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This study prepared six different ice creams to investigate the effect of yeast protein (YP) on their sensory, rheological, thermal properties and fat destabilisation. Results indicated that YP could improve sensory quality, flow and viscoelastic properties. The thermal property was also positively influenced by YP with a significant decrease in frozen water percentage and an increase in glass transition temperature (P < 0.05). Additionally, the particle size and confocal laser scanning microscopy results illustrated that YP could moderately promote the fat aggregate percentage and size. Overall, YP could serve as a fat replacer to produce reduced‐fat ice cream. [ABSTRACT FROM AUTHOR]

We use digital elevation models (DEMs) and ICESat‐2 data to study the filling and outflow from a large subglacial lake under Manson Icefield in the Canadian Arctic. When full, the lake is ∼17 × 3 km with an area of 52 km2. Early in 2021 the ice surface over the center of the lake sank by >140 m implying a subglacial outburst flood of ∼4 km3. Rapid outflow occurred over ∼30 days at an average rate of ∼1,500 m3s−1 resulting in the formation of a single ∼15 km subglacial outflow path detectable from post‐outflow surface depression. The shape of the surface depression, 600–800 m wide by 2–4 m deep, reflects the shape of the subglacial channel prior to closure. Downstream ice movement appears unaffected by the outflow. After outflow ends the surface depression persisted over weeks, apparently dependent on the difference between water and overburden pressures. Plain Language Summary: Using satellite observations, we discovered a large lake under the Manson Icefield in the Canadian Arctic. Early in 2021 the ice surface over the center of the lake sank by around 140 m implying a total subglacial water outflow of around 4 km3, the largest reported outside of Iceland and Antarctica. Most of this water drained from the subglacial lake within 30 days melting some of the ice along the outflow path. For the first time we map the position and size of the subglacial output channel between the downstream end of the lake and the ocean using post‐outflow surface depression as the ice sank downward to close the channel after the water outflow. These results help in understanding the ways in which the presence, movement, and volume of water beneath glaciers influence ice movement and climate related glacial ice loss. Key Points: Using satellite height change data we document the discovery of a 52 km2 subglacial lake under the Manson Icefield, Nunavut, CanadaThe lake filled for around 14 years until early 2021 when the level in the center of the lake dropped by 130 m over 30 daysThe outflow volume was around 4 cubic kilometers and created a wide and shallow subglacial channel that could be tracked for over 15 km [ABSTRACT FROM AUTHOR]

CryoSat‐2 has been successful in observing sea ice thickness from space by providing ice freeboard information. The initial estimate of the ice freeboard, called radar freeboard, is obtained by analyzing the observed waveform using a retracker. A series of corrections are needed to convert the radar freeboard to the ice freeboard. Those are the physical effects (e.g., changes in wave propagation speed and the distribution of scattering at snow and ice surfaces, etc.) and the bias of the retracker; however, traditionally, only the wave speed correction has been applied due to lack of enough information to perform the complete correction. Here, an alternative correction method for the CryoSat‐2 radar freeboard derived using the Threshold First‐Maximum Retracker Algorithm with a 50% threshold (TFMRA50) is proposed. Snow depth was used as a predictor for the correction, similar to the traditional wave speed correction, but the coefficients were empirically determined by performing a direct comparison of the radar freeboard from CryoSat‐2 and the ice freeboard from airborne observations. Consequently, this new empirical correction treats the physical effects and the retracker bias as a whole, which have been difficult to separate in the retrieval process. In this paper, we demonstrate that the retrieval accuracy of snow and ice variables and the consistency of the two independent retrieval methods are improved when the new correction is applied. The result of this study emphasizes the importance of compatibility between the retracker and the freeboard correction method. Plain Language Summary: Sea ice thickness and snow depth are considered essential climate variables because they are crucial for understanding climate change. The satellite CryoSat‐2 has successfully contributed to obtaining those variables by estimating the elevation of the sea ice surface from space. However, the estimation of the sea ice elevation can be affected by several error sources related to snow and ice conditions. Traditionally, it was challenging to perform a complete correction because there has not been enough detailed information on the snow and ice conditions. Considering the complex nature of sea ice, an alternative simple empirical correction method is proposed based on actual CryoSat‐2 and reference airborne observations. Accordingly, the proposed correction doesn't require detailed information on the surface conditions. We verify that the estimation of the snow and ice variables is improved when the new correction is applied. Additionally, the new correction also increases the consistency of two independent products. Based on its robustness and simplicity, we expect this new method to enhance our understanding of climate change by improving the quality of satellite snow and sea ice data. Key Points: The behavior of the CryoSat‐2 radar freeboard from the widely used retracker was found to be incompatible with conventional correctionAn alternative empirical method for improving the CryoSat‐2 radar‐to‐ice freeboard correction for a threshold retracker was developedThe new method can be generally applied to existing retrieval methods to improve the quality of snow depth and ice thickness retrievals [ABSTRACT FROM AUTHOR]

Differential interferometric synthetic aperture radar (InSAR) is a remote sensing technique for measuring surface displacements with precision down to millimeters, most commonly from satellites. In permafrost landscapes, InSAR measurements can provide valuable information on geomorphic processes and hazards, including thaw subsidence and frost heave, thermokarst, and permafrost creep. We first review recent progress in InSAR data availability, InSAR processing and uncertainty analysis methods relevant to permafrost studies. These technical advances have contributed to our understanding of surface deformation in flat and sloping terrain in polar and mountainous regions. We emphasize two emerging trends. First, InSAR increasingly enables insight into the mechanisms, controls, and drivers of permafrost landscape dynamics on subseasonal to decadal time scales. Second, InSAR observations in conjunction with models enable novel ways to infer subsurface parameters, such as near‐surface ground ice content and active layer thickness. We anticipate that in the coming decade, InSAR will mature into a widely used operational tool for monitoring, modeling, and planning across rapidly changing permafrost landscapes. [ABSTRACT FROM AUTHOR]

Substantial seafloor morphological changes are rapidly occurring along the Canadian Arctic shelf edge. Five multibeam bathymetric mapping surveys, each partially covering a 15 km2 study area between 120‐ and 200‐m water depth, were conducted over a 12‐year time period. These surveys reveal that 65 new craters have developed between 2010 and 2022, averaging 6.5 m and reaching up to 30 m deep. Remotely operated vehicle investigations revealed massive ice outcrops exposed on two newly formed crater flanks. This ice is not relict subaerially formed Pleistocene permafrost because it is hosted in sediments which were deposited in a submarine setting post‐deglaciation. Low salinity porewater and sediment core ice samples with depleted oxygen isotopic compositions indicate waters with a meteoric signature are discharging and freezing in this area. These ascending brackish groundwaters are likely derived in part from thawed relict permafrost hundreds of meters under the continental shelf. They refreeze as they approach the −1.4°C seafloor, leading to the development of widespread, near seafloor, sub‐bottom ice layers. Conditions appropriate for ice melting also exist nearby where ice is exposed to seawater or warmed by ascending groundwater. Small variations in temperature and salinity lead to shifts between freezing of ascending brackish groundwater or melting of near seafloor ice layers. These conditions have produced a dramatic submarine thermokarst morphology riddled with multi‐aged depressions. Thermokarst geohazards may exist, unmapped, on other Arctic margins with groundwater channeled toward the shelf edge by a relict permafrost cap, and sufficiently cold shelf edge bottom water temperatures. Plain Language Summary: Significant seafloor changes are rapidly happening along the Canadian Arctic shelf edge, where numerous craters and mounds occur. Five seafloor mapping surveys collected over 12 years covering the same area reveal 65 new craters, reaching up to 30 m but averaging 6.5 m deep, were formed between 2010 and 2022. Observations from a remotely operated vehicle showed massive ice outcrops along the flanks of two newly formed craters. Chemical analyses of the ice show that the source of the frozen water is ascending brackish groundwaters that refreeze near the −1.4°C seafloor, forming widespread sub‐bottom ice layers that blister the seafloor producing ice‐cored mounds. The source of the groundwaters is likely melted relict permafrost from beneath the continental shelf. Where ice is exposed to seawater salinity or warmer groundwater, ice melting causes seafloor collapses. Minor temperature and salinity variations cause shifts between freezing of ascending brackish groundwater and melting of near‐seafloor ice layers. These ongoing processes create a dramatic submarine landscape composed of numerous depression and ice‐filled mounds of varying ages. This discovery of sub‐seafloor ice with a groundwater origin significantly expands our understanding of submarine permafrost within the Arctic continental shelves. Key Points: Massive outcrops of submarine ice layers were found within recently formed seafloor craters along the edge of the Arctic continental shelfOn‐going ice growth and decomposition is occurring around seafloor seepages to produce a distinctive submarine thermokarst topographyThermokarst geohazards may exist on other Arctic margins where sub‐zero water temperatures and submarine groundwater seepage occur [ABSTRACT FROM AUTHOR]

Much of the Antarctic coast is covered by seasonal landfast sea ice (fast ice), which serves as an important habitat for ice algae. Fast‐ice algae provide a key early season food source for pelagic and benthic food webs, and contribute to biogeochemical cycling in Antarctic coastal ecosystems. Summertime fast ice is undergoing a decline, leading to more seasonal fast ice with unknown impacts on interconnected Earth system processes. Our understanding of the spatiotemporal variability of Antarctic fast ice, and its impact on polar ecosystems is currently limited. Evaluating the overall productivity of fast‐ice algae has historically been hampered by limitations in observations and models. By linking new fast‐ice extent maps with a one‐dimensional sea‐ice biogeochemical model, we provide the first estimate of the spatio‐seasonal variability of Antarctic fast‐ice algal gross primary production (GPP) and its annual primary production on a circum‐Antarctic scale. Experiments conducted for the 2005–2006 season provide a mean fast ice‐algal production estimate of 2.8 Tg C/y. This estimate represents about 12% of overall Southern Ocean sea‐ice algae production (estimated in a previous study), with the mean fast‐ice algal production per area being 3.3 times higher than that of pack ice. Our Antarctic fast‐ice GPP estimates are probably underestimated in the Ross Sea and Weddell Sea sectors because the sub‐ice platelet layer habitats and their high biomass are not considered. Plain Language Summary: Antarctic landfast sea ice (fast ice) is sea ice fastened to the coastline of Antarctica and provides a prolific habitat for microalgae. These ice algae are ecologically important because their production takes place early in the season when water column primary production is low. By combining a new satellite data set and a biogeochemical sea‐ice algal growth model, this study provides the first estimate of circum‐Antarctic fast‐ice algal production: 2.8 million tonnes of carbon per year, which is about 12% of the total Antarctic sea‐ice algal production. The mean algal primary production per area in fast ice is 3.3 times higher than that of pack ice. Key Points: First estimate of circum‐Antarctic landfast sea‐ice annual gross primary production, with a focus on the 2005–2006 seasonMean landfast sea‐ice algal primary production is 2.8 TgC/y, representing 12% (range 5%–19%) of total Southern Ocean ice algal productivityMean modeled landfast sea‐ice algal production per area is 3.3 times higher than that of pack ice [ABSTRACT FROM AUTHOR]

In the context of glacier retreat and increased precipitations, Arctic glacier basin slopes are subject to stress leading to visible transformations. In this work, subsurface features of a small Arctic glacier basin slopes are mapped using ground‐penetrating RADAR. In combination with surface topography data, eight transects were surveyed ranging from the areas furthest from the current glacier extent to the areas still in contact with the glacier. This allowed for a reconstitution of the successive stages ice‐cored slopes go through when glaciers retreat. It appears that slopes evolve from thick debris‐covered ice bodies connected with the glacier, to residual ice and ice/debris mixes covered in debris. At the same time, surface morphology of the slopes shifts from homogeneous ice‐cored slope gradients to more complex talus‐type slopes at the end of the process. The stages of these evolutions are in compliance with former glacier extents. The main driving factors of the slopes successive stages are the constant slope adjustments linked to debris movements, and the melting of ice cores. All these factors are exacerbated by the warmer and wetter conditions they are subject to. [ABSTRACT FROM AUTHOR]

Despite optimal cognitive function being essential for performance, there is a lack of research on the effectiveness of combined cooling interventions on team sport athlete's cognitive function when exercising in the heat. In a randomised, crossover design, 12 unacclimatised men (age: 22.3 ± 3.0 years, body mass: 73.4 ± 5.1 kg, height: 181.0 ± 5.3 cm and V˙O2 $\dot{\mathrm{V}}{\mathrm{O}}_{2}$ max: 51.2 ± 9.5 mL/kg/min) participated in a control (CON) and combined cooling trial (ice slurry and ice collar; COOL). A battery of cognitive tests were completed prior to, during (at half‐time) and following a 90‐min intermittent running protocol in the heat (33°C, 50% relative humidity (RH)). Perceptual and physiological measures were taken throughout the protocol. In CON, response times were quicker on the Stroop task complex level (p = 0.002) and the visual search test complex level at full‐time (p = 0.014) compared to COOL. During COOL, response times were quicker at half‐time on the Stroop task complex level (p = 0.024) compared to CON. Lower rectal temperatures were seen during COOL (CON: 37.44 ± 0.65°C and COOL: 37.28 ± 0.68°C) as well as lower skin, neck and forehead temperatures (main effect of trial, all p < 0.05). Lower ratings of thermal sensation and perceived exertion and enhanced thermal comfort were recorded during COOL (main effect of trial, all p < 0.05). Whilst minimal differences in cognitive function were found when using the combined cooling intervention, the findings highlight a practical and effective strategy to improving many physiological and perceptual responses to intermittent exercise in the heat. Highlights: Many studies have investigated the use of a combined cooling strategy on endurance exercise in the heat and found positive benefits on physiological, perceptual and cognitive responses to the intervention; however, there is a lack of research on intermittent exercise.The combined cooling intervention, consisting of an ice slurry and ice collar, was successful at lowering rectal, neck, forehead and skin temperatures as well as perceptual ratings of thermal sensation, comfort and perceived exertion.However, the combined cooling strategy did not elicit any consistent findings regarding cognitive function. [ABSTRACT FROM AUTHOR]

Antarctica has an active subglacial hydrological system, with interconnected subglacial lakes fed by subglacial meltwater. Subglacial hydrology can influence basal sliding, inject freshwater into the sub‐ice‐shelf cavity, and impact sediment transport and deposition which can affect the stability of grounding lines (GLs). We used satellite altimetry data from the ICESat, ICESat‐2, and CryoSat‐2 missions to document the second recorded drainage of Engelhardt Subglacial Lake (SLE), which began in July 2021 and discharged more than 2.3 km3 of subglacial water into the Ross Ice Shelf cavity. We used differential synthetic aperture radar interferometry from RADARSAT‐2 and TerraSAR‐X alongside ICESat‐2 repeat‐track laser altimetry (RTLA) and REMA digital elevation model strips to detect 2–13 km of GL retreat since the previous drainage event in 2003–06. Combining these satellite observations, we evaluated the mechanism triggering SLE drainage, the cause of the observed GL retreat, and the interplay between subglacial hydrology and GL dynamics. We find that: (a) SLE drainage was initiated by influx from a newly identified upstream lake; (b) the observed GL retreat is mainly driven by the continued retreat of Engelhardt Ice Ridge and long‐term dynamic thinning that caused a grounded ice plain to reach flotation; and (c) SLE drainage and GL retreat were largely independent. We also discuss the possible origins and influence of a 27 km grounded promontory found to protrude seaward from the GL. Our observations demonstrate the importance of high‐resolution satellite data for improving the process‐based understanding of dynamic and complex regions around the Antarctic Ice Sheet margins. Plain Language Summary: Large volumes of water flow beneath the Antarctic Ice Sheet through an interconnected network of rivers and lakes. This water system impacts slipperiness at the base of the ice, affecting how fast it moves. It also delivers freshwater into the ocean, directly contributing to sea‐level rise and increasing melt beneath the floating ice shelves. In this study, we use satellite data to track the 2021–24 drainage of Engelhardt Subglacial Lake in West Antarctica. This lake is located close to the Ross Ice Shelf grounding line, the point at the edge of the ice sheet where the ice first lifts off the bedrock and starts to float on the ocean. This region of the grounding line has retreated by up to 13 km since the last lake drainage in 2003–06. Here, we investigate what caused the drainage, the reasons for the grounding line retreat, and whether the two processes are connected. We also report the growth of a grounded promontory extending 27 km out to sea, which may be evidence of a former ice stream moraine or melt channel. These findings help to improve our limited understanding of the relationship between subglacial hydrology and grounding line dynamics in Antarctica. Key Points: Satellite altimetry detects second recorded drainage of Engelhardt Subglacial Lake in July 2021, triggered by an influx from an upstream lakeThe grounding line retreated by 2–13 km since the last drainage in 2003, linked to the retreat of Engelhardt Ice Ridge and ice plain ungroundingSatellite observations suggest that the 2021–24 lake drainage and grounding line retreat were largely independent processes [ABSTRACT FROM AUTHOR]

This study analyzes hydrometeor evolution during rapid intensification (RI) and tropical cyclone (TC) intensity dependence using satellite data. Previous studies have suggested ice cloud water or non‐convective precipitation as a predictor of RI from different perspectives. However, few studies have focused on the impact of TC intensity or comprehensive comparisons to identify better indicators. During RI, hydrometeor contents in weak TCs increase over the entire region, whereas they increase mainly in the inner‐core region and decrease in advance in the outer‐core region for strong TCs. Hydrometeor contents in the inner‐core are higher in RI than in slow intensification, and their maxima location is related to TC intensity and intensification rate. Cloud water path (CWP) in the inner‐core region is most correlated with the intensification rate, especially in weak TCs. Therefore, the CWP can serve as a predictor of RI and can be applied to all TC intensities. Plain Language Summary: Stronger tropical cyclones (TCs) often undergo rapid intensification (RI) and cause significant damage. However, accurately predicting its intensity is difficult. A close relationship exists between TC intensity changes and cloud content. Previous studies have shown a connection between the ice water content, precipitation, and RI of TCs. However, few studies have comprehensively compared the hydrometeors and precipitation associated with RI and the impact of TC intensity. During the RI, various cloud contents increase in the entire area of a weak TC, while they increase mainly in the inner‐core area and decrease in advance in the outer‐core area of a strong TC. The cloud contents in the inner‐core are higher in RI than in slow intensification, and their maximum locations are related to the TC intensity and intensification rate. Among the cloud content and precipitation types, the water cloud content in the TC inner‐core area is the best indicator of the intensification rate, applicable to all TC intensities, especially for weak TCs. Understanding the relationship between clouds and TC intensification facilitates prediction of TC intensity and reduces the impact of disasters. Key Points: Hydrometeor contents increase in the entire area of a weak TC but mainly in the inner‐core of a strong TC during rapid intensification (RI)RI has higher inner‐core hydrometeor contents than slow cases, and the maxima location is linked to TC intensity and intensification rateThe cloud water content in the inner‐core area has the largest correlation with the TC intensification rate, especially in a weak TC [ABSTRACT FROM AUTHOR]

Mars' polar ice deposits are thought to preserve a record of climate throughout their evolution. In addition to the large north polar layered deposits (NPLD) at Mars' north pole, smaller ice deposits are preserved in craters nearby. These outlying deposits were potentially formed by the same mechanisms that drive NPLD formation, or may represent more local mechanisms. Distinguishing between these possibilities would help elucidate the spatial homogeneity of Martian climate processes. Here, we analyzed SHARAD radar depth profiles from 34 locations across the NPLD and 5 locations within the Korolev crater ice deposit using Fourier transform analysis and dynamic time warping to quantitatively assess the similarity between the internal layered stratigraphy of the two deposits. We identify broad stratigraphic similarities between the Korolev deposit and the NPLD, suggesting they likely formed due to the same climate forcing mechanism, with local variability also observed across the NPLD. Plain Language Summary: Mars has two large ice caps at its poles, which combined contain a similar volume of ice to Greenland on Earth. Near these large ice caps are craters that are also filled with ice, which may or may not have formed due to the same mechanisms that formed the large neighboring ice cap. Ground penetrating radar observations of ice on Mars can allow us to see layers of ice and dust that are present throughout the interior of these deposits, and represent climate events that have taken place during the deposit's formation and evolution. We analyze radar observations from two deposits near Mars' north pole and quantitatively show that these deposits have a similar pattern of layering. These results could indicate that they have shared a similar climate history, therefore implying the importance of regional‐scale climate processes on Mars in addition to local processes for forming these ice deposits. Key Points: We use Fourier transform analysis and dynamic time warping to assess the similarities between two ice deposits near Mars' north poleWe identified a periodic signal with an average wavelength of ∼45 m in radar observations of the ice mound in Korolev crater and the NPLDWe identify similar broad climate forcing for both Korolev and NPLD ice, with local variability across the NPLD also observed [ABSTRACT FROM AUTHOR]

Two outstanding questions for the future of the Greenland Ice Sheet are (a) how enhanced meltwater draining beneath the ice will impact the behavior of large tidewater glaciers, and (b) to what extent tidewater glacier velocity is driven by changes at the terminus versus changes in sliding velocity due to meltwater. We present a two‐way coupled framework to simulate the nonlinear feedbacks of evolving subglacial hydrology and ice dynamics using the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model within the Ice‐sheet and Sea‐level System Model (ISSM). Through coupled simulations of Helheim Glacier, we find that terminus effects dominate the seasonal velocity pattern up to 15 km from the terminus, while hydrology drives the velocity response upstream. With increased melt, the hydrology influence yields seasonal acceleration of several hundred meters per year in the interior, suggesting that hydrology will play an important role in future mass balance of tidewater glaciers. Plain Language Summary: Water draining under glaciers and ice sheets affects the friction between the ice and the bed, and controls how fast the ice can slide into the ocean, contributing to sea‐level rise. We present a framework for simulating the feedbacks between hydrology and ice flow. We investigate the relative influence of changes at the terminus of the glacier where it meets the ocean, versus changes in meltwater drainage, in determining how fast the glacier moves. Our modeling of Helheim Glacier in southeast Greenland highlights the importance of terminus effects up to 15 km from the terminus, and hydrology farther upstream, with increased melt yielding higher inland acceleration. These results suggest that meltwater will play an increasingly important role in the future behavior of glaciers. Key Points: We couple a subglacial hydrology model with an ice flow model to simulate the relationship between sliding velocity and effective pressureTerminus effects at Helheim Glacier drive velocity up to 15 km upstream, but seasonal hydrology controls velocity patterns further inlandIncreased melt accelerates ice inland of the main trunk, implying importance of hydrology in tidewater glacier future mass balance [ABSTRACT FROM AUTHOR]

Sea ice formation over open water exerts critical control on polar atmosphere‐ocean‐ice interactions, but is only crudely represented in sea ice models. In this study, a collection depth parameterization of new ice for flux polynya models is modified by including the sea ice concentration and ice growth rate as additional factors. We evaluated it in a climate model BCC‐CSM2‐MR and found that it improves simulation of Antarctic sea ice concentration and thickness in most of Indian and Atlantic sectors. Disagreement between the observed Antarctic sea ice expansion during 1981–2014 and the modeled decline still exists but is mitigated when the modified scheme is implemented. Further analysis indicates that these improvements are associated with the overcoming of premature closure of open water, which enhances the response of ocean to surface wind intensification during 1981–2014, and consequently slowdowns the sea surface temperature increase and the resulting Antarctic sea ice reduction. Plain Language Summary: Open water ice formation critically modulates sea ice variations and the associated polar atmosphere‐ocean interaction, but is not well represented in sea ice models. In this study, a modified collection depth parameterization of new ice based on an existing scheme is presented after including sea ice concentration and ice growth rate as additional factors. We evaluated this modified scheme in BCC‐CSM2‐MR and found that it can improve the simulation of mean Antarctic sea ice thickness and concentration in winter as well as Antarctic sea ice expansion from 1981 to 2014. Further analysis implies that these improvements can be attributed to the overcoming of the premature closure of open water areas in model simulations. Key Points: A modified collection thickness parameterization of new ice suitable for large‐scale climate simulations is presentedIt improves the simulation of Antarctic sea ice thickness and concentration, as well as Antarctic sea ice expansion during 1981–2014The improved simulations can be attributed to the overcoming of the premature closure of open water areas where new ice forms [ABSTRACT FROM AUTHOR]

The winter hydrological period is in transition across the Canadian subarctic, as climate warming is shifting precipitation regimes, thawing permafrost, and altering active layer dynamics, and thus increasing the overall amount, and variability, of winter streamflow. Effects of these changes are poorly understood on the Taiga Shield, which comprises ~20% of North America's permafrost‐covered area, and is characterized by a unique 'fill‐and‐spill' hydrology whereby runoff generation requires the exceedance of lake basin storage thresholds. Here, we assessed lake hydrostatic levels and used trail camera images of icings, which are sheet‐like masses of layered ice that are common manifestations of wintertime flow on the Taiga Shield, to understand landscape controls on winter water movement in this region. We further used paired geochemical measurements to explore how source water characteristics affect icing chemistry, and the degree to which icings may modify the chemical composition of active winter flow. We undertake this work over 2 years, and across watersheds of different sizes and lake basin characteristics. We show that icing growth is driven by hydroclimatic controls that include fill‐and‐spill hydrologic constraints and winter air temperatures, and that pre‐freshet pulses of water flow are common within this landscape. Across winters with variable antecedent precipitation levels, a larger catchment was able to support icing growth via continued runoff generation, while small catchments were not. Icings were often chemically dilute compared with source waters, indicating that solute exclusion may actively enrich geochemical concentrations in flowing water. Across icings, chemical variation appeared related to source water type (groundwater versus lake; lake size) and apparent redox conditions. These results highlight that streamwater hydrology and biogeochemistry can be dynamic during the understudied winter period, and illustrate that icings may alter the composition of wintertime flow as it moves through fluvial networks. [ABSTRACT FROM AUTHOR]

The Antarctic marginal ice zone, the regularly wave‐affected outer band of the sea ice covered Southern Ocean, typically contains an unconsolidated ice cover comprised of smaller, thinner floes than the inner ice pack. Thus, it is a highly dynamic region and susceptible to rapid expansion and contraction, making it a focal area for understanding and predicting the response of Antarctic sea ice to a changing climate. This novel study uses unsupervised statistical clustering of sea ice data simulated by a global sea ice model (standalone CICE6 combined with a wave propagation module and prescribed ocean) to address the outstanding challenge of separating the marginal ice zone from the inner ice pack in sea ice data sets. The method identifies a marginal ice zone with the desired characteristics and floe size is shown to be the key variable in the classification. Simulated marginal ice zone widths are similar to those derived from satellite observations of wave penetration distances, but contrast with those using the standard 15%–80% areal sea ice concentration proxy, particularly during austral winter. The simulated marginal ice zone is found to undergo a seasonal transition due to new ice formation in winter, increased drift in spring, and increased rates of wave‐induced breakup and melting in summer. The understanding gained from the study motivates incorporation of wave and floe‐scale processes in sea ice models, and the methods are available for application to outputs from high‐resolution and coupled sea ice–ocean–wave models for more detailed studies of the marginal ice zone (in both hemispheres). Plain Language Summary: The record‐setting responses of Antarctic sea ice extent to climate change over recent decades have generated intense research interest in the marginal ice zone at the outskirts of the ice cover. The presence of ocean waves in this region creates a granular ice cover composed of small floes, affecting heat fluxes between the atmosphere and ocean, whilst shielding inner‐pack ice, fast ice, and ice shelves from waves. Studies of the marginal ice zone are hindered by the lack of a pragmatic approach to extract the marginal ice zone from sea ice data, which aligns with its characterization as the regularly wave‐affected sea ice region. Most studies use a concentration‐based proxy, although it overlooks large wave‐affected areas. We develop new insights into the evolution of the marginal ice zone by applying a modern machine‐learning approach to model outputs, leveraging recent modeling advances. Our findings reveal a marginal ice zone composed of young, small floes during winter and older, fractured floes during summer. Simulated widths are consistent with wave‐penetration distance observations and provide evidence of the marginal ice zone's unique properties, including high melt rates. The proposed approach may provide the basis for future studies on its contribution to Antarctic sea ice variability. Key Points: A new method to identify the Antarctic marginal ice zone is proposed based on statistical clustering of sea ice propertiesSimulated marginal ice zone widths are similar to satellite observations of wave penetration distancesNew understanding gained of differences in ice melt rates and drift speeds between the marginal ice zone and the interior ice pack [ABSTRACT FROM AUTHOR]

A new ice refractive index compilation is reported for a broad spectrum ranging from 0.0443 to 106 μm, focusing on the pronounced temperature‐dependence of ice optical properties in the far‐infrared (far‐IR) segment (15–100 μm). A sensitivity study assuming spherical particles shows that selecting ice refractive indices at 12 temperatures and 215 wavelengths in the far‐IR region gives sufficient accuracy in interpolated refractive indices for developing a new ice crystal optical property database. Furthermore, we demonstrate the differences between the bulk single‐scattering properties computed for hexagonal ice particles with this new compilation compared to a previous iteration at three far‐IR wavelengths where substantial differences are noticed between the two ice refractive index compilations. We suggest that our new ice refractive index data set will improve downstream light‐scattering applications for upcoming far‐IR satellite missions and allow robust modeling of outgoing longwave radiation under ice cloud conditions. Plain Language Summary: An imbalance between absorbed solar energy at ultraviolet (0.01–0.38 μm), visible (0.38–0.75 μm), and near‐infrared (IR) (0.75–2.5 μm) wavelengths and outgoing longwave radiation energy emitted from the Earth at mid‐IR (2.5–15 μm) and far‐IR (15–100 μm) wavelengths leads the surface temperature to change. Solar and mid‐IR energy is well‐observed by satellite sensors. However, it has been challenging to conduct spaceborne radiometric measurements in the far‐IR regime, which accounts for more than half of the OLR in cold areas such as polar regions. This study develops a new compilation of temperature‐dependent ice refractive index for application to the first far‐IR satellite missions extending beyond 25 microns, particularly toward a better understanding of ice clouds. It is shown that the improvements in the ice refractive index have a substantial impact on downstream light‐scattering computation in the far‐IR regime. Furthermore, the present study also explores adequate spectral and temperature resolutions for computing a new ice cloud optical property database to guarantee that the optical property values at other wavelengths and temperatures not included in the direct light‐scattering computations can be accurately obtained through interpolation. Key Points: A new compilation of ice refractive index covering the entire solar and terrestrial thermal spectrum is presentedThis study focuses on the far‐infrared spectrum, which is not well studied but accounts for most terrestrial emissions in cold regionsImplications of improved ice cloud modeling with temperature‐dependent ice refractive indices are discussed [ABSTRACT FROM AUTHOR]

Subglacial lakes have been mapped across Antarctica with two methods, radio‐echo sounding (RES) and ice‐surface deformation. At sites where both are coincident, these methods typically provide conflicting interpretations about the ice‐bed interface. With a single exception, active subglacial lakes identified by surface deformation do not display the expected flat, bright, and specular bed reflection in RES data, characteristic of non‐active lakes. This observational conundrum suggests that our understanding of Antarctic subglacial hydrology, especially beneath important fast‐moving ice streams, remains incomplete. Here, we use an airborne RES campaign that surveyed a well‐characterized group of active subglacial lakes on lower Mercer and Whillans ice streams, West Antarctica, to explore inconsistency between the two observational techniques. We test hypotheses of increased scattering and attenuation due to the presence of an active subglacial lake system that could suppress reflected bed‐echo power for RES observations in these locations, finding that entrained water is most plausible. Plain Language Summary: The bottom of an ice sheet is insulated from cold air temperatures, often warm enough to melt and pond liquid water into lakes. These lakes beneath the ice sheet have been identified by two independent measurements, first with radar methods and second with changes in height of the ice surface (altimetry). Interestingly, the two methods rarely identify the same lakes: radar generally detects lakes in the ice‐sheet interior, whereas altimetry detects active lakes near the ice‐sheet margins that fill and drain within the time series of repeated measurements (∼years). In this study, we investigate a group of active subglacial lakes at which both radar and altimetry data sets are available. We demonstrate that the radar returns from active lake reflections are much dimmer than expected based on non‐active lake signatures and investigate the physical processes controlling those dim reflections. We argue that water moves into the ice when the lake fills or drains and that is the most plausible explanation for the observational discrepancy. Key Points: Active subglacial lakes, identified by surface deformation, do not create the expected bright and specular radar reflectionEntrained water in basal ice suppresses radar power by scattering and attenuation, and it also likely alters the basal ice mechanicsUnderstanding the radar expression of subglacial water on Earth provides context for investigations of subsurface water on planetary bodies [ABSTRACT FROM AUTHOR]

In chemistry, biology, and materials science, ice‐mediated reactions and ice‐template assembly techniques are garnering increasing attention due to their unique advantages. Such approaches not only offer deep insights into the fundamental roles of ice in nature but also pave new avenues for various applications. This review comprehensively explores the mechanisms and applications of ice‐mediated reactions and assembly. It begins by examining the principles of ice‐mediated reactions, particularly how certain chemical reactions are accelerated in the micro‐environment of ice through freeze‐concentration and freeze‐potential effects, and the relationship between the surface structure and properties of ice and chemical reactions. This work then studies significant chemical reactions within the realms of environmental, biological, and materials science engineering, shedding light on the role of ice in these reactions. Furthermore, this work explores the fundamentals of ice templating in material assembly, describe the main ice‐templating methods, and highlight the ice‐templated materials along with their diverse applications. This work concludes by summarizing the prospective challenges and untapped potentials in the field of ice‐mediated reactions and assembly. This review not only accentuates the transformative impact of ice‐mediated techniques in scientific domains but also serves as an useful guide for future research initiatives and practical applications in this burgeoning field. [ABSTRACT FROM AUTHOR]

Frozen water bodies provide a physiological challenge to fauna by physically limiting access to atmospheric oxygen. To tolerate low temperatures, reptiles use brumation as a physiological strategy in winter. Cryptodira vary in their tolerance to freezing conditions but the extent of tolerance in pleurodirans is largely unknown. Australia's freshwater turtles inhabit warmer regions with less severe winters and have well‐developed mechanisms to cope with high temperatures and drying waterbodies, rather than extreme cold tolerance. Chelodina longicollis is a widespread Australian freshwater turtle species that tolerates high temperatures and desiccation during hot, dry periods while also undergoing brumation during winter months. Despite extensive research, limited observations exist on their behaviour during severe winter periods at the extremes of their range. In an 11‐month tracking study, we monitored adult C. longicollis, noting their movements, locations, and temperature weekly. We observed an adult female C. longicollis which, during a seven‐month period within a single creek pool, survived brumation in extreme cold water including a 15‐day period of total freezing of the surface water. After the ice melted following a rain event, the turtle was recaptured alive. This marks the first observation of brumation for an Australian chelid species under ice. [ABSTRACT FROM AUTHOR]

Introduction: In hemodialysis patients, pain associated with needle insertion into an arteriovenous fistula is a physical and psychological problem. The aim of this study was to assess the effectiveness of pre‐puncture application of an ice pack, EMLA cream, or lidocaine spray to reduce pain associated with access puncture. Methods: This was a multicenter study done in nine hemodialysis centers in Iraq. The study utilized a randomized, parallel‐group design, in which patients being dialyzed using an arteriovenous access were allocated into one of four groups. Access puncture was preceded by nothing (control group), by use of ice pack cooling at the puncture site, by application of EMLA cream, or by application of lidocaine spray. Pain after access puncture was assessed during a single treatment for each patient. Pain was quantified using a Visual Analogue Scale. Findings: A total of 1548 patients agreed to participate, and 1041 patients were included in the data analysis. Use of an ice pack, EMLA cream, or lidocaine spray each was associated with a lower pain score on access puncture compared with no pretreatment. The mean Visual Analogue Scores in the four groups were: 69.7 ± 15.7 in the controls, 39.8 ± 13.2 in the ice pack group, 45 ± 18.4 in the EMLA group, and 52.9 ± 15.2 in lidocaine group. Ranking of the pain severity scores suggested that ice pack use was associated with the least pain, followed by use of EMLA cream and use of lidocaine spray (severity score ranking, from lowest to highest, being 1.62, 2.18, and 2.63, respectively). Discussion: Application of an ice pack prior to vascular access puncture is a fast and inexpensive technique to limit pain associated with this procedure. [ABSTRACT FROM AUTHOR]

Temperate reservoirs and lakes worldwide are experiencing decreases in ice cover, which will likely alter the net balance of gross primary production (GPP) and respiration (R) in these ecosystems. However, most metabolism studies to date have focused on summer dynamics, thereby excluding winter dynamics from annual metabolism budgets. To address this gap, we analyzed 6 years of year‐round high‐frequency dissolved oxygen data to estimate daily rates of net ecosystem production (NEP), GPP, and R in a eutrophic, dimictic reservoir that has intermittent ice cover. Over 6 years, the reservoir exhibited slight heterotrophy during both summer and winter. We found winter and summer metabolism rates to be similar: summer NEP had a median rate of −0.06 mg O2 L−1 day−1 (range: −15.86 to 3.20 mg O2 L−1 day−1), while median winter NEP was −0.02 mg O2 L−1 day−1 (range: −8.19 to 0.53 mg O2 L−1 day−1). Despite large differences in the duration of ice cover among years, there were minimal differences in NEP among winters. Overall, the inclusion of winter data had a limited effect on annual metabolism estimates in a eutrophic reservoir, likely due to short winter periods in this reservoir (ice durations 0–35 days), relative to higher‐latitude lakes. Our work reveals a smaller difference between winter and summer NEP than in lakes with continuous ice cover. Ultimately, our work underscores the importance of studying full‐year metabolism dynamics in a range of aquatic ecosystems to help anticipate the effects of declining ice cover across lakes worldwide. Plain Language Summary: Lakes and reservoirs around the world are experiencing decreases in ice cover duration, with many waterbodies starting to experience non‐continuous ice cover throughout the winter. These changes in ice duration have the potential to influence carbon cycling, but to date few long‐term studies have included winter data. We analyzed 6 years of minute‐resolution oxygen data from a small reservoir that experiences non‐continuous ice cover to estimate whether the surface water was a source or sink of carbon at daily, seasonal, and annual scales. We found that the reservoir was often a source of carbon to the atmosphere, regardless of whether data from winter were included. Our results differed from previous studies conducted in higher‐latitude lakes that experience continuous ice cover throughout the winter, potentially due to the already‐short duration of ice cover in this reservoir. As the duration of ice cover continues to decrease across lakes and reservoirs worldwide, our work highlights the need for studying how changing winter conditions—especially non‐continuous ice cover—affects year‐round carbon cycling. Key Points: Winter data have rarely been included in lake metabolism studies, limiting our understanding of how ice affects metabolism estimatesAnnual metabolism estimates were similar across 6 years with widely varying ice coverWater chemistry explained variability in daily gross primary production, but not respiration or net ecosystem production, over 6 years [ABSTRACT FROM AUTHOR]

Climatic and environmental change is leading to increased frequency and intensity of permafrost degradation processes; however, our knowledge of their mechanisms and rate is still limited. We examined structure of deposits, surface topography, and weather conditions during the initiation of a thermo‐erosion gully in eastern Siberia and monitored its changes between 2020 and 2022. The initiation of the gully was caused by a combination of processes: (1) the catchment area of the gully was artificially increased several decades ago as a result of the interception of runoff by the winter road; (2) ice‐wedge degradation led to surface runoff concentration above the gully head, while a large volume of ground ice remained in other parts of the slope, and frost cracking continued; (3) the entry of water into frost cracks formed underground tunnels; and (4) high air temperatures and heavy rainfall immediately before the gully appearance resulted in the expansion of the tunnels and collapse of their roof. In 2 years, the volume of the gully reached 1000 m3; at least 40% of that volume consists of ground ice. The gully development did not significantly change the water chemistry due to significant water freshening caused by melting of ground ice. [ABSTRACT FROM AUTHOR]

Permafrost ground ice melting could alter hydrological processes in cold regions by releasing water. Currently, there is a lack of gridded data of ground ice from the Qinghai‐Tibet Plateau (QTP). Using 664 borehole sample records, we applied a random forest (RF) method to predict the ground ice content of permafrost between 2 and 10 m depth in three layers (2–3, 3–5, and 5–10 m) at a spatial resolution of 1 km. The RF predictions demonstrated an R2 value exceeding 0.80 for all three layers with a negligible positive overestimation (0.98%–1.85%). The ground ice content of the first layer (2–3 m) can be predicted primarily using climate variables, but the contribution of terrain and soil variables increases as the depth increases. The total water storage of ground ice across the QTP permafrost (2–10 m depth) is approximately 3330.0 km3, with 403.5 km3 in the 2–3 m layer, 857.2 km3 in the 3–5 m layer, and 2069.3 km3 in the 5–10 m layer. This study generated for the first time a gridded dataset of the shallow permafrost ground ice content across the entire QTP which can be used to improve simulations of hydrological processes in the permafrost regions. [ABSTRACT FROM AUTHOR]

Glaciers and ice streams flowing over sediment beds commonly have a layer of ice‐rich debris adhered to their base, known as a "frozen fringe," but its impact on basal friction is unknown. We simulated basal slip over granular beds with a cryogenic ring shear device while ice infiltrated the bed to grow a fringe, and measured the frictional response under different effective stresses and slip speeds. Frictional resistance increased with increasing slip speed until it plateaued at the frictional strength of the till, closely resembling the regularized Coulomb slip law associated with clean ice over deformable beds. We hypothesize that this arises from deformation in a previously unidentified zone of weakly frozen sediments at the fringe's base, which is highly sensitive to temperature and stress gradients. We show how a rheologic model for ice‐rich debris coupled with the thermomechanics of fringe growth can account for the regularized Coulomb behavior. Plain Language Summary: Many glaciers move by sliding over sediment beds. As the glacier flows downslope, ice can infiltrate the underlying sediments, forming a layer of ice‐rich debris attached at the glacier's base. We investigated how this frozen fringe impacts glacier motion by simulating glacier slip in a cold‐room facility with a specialized ring shear device. We recreated glacier conditions, sliding ice over granular beds to form the fringe, and then assessed how frictional resistance at the slip interface varied under different stresses and ice speeds. We found that frozen fringe influences the relationship between ice speed and frictional resistance, known as the "slip law." As ice speed increased, basal friction increased to a threshold that matches the strength of the ice‐free sediment bed—mirroring the "regularized Coulomb slip law" inferred for clean ice over soft beds. We attribute this behavior to deformation in a weakly frozen zone at the base of the frozen fringe and show how this behavior can be incorporated into existing parameterizations of glacier slip. Key Points: Ring shear experiments show frozen fringe alters basal slip dynamics for soft‐bedded glaciersDeformation in a zone of weakly frozen sediments within the fringe leads to a regularized Coulomb slip response [ABSTRACT FROM AUTHOR]

Whispering gallery mode (WGM) optical microcavities have played an essential role in both fundamental research and practical applications, such as cavity quantum electrodynamics, optomechanics, microlasers, and optical sensors. While microcavities made of various materials (e.g., SiO2, As2S3, polymethylmethacrylate) have been extensively investigated, exploiting new materials for microcavities holds great promise for expanding the functionalities of the microcavities. As one of the most ubiquitous and important solids on earth's surface, ice exhibits intriguing optical properties that render it an excellent material for optical applications. Here, ice microsphere optical cavities are demonstrated for the first time. By rapidly freezing water microdroplets, ice microspheres are batch‐fabricated with relatively smooth surfaces and diameters of 5–50 µm. Excitation of a series of WGMs within ice microsphere cavities is achieved over a broad spectral range from near‐ultraviolet to near‐infrared region (380–1600 nm) with quality factors up to 1.4 × 103. Considering the extremely low absorption coefficient of ice in the ultraviolet, this work provides an exceptional platform for exploring ultraviolet microcavity photonics and its diverse applications. [ABSTRACT FROM AUTHOR]

Ice has been suggested to have played a significant role in the origin of life partly owing to its ability to concentrate organic molecules and promote reaction efficiency. However, the techniques for studying organic molecules in ice are absorption‐based, which limits the sensitivity of measurements. Here we introduce an emission‐based method to study organic molecules in water ice: the phosphorescence displays high sensitivity depending on the hydration state of an organic salt probe, acridinium iodide (ADI). The designed ADI aqueous system exhibits phosphorescence that can be severely perturbed when the temperature is higher than 110 K at a concentration of the order of 10−5 M, indicating changes in hydration for ADI. Using the ADI phosphorescent probe, it is found that the microstructures of water ice, i.e., crystalline vs. glassy, can be strongly dictated by a trace amount (as low as 10−5 M) of water‐soluble organic molecules. Consistent with cryoSEM images and temperature‐dependent Raman spectral data, the ADI is dehydrated in more crystalline ice and hydrated in more glassy ice. The current investigation serves as a starting point for using more sensitive spectroscopic techniques for studying water‐organics interactions at a much lower concentration and wider temperature range. [ABSTRACT FROM AUTHOR]

The relationship between precipitation and cloud properties in Southwest China are investigated by using the CLARA‐A2 cloud parameters data and TRMM‐3B43 precipitation data from 1998 to 2015. Ice water path (IWP) and cloud top height (CTH) are significantly and positively correlated with precipitation in all regions, indicating that ice‐phase processes and cloud development processes are the critical processes influencing precipitation. Precipitation is also directly associated with cloud fractional coverage (CFC) due to the significant positive correlation between CFC and precipitation in all regions except the Sichuan Basin (SCB). A positive correlation between liquid water path (LWP) and precipitation is found in the Eastern Tibetan Plateau (ETP) and Yunnan‐Kweichow Plateau (YKP), but not in the Western Tibetan Plateau (WTP) and SCB. Notably, the response of precipitation to LWP is not as good as that to IWP in SCB. Precipitation is significantly negatively correlated with ice effective radius (IREF) in WTP and ETP and positively correlated with liquid effective radius (LREF) in ETP, YKP and SCB. IREF and LREF are closely related to cloud microphysical processes. Specifically, small IREF could accelerate the Bergeron process and thus increase precipitation, while large LREF is closely related to the cloud droplets coalescence process. Results indicate that the difference in precipitation between the cold and warm seasons is related to convective available potential energy (CAPE) and low troposphere relative humidity (RH). High CAPE and RH favour the precipitation occurrence in Southwest China. The influence of CAPE and RH on precipitation is more significant in the ETP than that in the WTP, owing to the orographic lifting and moisture transport from the Indian Ocean. Thermodynamic and humidity conditions have a greater impact on precipitation by influencing LREF, LWP and IWP in YKP. In SCB, precipitation shows a strong dependence on CAPE, IWP and LREF, but not on RH. [ABSTRACT FROM AUTHOR]

Predicting the productivity of the freeze desalination process is of key importance. This paper describes an analytical method to predict the productivity for the progressive freeze desalination process utilizing the rectangular channel crystallizer design. The mass of ice produced during the process is considered a measure of productivity. The model was developed using heat and mass transfer modeling. The effect of coolant temperature (from −8 to −16 °C), liquid flow rate (4400–6000 mL min−1), and initial salt concentration of the liquid (1.5–7 wt%) on the mass of ice produced was investigated. The analytical results of the mass of ice produced were compared with the experimental data. A plausible match was found between the analytical and experimental results, with an error range between 6 % and 9 %. The model can predict the mass of ice produced for given values of the initial salt concentration of the liquid, initial mass of the liquid, salt concentration of thawed ice, liquid flow rate, and coolant temperature. [ABSTRACT FROM AUTHOR]

Partial storage strategy can save energy and reduce emissions. In this study, analysis of the partial melting process of ice inserted with nanoparticles inside a square enclosure is investigated for thermal energy storage. The lattice Boltzmann method is for melting and heat transfer in the storage unit. The validation demonstrates strong concurrence between the current findings and the experimental data documented in the literature. The analysis is performed for various Rayleigh numbers, nanoparticle volume fractions, and their effect on melting time and energy storage. Two types of nanoparticles are tested that is, copper and alumina. The outcomes indicate that the Rayleigh number and volume fraction of nanoparticles have a significant impact on the phase change process. The nanoparticles addition leads to homogenous and hence expedited melting process including the final stage of the ice melting process which is very slow without nanoparticles. Furthermore, copper nanoparticles are slightly more effective than alumina. Moreover, using 6% copper nanoparticles can reduce the melting time by up to 12.4%. [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]

Multiple Earth system models (ESMs) discretize surface albedo into two semi‐broadbands comprising the UV/visible and near‐infrared (NIR) wavelengths. Here, we use an offline single‐column radiative transfer model to investigate the radiative effects of spectrally resolving the surface albedo. We use the Snow, Ice, and Aerosol Radiative model, extended to simulate liquid water, to calculate snow, ice, and liquid water albedo. We flux‐weight the hyperspectral albedo into the coarser spectral bands used by the atmospheric shortwave radiative transfer model. We establish representative atmospheric profiles for the three surface types and compare their shortwave fluxes and atmospheric warming rates with the spectrally resolved albedo to those calculated with the semi‐broadband approximation. Spectrally resolved surface albedo over snow and ice reduces atmospheric warming by darkening the albedo of NIR bands, correcting the too‐strong surface absorption in visible bands, and too‐weak surface absorption in shortwave infrared bands caused by the semi‐broadband approximation. We explore the effects on surface and atmospheric warming rates of varying solar zenith angle, cloud cover, relative humidity, and snow grain/air bubble radii. The semi‐broadband albedo biases can exceed 10% and 2% for the surface and atmospheric net flux respectively, being particularly strong under conditions which alter the distributions of surface insolation (i.e., cloud cover or increased atmospheric water vapor). These results show that transmitting a higher resolution spectral radiation field between the atmosphere and surface reduces biases in surface absorption and atmospheric heating present in ESMs that currently use the semi‐broadband approximation. Plain Language Summary: Snow, ice, and (to a lesser extent) liquid water reflectances depend on the wavelength of light. Snow, for example, reflects almost all light at shorter, or visible, wavelengths, while absorbing longer, near‐infrared wavelengths. Some Earth System Models (ESMs) approximate this spectrally varying reflectance with two bands. This eases the computational burden, yet fails to accurately capture the spectrally structured absorption of the surface, and changes the distribution of flux that is reflected back to the atmosphere. Here we use a single‐column radiative transfer model to expand the spectral representation of snow, ice, and liquid water albedo to 14 bands (matching those used by the atmospheric model in ESMs). By implementing this moderately resolved albedo, we change the radiation absorbed by the surface, as well as the atmosphere. Depending on environmental conditions, implementing a 14 band albedo over snow changes surface absorption by over 10%, relative to the semi‐broadband approximation, which increases or reduces the susceptibility of snow to melting. Furthermore, changes to the spectral distribution of sunlight reduce atmospheric absorption by nearly 2%. These results highlight the importance of accurately representing the spectral albedo for snow and ice‐covered surfaces in ESMs that adopt the semi‐broadband albedo approximation. Key Points: Spectrally varying surface albedo and cloud extinction cause the largest biases in semi‐broadband albedo approximationsSuch approximations simultaneously overestimate surface and atmospheric heating under clear skies, and destabilize the lower atmosphereSpectrally resolved albedo of snowpack can change clear and cloudy sky surface absorption by up to 1% and 10%, respectively [ABSTRACT FROM AUTHOR]

At high latitudes, submesoscale dynamics act on scales of O $\mathcal{O}$(100 m–1 km) and are associated with the breakdown of geostrophic balance, vertical velocities, and energy cascading to small scales. Submesoscale features such as fronts, filaments, and eddies are ubiquitous in marginal ice zones forced by the large horizontal density gradients. In July 2020, we identified multiple fronts and filaments using a towed undulating vehicle near the sea ice edge in central Fram Strait, the oceanic gateway to the Arctic Ocean between Greenland and Svalbard. Sea ice covered the entire study region 1–2 weeks earlier, and a stratified meltwater layer was present. We observed a front between warm and saline Atlantic Water (AW) and cold and fresh Polar Water (PW) at 30–85 m depth, where we identified a subsurface maximum in chlorophyll fluorescence and other biogeochemical properties extending along the tilted isopycnals down to 75 m, indicating subduction of AW (mixed with meltwater) that had previously occurred. The meltwater layer also featured multiple shallow fronts, one of which exhibited high velocities and a subsurface maximum in chlorophyll fluorescence, possibly indicating subduction of PW below the meltwater layer. The fronts at different depth levels suggest a stepwise subduction process near the ice edge, where water subducts from the surface below the meltwater and then further down along subsurface fronts. The submesoscale features were part of a larger‐scale mesoscale pattern in the marginal ice zone. As sea ice continuously retreats, such features may become more common in the Arctic Ocean. Plain Language Summary: Submesoscale dynamics are small‐scale (100 m–1 km) horizontal and vertical flows that create fronts and whirls. These features are typical in the transition from open ocean to sea ice. In the summer of 2020, we observed multiple fronts near the sea ice edge in central Fram Strait. Fram Strait is the oceanic gateway between the Atlantic Ocean and the Arctic Ocean. At the time, fresh meltwater covered the area. Below the meltwater layer, we observed a front between warm and saline Atlantic Water (AW) and cold and fresh Polar Water (PW). The amount of fluorescence (a measure of biomass) observed below the PW showed that AW moved downwards. Prior observations show that AW is in touch with the sea surface in the eastern part of Fram Strait. Our observations thus suggest a step‐by‐step process happening near the ice edge. AW moves from the surface below the meltwater in the first step and down below PW in the second step. This process can increase the vertical transport of biological material (i.e., carbon) near the ice edge in summer. The vertical transport is part of the global carbon cycle. Key Points: We present a study of temporally and spatially highly resolved observations of a front system near the ice edgeWe observe no mixed layer and the ocean is stratified up to the surfaceWe propose that subduction occurs stepwise along surface meltwater fronts and subsurface fronts separating Polar Water and Atlantic Water [ABSTRACT FROM AUTHOR]

Present understanding of Greenland's subglacial geology is derived mostly from interpolation of geologic mapping of its ice‐free margins and unconstrained by geophysical data. Here we refine the extent of its geologic provinces by synthesizing geophysical constraints on subglacial geology from seismic, gravity, magnetic and topographic data. North of 72°N, no province clearly extends across the whole island, leaving three distinct subglacial regions yet to be reconciled with margin geology. Geophysically coherent anomalies and apparent province boundaries are adjacent to the onset of faster ice flow at both Petermann Glacier and the Northeast Greenland Ice Stream. Separately, based on their subaerial expression, dozens of unusually long, straight and sub‐parallel subglacial valleys cross Greenland's interior and are not yet resolved by current syntheses of its subglacial topography. Plain Language Summary: The Greenland Ice Sheet obscures the rocks beneath 79% of Greenland. By necessity, scientists have relied mostly on studying the rocks exposed along Greenland's edge to understand the island's interior geology. We examine geophysical data from seismometers on the ground, satellites that measure Earth's gravity and magnetic fields and surface topography, and aircraft that measure those same properties and ice thickness. We draw a new map of Greenland's geology beneath the ice sheet by examining where those data show similar signals regarding the nature of the underlying rock, and where they could be related to mapped rock exposures. We also find evidence of some areas with geophysical expressions that are distinct from the rocks found at the island's edges. Some geologic structures, which are entirely covered by ice, may affect how ice flows from Greenland's vast interior toward its coast. Finally, we identify many valleys beneath the ice that are very long and often aligned with each other, but which are not yet fully captured in present maps of the topography beneath the ice. Key Points: We produced a new synthesis of subglacial boundaries for Greenland's geologic provinces from seismic, gravity, magnetic and topography dataThree subglacial regions in central and northern Greenland cannot yet be reconciled with surface‐exposed geologic provincesWe find evidence for a large subglacial valley network that is not fully resolved by subglacial topography syntheses for Greenland [ABSTRACT FROM AUTHOR]

The roles of surface characteristics of the feldspar surface on ice nucleation have remained elusive. Here, simple strategies are reported to quantitatively analyze the effects of the surface morphology and molecular composition of the potassium‐feldspar surface on ice nucleation. The steps are found to be responsible to the high ice nucleation efficacy according to the fact that water drop freezing temperature increases by about 4.5 °C atop the freshly cleavage feldspar surface being rich of steps comparing to the flattened ones. After the molecular component and atomic structure are destroyed by the fluorination, a tremendous decrease of the ice nucleation temperatures by around 9.0 °C is observed on both cleavage and flattened surfaces, and the steps still improve the ice nucleation activity of the hydrophobic cleavage surfaces. The influence of the surface composition also implies the importance of the molecular component and structure specificity on K‐feldspar in facilitating ice nucleation. [ABSTRACT FROM AUTHOR]

The Monte‐Carlo ice microphysics model McSnow is extended by an explicit habit prediction scheme, combined with the hydrodynamic theory of Böhm. Böhm's original cylindrical shape assumption for prolates is compared against recent lab results, showing that interpolation between cylinder and prolate yields the best agreement. For constant temperature and supersaturation, the predicted mass, size, and density of the ice crystals agree well with the laboratory results, and a comparison with real clouds using the polarizability ratio shows regimes capable of improvement. An updated form of the inherent growth function to describe the primary habit growth tendencies is proposed and combined with a habit‐dependent ventilation coefficient. The modifications contrast the results from general mass size relations and significantly impact the main ice microphysical processes. Depending on the thermodynamic regime, ice habits significantly alter depositional growth and affect aggregation and riming. The influence of primary ice behavior on precipitation formation needs to be considered in future development of microphysical parameterizations, but the consideration of secondary habits and the geometry of aggregates should be further improved in future work. Plain Language Summary: The McSnow model was extended to predict the shape of ice crystals. A comparison of the falling behavior of modeled and 3D‐printed ice crystals shows a discrepancy that can be improved by interpolation. At constant temperature and supersaturation, simulated crystal properties agree well with laboratory results, and by comparison to real clouds, we have updated the function to describe growth tendencies. Ice shape is shown to have a significant influence on the main microphysical processes. Key Points: McSnow is extended by an explicit habit prediction including the revision of corresponding parameterizationsA new inherent growth ratio overcoming existing deficiencies is proposedThe impact of the modifications on the depositional growth, aggregation, and riming is shown for two distinct case studies [ABSTRACT FROM AUTHOR]

This study proposes a novel framework for ice‐rich saturated porous media using the phase‐field method (PFM) coupled with a thermo‐hydro‐mechanical (THM) formulation. By incorporating the PFM and THM approaches based on the continuum theory, we focus on the mechanical responses of fully saturated porous media under freeze‐thaw conditions. The phase transition between liquid water and crystalline ice can be explicitly expressed as captured by evaluating the internal energy and implementing thermal, mechanical, and hydraulic couplings at a diffused interface using PFM. Accurately modeling the coupled mechanical behaviors of ice and soil presents significant challenges. Therefore, in previous numerical frameworks, ad hoc constitutive models were adopted to phenomenologically estimate the overall behavior of frozen soil. To address this, we employ a method that differentiates between the kinematics of the solid and ice constituents, enabling our framework to accommodate distinct constitutive models for each constituent. Within this framework, we naturally introduce anisotropy of frozen soil as it undergoes the freezing process by integrating a transversely isotropic plastic constitutive model for ice. We illustrate the capabilities of our proposed approach through numerical examples, demonstrating its effectiveness in modeling the phase transition process and revealing the overall anisotropic responses of frozen soil. [ABSTRACT FROM AUTHOR]

We extend a numerical modeling approach developed to explicitly model convective heat transfer in periglacial landforms to represent the ground thermal regime of low‐altitude talus slopes. Our model solves for heat conduction and accounts explicitly for air convection adopting a Darcy term with a Boussinesq approximation for air circulation in the porous ground. Numerical model experiments for the low‐altitude talus slope Dreveneuse, Switzerland, confirm that air convection is the key to forming and maintaining ground ice. In the model, the porous talus slope is underlain by a layer of water‐bearing morainic material. In years, where the gradient between air and talus temperature is sufficiently large to result in increased convection and therefore cooling, ground ice forms due to air convection within the porous material and lasts for more than a year. It is only by considering convection that the model is able to represent the occurrences of ground ice, in accordance with temperature observations on‐site. These findings are important, as they confirm that ground ice can be formed and maintained in landforms with a mean annual air temperature > 0°C if ground air convection is present combined with the presence of water. [ABSTRACT FROM AUTHOR]

Eruptions of the Askja Volcano in Northern Iceland in 1875 and 1961 blanketed the caldera with rhyolitic and basaltic tephra deposits, respectively, which preserved layers of seasonal snowpack as massive ice. Askja serves as an operational and geophysical analog to test ground‐penetrating radar field and analysis techniques for in situ resource utilization objectives relevant to the martian and lunar environments. We conducted ground‐penetrating radar surveys at center frequencies of 200, 400, and 900 MHz to map the thickness and extent of tephra deposits and underlying massive ice at three caldera sites. We identified up to 1 m of tephra preserving up to 4.4 m of massive ice. We measured the real dielectric permittivity of the overlying tephra and the total attenuation at each frequency of the tephra and ice. A key objective of our investigation was to determine if attenuation (or loss) could be used as an additional diagnostic signature of massive ice preserved at depth when compared to ice‐free stratigraphy. Loss rates of the ice‐rich subsurface decrease with increasing ice thickness relative to the overburden, which may constitute a possible signature. Attenuation also increased with increasing frequency. The tephra, ice, and other volcanic deposits at each of our three caldera sites and the ice‐free, pumice‐mantled 1961 Vikrahraun lava flow exhibited consistently low loss rates at all frequencies. This result highlights the ambiguity associated with identifying the unique signature of ice within low‐loss stratigraphies, a possible challenge for its identification in the martian or lunar subsurface using radar. Plain Language Summary: The Askja Volcano in Northern Iceland is considered to be a planetary analog for other terrestrial worlds such as Mars and the Moon. We conducted ground‐penetrating radar surveys of the Askja caldera where seasonal snowpack was buried by eruptions of low‐density ash and tephra in 1875 and 1961. This erupted volcanic material protected the snowpack long‐term, where it later densified into thick layers of ice. We successfully mapped up to 4.4 m of this ice preserved beneath up to 1 m of erupted material. Transmitted radar signals decay naturally as their distance from the source increases. Some materials such as water ice are less conducting than others and are therefore less lossy to this transmitted signal. We used the ice and tephra deposits at Askja as a test case to determine if large quantities of buried ice would result in a detectable signature that indicates its presence when compared to ice‐free regions. We found that increases in ice layer thickness relative to the overlying volcanic material result in columns of material with bulk properties that are less dissipative to the radar signal and therefore may indicate a signature of buried ice in the subsurface. Key Points: Multi‐frequency Ground‐penetrating radar (GPR) surveys identified massive ice up to 4.4 m thick buried by up to 1 m of tephra from two Holocene eruptions of AskjaGPR readily maps vertical and horizontal extents of subsurface ice and tephra overburden; ice concentration transitions are not detectedIce‐rich and ice‐free sites present a similar attenuation; ice‐rich sites demonstrate a lower attenuation rate with increasing ice thickness [ABSTRACT FROM AUTHOR]

In each of the last three decades of the 20th century there were unprecedented expansions of sea‐ ice over the Labrador Sea basin and influxes of cold fresh water into the subpolar gyre (SPG) which have been described as the Great Salinity Anomalies (GSAs). Employing data for sea surface temperature, salinity, and sea‐ice cover, we propose that these events were downstream consequences of the expansion and subsequent melting of so‐called “Odden” ice formed over the deep basin of the Greenland‐Iceland‐Norway (GIN) Sea in the 1960s, 1970s, and 1980s and additional to the normal East Greenland shelf sea‐ice. We extend previous findings that Odden ice expansions were linked to winter episodes of high atmospheric pressure north of Greenland that directed freezing Arctic winds across the GIN Sea and may also have been associated with increased Arctic sea‐ ice volume leading to enhanced ice export through Fram Strait. We show that cold water and ice derived from Odden melting in the summer passed through Denmark Strait and along the East Greenland shelf, and accumulated in the Labrador Sea, creating favorable conditions for winter ice formation during particularly cold years in southwest Greenland. Meltwater from Odden and Labrador Sea ice appeared to break out into the SPG in the fall of 1982 and 1984 respectively and this cold water represents the likely source of the 1982–1985 GSA. These findings further our understanding of the physical processes linking ice formation and melt with ocean circulation in this key component of the climate system. [ABSTRACT FROM AUTHOR]

Turbulence in clouds is known to enhance particle collision rates, as widely demonstrated for warm rain formation. A similar impact on ice growth processes is expected but a solid observational basis is missing. A statistical analysis of a 15‐month data set of cloud radar observations allows for the first time to quantify the impact of turbulence on ice aggregation and riming in Arctic low‐level mixed‐phase clouds. Increasing eddy dissipation rate (EDR), from below 10−4 to above 10−3 m2 s−3, yields larger ice aggregates, and higher particle concentration, likely caused by increasing fragmentation. In conditions more favorable to riming, higher EDR is associated with dramatically higher particle fall velocities (by up to 125%), under similar liquid water paths, indicative of markedly higher degrees of riming. Our findings thus reveal the key role of turbulence for cold precipitation formation, and highlight the need for an improved understanding of turbulence‐hydrometeor interactions in cold clouds. Plain Language Summary: Liquid and frozen precipitation mainly forms by collision and subsequent aggregation of small particles. Collisions between cloud particles, such as droplets and ice crystals, are thought to be increased by turbulence. While this effect has been intensively studied for liquid‐only clouds, the impact of turbulence on ice‐ice collisional growth (aggregation) and ice‐liquid collisional growth (riming) is expected but has so far been poorly quantified. We study the effect of turbulence on aggregation and riming based on a long‐term remote‐sensing data set of low‐level clouds containing both ice and liquid particles, recorded at the Arctic site of Ny‐Ålesund, Svalbard. Cloud radar observations are used to retrieve the dissipation rate of turbulent kinetic energy (i.e., the eddy dissipation rate; EDR), which is the relevant quantity driving increases in collision rates, and to characterize ice particle properties. We find evidence that higher EDR regimes enhance the aggregation of particles, and are associated with signatures of increased ice particle concentration, possibly caused by the production of particle fragments upon collision. In temperature regimes more favorable to riming, turbulence dramatically enhances the particles' fall velocity, denoting higher degrees of riming. Our findings thus highlight a key role of turbulence for the formation of precipitable ice. Key Points: Relation between turbulence and ice growth investigated based on long‐term remote sensing data set of Arctic low‐level mixed‐phase cloudsHigher eddy dissipation rate (EDR) correlates with larger ice aggregates, and possibly higher degrees of fragmentationHigh EDR is an essential component needed for the formation of rimed particles [ABSTRACT FROM AUTHOR]

We determined the frictional strength and stability of polycrystalline ice and ice‐ammonia to constrain fault behavior on icy satellites such as Enceladus and Europa. Friction experiments including velocity steps and slide‐hold‐slide tests were conducted to measure the steady‐state coefficient of friction, velocity dependence and healing between temperatures of 98 and 248 K at a normal stress of 100 kPa. Rate‐state friction parameters determined from velocity steps provide stability values. The friction results are used to infer fault strength and frictional heating of an icy crust with depth for both a pure ice crust and one containing ammonia. We find a reduced coefficient of friction for an ammonia‐bearing crust and stronger velocity dependence in the presence of partial melt. The temperature dependence of fault stability maps a seismogenic zone with depth analogous to the synoptic model for terrestrial fault stability, where we find instability between 0.7 and 3.9 km with a return to stability from 4.6 km if we assume a 6 km ice shell. We consider the role of sliding velocity and fault thickness on localized frictional heating in both systems and estimate the depth of melt generation in an ammonia‐bearing crust. Our results imply that faults at conditions similar to icy satellites can be seismogenic. Plain Language Summary: We performed laboratory friction experiments with ice at conditions (e.g., temperature, composition, stresses) analogous to tidally driven faults on icy satellites in the outer solar system. We observed a temperature dependence on the coefficient of friction of ice under these conditions, which may help improve shear heating models on icy faults. We use the velocity dependence of friction observed in the experiments to constrain the depths (based on temperature) in a 6 km ice shell where seismic activity may occur. We find instability between 0.7 and 3.9 km with a return to stability from 4.6 km. We explored the effect of partial melt on ice friction and fault stability using ice‐ammonia mixtures and found that the presence of ammonia decreases the coefficient of friction while the presence of partial melt increases the velocity dependence. Key Points: Velocity weakening friction behavior is observed below 220 K, indicating a potential seismogenic zone with depth on icy moonsWe establish temperature dependence of the coefficient of friction for water ice that can be used to improve shear heating modelsThe effect of solid‐state impurities on friction is constrained using homologous temperature and melt fraction with ice + ammonia mixtures [ABSTRACT FROM AUTHOR]

Cold climate rivers can experience avulsions due to both open water and ice jam flooding; however, most existing models for evaluating avulsions only consider open water flows. We present a novel approach for determining site‐specific probabilities of avulsion cause (open water vs. ice jam flooding) by combining historical flow data, channel cross‐sections and known avulsion history for the study area. The approach is applied to the Cumberland Marshes region of the Saskatchewan River in Central Canada, which experienced an avulsion in the mid‐1870s that some researchers have suggested may have been triggered by an ice jam. For the study area, overbank flooding was found to occur much more frequently due to ice jams than open‐water floods. Based on an average avulsion return period of 660 years in the study area, the probability of historical avulsions being caused by ice jam flooding was estimated to range from 61% and 80%, using a range of annual ice jam probabilities between 0.1 and 0.5. Results from the study suggest ice jam flooding as the most likely cause of the 1870s avulsion, which is also supported by historical evidence. The developed methodology is relatively simple to apply and could be easily implemented at other cold‐climate sites to evaluate avulsion risks. [ABSTRACT FROM AUTHOR]

Aufeis (also known as icings) are large sheet‐like masses of layered ice that form in river channels in arctic environments in the winter as groundwater discharges to the land surface and subsequently freezes. Aufeis are important sources of water for Arctic river ecosystems, bolstering late summer river discharge and providing habitat for caribou escaping insect harassment. The aim of this research is to use numerical simulations to evaluate a conceptual model of subsurface hydrogeothermal conditions that can lead to the formation of aufeis. We used a conceptual model based on geophysical data from the Kuparuk aufeis field on the North Slope of Alaska to develop a two‐dimensional heterogeneous vertical profile model of groundwater flow, heat transport, and freeze/thaw dynamics. Modelling results showed that groundwater can flow to the land surface through subvertical high permeability pathways during winter months when the lower permeability soils near the land surface are frozen. The groundwater discharge can freeze on the surface, contributing to aufeis formation throughout the winter. We performed sensitivity analyses on subsurface properties and surface temperature and found that aufeis formation is most sensitive to the volume of unfrozen water available in the subsurface and the rate at which the subsurface water travels to the land surface. Although a trend of warming air temperatures will lead to a greater volume of unfrozen subsurface water, the aufeis volume can be reduced under warming conditions if the period of time for which air temperatures are below freezing is reduced. [ABSTRACT FROM AUTHOR]

Recent observations revealed the existence of ice slabs and aquifers on the Greenland ice sheet (GrIS). Both affect the ice sheet's hydrology: ice slabs facilitate runoff and aquifers modulate drainage to the bed. However, their climatic drivers and history remain unclear, as most observations cover only two decades. Here, we present a model simulation of the evolution of GrIS ice slabs and aquifers (1980–2020), evaluated using radar measurements. The results show that accumulation, melt and rain rates are good predictors for the spatial distribution of ice slabs and aquifers. Both features were already present in the late 1980s, and their extent remained relatively constant until the beginning of this century, after which increased melt led to their expansion. We show that almost any transect from the coast to the ice‐sheet interior will cross either an ice slab region, or an aquifer, or both. Plain Language Summary: The Greenland ice sheet is covered by a layer of old, porous snow called firn, which has the capacity to prevent surface melt runoff. The firn can however, form thick ice slabs or store large amounts of water underground. These change the fate of surface melt by respectively enhancing runoff and draining water to the ice sheet's bed. While observations have shown where these phenomena occur, it is still unknown what the exact atmospheric conditions are that lead to their formation. Here, we tackle this problem using computer simulations. Our results show that the amount of snowfall, melt and rain determine whether ice slabs or aquifers can form. The results also suggest that ice slabs and aquifers are more abundant than previously assumed, and that their observed expansion started only in the early 2000s, and they will continue to expand if the climate gets warmer and melt and rain become more abundant. Key Points: Accumulation, melt and rain are good predictors of ice slab and firn aquifer locationsThe expansion of modeled ice slabs and aquifers on the Greenland ice sheet started in the early 2000sWe show that, in between the ablation zone and the accumulation zone, there are always ice slabs and/or aquifers present [ABSTRACT FROM AUTHOR]

In some areas of Antarctica, blue‐colored bare ice is exposed at the surface. These blue ice areas (BIAs) can trap meteorites or old ice and are vital for understanding the climatic history. By combining multi‐sensor remote sensing data (MODIS, RADARSAT‐2, and TanDEM‐X) in a deep learning framework, we map blue ice across the continent at 200‐m resolution. We use a novel methodology for image segmentation with "noisy" labels to learn an underlying "clean" pattern with a neural network. In total, BIAs cover ca. 140,000 km2 (∼1%) of Antarctica, of which nearly 50% located within 20 km of the grounding line. There, the low albedo of blue ice enhances melt‐water production and its mapping is crucial for mass balance studies that determine the stability of the ice sheet. Moreover, the map provides input for fieldwork missions and can act as constraint for other geophysical mapping efforts. Plain Language Summary: While most of the continent of Antarctica is covered by snow, in some areas, ice is exposed at the surface, with a typical blue color. At lower elevations, blue ice enhances melt‐water production, which is important for studying the future of the ice sheet. Moreover, scientific teams frequently visit blue ice areas (BIAs) as they act as traps for meteorites and very old ice. In this study, we map the extent and the exact location of BIAs using various satellite observations. These diverse observations are efficiently combined in an artificial intelligence algorithm. We develop the algorithm so that it can learn to map blue ice even though existing training labels, which teach the algorithm what blue ice looks like, are imperfect. We quantify that the new map scores better on various performance metrics compared to the current most‐used blue ice map. Moreover, for the first time, we estimate uncertainties of the detection of blue ice. The map indicates that ca. 1% of the surface of Antarctica exposes blue ice and will be important for fieldwork missions and understanding surface processes leading to melt and potential sea level rise. Key Points: We map blue ice areas in Antarctica by combining multi‐sensor satellite observations in a convolutional neural networkBlue ice covers ca. 140,000 km2 (∼1%) of Antarctica, of which ca. 50% located in the grounding zoneOur map will improve mass balance estimates and studies on ice‐shelf stability, and will support searches for meteorites or old ice [ABSTRACT FROM AUTHOR]

The freezing point of water is negatively dependent on pressure; therefore in any ocean without external forcing it is warmest at the surface and grows colder with depth. Below floating ice on Earth (e.g., ice shelves or sea ice), this pressure dependence combines with gradients in the ice draft to drive an ice redistribution process termed the "ice pump": submerged ice melts, upwells, and then refreezes at shallower depths. Ice pumping is an exchange process between the ocean and overhead ice that results in unique ice compositions and textures and influences the distribution of sub‐ice habitats on Earth. Here, we scale recent observations from Earth's ice shelves to planetary conditions and find that ice pumping is expected for a wide range of possible sub‐ice shell pressures and salinity at other ocean worlds such as Europa and Enceladus. We show how ice pumping would affect hypothetical basal ice shell topography and ice thickness under varying ocean conditions and demonstrate how remote sensing of the ice shell draft can be used to estimate temperature gradients in the upper ocean ahead of in situ exploration. For example, the approximately 22 km gradient observed in Enceladus' ice shell draft between the south pole and the equator suggests a temperature differential of 0.18 K at the base of the ice shell. These concepts can extend the interpretation of observations from upcoming ocean world missions, and link ice shell topography to ice‐ocean material exchange processes that may prove important to overall ocean world habitability. Plain Language Summary: The freezing point of water depends on pressure. As pressure increases, the freezing point decreases, which can influence the melting or freezing of ice in an ocean. A helpful way to conceptualize this dependency is to recall that water expands as it freezes. As pressure increases, this expansion requires more work to displace the higher pressure surroundings, so the water must be even colder to freeze—a decrease in the freezing point. If ice is submerged, the deeper ice where the freezing point is colder can melt faster. This forms freshened meltwater that may rise to shallower depths where it is now colder than the shallower, lower pressure freezing point and can refreeze underwater. This process is referred to as an "ice pump", because it acts to equilibrate topography in submerged ice. In ice‐covered oceans on Earth, the ice pump is an important process that influences the composition and texture of the ice, and therefore the sub‐ice ecosystems. Here, we find that ice pumping is also likely at other ocean worlds in our solar system where it may similarly influence potential sub‐ice ecosystems and show how observations of planetary ice shell thicknesses can be used to bound ocean conditions. Key Points: When ice is submerged, a melting and freezing exchange process termed the "ice pump" can affect ice composition, texture, and thicknessWe find that ice pumping is likely beneath the ice shells of several ocean worlds in our solar systemThe ice pump concept enables inversion between ocean world ice shell thickness and ice‐ocean interface temperature ranges [ABSTRACT FROM AUTHOR]

Double ridges are sprawling features observed globally across the icy surface of Europa. They consist of two topographic highs flanking a trough. The topographic relief of the ridges is approximately 100 m, and the ridges extend up to hundreds of kilometers in length. The interior structure and dynamics of Europa's ice shell are currently poorly constrained. Therefore, accurate models for the formation of these prominent surface features can be useful for determining how the ice shell operates. We hypothesize that double ridges form as a result of incremental ice wedging. We use both analytical and numerical finite element models to quantify the deformation that occurs as an ice wedge grows incrementally within the ice shell. We show that incremental growth of the ice wedge results in surface deformation that matches the size and shape of typical Europan double ridges, including their topographic relief and surrounding troughs. We find that as the depth of the ice wedge increases, double ridges become broader and shorter. We explore the possibility of local and non‐local sources for the liquid water that freezes to produce the wedge and ultimately argue in favor of local sources of liquid water within the ice shell. Plain Language Summary: Europa, the second Galilean satellite, is hypothesized to have a global salt‐water ocean underneath its outer icy shell. Double ridges are a common feature on Europa's icy surface. They consist of a long trough bordered on either side by uplifted hills of ice. The height of the ridges above the surface is approximately 100 m, and the ridges may extend for hundreds of kilometers over the surface of the moon. Models that show how surface features, like double ridges, may form can tell us about characteristics of the ice shell and underlying ocean that are otherwise hard to measure. We use two different techniques to model a process for how double ridges might form. In this process, water, possibly from the subsurface ocean, enters a long vertical crack in the ice shell and freezes along the sides of the crack. Over time as water continues to enter and freeze in the same place, a new wedge of ice grows inside the ice shell and pushes on material around it. The ice wedge forces ice at the surface of the shell to deform into the same size and shape of double ridges that have been observed on Europa. Key Points: Numerical modeling suggests that double ridges are produced by wedges of ice that grow within Europa's ice shellAnalytical and numerical models show that an ice wedge within Europa's ice shell elastically deforms the surface into double ridgesIce wedge material may be sourced from the ocean or locally from cryovolcanic dikes or water reservoirs within the shell [ABSTRACT FROM AUTHOR]

Excess ground ice formation and melt drive surface heave and settlement, and are critical components of the water balance in Arctic soils. Despite the importance of excess ice for the geomorphology, hydrology and biogeochemistry of permafrost landscapes, we lack fine‐scale estimates of excess ice profiles. Here, we introduce a Bayesian inversion method based on remotely sensed subsidence. It retrieves near‐surface excess ice profiles by probing the ice content at increasing depths as the thaw front deepens over summer. Ice profiles estimated from Sentinel‐1 interferometric synthetic aperture radar (InSAR) subsidence observations at 80 m resolution were spatially associated with the surficial geology in two Alaskan regions. In most geological units, the estimated profiles were ice poor in the central and, to a lesser extent, the upper active layer. In a warm summer, units with ice‐rich permafrost had elevated inferred ice contents at the base of the active layer and the (previous years') upper permafrost. The posterior uncertainty and accuracy varied with depth. In simulations, they were best (≲0.1) in the central active layer, deteriorating (≳0.2) toward the surface and permafrost. At two sites in the Brooks Foothills, Alaska, the estimates compared favorably to coring‐derived profiles down to 35 cm, while the increase in excess ice below the long‐term active layer thickness of 40 cm was only reproduced in a warm year. Pan‐Arctic InSAR observations enable novel observational constraints on the susceptibility of permafrost landscapes to terrain instability and on the controls, drivers and consequences of ground ice formation and loss. Plain Language Summary: Permafrost soils can contain substantial quantities of ice. When the ice melts due to warming or disturbance, the ground becomes unstable, threatening infrastructure, water resources and ecosystem services. We lack fine‐scale ground ice maps across essentially the entire Arctic, limiting our ability to sustainably plan in the Arctic. Here, we develop the first satellite‐based technique for mapping ground ice near the surface, including seasonal ground ice in that part that freezes and thaws every year and also perennial ground ice in soil that had previously remained frozen for long times. The central idea is to measure the subsidence over the summer from satellites and relate this to the ice profile near the surface. In exceptionally warm summers, layers that had previously been frozen for a long time may thaw; where they are ice‐rich, elevated but limited subsidence toward the end of this summer can be used to identify areas whose large ice contents render them susceptible to long‐term terrain instability. The regional to pan‐Arctic maps our novel method can provide promise to bolster sustainable planning and stewardship in the Arctic and to help us understand how these landscapes are changing. Key Points: Remotely sensed subsidence provides insight into near‐surface excess ice profilesThe estimated excess ice profiles were largely consistent with in‐situ observations and associated with the surficial geologyIn warm summers, maps of ice contents in the (previous years') upper permafrost constrain the susceptibility to thaw instability [ABSTRACT FROM AUTHOR]

Adélie‐George V Land in East Antarctica, encompassing the vast Wilkes Subglacial Basin, has a configuration that could be prone to ice sheet instability: the basin's retrograde bed slope could make its marine terminating glaciers vulnerable to warm seawater intrusion and irreversible retreat under predicted climate forcing. However, future projections are uncertain, due in part to limited subglacial observations near the grounding zone. Here, we develop a novel statistical approach to characterize subglacial conditions from radar sounding observations. Our method reveals intermixed frozen and thawed bed within 100 km of the grounding‐zone near the Wilkes Subglacial Basin outflow, and enables comparisons to ice sheet model‐inferred thermal states. The signs of intermixed or near thawed conditions raises the possibility that changes in basal thermal state could impact the stability of Adélie‐George V Land, adding to the region's potentially vulnerable topographic configuration and sensitivity to ocean forcing driven grounding line retreat. Plain Language Summary: East Antarctica's Adélie‐George V Land has been relatively stable over the last few decades. However, this region contains the Wilkes Subglacial Basin, which has a downward‐sloping bed inland of the grounding zone. This could make irreversible retreat possible if warming seawater off the coast enters beneath the ice sheet. However, predicting the region's vulnerability is difficult, in part, because there is limited information about the conditions beneath the ice sheet. In this study, we develop a new statistical approach to synthesize radar sounding data and classify the conditions at the ice‐bed interface into frozen‐bed and thawed‐bed, which can then provide comparisons to ice sheet model output. We find that areas near the outflow of the Wilkes Subglacial Basin, critical in maintaining the stability of the region, might consist of mixed frozen‐bed and thawed‐bed or near‐thawed conditions on the scale of tens of kilometers across. This finding is important since the extent of basal thaw affects how easily ice can flow or slide over the bed. If parts of the bed are close to thawed, this could make Adélie‐George V Land more sensitive to climate forcing, possibly resulting in mass loss. Key Points: We develop an adaptable statistical framework using radar sounding data to classify the basal thermal state of ice sheetsApplied to the Adélie‐George V Coast, the framework reveals a mix of frozen and thawed‐bed, along with confidence in the classificationsAreas maintaining the region's stability have varied thermal states and we consider how this could increase sensitivity to climate forcing [ABSTRACT FROM AUTHOR]

Under‐ice phytoplankton "blooms" have been observed in the Southern Ocean, although irradiance is extremely low and vertical mixing is assumed to be deep. Most under‐ice data have been collected using Argo floats, as research expeditions during austral fall and winter are limited. Hydrographic measurements under dense ice cover indicate that vertical mixing in weakly stratified systems may be less than previously suggested, and that the accepted determinations of mixed layer depths are inappropriate in regions with extremely weak stratification, such as those under ice. Vertical gradients in density suggest that mixed layers in the Ross Sea in early October are not extremely deep; furthermore, while phytoplankton biomass is low, it has begun to accumulate under ice. Growth rates indicate that phytoplankton growth in the Ross Sea begins in early September. Extending the period of growth may have substantial impacts on carbon biogeochemistry and food web energetics in ice‐covered waters. Plain Language Summary: Data from profiling floats under Southern Ocean ice indicate that some growth of plankton occurs there, even though available irradiance is extremely low and vertical mixing is deep. Few research expeditions during austral fall and winter occur due to the difficulty of sampling and penetrating deep into ice. Estimates of vertical mixing in October from the Ross Sea suggest that the accepted criterion of mixed layer depths are inappropriate in regions with extremely weak stratification, such as those under ice. Mixed layers in the Ross Sea in early October are not extremely deep; furthermore, while phytoplankton biomass is low, it has begun to accumulate under ice. Growth rates indicate that the onset of phytoplankton growth in the Ross Sea likely occurs by early September, soon after positive irradiance occurs. Extending the period of growth may have substantial impacts on carbon biogeochemistry and food web energetics in ice‐covered waters. Key Points: Mixed layer depths under extremely weak vertical stratification (like under ice) are overestimated using conventional criteriaPhytoplankton growth in the Ross Sea is initiated soon after the start of solar day, far earlier than has been previously suggestedEarly spring growth can potentially alter our views of Southern Ocean carbon biogeochemistry and food web phenology [ABSTRACT FROM AUTHOR]