregates, which increased sinking velocities up to tenfold. High carbon fluxes occurred in the AW and at the front, while export in PW was lower, highlighting the role of water mass characteristics and ballasting in regulating export efficiency. The results suggest that continued Atlantification and expansion of the MIZ could enhance carbon export across larger Arctic areas as sea ice retreats.

A hybrid particle-continuum method for simulating landfast sea ice via subgrid iceberg interaction

A novel Subsea Winched Profiling System (SWIPS) was deployed in the Atlantic Water (AW) inflow to the Arctic Ocean north of Svalbard, providing high-resolution, year-round observations of upper ocean hydrography and biogeochemistry. Between July 2022 and July 2023, SWIPS collected 85 vertical profiles from ∼125 m to 10 m depth at 4-day intervals, capturing seasonal transitions and fine-scale variability across open water and ice-covered conditions. The autonomous system provides a sustained Eulerian perspective of upper ocean dynamics, resolving the evolving water mass distribution, seasonal stratification, the deepening of the mixed layer in autumn and winter, and the persistent influence of AW beneath a strongly stratified surface layer. SWIPS captured an under-ice phytoplankton bloom in May 2023, occurring under > 80% sea ice concentrations and preceding the onset of Polar Day by more than one week. During peak bloom periods, satellite-derived chlorophyll concentrations underestimated in-situ values by up to an order of magnitude due to persistent subsurface chlorophyll maxima and ice cover. The profiler also detected two episodes of anomalous winter hydrography during which AW reached the surface and disrupted the expected cold, stratified regime. The hydrographic data and satellite sea surface temperature suggest these events were driven by upstream AW advection from Fram Strait and facilitated localized convection to depths exceeding 100 m, reinforcing the role of remote forcing in shaping local upper ocean and ice conditions. By capturing both gradual seasonal evolution and short-lived anomalies, SWIPS provides critical in-situ observations that complement traditional observational methods and improve understanding of ocean–ice–ecosystem interactions under Arctic amplification.

High-Rate compression and constitutive representation of laboratory-grown sea ice

Spatial contaminant assessment (PAHs, PCBs, OCs, PBDEs) and lipid composition in Beaufort Sea (2011-2020) and Chukchi Sea polar bear (2015-2016) subpopulations, Alaska, USA.

ABSTRACT Polar sea ice monitoring is essential for understanding climate variability and predicting environmental change. Global Navigation Satellite System Reflectometry (GNSS-R) provides a unique opportunity for large-scale, all-weather, and cost-effective sea ice observations. This study evaluates the potential of the Tianmu-1 constellation – a multi-system GNSS-R mission – for detecting sea ice in polar regions. Using 30 days of Delay-Doppler Map (DDM) data from GPS-R, BDS-R, GAL-R, and GLO-R signals, we derived five DDM observables: Normalized DDM Average (NDDMA), Trailing Edge Slope (TES), Pixel Number (PN), Power Summation (PS), and Centroid-to-Maximum Distance (CM Distance). These observables characterize scattering differences between sea ice and sea water. Validation against OSI SAF sea ice edge products yields detection accuracies exceeding 94% across all GNSS systems, with PN and PS exhibiting the highest robustness. These results demonstrate that Tianmu-1 delivers high-temporal-resolution, data-rich observations for reliable polar sea ice detection. The study underscores the potential of multi-system GNSS-R to complement conventional microwave remote sensing, thereby advancing climate research, operational forecasting, and long-term monitoring of polar environmental change.

Antarctic sea ice extent began declining in 2015, reaching its minimum in the post-1970s observational era in 2023. To diagnose the drivers of this decline, we analyze an observationally constrained sea ice-ocean model spanning 2013-2023 and identify three distinct phases of sea ice retreat. First, intensifying westerlies preconditioned the Southern Ocean via increased upwelling of warm, saline circumpolar deep water (CDW). Second, strong winds in 2015-2016 enhanced the mixing of CDW into the upper ocean, thereby initiating sea ice loss, particularly in East Antarctica. Third, sustained mixing of CDW into the surface layer, combined with reduced equatorward sea ice-derived freshwater export, maintained an unprecedentedly low sea ice state. East Antarctic sea ice loss was primarily subsurface driven via enhanced upward CDW flux, whereas West Antarctic sea ice loss was also forced by longwave radiative flux anomalies. Our findings suggest that persistent upwelling-favorable conditions under anthropogenic forcing may push the Southern Ocean into a prolonged low sea ice state.

A 43-year Climate Data Record (CDR) of combined global sea and sea-ice surface temperature (SST/IST) from 1982 to 2024 has been produced from satellite observations within the Copernicus Climate Change Service (C3S). Infrared and microwave satellite data are integrated using optimal interpolation to provide daily, gap-free (L4, 0.05°) global SST/IST fields. Consistent and accurate sea-ice concentration (SIC) fields are derived by combining passive microwave SIC CDRs with sea ice charts, improving SST and IST characterization. The product also includes under-ice SST (UISST) derived from SIC and monthly salinity climatologies. Validation against in situ SSTs shows median differences of -0.04 °C and robust standard deviations of 0.17-0.28 °C. For sea ice, the median differences range from 1.41 °C to -4.62 °C, with robust standard deviations of 2.55-4.99 ∘C. This CDR provides a novel and consistent dataset for assessing climate change and extremes in polar regions and globally, independently of sea-ice cover. From 1982-2024, global SST/IST increased by ~0.75 °C, with amplified Arctic warming (~4.36 °C) and modest Antarctic warming ~0.54 °C), although recent years have been record-breakingly warm in Antarctica.

Abstract To date, there are few records of Holocene changes in sea ice in the south-eastern Weddell Sea, which limits our understanding of how sea ice has interacted with climate in this sector of the Southern Ocean. Here, we present a multi-proxy analysis of a snow petrel stomach-oil deposit that records occupation history and dietary fluctuations from ~1800 to 800 calibrated (cal.) yr bp . Lipid biomarkers (fatty acids (FAs), sterols and alkanols), bulk stable isotopes (δ 13 C and δ 15 N) and trace elements show distinct dietary shifts, which are linked to centennial-scale changes in summer sea-ice extent. From ~1730 to 1370 cal. yr bp , foraging in pelagic waters near the edge of the sea-ice pack is suggested by low nest occupation rates and Antarctic krill contributions to the diet. From ~1370 to ~1180 cal. yr bp , an increase in nest occupation and a fish-dominated diet reflect foraging within open water (polynyas) during a period of more extensive summer sea ice. A decrease in nest occupation after ~1180 cal. yr bp is attributed to local sea-ice readvance, resulting in reduced access to open water, impeding foraging success. Our results highlight the use of multi-proxy geochemical records from snow petrel stomach-oil deposits to reconstruct seasonal sea-ice fluctuations in the Weddell Sea and their interactions with late Holocene climate records.

The Arctic stratospheric polar vortex (SPV) is known to influence winter surface climate through dynamical coupling. Here, we demonstrate that beyond this established pathway, variations in SPV strength also modulate Arctic high clouds, inducing persistent radiative effects at the surface. This previously less well recognized mechanism shows that a strengthened SPV increases Arctic high-cloud cover, generating a positive net cloud radiative effect that amplifies Arctic Ocean warming and sea ice loss over the Barents-Kara Sea; a weakened SPV produces opposing effects. Our results establish this radiative pathway as one of the primary drivers of the winter-mean Arctic response to stratospheric variability. Numerical experiments confirm that this radiative pathway can cause up to 1.7 K of Arctic Ocean warming during the delayed phase of strong SPV events relative to climatology. Notably, the radiative influence operates more persistently than the transient dynamical response, offering enhanced predictive potential for subseasonal-to-seasonal Arctic surface conditions. These findings reveal a key radiative mechanism underlying SPV-driven Arctic climate variability, which is essential for understanding present and future winter Arctic changes.

The Marginal Ice Zone (MIZ) is a dynamic region where the atmosphere, ocean, and sea ice actively interact, giving rise to frequent eddy formation. Clarifying the processes governing this zone is crucial for both accurate modeling of local circulation and improved prediction of Arctic climate change, particularly sea-ice retreat and ecosystem shifts. This study investigates a mesoscale eddy in the poorly studied northeastern Kara Sea MIZ using a joint analysis of in situ and satellite measurements from summer 2024. We also apply principles from ellipsoidal vortex theory. The eddy's complex evolution is described, and its key parameters are quantified. The eddy was found to contain and transport a substantial volume of freshened cold water, potentially modifying the structure of surrounding waters. Two potential mechanisms for the eddy's formation were proposed, each requiring further investigation through dedicated modeling and observational efforts. Significant differences in the phytoplankton biomass and production rates were identified across the eddy, whereas species composition showed no significant variation. These results highlight the role of mesoscale eddies in freshwater redistribution and biophysical coupling in the MIZ, while underscoring the need to advance theories of eddy dynamics and incorporate these processes into regional and climate models.

A study was conducted on the interaction of surface gravity waves with a relatively thin, free-floating ice floe compared to the height of the waves. Physical and numerical modeling, as well as analytical research, were used. An overview of scientific works on the research topic is presented. The physical model consisted of an experimental setup (wave flume) with a wooden plate exposed to gravitational harmonic waves of different lengths and periods. The numerical model is based on calculations performed in the LS-DYNA program, where the fluid was simulated using the Euler–Lagrange method, and solid bodies were considered rigid. Analytical studies use the theory of interaction of small-amplitude waves with floating breakwaters. It is shown that as the wave height increases for conditions of interaction between waves and ice floes of almost identical horizontal dimensions, one end of the floating body sinks into the water, which leads to a significant reduction in the drift speed of the ice floe. Formulas have been obtained that express the ratio of the ice floe’s speed to the wave velocity, as well as the ratio of the height of the incident waves to the height of the transmitted waves, depending on the ratio of the wavelength to the horizontal dimensions of the floating ice floe.

In situ spectral analysis of sea ice contaminated with multiple substances in Liaodong Bay, Bohai Sea.

Snow atop Antarctic sea ice plays a critical role in modulating sea ice growth, surface energy balance, and ocean–atmosphere interactions. However, it also introduces substantial uncertainty into satellite altimeter-based sea ice thickness (SIT) estimates. Ku-band radar altimeters, such as CryoSat-2 (CS-2), are often processed using threshold-based retrackers that implicitly assume the maximum radar intensity return originates near the snow–ice interface. In practice, layered snowpacks featuring wet snow, brine infiltration, and ice lenses can shift the primary scattering contribution upward, leading to overestimated freeboard and higher SIT estimates. In Part I of this study, we used physically based waveform decomposition to quantify the vertical distribution of radar backscatter under Weddell Sea conditions. Building on these insights, Part II introduces an optimized threshold first-maximum retracker algorithm (TFMRA) for CS-2, tuned using airborne observations from NASA’s Operation IceBridge (OIB) over the Weddell Sea. We identify a 70% retracking threshold that minimizes freeboard bias and improves consistency with independent observations. Applying this snow-aware retracker to 46 CRYO2ICE collocated tracks (2020–2022), we retrieve snow depth from the ICESat-2 and CS-2 freeboard difference and reduce mean SIT by ∼ 0.1 m relative to the ESA Baseline-E product in the southern Weddell Sea. Monte-Carlo (MC) perturbations of OIB snow retrievals, combined with CS-2 threshold-sensitivity tests, indicate an intrinsic ∼ 0.2 m uncertainty in OIB snow depth and a similar lower-bound CRYO2ICE snow-depth uncertainty of ∼ 0.21-0.24 m at 10 km scales. Our results offer practical guidance for altimeter algorithm development and are directly relevant to upcoming dual-frequency radar missions such as ESA’s CRISTAL. • A 70% TFMRA threshold reduces radar freeboard bias, and improves Antarctic CryoSat-2 SIT. • Snow-aware CS-2 retracking tuned with OIB and CRYO2ICE sharpens snow depth and SIT. • OIB and CRYO2ICE snow depth errors ≥ 0.2 m constrain altimetry and guide CRISTAL.

Sea ice affects Earth's climate system on both regional and global scales. Its incorporation into climate can be used to achieve more accurate predictions of future climate. However, instrumental records of sea-ice concentration do not extend earlier than 1978. In an effort to extend this record, we constructed a proxy using the generalized additive model based on relative abundances of five easy-to-identify diatom species found in sediment samples across the Bering and Chukchi seas. Here we present the first quantitative diatom-based sea-ice proxy developed for Beringia. The developed proxy has been applied to two sediment cores in the Bering Sea ranging from 0 to 25.7 ka (HLY0204 51JPC) and 369 to 430 ka (IODP Exp 323 Site U1345) and one in the Chukchi Sea ranging from 2.7 to 10 ka (HLY0204 24JPC). The obtained reconstructions of sea-ice concentrations are similar, but not identical to previously published qualitative and nearby records based on other proxies. Because our results are quantitative, they can be incorporated into regional climate models. The proxy is publicly available as an R Shiny application (app) and can be applied to any diatom count from marine sediments in the region. • Bering and Chukchi sea diatoms have varying associations with sea ice today. • Diatoms were used to build a quantitative sea ice proxy in the Bering/Chukchi seas. • The proxy uses 5 species of diatoms in a generalized additive model. • The model is freely available online for forthcoming sea ice reconstructions.

Neon (Ne) and Helium (He) isotope data sets collected in the ‘Switchyard’ region of the Arctic Ocean between 2005 and 2013 show a distinct excess in Ne concentrations in the upper waters, mostly in the surface mixed layer of ice-covered waters. The average ΔNe values have an excess in the ice-covered surface layer of about 7.5 %. These observed Ne concentrations fall above those expected from solubility equilibrium with the atmosphere and typical excess air concentrations due to partial and/or full bubble dissolution. Meanwhile, the average Δ 4 He values which are close to 3.5 %, are constant with depth in the Switchyard Region. In contrast, data sets from several Greenland and Norwegian seas (GSNS) cruises where samples were collected in waters without sea ice cover show that both ΔNe and Δ 4 He values are nearly constant with depth. The Greenland and Norwegian Seas serve as a control region, representing a similar open-ocean field environment but lacking sea-ice formation in the regions where our samples were taken. This contrast allows us to isolate the neon saturation anomalies that arise specifically due to sea-ice formation processes in the Arctic Ocean. We attribute the near surface ΔNe anomaly in the Switchyard area of the Arctic Ocean to the rejection of Ne during sea-ice formation. Using sea-ice formation estimates from the oxygen isotope (δ 18 O) method as a base line, we derive a central Arctic Ocean, field-based Ne sea-ice/seawater partition coefficient of 0.38 ± 0.05. This estimate indicates stronger rejection of Ne during ice formation into surface waters than has been previously reported. This analysis contributes to our understanding of the Ne budget in the sea-ice covered Arctic Ocean and can serve as a framework for studying other ice-covered surface ocean regions. • Surface waters beneath Arctic sea ice contain a clear excess of neon, revealing a distinct gas imbalance. • Sea-ice formation drives the neon anomaly by rejecting neon into surface ocean waters. • A new field-based central Arctic Ocean estimate of the Ne sea-ice/seawater partition coefficient of 0.38 ± 0.05, calculated using δ 18 O-derived ice formation rates, indicates that neon is excluded more strongly during sea-ice formation than previously reported.

ABSTRACTThe Arctic Ocean is warming rapidly, prompting increased attention to the ecosystem's response to sea‐ice loss and the influx of organisms from lower latitudes. Recent studies have shown that these exogenous organisms are affecting the biodiversity of Arctic ecosystems, but their impact on biogeochemical cycles remains unclear. This study provides evidence that diazotrophs transported from outside the Arctic can significantly contribute to the Arctic new production. From 2015 to 2020, we conducted broad observations in the Chukchi and Beaufort Seas during late summer and autumn, measuring nitrogen fixation rates, diazotroph community composition, and key processes related to new production (nitrate assimilation and nitrification). In 2017, we observed a marked increase in nitrogen fixation, especially in the off‐shelf region undergoing oligotrophication, where it constituted a significant fraction of the new production (interquartile range 10.8%–62.5%, median: 21.5%). UCYN‐A2 (Candidatus Atelocyanobacterium thalassa) emerged as the dominant diazotroph across all regions in that year, with a significant positive correlation between its abundance and nitrogen fixation rates, suggesting its key role in the elevated nitrogen fixation. Water mass analyses, sea ice observation, and numerical simulations indicated that UCYN‐A2 likely originated in the Bering Sea and was transported to the Arctic off‐shelf region, and proliferated there with increasing temperature as a result of unusually early sea ice melt in 2017. These findings indicate that as warming and earlier sea ice retreat continue, the influence of exogenous diazotrophs on Arctic biogeochemical cycles can become increasingly pronounced.

Abstract This study presents a sea‐ice‐enhanced K‐profile parameterization to improve simulations of the Atlantic Meridional Overturning Circulation (AMOC) in ocean–sea ice coupled models. The modified KPP dynamically scales the background vertical diffusivity with local sea‐ice fraction, representing the insulating and turbulence‐suppressing effects of sea ice on upper‐ocean mixing. Sensitivity experiments forced by the JRA55‐do (1958–2018) data set show that the proposed schemes strengthen deep‐water formation in the subpolar and Nordic Seas, leading to a more realistic AMOC representation. In addition to AMOC strengthening, the modified scheme produces consistent upper‐ocean salinity increases under sea‐ice conditions, which enhance density and support deep convection. The enhanced AMOC arises through two main physical pathways: (a) intensified deep‐water formation in the Labrador Sea, strengthening the southward branch of the overturning circulation, and (b) increased transport of denser waters to the Nordic Seas, which uplifts isopycnal surfaces across the Greenland–Iceland–Scotland Ridge and promotes the Denmark Strait overflow. Together, these processes reinforce the AMOC and improve agreement with observations. This study establishes a physically based framework for incorporating sea‐ice‐controlled vertical mixing and demonstrates how Arctic sea‐ice‐induced density changes can modulate large‐scale overturning circulation and its variability.