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In this study, we provide an ~47.0‐kyr mercury (Hg) deposition record derived from a lacustrine sedimentary sequence in Dahu swamp in the eastern Nanling Mountains, China. The results indicate that organic matter (OM) input played a role in Hg accumulation, whereas the contribution of inorganic weathering detritus had a negligible impact. On the other hand, evolution of the plant community and wildfire events were also important factors affecting Hg accumulation. Compared to arboreal plants, lower (herbs and ferns) plants had stronger absorption and enrichment ability for Hg thus favoring enhanced Hg accumulation in the sediments. We therefore infer that Hg deposition in Dahu sediments was greatly controlled by changes in climatic conditions. Relatively dry and cold climatic conditions, which resulted in reduced arboreal plant communities and increased lower plants, would favor an increased Hg accumulation rate; furthermore, dry conditions may cause more wildfire events thus leading to enhanced release of Hg into the environment and increased contribution of Hg to the sediments, whereas relatively wet and warm conditions would result in the opposite situation. The record of Hg deposition demonstrates a synchronous orbital‐scale variation trend with the intensity of the East Asian summer monsoon. Period analysis reveals several millennial‐ and centennial‐scale cycles similar to solar insolation, together with several millennial events of increased Hg concentration and accumulation rate, which coincided with the corresponding Heinrich events, suggesting joint impacts of solar irradiation and the action of melting water as well as changes in zonal atmospheric circulation on Hg accumulation in Dahu sediments. [ABSTRACT FROM AUTHOR]

Surface freshening of the Southern Ocean driven by meltwater discharge from the Antarctic ice sheet has been shown to influence global climate dynamics. However, most climate models fail to account for spatially and temporally varying freshwater inputs from ice sheets, introducing significant uncertainty into climate projections. We present the first historically calibrated projections of Antarctic freshwater fluxes (sub‐shelf melting, calving, and surface meltwater runoff) to 2300 that can be used to force climate models lacking interactive ice sheets. Our findings indicate substantial changes in the magnitude and partitioning of Antarctic freshwater discharge over the coming decades and centuries, particularly under very‐high warming scenarios, driven by the progressive collapse of the West Antarctic ice shelves. We project a shift in the form and location of Antarctic freshwater sources, as liquid sub‐shelf melting increases under the two climate scenarios considered, and surface meltwater runoff could potentially become a dominant contributor under extreme atmospheric warming. Plain Language Summary: Melting Antarctic ice releases freshwater into the Southern Ocean, which can have profound impacts on the regional and global climate. In a warming world, the freshwater input into the ocean is expected to increase. However, climate models often poorly represent ice‐sheet mass loss, leading to uncertainty in climate predictions. This study provides new projections of Antarctic freshwater discharge, including contributions from melting at the base of the floating ice shelves, iceberg calving and surface meltwater runoff, up to the year 2300. These projections can be integrated into climate models that lack interactive ice sheets. The results indicate substantial changes in the amount and nature of freshwater discharge from Antarctica in the coming decades and centuries, especially under extreme warming scenarios. We show that liquid melting beneath the floating ice shelves will increase under the two climate scenarios considered, and that surface meltwater runoff could become a major source of freshwater under very high atmospheric warming conditions. Key Points: Up to a four‐fold increase in the magnitude of Antarctic freshwater discharge is projected by 2300 for an extreme climate scenarioWe project a shift in the form and depth of Antarctic freshwater export, as sub‐shelf (and potentially surface) melt outpaces solid calvingOur key findings align with satellite‐based observations and are robust despite uncertainties in climate and ice‐dynamical response [ABSTRACT FROM AUTHOR]

Glacier speedups occur on daily to centennial timescales. While basal water and subglacial drainage configuration are thought to drive glacier speedups across these timescales, it remains unclear whether this forcing always occurs through the same mechanisms. Here, we explore whether the enthalpy model of glacier surging can explain speedups over a broader range of timescales if modified to account for seasonality in surface melt and continuous water supply to the glacier bed. We simulate velocity oscillations that range from seasonal to >100 ${ >} 100$ years. Our model results more closely resemble observations of surges than previous model versions because ice flow variability at seasonal and multi‐year timescales is reproduced simultaneously through hydrological forcing. Under favorable conditions, seasonal water delivery to the bed gradually accumulates in a poorly‐connected basal drainage system, priming the glacier to surge. Surges themselves are marked by high water fluxes and enthalpy drainage from the glacier base. Plain Language Summary: Glacier speeds vary over time periods ranging from hours to centuries. Liquid water present at the base of glaciers affects ice speed but it is unclear whether the links between liquid water and ice speed are the same across all timescales. Recent efforts to model multi‐year cycles of fast glacier flow, known as glacier surges, show that a gradual build‐up of heat and/or water at the base of glaciers could drive ice flow instabilities. However, this modeling approach has thus far not accounted for seasonal variations in water flux through glaciers and their influence on glacier flow. In this work we implement seasonal variability in air temperatures within an existing model of glacier surges. We explore the effects of changing the water supply to the glacier base, finding that glaciers that do not transmit surface water through the glacier easily are more prone to surging and that glaciers with a poorly connected drainage system at their base might be more likely to surge. The simulation of surges here demonstrate that a single set of physical relationships between water within glaciers and glacier motion can reproduce a spectrum of observed behaviors, without the need for invoking more complicated physics. Key Points: An enthalpy model is used to simulate realistic variability in glacier velocities, simultaneously over seasonal to multi‐year timescalesEnthalpy modeling can simulate realistic surges, but only under low water supply to the bed and low basal hydraulic transmissivityModeling suggests that poor drainage primes the glacier to surge, but the surge itself is marked by improved basal water flow [ABSTRACT FROM AUTHOR]

Decarbonizing the glass industry requires alternative melting technology, as current industrial melting practices rely heavily on fossil fuels. Hydrogen has been proposed as an alternative to carbon‐based fuels, but the ensuing consequences on the mechanical behavior of the glass remain to be clarified. A critical distinction between hydrogen and carbon‐based fuels is the increased generation of water during combustion, which raises the equilibrium solubility of water in the melt and alters the behavior of the resulting glass. A series of five silicate glasses with 80% silica and variable [Na2O]/([H2O] + [Na2O]) ratios were simulated using molecular dynamics to elucidate the effects of water on fracture. Several fracture toughness calculation methods were used in combination with atomistic fracture simulations to examine the effects of hydroxyl content on fracture behavior. This study reveals that the crack propagation pathway is a key metric to understanding fracture toughness. Notably, the fracture propagation path favors hydrogen sites over sodium sites, offering a possible explanation of the experimentally observed effects of water on fracture properties. [ABSTRACT FROM AUTHOR]

The Ediacaran Period, immediately following the Neoproterozoic Cryogenian glaciations, marked a crucial phase in the Earth's evolutionary history. The paleo‐oceanic environment helped shape the habitability, yet the links between oceanic redox state, hydrochemistry, biological activity, and elemental cycling during this time remain poorly understood. Here, we address this scientific issue based on high‐resolution geochemical data from black shale‐hosted, manganese (Mn)‐rich carbonates within the upper Ediacaran Doushantuo Formation, located on the northern margin of the Yangtze Block, South China. Multiple redox proxies indicate that while the open ocean may have been intermittently oxygenated during the late Ediacaran glaciation, the continental margin slope was characterized by redox stratified conditions with a fluctuating redox interface. These fluctuations were driven by climatic shifts. During the deposition of black shales, a relatively warm and humid climate caused a notable increase in freshwater runoff and glacial meltwater, raising water levels and lowering salinity. The influx of bioessential elements carried by terrestrial runoff promoted primary productivity. By contrast, the deposition of the Mn(II) carbonates occurred under colder, more arid conditions, with limited terrigenous nutrient input, leading to lower organic carbon production. This resulted in the deepening of the redox chemocline over the continental shelf, promoting Mn(II) oxidation and subsequent mineralization. Paleoclimate‐driven redox fluctuations were key in controlling elemental cycling during the late Ediacaran. This may offer insights into similar processes throughout Earth's history. Plain Language Summary: If the late Ediacaran ocean is oxygenated or reducing remains a topic of debate. Here we propose a stratified scenario with an intermittently fluctuating redox interface between O2‐bearing surface waters and O2‐depleted deep waters on the continental margin slope as represented by the Doushantuo Formation of South China. We further establish coupled links between the ancient oceanic redox state, paleoclimate, marine hydrochemistry, biological activity, and Mn‐cycle during this period based on multiple geochemical proxies. Warm and humid climate supplied nutrient elements that fueled high primary productivity, sustaining higher redox interface and widespread H2S‐bearing conditions conducive to black shale deposition. In contrast, a colder, more arid climate limited nutrient supply and productivity, leading to diminished organic carbon synthesis, descending redox interface, and contracted deep O2‐depleted zone, which favored Mn(II) carbonate formation. The fluctuating redox interface created optimal conditions for Mn(II) oxidation, Mn(IV) reduction, and Mn(II) carbonate mineralization during the transformative phase of oxygenation event in the late Ediacaran. This might be general throughout geological history. Key Points: The redox conditions along the continental marginal slope were stratified and fluctuating in the late Ediacaran oceanPaleoclimate variations influenced the basin's hydrochemistry and biological activity, driving shifts in the redox chemoclineThe shifts in the slope's redox chemocline regulated distinct oceanic manganese cycling and mineralization processes in South China [ABSTRACT FROM AUTHOR]

The sliding speed of glaciers depends strongly on the water pressure at the ice‐sediment interface, which is controlled by the efficiency of water transport through a subglacial hydrological system. The least efficient component of the system consists of "distributed" flow everywhere beneath the ice, whereas the "channelized" drainage through large, thermally eroded conduits is more efficient. To understand the conditions under which the subglacial network channelizes, we perform a linear stability analysis of distributed flow, considering competition between thermal erosion and viscous ice collapse. The calculated growth rate gives a stability criterion, describing the minimum subglacial meltwater flux needed for channels to form, but also indicates the tendency to generate infinitely narrow channels in existing models. We demonstrate the need to include lateral heat diffusion when modeling melt incision to resolve channel widths, which allows continuum models to recover Röthlisberger channel behavior. We also show that low numerical resolution can suppress channel formation and lead to overestimates of water pressure. Our derived channelization criterion can be used to predict the character of subglacial hydrological systems without recourse to numerical simulations, with practical implications for understanding changes in ice velocity due to changes in surface melt runoff. Plain Language Summary: Glacier sliding speed depends on the degree of lubrication by water at the bed. During summer months, when there is a lot of water present, heat produced by the water flow can melt large channels into the base of the ice. These channels efficiently drain water out from the bed of the glacier, slowing down the ice flow. We study when and where channels are likely to form by considering whether local increases in water depth grow larger via positive feedback loops, or shrink away. We also look at ways to make simulations less prone to numerical artifacts. We develop a criterion for when channels form and show that our criterion matches the results of numerical simulations, but is much faster to calculate. This can be used to efficiently predict meltwater drainage beneath glaciers, seasonal patterns of ice velocity, and how these will evolve under warming conditions. Key Points: Feedbacks between subglacial water flow and ice melt determine the rate of incision of drainage channels, depending on their spacingWe derive a threshold meltwater input above which channels form under glaciers, a function of ice thickness and geothermal fluxIncluding lateral heat transport allows continuum models of subglacial hydrology to reproduce Röthlisberger channel behavior [ABSTRACT FROM AUTHOR]

Glacial kettles are surficial depressions that form in formerly glaciated terrain when buried stagnant ice melts within pro‐glacial sediments, often deposited by meltwater streams. Kettles, like other glacial landforms, provide insight into the impact of climate on landscape evolution, such as the extent and timing of glaciations. The geometry of kettle features is variable, but existing theory does not explain the range of observed morphologies. Our study aims to establish a quantitative relationship between the depth of ice burial and the resulting morphology of terrain collapse in kettle depressions. To do so, we simulated kettle formation in the laboratory by burying ice spheres of four sizes in well‐sorted coarse sand at four different depths. As the spheres melt at room temperature, a glacial kettle analog forms at the surface. We scanned the resulting kettle topography with a portable LiDAR scanner to produce 3D digital elevation models of each depression, from which we measured each depression's depth and width and, in one instance, the time series of kettle formation. Using this data, we quantified the relationship between the sphere diameter, burial depth and resulting dimensions of the kettle by developing a set of equations, which we then applied to full‐scale features. Our results indicate that ice burial deeper than one sphere diameter corresponds to a decrease in depression depth and an increase in depression width. This application offers insight into the interdependence of ice burial depth and kettle geometry. [ABSTRACT FROM AUTHOR]

Arctic fjords, being transitional areas between glacier‐covered land and the ocean, are characterized by strong environmental gradients. The seasonal melting of glaciers generates strong turbidity and primary production antagonist gradients, which can affect benthic habitats. Two sampling campaigns were carried out in Kongsfjorden (Svalbard, Arctic Ocean) in May and August 2021 to investigate seasonal changes in benthic foraminifera spatial distribution and ecosystem functioning along a longitudinal transect of 10 km from the Kronebreen tidewater glacier front. Concurrently, organic matter quantity and biochemical composition, sediment grain size, and physical parameters of the water masses were investigated as possible driving factors of benthic ecosystem responses. In a previous study, three statistically determined foraminiferal biozonations (glacier proximal, medial, and distal) were observed on the basis of their species content within the closest 10 km from the glacier front, presenting similar assemblages in both seasons. Our results indicate that foraminiferal distribution at the local scale is mainly driven by physical and geochemical gradients induced by melting waters and sediment discharges from the tidewater glacier occurring during summer. Due to the climate change, the melting season is expected to last longer and increasing global temperature will much probably accelerate the melting processes. Our findings strongly support the use of foraminifera as bioindicators to monitor the effects of ongoing climate change on the benthic ecosystems of Arctic fjords and, accessorily, as proxies for reconstructing glacier front positions in the recent past. [ABSTRACT FROM AUTHOR]

The Western Antarctic Peninsula (WAP) has been experiencing rapid regional warming since at least the 1950s, however, the impacts of this warming at the local scale are variable and nuanced. Previous studies that have linked sea‐ice variability to biogeochemical cycles and food web dynamics often combine local‐scale biogeochemical data with coarse‐resolution regional satellite sea‐ice data, which may not adequately capture local sea‐ice conditions. In this study, we analyzed local‐scale in situ sea‐ice observations collected as part of a 28‐year record (1992–2020) from the Palmer Long‐Term Ecological Research site at Anvers Island, mid‐WAP, in conjunction with isotopically‐derived sea‐ice meltwater (SIM) fractions and satellite‐derived sea‐ice motion and concentration, to quantify the variability and long‐term trends in local sea‐ice behavior. In situ sea ice observations at Palmer Station displayed higher variability than satellite observations and showed no significant declines over this time, despite region‐wide declines identified in prior studies. Higher spring SIM fractions were attributed to strong northward sea‐ice motion throughout the winter. Applying these local‐scale sea‐ice insights to similarly scaled stratification and chlorophyll‐a measurements, we found that a longer‐lasting, more consistent sea‐ice pack led to greater water column stratification following the spring sea‐ice retreat. Greater sea‐ice persistence and stronger stratification led to larger peaks in chlorophyll‐a, though sea‐ice metrics did not explain the positive temporal trends in either stratification strength or chlorophyll‐a. Through this study, we identify how local sea‐ice observations and meltwater data can enhance satellite data to build an understanding of the intricate connections between ice, water column dynamics, and phytoplankton. Plain Language Summary: The western coast of the Antarctic Peninsula is one of the fastest‐warming places on the planet. The coastal ocean here is home to large amounts of marine algae (phytoplankton), which supports a rich ecosystem. Prior studies have noted that sea ice plays a role in determining how abundant phytoplankton are in the water, but these studies typically use sea‐ice measurements from regional‐scale satellites, which do not always provide details about how sea ice is behaving at the local scale. Here, we analyze a daily sea‐ice record that was acquired locally through visual observation, as well as local‐scale ocean water samples that detect how much sea‐ice meltwater is present. We found that, despite regional warming, high year‐to‐year variability masks long‐term trends in the local sea‐ice record, and that the movement of sea ice during winter influences how much sea ice melts in place when it retreats in the spring. We also found that years with greater winter sea‐ice coverage led to summers with more ideal conditions for phytoplankton growth (e.g., shallower and more stratified water), though sea ice does not appear to be the primary driver behind recent increases in phytoplankton. Key Points: Local‐scale sea‐ice measurements at Palmer Station show higher daily and interannual variability than satellite‐based measurementsNorthwestward winter ice movement typically preceded elevated spring sea‐ice meltwater near Palmer StationLocal sea‐ice retreat influences water column stratification and Chlorophyll‐a but does not explain increasing trends in these parameters [ABSTRACT FROM AUTHOR]

Ice penetrating radar sounding is the primary geophysical technique for imaging the subsurface of planetary ice shells and has the potential to directly detect the ice–ocean interface. However, many sounding measurements may lack laterally extensive features that would aid their physical interpretation. In this scenario, the detection of sparse echoes can also provide rich information on ice shell properties. To explore and demonstrate this possibility, we consider three cases of isolated radar signatures: pore‐curing, eutectic melt, and unattributed echoes. We show that through detection of unattributed sparse echoes, the thickness of the conductive portion of Europa's ice shell can be constrained. These constraints can be improved by attributing sparse echoes to thermally diagnostic signatures such as pore‐curing and eutectic melt. Notably, this approach to radar sounding echo analysis is particularly compatible with joint inversions with other planetary geophysical observations such as tidal deformation, magnetic induction, and rotation state. Plain Language Summary: Upcoming missions to explore Europa, the icy moon of Jupiter, include ice penetrating radar sounders as part of their instrument payloads. One of the primary goals of these instruments is to investigate the subsurface structure and thickness of Europa's ice shell. It's possible that the radar profiles returned by these instruments will include imagery of the ice‐ocean interface across much of the moon, providing a direct measurement of ice‐shell thickness. However, we show that, even in the absence of such imagery, a small number of isolated radar echoes can be used to measure the thickness and structure of the ice shell. These echoes include scattering from porous ice near the moon's surface and pockets of melt water within the shell. Key Points: Radar‐detectable interfaces from the subsurface of Europa's ice shell can be thermally diagnosticThe thickness of the conductive portion of Europa's ice shell can be constrained without direct detection of the ice—ocean interfaceThe detection of sparse echoes places a lower bound on conductive ice shell thickness based on the two‐way integrated radar attenuation [ABSTRACT FROM AUTHOR]

Various electrospun fibrous membranes have been addressed for oil/water separation owing to their advantages of high specific surface ratio, lightweight, and high porosity. However, they are commonly obtained by solution electrospinning of non‐green raw materials, which could cause serious environmental issues. To realize effective oil/water separation, the optimal processing parameters for melt electrospun polylactic acid (PLA) were determined through orthogonal experiments. Subsequently, PLA fibrous films with cellulose nanofiber (CNF) or sodium chloride (NaCl) for oil/water separation were produced via melt electrospinning. The effects of incorporating CNF or NaCl on the physiochemical properties of melt electrospun PLA fibrous membranes were investigated. In contrast to the pure PLA membranes, the obtained PLA/CNF and PLA/NaCl composite membranes exhibit a finer average fiber diameter and an increased porosity. Also, the oil absorption characteristics and oil/water separation abilities of these fibrous membranes were experimentally studied. In contrast to the 84.55% oil/water separation efficiency of melt‐electrospun PLA fibrous membranes, PLA/CNF exhibits the highest oil/water separation efficiency at 93.54%, whereas PLA/NaCl achieves a maximum efficiency of 90.29%. These findings show the applicability of the eco‐friendly PLA‐based melt electrospun fibrous membrane in the treatment of oily wastewater. [ABSTRACT FROM AUTHOR]

In a review paper in this same volume, we present the state of the art on modeling of compressible viscous flows ranging from single‐phase to two‐phase systems. It focuses on mathematical properties related to weak stability because they are important for numerical resolution and on the homogenization process that leads from a microscopic description of two separate phases to an averaged two‐phase model. This review serves as the foundation for Parts I and II, which present averaged two‐phase models with phase exchange applicable to magma flow during volcanic eruptions. Part I establishes a two‐phase transient conduit flow model ensuring: (1) mass and volatile species conservation, (2) disequilibrium degassing considering both viscous relaxation and volatile diffusion, and (3) dissipation of total energy. The relaxation limit of this model is then used to obtain a drift‐flux system amenable to simplification. Here, in Part II, we summarize this model and propose a 1.5D simplification of it that alleviates three issues causing difficulties in its numerical implementation. We compare our model outputs to those of another steady‐state, equilibrium degassing, isothermal model under conditions typical of an effusive eruption at an andesitic volcano. Perfect equilibrium degassing is unreachable with a realistic water diffusion coefficient because conduit extremities always contain melt supersaturated with water. Such supersaturation has minor consequences on mass discharge rate. In contrast, releasing the isothermal assumption reduces significantly mass discharge rate by cooling due to gas expansion, which in turn increases liquid viscosity. We propose a simplified system using Darcy's law and omitting several processes such as shear heating and liquid inertia. This minimal system is not dissipative but approximates the steady‐state mass discharge rate of the full system within 10%. A regime diagram valid under a limited set of conditions indicates when this minimal system captures the ascent dynamics of effusive eruptions. Interestingly, the two novel aspects of the full model, diffusive degassing and heat balance, cannot be neglected. In some cases with high diffusion coefficients, a shallow region where porosity and velocities tend toward zero develops initially, possibly blocking an eventual steady state. This local porosity loss also occurs when a steady‐state solution is subjected to a change in shallow permeability. The resulting shallow porosity loss features many characteristics of a plug developing prior to a Vulcanian eruption. [ABSTRACT FROM AUTHOR]

Climate change is rapidly transforming the coastal margins of Greenland. At the same time, there is increasing recognition that marine‐terminating glaciers provide unique and critical habitats to ice‐associated top predators. We investigated the connection between a top predator occupying glacial fjord systems in Northwest Greenland and the properties of Atlantic‐origin water and marine‐terminating glaciers through a multiyear interdisciplinary project. Using passive acoustic monitoring, we quantified the summer presence and autumn departure of narwhals (Monodon monoceros) at glacier fronts in Melville Bay and modeled what glacier fjord physical attributes are associated with narwhal occurrence. We found that narwhals are present at glacier fronts after Greenland Ice Sheet peak summer runoff and they remain there during the period when the water column is becoming colder and fresher. Narwhals occupied glacier fronts when ocean temperatures ranged from −0.6 to 0.8°C and salinities between 33.2 and 34.0 psu at around 200 m depth and they departed on their southbound migration between October and November. Narwhals' departure was approximately 4 weeks later in 2019 than in 2018, after an extreme 2019 summer heatwave event that also delayed sea ice formation by 2 months. Our study provides further support for the niche conservative narwhal's preference for cold ocean temperatures. These results may inform projections about how future changes will impact narwhal subpopulations, especially those occupying Greenland glacial fjords. [ABSTRACT FROM AUTHOR]

Greenland's marine‐terminating glaciers connect the ice sheet to the ocean and provide a critical boundary where heat, freshwater, and nutrient exchanges take place. Buoyant freshwater runoff from inland ice sheet melt is discharged at the base of marine‐terminating glaciers, forming vigorous upwelling plumes. It is understood that subglacial plumes modify waters near glacier fronts and increase submarine glacier melt by entraining warm ambient waters at depth. However, ocean observations along Greenland's coastal margins remain biased toward summer months which limits accurate estimation of ocean forcing on glacier retreat and acceleration. Here, we fill a key observational gap in northwest Greenland by describing seasonal hydrographic variation at glacier fronts in Melville Bay using in situ observations from moorings deployed year‐round, CTDs, and profiling floats. We evaluated local and remote forcing using remote sensing and reanalysis data products alongside a high‐resolution ocean model. Analysis of the year‐round hydrographic data revealed consistent above‐sill seasonality in temperature and salinity. The warmest, saltiest waters occurred in spring (April–May) and primed glaciers for enhanced submarine melt in summer when meltwater plumes entrain deep waters. Waters were coldest and freshest in early winter (November–December) after summer melt from sea ice, glacier ice, and icebergs provided cold freshwater along the shelf. Ocean variability was greatest in the summer and fall, coincident with increased freshwater runoff and large wind events before winter sea ice formation. Results increase our mechanistic understanding of Greenland ice‐ocean interactions and enable improvements in ocean model parameterization. Plain Language Summary: Many of Greenland's glaciers terminate in the ocean and form an important boundary between coastal waters and the ice sheet. During summer months, meltwater from the ice sheet flows out below glaciers that terminate in the ocean. The less‐dense meltwater rises to the surface as a plume, increasing near‐glacier ocean mixing and submarine glacier melt. Understanding processes at the glacier‐ocean interface, including how plumes modify nearshore waters, requires sustained observations near glacier termini. However, ocean measurements are largely taken during the summer and do not necessarily represent the total variability observed in the system. Here, we fill an important knowledge gap by presenting year‐round measurements of temperature and salinity near glacier fronts in Northwest Greenland. We found the warmest, saltiest waters in the spring and coldest, freshest waters in early winter at all sites. Warm waters in the spring prime deep glaciers for submarine melt during summer. Increased winds in the fall initiated vertical mixing in nearshore waters before winter sea ice created a surface barrier, stabilizing the water column. Results advance our understanding of the ocean's role in the acceleration and retreat of Greenland's glaciers, which is important for estimating large‐scale ocean circulation and Greenland's ice sheet mass loss. Key Points: Moored hydrographic observations at glacier fronts in NW Greenland revealed consistent above‐sill seasonality in temperature and salinityOcean temperatures reached a maximum in spring, priming deep glaciers for submarine melt during summerRemote forcing supplied the renewal of warm, salty water in the spring and local forcing controlled increased variability in the summer/fall [ABSTRACT FROM AUTHOR]

The last deglaciation experienced the retreat of massive ice sheets and a transition from the cold Last Glacial Maximum to the warmer Holocene. Key simulation challenges for this period include the timing and extent of ice sheet decay and meltwater input into the oceans. Here, major uncertainties and forcing factors for the last deglaciation are evaluated. Two sets of transient simulations are performed based on the novel ice‐sheet reconstruction PaleoMist and the more established GLAC1D. The simulations reveal that the proximity of the Atlantic meridional overturning circulation (AMOC) to a bifurcation point, where it can switch between on‐ and off‐modes, is primarily determined by the interplay of greenhouse gas concentrations, orbital forcing and freshwater forcing. The PaleoMist simulation qualitatively replicates the Bølling‐Allerød (BA)/Younger Dryas (YD) sequence: a warming in Greenland and Antarctica during the BA, followed by a cooling northern North Atlantic and an Antarctic warming during the YD. Plain Language Summary: The last deglaciation, spanning roughly 20,000 to 10,000 years ago, marked a period of Earth's history characterized by the retreat of massive ice sheets that had covered large parts of the planet. During this phase, a drastic transition occurred from the cold Last Glacial Maximum to the warmer and more stable climate of the Holocene. A main challenge for simulating the last deglaciation is the timing and amplitude of the ice sheet decay and the amount of meltwater that enters into the oceans. Using two different reconstructions of ice sheets, we employ an efficient climate model to explore changes at the end of the last ice age. Our comparison shows notable differences in the timing and amplitude of abrupt climate events in the simulations using two different ice‐sheet reconstructions. Furthermore, we investigate the effects of factors such as greenhouse gases and Earth's orbital changes on the large‐scale ocean currents with respect to underlying ice sheets. Ultimately, our study sheds light on how different elements of the Earth's system shape the termination of the last ice age, enriching our understanding of Earth's climate history and guiding further deglaciation scenarios. Key Points: Transient simulations of the last deglaciation using GLAC1D and the new PaleoMist ice sheet reconstruction are compared for the first timeAMOC stability is impacted by ice sheet reconstruction used and the combination of forcings, indicating its proximity to a bifurcation pointPaleoMist simulation captures the BA/YD sequence signature in the northern North Atlantic [ABSTRACT FROM AUTHOR]

Marine‐terminating glacier fjords play a central role in the transport of oceanic heat toward ice sheets, regulating their melt. Mixing processes near glacial termini are key to this circulation but remain poorly understood. We present new summer measurements of circulation and mixing near a marine‐terminating glacier with active sub‐glacial discharge. 65% of the fjord's vertical overturning circulation is driven by the buoyant plume, however we newly report intense vertical and horizontal mixing in the plume's horizontal spreading phase, accounting for the remaining 35%. Buoyant plume theory supports 2%–5% of total glacial melt. Thus, most of the heat associated with vertical overturing short‐circuits the glacial front. We find however that turbulence in the horizontal spreading phase redistributes the short‐circuited heat back into the surface waters of the near‐glacial zone. Our findings highlight the need for further research on the complex mixing processes that occur near the glacier terminus. Plain Language Summary: Melting of glacial ice is the single largest contributor to global sea‐level rise. Many glaciers flow into the ocean where the near‐vertical ice wall is bathed in relatively warm sea water. Freshwater from ice surface melting seeps down through cracks and crevasses in the glacier to be discharged at the base of the ice wall, many tens to hundreds of meters below the sea surface. This fresh water rises from the depths as a highly turbulent plume, drawing in and pushing upwards the surrounding seawater, eventually spreading horizontally as a mixture of fresh discharge and mixed‐in seawater. Few measurements exist in the dangerous zone where iceberg often calve. Using data from a robotic platform we show that the vertical rise and the horizontal spreading of fresh water both play important roles in the total ocean‐induced melting of the glacial face in this type of system. Key Points: Entrainment into the buoyant plume drives ∼65% of fjord vertical overturning circulationIntense turbulent mixing in the horizontal spreading phase of the plume drives the remaining ∼35%95%–98% of the heat in the rising plume short‐circuits the glacier, to be redistributed into glacial proximal waters by horizontal mixing [ABSTRACT FROM AUTHOR]

To evaluate the effectiveness of the wet cavity strategy, the authors developed a stochastic evaluation method that considers the uncertainties of the molten material conditions ejected from reactor pressure vessels. This study analyzed the probability of ex‐vessel debris coolability under the wet cavity strategy. The first step was uncertainty analysis using the severe accident analysis code MELCOR to obtain the melt condition. Five uncertainty parameters related to the core degradation and transfer process were chosen. With the assumed probabilistic distributions, the input parameter sets were generated using the Latin hypercube sampling (LHS) method. Analyses were conducted, and the conditions of the melt were obtained. The second step was to analyze the melt behavior in the water and the spreading radius using the JASMINE code and to calculate the height of the debris on the floor. The probabilistic distribution of parameters for the JASMINE analyses was determined from the MELCOR analysis results. LHS generated 200 parameter sets. The depths of the water pool in the analysis were 0.5, 1.0, and 2.0 m. The debris height was compared with the criterion to judge its coolability. Consequently, the probability of successful debris cooling was obtained through the sequence of calculations. The feasibility and technical difficulties in the MELCOR‐JASMINE combined analysis were also discussed. [ABSTRACT FROM AUTHOR]

Projections of sea‐level rise from ice‐sheet shrinkage in a warming world have large uncertainties, linked to limited knowledge of changes at the ocean‐ice sheet interface. This interface most typically is modeled as a grounding line, across which still‐connected ice flows into the ocean to float as an ice shelf, or where icebergs calve from a cliff before the ice begins to float. But, extensive and rapidly increasing evidence shows that this is really a grounding zone, and that processes in this grounding zone omitted from many models could exert major controls on sea‐level rise. Plain Language Summary: Marine‐terminating glaciers flow into the ocean across extensive grounding zones. These kilometers‐long and glacier‐wide zones represent the last broad region of glacier contact with the rock and sediments below before the ice enters the ocean as a floating ice shelf or calved icebergs. Loss of this basal drag along with enhanced basal melting caused by tidally driven seawater intrusion leads to faster outflow and rapid thinning of the overlying ice. As a result of the local thinning, grounding zones retreat inland and sea level rises with more loss of previously grounded ice. Most ice‐sheet models used in sea‐level projections do not include grounding‐zone processes, but rather stop their ice‐ocean interactions at a grounding line. They are thereby omitting important dynamic feedbacks and underestimating future sea‐level contributions from the marine‐based sectors of the Greenland and Antarctic ice sheets. Key Points: Tidally modulated seawater intrusion leads to loss of ice‐bed contact as well as significant (maximal) basal melting within grounding zonesThe future dynamics of marine outlet glaciers are ultimately controlled by coupled processes operating within and through grounding zonesDespite the importance of grounding zones to ice‐sheet dynamics, most ice‐sheet models used in sea‐level projections do not include them [ABSTRACT FROM AUTHOR]

There is ample evidence for ice layers and lenses within glacial firn. The standard model for ice layer formation localizes the refreezing by perching of meltwater on pre‐existing discontinuities. Here we argue that even extreme melting events provide insufficient flux for this mechanism. Using a thermomechanical model we demonstrate a different mechanism of ice layer formation. After a melting event when the drying front catches up with the wetting front and arrests melt percolation, conductive heat loss freezes the remaining melt in place to form an ice layer. This model reproduces the depth of a new ice layer at the Dye‐2 site in Greenland. It provides a deeper insight into the interpretation of firn stratigraphy and past climate variability. It also improves the simulation of firn densification processes, a key source of uncertainty in assessing and attributing ice sheet mass balance based on satellite altimetry and gravimetry data. Plain Language Summary: Firn covers a significant portion of Earth's glaciers and ice sheets. It can store surface meltwater and prevent runoff into the ocean. The widespread presence of ice layers embedded in firn formed by meltwater refreezing may prevent meltwater storage and contribute to sea level rise. However, current models of ice layer formation, originally developed for snow, do not seem to work in firn. This work presents a different mechanism for ice layer formation without invoking pre‐existing ice layers within the firn. Our model shows that the sequencing of ice layers formed by subsequent melting events depends on the overall heat added to the firn. Deeper layers occur in warmer, more porous firn during intense melt events in a warming climate. This insight enhances our understanding of firn layering and can help deduce past climate variations. Our model aids in understanding the density evolution of firn to reduce uncertainties in remote sensing data that determines the ice sheet mass loss and its contribution to global sea‐level rise. Key Points: A new ice layer forms without meltwater perching when freezing localizes after a melt event as heat conduction dominates over advectionDeeper ice layers form in warming climatic conditions whereas denser ice layers form near surface in net‐zero climatic conditionsResults indicate the possibility of deducing past variability in climate from firn stratigraphy and vice versa [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]

Terminus change is a complex outcome of ice‐ocean boundary processes and poses challenges for ice sheet models due to inadequate calving laws, creating uncertainty in sea level change projections. To address this, we quantify glacier termini sinuosity and convexity, testing the hypothesis that terminus morphology reflects dominant calving processes. Using 10 glaciers with diverse calving styles in Greenland over the period from 1985 to 2021, we establish a supervised classification of calving style by comparing morphology and literature‐derived calving observations. Validation with four of these glaciers and flotation conditions and subglacial discharge routing observations confirms concave, smooth termini indicate buoyant flexure dominated‐calving, while convex, sinuous termini suggest serac failure dominated‐calving. We also identify a mixed style where both calving types may occur. We use these classes to label calving style from 1985 to 2021 for all 10 glaciers and explore how this changes over time as glaciers retreat. Plain Language Summary: The ice‐ocean boundary (terminus) of the Greenland ice sheet changes over space and time due to the melt and calving of ice. There is a range of calving behaviors due to many environmental and geometric factors, including changing ocean temperatures, glacier melting, and the geometry of the glacier. This makes representing how these boundary changes in ice sheet models are difficult, leading to uncertainties in predicting sea level rise from retreating glaciers. The study focuses on the shape (morphology) of 10 glaciers from 1985 to 2021, finding that smooth, concave termini indicate a type of calving related to the flotation of the glacier, while sinuous, convex termini indicate melt‐dominated calving. The research helps classify calving styles and understand how they change over time as glaciers retreat. Key Points: Two calving styles are linked to distinct terminus morphologies but both can exist for a single glacier (over time or space)Mixed styles of calving are more difficult to classifyClassifying terminus morphology over time can aid in identifying how terminus calving mechanisms change over time [ABSTRACT FROM AUTHOR]

Machine learning (ML) is used to build a bulk microphysical parameterization including ice processes. Simulations of the Lagrangian super‐particle model McSnow are used as training data. The ML performs a coarse‐graining of the particle‐resolved microphysics to multi‐category two‐moment bulk equations. Besides mass and number, prognostic particle properties (P3) like melt water, rime mass, and rime volume are predicted by the ML‐based bulk model. The ML‐based scheme is tested with simulations of increasing complexity. As a box model, the ML‐based bulk scheme can reproduce the simulations of McSnow quite accurately. In 3d idealized squall line simulations, the ML‐based P3‐like scheme provides a more realistic extended stratiform region when compared to the standard two‐moment bulk scheme in ICON. In a realistic case study, the ML‐based scheme runs stably, but can not significantly improve the results. This shows that ML can be used to coarse‐grain super‐particle simulations to a bulk scheme of arbitrary complexity. Plain Language Summary: Numerical weather prediction and climate models need a description of unresolved cloud microphysical processes. Such microphysical parameterizations are usually formulated as systems of equations for bulk variables that describe the time evolution of clouds and precipitation. In this study, we use machine learning (ML) techniques to build such a parameterization. As input or training data simulations of a very detailed cloud model are used. This detailed model provides information not only on the mass and number of cloud particles but also other properties like the degree of melting or the mass of liquid drops frozen on the ice particles called rime mass. The ML approach can successfully construct the necessary statistical relations that are needed for microphysical parameterization. This parameterization is then tested in simulations of increasing complexity. The new ML‐based scheme provides physically reasonable solutions and improves the simulation of a line of thunderstorms. Key Points: Machine learning (ML) is successfully applied to build a complex bulk ice microphysics scheme by coarse‐graining output of a Lagrangian particle microphysics modelThe ML‐based P3‐like microphysics scheme improves the representation of the stratiform region of an idealized squall line compared to a classic two‐moment schemeThe ML‐based P3‐like microphysics scheme runs stable and provides meaningful results in three‐dimensional real‐case simulations [ABSTRACT FROM AUTHOR]

Seismology is increasingly used to infer the magnitude and direction of glacial ice flow. However, the effects of interstitial meltwater on seismic properties remain poorly constrained. Here, we extend previous studies on seismic anisotropy in temperate ices to consider the role of melt preferred orientation (MPO). We used the ELLE numerical toolbox to simulate microstructural shear deformation of temperate ice with variable MPO strength and orientation, and calculated the effective seismic properties of these numerical ice‐melt aggregates. Our models demonstrate that even 3.5% melt volume is sufficient to rotate fast directions by up to 90°, to increase Vp anisotropy by up to +110%, and to modify Vs anisotropy by −9 to +36%. These effects are especially prominent at strain rates ≥3.17 × 10−12 s−1. MPO may thus obscure the geophysical signatures of temperate ice flow in regions of rapid ice discharge, and is therefore pivotal for understanding ice mass loss. Plain Language Summary: Ice on Earth is pulled toward the sea by gravity, contributing to global mean sea level rise. To better understand the flow, or movement, of ice at the continent scale, geophysical surveys are increasingly being used to measure the microscopic alignment ("fabric") of ice crystals, since ice with a strong fabric flows more readily. However, in temperate regions close to the ice melting point, melt pockets may also become aligned, creating additional macroscopic geophysical signatures. Here, we use numerical simulations to examine the combined effects of ice crystal fabric and melt alignment on the geophysical (seismic) properties of ice containing small amounts of melt. We show that melt can change the seismic fast direction (related to the inferred flow direction) of ice by up to 90°, particularly as the volume of melt exceeds 3.5%, and that different melt orientations can either enhance or diminish the anisotropy‐based estimates of flow that some studies use to predict ice mass loss. These effects are especially prominent in faster‐flowing ice, highly relevant to ice mass loss in warming regions. Geophysical studies that do not account for melt orientation may therefore produce incorrect estimates of flow, leading to inaccuracies in future climate models. Key Points: We used simulations of deforming temperate ice to show that the alignment of interstitial meltwater changes bulk seismic propertiesThe amount of melt required to significantly modify seismic properties is at least 50% lower than previously reportedMelt should be considered when using seismic and radar anisotropy to interpret viscous ice deformation and enhancement [ABSTRACT FROM AUTHOR]

The dynamics of the last Fennoscandian Ice Sheet (FIS) are relatively well constrained in the Nordic countries. Ice‐sheet dynamics in NW Russia, however, are comparatively less well understood owing to the scale and resolution of existing studies. New large‐scale glacial geomorphological datasets from NW Russia based on high‐resolution remotely sensed imagery allow for an independent reassessment of the extent and dynamics of the FIS during the Younger Dryas and Early Holocene (c. 12.9–10 ka) in NW Russia. The reconstruction provides a more detailed link between geomorphological expressions of palaeoglaciation than previous proposals. Rather than a continuous Younger Dryas ice marginal zone (IMZ) stretching from Finland to northern Norway, the geomorphological signature of NW Russia reveals 14 IMZs that document discrete stationary ice‐margin positions (possibly standstill and/or readvance events) during the overall retreat. The relative age sequence of the IMZs, supported by an updated numerical age database, suggests that they formed time‐transgressively during the Younger Dryas and Early Holocene rather than contemporaneously. Moreover, specific landform assemblages reveal contrasting glacial landsystems in NW Russia: (i) a northern subpolar glacial landsystem; and (ii) a southern temperate glacial landsystem. The model presented herein provides robust empirical constraints for testing and validating numerical ice‐sheet models and understanding ice‐sheet responses to rapid climate change. [ABSTRACT FROM AUTHOR]

Ice shelves in the Amundsen Sea have experienced the most rapid melting in the Antarctic and are expected to accelerate throughout this century under climate warming. In this study, a high‐resolution ocean‐sea ice‐ice shelf model is employed to conduct sensitivity experiments to explore the effects of increasing melt rates of the Amundsen Sea ice shelves on hydrography, sea ice and ice shelf in the Ross Sea. The results indicate that the substantial inflow of meltwater significantly freshens the Ross Sea, inhibiting the formation and export of the Dense Shelf Water, the volume of which is reduced by 19%–33% on the shelf. Temperatures in the eastern and western Ross Sea exhibit different responses to the enhanced meltwater input. The freshening of the western Ross Sea weakens the mesoscale eddy activities which are efficient in carrying warm Circumpolar Deep Water onto the shelf, leading to an average temperature decrease of 0.02–0.08°C. Conversely, in the eastern Ross Sea, there is a marked warming outside the shelf under increased meltwater, which results from zonal pressure gradients associated with the meltwater distributions. This consequently causes stronger on‐shelf heat transport and shows warming of 0.12–0.22°C on the eastern Ross Sea shelf. The narrow shelf in the eastern Ross Sea allows the warmer water to reach the Ross Ice Shelf (RIS) front, resulting in an about 6%–9% increase in the RIS melting. These results suggest a possible mechanism for acceleration in the RIS melting in the future that is associated with enhanced meltwater inflow. Plain Language Summary: Many studies suggest that the Amundsen Sea ice shelf will experience accelerated melting throughout this century, leading to the release of a substantial amount of freshwater, which will be transported westward and impact the Ross Sea downstream. In this study, a numerical model including ocean, ice shelves and sea ice is used to simulate the effects of increased melting rates of the Amundsen Sea ice shelves on the Ross Sea ocean and ice environments. The results indicate pronounced differences in temperature changes in the eastern and western Ross Sea under enhanced meltwater input. The freshening of the western Ross Sea weakens the warm water intrude onto the shelf, resulting in cooling of the western Ross Sea. In the eastern Ross Sea, there is warming associated with changes in large‐scale flows caused by the distributions of meltwater. More heat transport into the eastern Ross Sea shelf can reach the front of the Ross Ice Shelf (RIS) — the largest Antarctic ice shelf and promotes its melting. Our study proposes a mechanism for acceleration in the RIS melting in the future, highlighting the role of meltwater from the Amundsen Sea ice shelves. Key Points: Enhanced Amundsen Sea ice shelf melting causes marked freshening of the Ross Sea and inhibits the formation of Antarctic Bottom WaterThe increased meltwater inflow from the Amundsen Sea causes cooling of the western Ross Sea and warming of the eastern Ross SeaMore heat transport into the eastern Ross Sea shelf can reach the front of the Ross Ice Shelf and increase its melting rate [ABSTRACT FROM AUTHOR]

This work evaluates glacial dust as a source of sediment, and associated iron (Fe), to the Fe‐limited Gulf of Alaska (GoA). A reanalysis of GoA sediment data, using rare earth elements and thorium as provenance tracers, suggests a flux to the ocean surface of Copper River (AK) glacial dust, and associated Fe, that is comparable to the flux of dust from Asia, at least 1,000 km from the narrow mountain valley glacial dust source area. This work suggests dust from Asia may not be the largest source of Fe to the GoA. Dust models fail to accurately simulate this glacial dust transport because their coarse resolution underestimates wind speeds, and the dust flux. This work suggests that glacial dust fluxes may have been important in the geologic past (e.g., the last glacial maximum) from locations where there was more extensive coverage by glaciers than at present. Plain Language Summary: The growth of phytoplankton, the base of the marine food web, is known to be limited by availability of the micronutrient iron in the Gulf of Alaska. We evaluated the importance of glacial dust in this region as a source of iron, and other trace metals, by using concentrations of the rare earth elements and thorium in particles as tracers of their geographic origin. We analyzed for these elements in glacial dust samples from the Copper River valley (Alaska), the largest source of glacier‐derived dust. Together with previously published concentrations for dust from Asia and volcanic material, we estimated the inputs of each source material to the sediments of the Gulf of Alaska. This information, together with published sediment mass accumulation rates, suggests an important contribution of Alaskan glacial dust and associated iron, to surface waters of the Gulf of Alaska, at least 1,000 km from the source. Dust models fail to accurately simulate this dust transport because their coarse spatial resolution substantially underestimates wind speeds. Glacial dust fluxes may have been important sources of iron in the geologic past (e.g., the Last Glacial Maximum) from New Zealand and South America, when there was more extensive glacial coverage. Key Points: Copper River glacial dust contributes substantially to Gulf of Alaska sediments, and associated iron to surface watersDust models lack sufficient spatial resolution to accurately simulate the winds that drive the flux of glacial dust from narrow valleysGlacial dust‐associated iron may have been important in the geologic past in times and locations with more extensive glacial coverage [ABSTRACT FROM AUTHOR]

This comprehensive study examines primary production (PP) within the Spitsbergen fjords, Hornsund, and Kongsfjord, over a 25‐year period (1994–2019), across 45 stations and 348 incubation levels at various depths. PP and hydrological parameters were measured at 28 sampling stations in Kongsfjorden and 17 in Hornsund, with the locations of "Glacier," "Inner," and "Outer" zones defined to reflect the varying influence of glacial meltwater. Our study revealed spatial and temporal variability in PP, both at the surface and within the water column with very high depth resolution. The highest PP values were observed in the Glacier and Inner zones of Hornsund, particularly in the water layer up to 3 m depth, exceeding 20 mgC m−3 h−1. A notable decline in PP with increasing depth was observed in both fjords, with the Glacier zones displaying the highest productivity at the surface. The study also highlights the influence of glacial meltwater on surface water conditions, affecting the PP in the upper layers of both fjords. The observed gradient in the depth of maximum PP toward the mouth of the fjord varied between the two fjords, with Kongsjord displaying more dynamic variations. The spatial distribution of integrated primary production (Pi) suggested lower productivity in the glacial regions, likely due to light limitation caused by high concentrations of mineral particulate matter. The values of Pi were considerably higher in Hornsund, approximately twice as high overall, with specific emphasis on the Glacier and Inner zones where Pi values were about 6.5 and 2.5 times higher, respectively, when compared to those observed in Kongsfjord. [ABSTRACT FROM AUTHOR]

Due to the incorrect speciation of iron during thermometry modelling, Coulthard et al. (2024) produced an incorrect olivine‐liquid equilibrium diagram, which failed to identify multiple potential equilibrium olivine‐melt pairs. With the new pairs identified here, the temperatures inferred from olivine‐groundmass pairs move closer in temperature space to those inferred from olivine‐glass pairs. Additionally, it is recognised that the most significant difference between these thermometry data is due to differences in inferred melt water mass fraction. If a mean value of water is used for all thermometry, the mean temperatures calculated for olivine‐glass and olivine‐groundmass pairs converge to within 10 °C of one another. This indicates that groundmass compositions inferred via the defocused beam analysis of a polyphase groundmass may reproduce enough information to confidently perform olivine‐melt thermometry despite the glass and groundmass data representing significantly different compositions in multivariate space. [ABSTRACT FROM AUTHOR]

The West Antarctic Ice Sheet is experiencing rapid thinning of its floating ice shelves, largely attributed to oceanic basal melt. Numerical models suggest that the Bellingshausen Sea has a key role in setting water properties in the Amundsen Sea and further downstream. Yet, observations confirming these pathways of volume and tracer exchange between coast and shelf break and their impact on inter‐sea exchange remain sparse. Here we analyze the circulation and distribution of glacial meltwater at the boundary between the Bellingshausen Sea and the Amundsen Sea using a combination of glider observations from January 2020 and hydrographic data from instrumented seals. Meltwater distributions over previously unmapped western regions of the continental shelf and slope reveal two distinct meltwater cores with different optical backscatter properties. At Belgica Trough, a subsurface meltwater peak is linked with hydrographic properties from Venable Ice Shelf. West of Belgica Trough, the vertical structure of meltwater concentration changes, with peak values occurring at greater depths and denser isopycnals. Hydrographic analysis suggests that the western (deep) meltwater core is supplied from the eastern part of Abbot Ice Shelf, and is exported to the shelf break via a previously‐overlooked bathymetric trough (here named Seal Trough). Hydrographic sections constructed from seal data reveal that the Antarctic Coastal Current extends west past Belgica Trough, delivering meltwater to the Amundsen Sea. Each of these circulation elements has distinct dynamical implications for the evolution of ice shelves and water masses both locally and downstream, in the Amundsen Sea and beyond. Plain Language Summary: Floating ice shelves in West Antarctica are thinning, which is largely due to melting of the ice shelf base by the ocean. Here, measurements of ocean temperature, salinity, and dissolved oxygen, collected by a remotely‐controlled underwater vehicle (a glider), are used to estimate the amount of ice shelf meltwater released in the Bellingshausen Sea. Distinct cores of meltwater can be distinguished by the amount of suspended material that is present in the water, which we attribute to meltwater following different circulation pathways after entering the ocean. Historical data from seals equipped with temperature and salinity sensors provide additional information about how the meltwater circulates in the region. The seal data show the presence of a narrow coastal current that brings meltwater from the Bellingshausen Sea into the Amundsen Sea. The pathways of meltwater revealed in this study suggest an important influence of the Bellingshausen Sea on ice shelves throughout West Antarctica. Key Points: Hydrographic observations identify both shelf‐break and coastal meltwater pathways from the western Bellingshausen Sea into the Amundsen SeaDifferences in optical backscatter properties associated with meltwater are related to distinct coast‐to‐shelf break pathwaysThe main pathway to the shelf break is via Seal Trough, identified as the de facto western boundary of the Bellingshausen Sea [ABSTRACT FROM AUTHOR]

The Indian Summer Monsoon (ISM) and meltwater from the Himalayan are the two most important sources of water in the Indian subcontinent. However, the impact of ISM on Himalayan glaciers and subsequent stream hydrology remains largely unknown. To provide new insight into the impact of rainfall on glacial hydrology, here we present hydro‐meteorological and time‐series observations of meltwater stable water isotope compositions from the snout of the Chorabari glacier in the Upper Ganga Basin, Central Himalayas across the ablation season corresponding to 2019. We observe that rainfall events (>2 mm d−1) on the glacier enhance discharge driven by ice meltwater in River Mandakini. Energy balance calculations reveal that one of the drivers behind enhanced ice meltwater contribution could be rain‐induced melting of the glacier where rainfall on the ice surface melts the glacier producing up to 13% of the total discharge at the glacier snout. Further, rainfall on glacier surface have other control on glacial processes—for example, snow metamorphism, ice flow dynamics such as short‐term acceleration in ice speed flow, and reorganization of the englacial and subglacial drainage network—that are poorly studied and needs further investigation. We conclude rainfall events on the glacier have a complex control on mountain hydrology. This study, therefore, provides an interpretative framework that calls for additional assessments of the direct and indirect impact of rainfall in glacial hydrology. Plain Language Summary: Understanding the drivers of elevated ice meltwater runoff in glacier‐fed Himalayan streams is critically important in constraining the role of climate change in glacial hydrology. The conventional thinking of elevated ice meltwater runoff in Himalayan rivers is mainly attributed to global warming. However, in this study, we find that rain events on the glacier are an additional driver of enhanced ice meltwater discharge in the glacier‐fed Himalayan streams. The additional flux of ice meltwater can be explained by the reorganization of the englacial and subglacial drainage network during rainfall events and/or rain‐induced melting of the glacier ice where raindrops falling on the ice surface are releasing sensible and latent heat by englacial cooling and freezing of rain, thereby raising ice temperatures to the melting point, in result, enhanced ice meltwater contributions. As the number of extreme rainfall events and their associated catastrophes has increased in recent decades, the observed causal relationship between ISM and enhanced ice meltwater contributions in the Himalayas is critical to better manage and predict important environmental problems such as floods in the Himalayas. Key Points: An isotope mixing model was developed to quantify the contributions of rain, ice, and snow meltwater to the total river dischargeWe show heavy monsoonal rainfall triggers the melting of glacier ice resulting in enhanced ice meltwater discharge in streamsWe conclude rainfall events have complex controls on glacial hydrology/processes [ABSTRACT FROM AUTHOR]

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

Freshwater input from Greenland ice sheet melt has been increasing in the past decades from warming temperatures. To identify the impacts from enhanced meltwater input into the subpolar North Atlantic from 1997 to 2021, we use output from two nearly identical simulations in the eddy‐rich model VIKING20X (1/20°) only differing in the freshwater input from Greenland: one with realistic interannually varying runoff increasing in the early 2000s and the other with climatologically (1961–2000) continued runoff. The majority of the additional freshwater remains within the boundary current enhancing the density gradient toward the warm and salty interior waters yielding increased current velocities. The accelerated boundary current shows a tendency to enhanced, upstream shifted eddy shedding into the Labrador Sea interior. Further, the experiments allow to attribute higher stratification and shallower mixed layers southwest of Greenland and deeper mixed layers in the Irminger Sea, particularly in 2015–2018, to the runoff increase in the early 2000s. Plain Language Summary: Global warming has accelerated the melting of the Greenland ice sheet over the past few decades resulting in enhanced freshwater input into the North Atlantic. The additional freshwater can potentially inhibit deep water formation and have future implications on ocean circulation. To determine the influence from Greenland melt, we compare two high‐resolution model experiments all with the same forcing but differing input of Greenland freshwater fluxes from 1997 to 2021. We find that in the experiment with realistically increasing Greenland meltwater, the water becomes fresher and cooler along the continental shelf and boundary of the subpolar gyre. The density difference between the shelf and interior increases with more freshwater, resulting in faster West Greenland Current speeds and enhanced eddy formation. Deeper mixed layers are found in the eastern Irminger Sea, particularly in 2015–2018. From 2009 to 2013, there were shallower mixed layers in the Labrador Sea where less Greenland meltwater was mixed downwards and spread eastward, causing mixed layers to deepen in the Irminger Sea. Key Points: The West Greenland Current (WGC) freshens and cools with the observed recent increase in meltwater runoff from GreenlandThe density gradient across the boundary current intensifies, strengthening the WGC and increasing local eddy formationEnhanced meltwater runoff contributed to an eastward shift in deep convection towards the Irminger Sea (2015–2018) [ABSTRACT FROM AUTHOR]

Herein, fast fracture initiation in glacier ice is modeled using a Material Point Method and a simplified constitutive law describing tensile strain softening. Relying on a simple configuration where ice flows over a vertical step, crevasse patterns emerge and are consistent with previous observations reported in the literature. The model's few parameters allows identification of a single dimensionless number controlling fracture spacing and depth. This scaling law delineates two regimes. In the first one, ice thickness does not play a role and only ice tensile strength controls the spacing, giving rise to numerous surface crevasses, as observed in crevasse fields. In this regime, scaling can recover classical values for ice tensile strength from macroscopic field observations. The second regime, governed by ice bending, produces large‐scale, deep fractures resembling serac falls or calving events. Plain Language Summary: In ice sheets and alpine glaciers, fast‐flowing sections are often characterized by crevasse fields that play a significant role in the cryo‐hydrologic system by facilitating meltwater flow, enhancing basal sliding, weakening the ice, and impacting glacier thermodynamics. Modeling these fractures at the glacier scale remains challenging and often necessitates integrating diverse models which hinders the straightforward consideration of physical issues associated with crevasse fields on a large scale. Here, a new numerical framework allows us to conduct field‐scale experiments and paves the way for a scaling law to elucidate the macroscopic factors influencing fracture fields and to easily incorporate crevasse depth and spacing into large‐scale models. A newly discovered scaling law highlights the transition between a mechanical behavior where the regular crevasse spacing is unaffected by geometry to a regime where geometry plays a significant role, particularly in large‐scale fracture processes like glacier calving. While the numerical experiments in this paper focus on glaciers, the model and conceptual framework is versatile and can address the mechanical behavior of fractures in broader geophysical contexts such as snow, rock or ice avalanches, tectonics and landslides. Key Points: Fractures in glacier flow are modeled using material point method with elastoplasticity and tensile strain softeningA dimensional analysis reveals a key dimensionless number characterizing two different regimes of fast fractureOne regime predicts acknowledged ice tensile strength from field observations and characterizes the regular crevasse spacing [ABSTRACT FROM AUTHOR]

Antarctic meltwater discharge has been largely emphasized for its potential role in climate change mitigation, not only by reducing global warming, but also by stabilizing the Atlantic Meridional Overturning Circulation (AMOC). Despite the tremendous impact of the AMOC on the climate system, its temporal evolution in response to the meltwater remains poorly understood. Here, we investigate the meltwater impacts on the AMOC based on the GFDL CM2.1 experiments and discover its fast weakening and slow strengthening to the Antarctic meltwater discharge. Cold ocean surface caused by meltwater spread throughout the globe and eventually strengthened the AMOC. However, in the early stages, the tropical temperature response could stimulate the Rossby wave teleconnection, modulating atmospheric circulation in the North Atlantic, and weakening convection and even the AMOC. This counterintuitive evolution implies a potential destabilizing effect of Antarctic meltwater, underscoring the importance of the atmospheric dynamics in the interaction between the two poles. Plain Language Summary: The climate system is made up of interactions between different subsystems, so that regional climate changes can have global effects. The freshwater discharge from Antarctica would increase in the future and result in regional cooling. Atmospheric and oceanic dynamics extend this local effect to the globe, reducing global surface temperature and strengthening the large‐scale ocean circulation in the Atlantic. These mitigating effects naturally put the spotlight on Antarctic meltwater. Our study however suggests that the mitigation effect depends on the time scale. Although the global mean temperature is always reduced, the ocean circulation in the Atlantic surprisingly slows down as an early response to Antarctic meltwater; fast atmospheric teleconnection enables it. This non‐monotonic evolution emphasizes the importance of the atmospheric teleconnection between the two poles, which should be carefully considered to understand the polar climate. Key Points: The response of the Atlantic Meridional Overturning Circulation to perennial meltwater‐induced cooling is investigated by GFDL CM2.1 experimentsBefore the cooling spreads out the Atlantic, tropical atmospheric teleconnection could weaken the Greenland ocean convectionThe fast and slow responses imply the importance of the atmospheric teleconnection to regulate polar climate [ABSTRACT FROM AUTHOR]

Taxon‐specific quantitative PCR (qPCR) assays are commonly used for environmental DNA sampling‐based inference of animal presence. These assays require thorough validation to ensure that amplification truly indicates detection of the target taxon, but a thorough validation is difficult when there are potentially many non‐target taxa, some of which may have incomplete taxonomies. Here, we use a previously published, quantitative model of cross‐amplification risk to describe a framework for assessing qPCR assay specificity when there is missing information and it is not possible to assess assay specificity for each individual non‐target confamilial. In this framework, we predict assay specificity against unsampled taxa (non‐target taxa without sequence data available) using the sequence information that is available for other confamilials. We demonstrate this framework using four case study assays for: (1) An endemic, freshwater arthropod (meltwater stonefly; Lednia tumana), (2) a globally distributed, marine ascidian (Didemnum perlucidum), (3) a continentally distributed freshwater crustacean (virile crayfish; Faxonius virilis, deanae and nais species complex) and (4) a globally distributed freshwater teleost (common carp; Cyprinus carpio and its close relative C. rubrofuscus). We tested the robustness of our approach to missing information by simulating application of our framework for all possible subsamples of 20—all non‐target taxa. Our results suggest that the modelling framework results in estimates which are largely concordant with observed levels of cross‐amplification risk using all available sequence data, even when there are high levels of data missingness. We explore potential limitations and extensions of this approach for assessing assay specificity and provide users with an R Markdown template for generating reproducible reports to support their own assay validation efforts. [ABSTRACT FROM AUTHOR]

Polar regions are relatively isolated from human activity and thus could offer insight into anthropogenic and ecological drivers of the spread of antibiotic resistance. Plasmids are of particular interest in this context given the central role that they are thought to play in the dissemination of antibiotic resistance genes (ARGs). However, plasmidomes are challenging to profile in environmental samples. The objective of this study was to compare various aspects of the plasmidome associated with glacial ice and adjacent aquatic environments across the high Arctic archipelago of Svalbard, representing a gradient of anthropogenic inputs and specific treated and untreated wastewater outflows to the sea. We accessed plasmidomes by applying enrichment cultures, plasmid isolation and shotgun Illumina sequencing of environmental samples. We examined the abundance and diversity of ARGs and other stress‐response genes that might be co/cross‐selected or co‐transported in these environments, including biocide resistance genes (BRGs), metal resistance genes (MRGs), virulence genes (VGs) and integrons. We found striking differences between glacial ice and aquatic environments in terms of the ARGs carried by plasmids. We found a strong correlation between MRGs and ARGs in plasmids in the wastewaters and fjords. Alternatively, in glacial ice, VGs and BRGs genes were dominant, suggesting that glacial ice may be a repository of pathogenic strains. Moreover, ARGs were not found within the cassettes of integrons carried by the plasmids, which is suggestive of unique adaptive features of the microbial communities to their extreme environment. This study provides insight into the role of plasmids in facilitating bacterial adaptation to Arctic ecosystems as well as in shaping corresponding resistomes. Increasing human activity, warming of Arctic regions and associated increases in the meltwater run‐off from glaciers could contribute to the release and spread of plasmid‐related genes from Svalbard to the broader pool of ARGs in the Arctic Ocean. [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]

Supraglacial lakes have been observed to drain within hours of each other, leading to the hypothesis that stress transmission following one drainage may be sufficient to induce hydro‐fracture‐driven drainages of other nearby lakes. However, available observations characterizing drainage‐induced stress perturbations have been insufficient to evaluate this hypothesis. Here, we use ice‐sheet surface‐displacement observations from a dense global positioning system array deployed in the Greenland Ice Sheet ablation zone to investigate elastic stress transmission between three neighboring supraglacial lake basins. We find that drainage of a central lake can place neighboring basins in either tensional or compressional stress relative to their hydro‐fracture scarp orientations, either promoting or inhibiting hydro‐fracture initiation beneath those lakes. For two lakes located within our array that drain close in time, we identify tensional surface stresses caused by ice‐sheet uplift due to basal‐cavity opening as the physical explanation for these lakes' temporally clustered hydro‐fracture‐driven drainages and frequent triggering behavior. However, lake‐drainage‐induced stresses in the up‐flowline direction remain low beyond the margins of the drained lakes. This short stress‐coupling length scale is consistent with idealized lake‐drainage scenarios for a range of lake volumes and ice‐sheet thicknesses. Thus, on elastic timescales, our observations and idealized‐model results support a stress‐transmission hypothesis for inducing hydro‐fracture‐driven drainage of lakes located within the region of basal cavity opening produced by the initial drainage, but refute this hypothesis for distal lakes. Plain Language Summary: Mass loss from the Greenland Ice Sheet is accelerating, partly due to increasing rates of ice flow to the ocean. Ongoing increases in ice‐sheet surface melting play a complex role in this process: meltwater flows down through conduits and fractures to the ice‐sheet bed, lubricates the ice‐bed interface, and modulates ice‐flow speeds on hourly to decadal timescales. Drainage of supraglacial lakes via hydro‐fracture—water‐driven fracture propagation—produces the highest rates of meltwater flux to the ice‐sheet bed. The geographical range of lakes on the ice sheet has expanded in recent decades, but not all supraglacial lakes drain by hydro‐fracture: whether a hydro‐fracture‐driven drainage occurs in any particular lake basin is controlled by the ice‐sheet stress state. Here, we investigate whether one lake drainage can generate stress changes in neighboring lake basins that trigger hydro‐fracture initiation. We find that the drainage of one lake does lead to tensional stresses that promote hydro‐fracture initiation in a neighboring lake basin, but also that this initial lake drainage leads to a more compressive stress state that inhibits hydro‐fracture initiation in a different neighboring lake basin. Key Points: Drainage of one lake can place neighboring basins in tensional or compressional stress, promoting or inhibiting hydro‐fracture initiationTensional surface stresses are predominantly caused by basal cavity opening, with smaller contributions from basal slipThe first‐order control on elastic stress‐coupling length scales is the region of the bed over which basal cavity opening occurs [ABSTRACT FROM AUTHOR]

Glacial moulins (cylindrical meltwater drainage shafts) provide valuable insights into glacier dynamics, but are inaccessible and hazardous environments for humans to study. Exploring them using passive sensor probes has revealed their complex geometry, which has limited further exploration with passive sensor probes. To overcome these challenges, we propose a tethered robot capable of autonomously exploring and capturing data in glacial moulins. Our novel robot is equipped with a tether to support its motion. Combined with novel estimation and control algorithms, the tethered robot is able to safely and efficiently maneuver in confined, chimney‐like structures, such as moulins. Laboratory and field experiments confirm the feasibility of the proposed design, showing successful localization in environments with no access to positional measurements. Field trials on the Mer de Glace glacier demonstrate the robot's capabilities, descending into the largest moulin to depths of 25 m, capturing valuable scientific data. Onboard sensors are used to capture data to reconstruct the moulin's three‐dimensional geometry and two sampling mechanisms are presented and evaluated to extract samples from the icy surface of the moulin. Our results show promising potential for future exploration of moulins, demonstrating the effectiveness of our tethered robot for safely gathering data from these hazardous environments. [ABSTRACT FROM AUTHOR]

Sunlight penetrates the ice surfaces of glaciers and ice sheets, forming a water‐bearing porous ice matrix known as the weathering crust. This crust is home to a significant microbial community. Despite the potential implications of microbial processes in the weathering crust for glacial melting, biogeochemical cycles, and downstream ecosystems, there have been few explorations of its microbial communities. In our study, we used 16S rRNA gene sequencing and shotgun metagenomics of a Svalbard glacier surface catchment to characterise the microbial communities within the weathering crust, their origins and destinies, and the functional potential of the weathering crust metagenome. Our findings reveal that the bacterial community in the weathering crust is distinct from those in upstream and downstream habitats. However, it comprises two separate micro‐habitats, each with different taxa and functional categories. The interstitial porewater is dominated by Polaromonas, influenced by the transfer of snowmelt, and exported via meltwater channels. In contrast, the ice matrix is dominated by Hymenobacter, and its metagenome exhibits a diverse range of functional adaptations. Given that the global weathering crust area and the subsequent release of microbes from it are strongly responsive to climate projections for the rest of the century, our results underscore the pressing need to integrate the microbiome of the weathering crust with other communities and processes in glacial ecosystems. [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]

The final deglaciation stages of the Laurentide Ice Sheet in northern Quebec–Labrador were marked by the incursion of the d'Iberville Sea into the coastal areas of Ungava Bay. Remote and field mapping of raised marine strandlines along the Ungava Peninsula east coast show that the maximum marine limit decreases from south (165 m) to north (100 m), reflecting differential uplift linked to an ice mass remnant located to the southwest of the bay. Reconstruction of the uppermost marine limit in two east–west transects extending into the Peninsula interior reveals distinct sea‐level stands with limited extents towards the west, indicating that the early stages of the marine incursion occurred in contact with the ice margin. The reconstruction also identifies the maximum eastward extent of ice‐dammed lakes that occupied the Arnaud River and Aux‐Feuilles River valleys. 10Be surface exposure dating of marine strandlines yielded consistent 10Be ages that indicate a rapid deglaciation of Ungava Bay between 8900 ± 200 a (north) and 7900 ± 200 a (south). These results provide constraints on the position of the Labrador Sector eastern and western ice margins during the late deglaciation, in addition to the timing of ice and meltwater discharges from the Ungava Bay region. [ABSTRACT FROM AUTHOR]

Icebergs modulate the effective location of freshwater input from ice sheets into the ocean and therefore play an important role for the climate, especially during times of increased ice discharge (e.g., Heinrich events). None of the models participating in the Paleo Modeling Intercomparison Project simulations of the Last Glacial Maximum or the last deglaciation included icebergs. Here, we present a newly developed dynamic/thermodynamic iceberg module that was specifically designed to be incorporated in climate models used for long‐term climate simulations with interactive ice sheets. In contrast to the widely used Lagrangian iceberg models, it is formulated in an Eulerian framework. This simplifies coupling to ocean models and enhances computational efficiency for glacial climates. In a set of sensitivity experiments, where the module was implemented into an Earth System Model, we validate the model for present‐day climate conditions and test its sensitivity to key parameters. Further, we investigate the effect of iceberg hosing on the Atlantic meridional overturning circulation (AMOC) as compared to traditional freshwater hosing. Varying the hosing rate slowly in time yields a good approximation of the hysteresis curve of the AMOC. We find that the sensitivity of the AMOC to iceberg hosing is stronger than to freshwater hosing in the same ocean point, but weaker as compared to a latitude belt forcing in the North Atlantic. This emphasizes the 2e necessity to include interactive icebergs in long‐term coupled climate simulations to realistically represent melt patterns and the response of the AMOC to freshwater input from melting ice sheets. Plain Language Summary: Icebergs transport frozen water from calving ice sheets far away from the coasts and release meltwater along their path while slowly melting. The sensitivity of the Atlantic meridional overturning circulation depends on the location of the meltwater input. As the transport and melt of icebergs determine the location of meltwater input into the ocean, it is obvious that icebergs are an important component of the climate system. Unfortunately, they are not included in most climate models, partly as they are computational quite expensive. Existing iceberg modules can follow groups of icebergs, and may be prohibitively computationally expensive when applied on very long timescales. Here we introduce a different approach. We do not follow each group of icebergs but describe the iceberg distribution using equations for concentrations and different size classes. This formulation is adequate for climate purposes, and simplifies the incorporation into ocean models. The difference in the climate response to iceberg calving and the widely used freshwater hosing is relatively large. This emphasizes the importance of including interactive iceberg modules into climate models for a realistic simulation of ice discharge events. Key Points: A new Eulerian iceberg module for climate studies is introducedThe Eulerian approach simplifies the incorporation of icebergs into standard ocean general circulation modelsExperiments with a comprehensive climate model demonstrate that iceberg discharge has different impact on Atlantic meridional overturning circulation compared to freshwater [ABSTRACT FROM AUTHOR]

The ice shelves in the Bellingshausen Sea are melting and thinning rapidly due to modified Circumpolar Deep Water (mCDW) intrusions carrying heat toward ice‐shelf cavities. Observations are, however, sparse in time and space, and extensive model‐data comparisons have never been possible. Here, using a circulation model of the region and ship‐based observations, we show that the simulated water mass distributions in several troughs traversing mCDW inflows are in good agreement with observations, implying that our model has the skills to simulate hydrographic structures as well as on‐shelf ocean circulations. It takes 7.9 and 11.7 months for mCDW to travel to the George VI Ice Shelf cavities through the Belgica and Marguerite troughs, respectively. Ice‐shelf melting is mainly caused by mCDW intrusions along the Belgica and Marguerite troughs, with the heat transport through the former being ∼2.8 times larger than that through the latter. The mCDW intrusions toward the George VI Ice Shelf show little seasonal variability, while those toward the Venable Ice Shelf show seasonal variability, with higher velocities in summer likely caused by coastal trapped waves. We also conduct particle experiments tracking glacial meltwater. After 2 years of model integration, ∼33% of the released particles are located in the Amundsen Sea, supporting a linkage between Bellingshausen Sea ice‐shelf meltwater and Amundsen Sea upper ocean hydrography. Plain Language Summary: The Bellingshausen Sea Ice Shelves have been affected by high ice‐shelf melt and ice‐loss rates in Antarctica. The reason for the ice loss is the presence of warm modified Circumpolar Deep Water (mCDW) over the continental shelf, which intrudes into ice‐shelf cavities. Recently, studies combining observations and models have significantly advanced our understanding of Ice‐Ocean interactions around Antarctica. For example, in the Amundsen Sea, the region neighboring the Bellingshausen Sea and contributing the most to Antarctic glacial ice loss, such an approach has revealed the drivers and pathways of ocean heat intrusions as well as the impact of glacial meltwater on the Antarctic coastal circulation. We follow this approach and evaluate our ocean model by comparing it with ship‐based and satellite‐based observations. Using this model simulation, we show that the simulated mCDW intrudes from the continental shelf break toward ice‐shelf cavities mainly through two deep cross‐shelf troughs. The glacial meltwater is transported by the westward Antarctic Coastal Current (AACC) flowing into the Amundsen Sea. The mCDW inflow and AACC in the coastal area show seasonal variabilities with higher velocities in the summer, which are likely caused by coastal trapped waves. Key Points: The simulated hydrographic structures over the Bellingshausen Sea continental shelf region are in good agreement with observationsThe warm water intrusions toward the Venable Ice Shelf show peaks of higher velocities in summer, likely caused by coastal trapped wavesGlacial meltwater from about 33% of the area underneath the BS ice shelves flows into the Amundsen Sea within 2 years [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas are hotspots of biological production with intensive springtime phytoplankton blooms that strongly depend on meltwater‐induced restratification in the upper part of the water column. However, the fundamental physics that determine spatial inhomogeneity of the spring restratification remain unclear. Here, we investigate how different meltwaters affect springtime restratification and thus phytoplankton bloom in Antarctic coastal polynyas. A high‐resolution coupled ice‐shelf/sea‐ice/ocean model is used to simulate an idealized coastal polynya similar to the Terra Nova Bay Polynya, Ross Sea, Antarctica. To evaluate the contribution of various meltwater sources, we conduct sensitivity simulations altering physical factors such as alongshore winds, ice shelf basal melt, and surface freshwater runoff. Our findings indicate that sea ice meltwater from offshore is the primary buoyancy source of polynya near‐surface restratification, particularly in the outer‐polynya region where chlorophyll concentration tends to be high. Downwelling‐favorable alongshore winds can direct offshore sea ice away and prevent sea ice meltwater from entering the polynya region. Although the ice shelf basal meltwater can ascend to the polynya surface, much of it is mixed vertically over the water column and confined horizontally to a narrow coastal region, and thus does not contribute significantly to the polynya near‐surface restratification. Surface runoff from ice shelf surface melt could contribute greatly to the polynya near‐surface restratification. Nearby ice tongues and headlands strongly influence the restratification through modifying polynya circulation and meltwater transport pathways. Results of this study can help explain observed spatiotemporal variability in restratification and associated biological productivity in Antarctic coastal polynyas. Plain Language Summary: Antarctic coastal polynyas are key habitats of regional marine ecosystems. During spring, the upper part of the polynya water column restratifies and forms a near‐surface layer of low‐salinity water. This process is important for springtime phytoplankton blooms, as the stable surface layer keeps phytoplankton in the well‐lit region and enhances phytoplankton growth. Employing high‐resolution models of idealized coastal polynyas, this work unravels the spatial variation of restratification processes in a polynya and investigates the physical factors that affect them. It shows that sea ice meltwater from offshore regions is the foremost contributor to the near‐surface restratification in a polynya. Meanwhile, low‐salinity water from basal melt of a neighboring floating ice shelf contributes little to the near‐surface restratification in a polynya because much of the meltwater mixes vertically with ambient waters as it rises. This is in contrast to the sea ice meltwater being directly injected into the ocean surface. Freshwater runoff from the surface melt of an ice shelf is also directly injected into the polynya surface. However, due to earth rotation, it is often confined in a narrow coastal region next to the ice shelf and thus does not contribute to restratification in most of the polynya area. Key Points: Biologically‐important springtime near‐surface restratification in Antarctic coastal polynyas varies spatially within a polynyaSea ice meltwater from regions offshore of the polynya is the primary buoyancy source of polynya near‐surface restratificationIce shelf basal meltwater mixes over the water column during its ascent and contributes little to polynya near‐surface restratification [ABSTRACT FROM AUTHOR]

Olivine‐hosted melt inclusions are an important archive of pre‐eruptive processes such as magma storage, mixing and subsequent ascent through the crust. However, this record can be modified by post‐entrapment diffusion of H+ through the olivine lattice. Existing studies often use spherical or 1D models to track melt inclusion dehydration that fail to account for complexities in geometry, diffusive anisotropy and sectioning effects. Here we develop a finite element 3D multiphase diffusion model for the dehydration of olivine‐hosted melt inclusions that includes natural crystal geometries and multiple melt inclusions. We use our 3D model to test the reliability of simplified analytical and numerical models (1D and 2D) using magma ascent conditions from the 1977 eruption of Seguam volcano, Alaska. We find that 1D models underestimate melt inclusion water loss, typically by ∼30%, and thus underestimate magma decompression rates, by up to a factor of 5, when compared to the 3D models. An anisotropic analytical solution that we present performs well and recovers decompression rates within a factor of 2, in the situations in which it is valid. 3D models that include multiple melt inclusions show that inclusions can shield each other and reduce the amount of water loss upon ascent. This shielding effect depends on decompression rate, melt inclusion size, and crystallographic direction. Our modeling approach shows that factors such as 3D crystal geometry and melt inclusion configuration can play an important role in constraining accurate decompression rates and recovering water contents in natural magmatic systems. Plain Language Summary: The water content of olivine‐hosted melt inclusions can reveal important information about the generation and storage of magma beneath basaltic volcanoes. Diffusion of hydrogen (as H+) through the olivine host crystal, however, can modify the water content of melt inclusions over minutes to hours. Here we develop a new 3D diffusion model for water loss from olivine‐hosted melt inclusions which includes natural crystal shapes and multiple melt inclusions. We use our model to test the reliability of different types of analytical and numerical models using conditions of magma ascent from the 1977 eruption of Seguam volcano, Alaska. We find that 1D and 2D numerical models underestimate water loss and magma decompression rates because they do not account for additional water loss from all directions. An anisotropic analytical solution that we present compares well with the 3D model giving decompression rates within a factor of 2. Multiple melt inclusions can also shield each other and help to reduce water loss. Our modeling approach shows that factors such 3D crystal geometry and melt inclusion configuration can play an important role in constraining accurate decompression rates, and recovering water contents in natural magmatic systems. Key Points: New 3D multiphase finite element diffusion model and anisotropic analytical solution for water loss from melt inclusions1D and 2D numerical models underestimate magma decompression rates compared to 3D models. The analytical solution performs wellShielding effect from multiple melt inclusions may limit water loss [ABSTRACT FROM AUTHOR]

Titan is an ocean world with a dense atmosphere, where photochemistry produces complex organic molecules that fall to the surface. An important astrobiological question is whether this material can mix with water and form molecules of biological interest. Large impacts heat the moon's subsurface and create liquid water melt pools. A recent study investigated impacts into Titan's clathrate‐covered ice shell. Methane clathrates are stable at Titan's surface conditions and have low thermal conductivity, making them efficient insulators that can lead to steep thermal gradients and a thin stagnant lid. The authors showed that the clathrate layer thickness primarily influences the melt distribution, while its volume is governed by the impactor size. Here, we investigate the fate of melt formed during an impact into a clathrate‐covered ice shell. Our results show two different behaviors: in cases when less melt is produced, the subsurface melt pool remains close to the surface and freezes on timescales ≲25 kyr; in cases when larger volumes of melt are produced, a downward‐oriented transport of the molten material occurs. As it descends, part of the melt freezes but some may reach the ocean within a few kyr under certain conditions; vertical impacts, high surface porosity, low viscosity, and tidal heating all favor this surface‐to‐ocean exchange. While providing insights on parameters that allow a subsurface melt pool to remain liquid beneath a Selk‐sized crater for a few kyr, this study suggests that Dragonfly may be able to sample melt deposits where organics reacted with liquid water to produce biomolecules. Plain Language Summary: Titan, Saturn's largest moon, harbors a subsurface ocean beneath its ice shell. The moon also has an atmosphere, which is rich in large organic molecules that settle onto its surface. When atmospheric methane reacts with surface water ice, it forms methane clathrate. A clathrate layer atop Titan's ice shell affects the formation of Titan's impact craters, as it is both stronger than ice and a better insulator. Here, we study the effect of this clathrate layer on the formation and subsequent fate of melt pools produced by impacts on Titan. We investigate whether the melt descends through the ice shell to reach the ocean or remains near the surface and freezes. Our results show only a limited range of scenarios where impact melt reaches the ocean. In the majority of models, impact melt freezes near the surface within short timescales, ranging from a few thousands to tens of thousands of years. This implies that surface organic molecules may have interacted with subsurface melt pools. These results provide a positive outlook for NASA's Dragonfly mission, which will explore Titan's Selk crater in search of organic materials that have reacted with water to potentially form molecules of biological interest. Key Points: We studied the evolution of impact melt pools in Titan's ice shell using numerical simulations of two‐phase thermal convectionWhile most melt pools never reach the ocean, we observe surface‐to‐ocean exchange in a small part of the investigated parameter spaceOur results suggest that Dragonfly may be able to sample melt deposits where organics reacted with liquid water to produce biomolecules [ABSTRACT FROM AUTHOR]

Extreme melt and rainfall events can induce temporary acceleration of Greenland Ice Sheet motion, leading to increased advection of ice to lower elevations where melt rates are higher. In a warmer climate, these events are likely to become more frequent. In September 2022, seasonally unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to ∼240% relative to pre‐event velocities. However, ice motion returned rapidly to pre‐event levels, and the speed‐ups caused a regional increase in annual ice discharge of only ∼2% compared to when the effects of the speed‐ups were excluded. Therefore, although late melt‐season events are forecast to become more frequent and drive significant runoff, their impact on net mass loss via ice discharge is minimal. Plain Language Summary: Extreme melt and rainfall events can cause the flow of ice on the Greenland Ice Sheet to accelerate, potentially causing more ice to move to lower elevations, where temperatures are warmer and melt rates are higher. In September 2022, there were multiple unprecedented melt events. Their intensity caused some glaciers on the ice sheet to speed up by 240% relative to pre‐event speeds. Despite these accelerations, our analyses show that these events had only a minimal long‐term impact on how much ice was moved to lower elevations due to the short duration of the speed‐ups. As a result, while these melt‐induced speed‐ups are expected to become more common in a warmer climate, their effect on the amount of ice transported toward the ice margins is minimal. Key Points: September 2022 saw multiple melt events over the west Greenland Ice Sheet, with the largest daily runoff of any late melt‐season since 1950Large quantities of surface‐generated meltwater overwhelmed the subglacial drainage system causing brief increases in ice velocityLate‐season runoff‐induced speed‐ups have only minimal impact on the mass balance of the Greenland Ice Sheet via dynamical processes [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]

The melting cryosphere adds heterogeneity to the abiotic and biotic characteristics of many high latitude and montane rivers. However, climate change threatens the cryosphere's persistence in many regions. While existing research has explored the impacts of cryospheric loss on the diversity and structure of freshwater communities, implications for functional traits of communities, such as production of aquatic invertebrates, remain unresolved. Here, we quantified aquatic invertebrate community structure and secondary production in southeast Alaska (USA) streams that represent a meltwater to non‐meltwater gradient, including streams fed primarily by: (1) glacier‐melt, (2) snowmelt, (3) rainfall, and (4) a combination of these sources. We found alpha diversity was highest in the snow‐fed stream and lowest in the glacier‐fed stream. Annual secondary production was also lowest in the glacier‐fed stream (0.56 g ash‐free dry mass m−2), but 2–5 times higher in the other stream types primarily due to greater production of shared taxa that were found in all streams. However, despite low invertebrate diversity and productivity, the glacier‐fed stream hosted distinct species assemblages associated with unique cycles of stream flow, water temperature, turbidity, and nutrient concentrations, which contributed to higher beta diversity between streams. Our findings suggest that the loss of glacier‐melt contributions to rivers may result in increased freshwater invertebrate production but reduced beta diversity, which could have implications for community stability and the capacity of landscapes to support higher‐level consumers, including fishes. [ABSTRACT FROM AUTHOR]