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We investigate the density isobar of water and the melting temperature of ice using six different density functionals. Machine-learning potentials are employed to ensure computational affordability. Our findings reveal significant discrepancies between various base functionals. Notably, even the choice of damping can result in substantial differences. Overall, the outcomes obtained through density functional theory are not entirely satisfactory across most utilized functionals. All functionals exhibit significant deviations either in the melting temperature or equilibrium volume, with most of them even predicting an incorrect volume difference between ice and water. Our heuristic analysis indicates that a hybrid functional with 25% exact exchange and van der Waals damping averaged between zero and Becke–Johnson dampings yields the closest agreement with experimental data. This study underscores the necessity for further enhancements in the treatment of van der Waals interactions and, more broadly, density functional theory to enable accurate quantitative predictions for molecular liquids. [ABSTRACT FROM AUTHOR]

Arctic fjords are inherently vulnerable to global warming, particularly because of the substantial freshwater influx resulting from the melting of glaciers. In this study, precipitation, river water, surface ice, and seawater samples from Kongsfjorden were collected to identify the main sources of freshwater. The dual water isotope (δ18O and δD) results and temperature–salinity profiles revealed that between 0% and 7% freshwater contributed to the fjord's water. Furthermore, different freshwater sources for surface and deep water were identified by the dual water isotope analysis. Turbidity profiles confirmed the alter in particle discharge associated with surface runoff and subglacial discharge. Our study highlighted the sensitivity of water isotope analysis in elucidating the hydrological processes within the fjord system and demonstrated its potential for investigating the impact of meltwater on biological processes in the Arctic. [ABSTRACT FROM AUTHOR]

Core LC42, retrieved from the Central Basin of the northwestern Ross Sea, contains three distinct sediment facies (IRD (ice-rafted debris)-poor bioturbated sandy mud, IRD-rich massive sandy mud, and laminated mud) that are interleaved with each other and deposited over the last 1 Ma. The biogenic components (biogenic opal, total organic carbon, and total nitrogen) of the laminated mud layers are consistently higher than the other two facies throughout the core. Based on the depositional succession of sediment facies and IRD-related depositional processes in the Antarctic continental margin, the laminated mud layers without IRD have been deposited during the glacial periods, but the enhanced paleoproductivity in terms of biogenic components during the mud deposition is unexpected. Backscattered electron imagery substantiates distinctly different componentry of the alternating light and dark laminae in the laminated mud. In particular, the light laminae contain scattered diatom fragments and eroded sand-sized lumps of fossil-bearing mud, whereas the dark laminae are clayey and diatomaceous. Both laminae thus are characterized by the high biogenic components, but they are interpreted to have been principally recycled from older deposits because diatom fragments are mostly reworked and old and their archives are poorly preserved. During the glacial periods, these laminated muds were deposited downward by milky plumes of meltwater discharged underneath the advancing glaciers that scoured the earlier-deposited and semi-consolidated diatom-rich sediments. Our study thus highlights that the recycling of biogenic particles should be precautious to avoid the fallacy of paleoclimatic interpretation in formulating climate-productivity models in the Antarctic continental margin. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms driving hydrological change in arid Central Asia over a range of time scales is crucial for making predictions for future changes in fragile desert-lake ecosystems. As of yet, the drivers of hydrological changes in lake systems of arid Central Asia over the Holocene remain largely unexplored. Aibi Lake, fed by rivers originating from the glaciated Tianshan Mountains and terminating in the arid Junggar Basin of northwestern China, presents a perfect natural laboratory to explore lake evolution in context to Holocene climate evolution in arid Central Asia. Here, a single-grain K-feldspar dating method was used to effectively date 20 paleolake shorelines with poorly bleached sediment to constrain lake level evolution over the past 18 k.y. Results indicate that Aibi Lake experienced a rapid increase in water levels, reaching a peak of ~36 m during the early to mid-Holocene period (10-7 ka). Subsequently, the lake level may have shown a general decline during the middle Holocene (7-4 ka), with the lake reaching a low level of less than 10 m at ca. 4 ka. In the late Holocene, lake levels fluctuated by 10-30 m above modern levels during 4-1 ka, with generally low levels of <9 m after 1 ka. The evolution of Aibi Lake underlines a clear out-of-phase relationship between Central Asian lake evolution and Westerlies precipitation changes, where Holocene lake changes were instead more directly controlled by the flux of glacial meltwater from the Tianshan Mountains, driven by change in Northern Hemisphere summer insolation. Glacier meltwater, in combination with variable delivery of Westerlies and East Asian summer monsoon precipitation, are responsible for asynchronous lake evolution trends across Central to East Asia. [ABSTRACT FROM AUTHOR]

The experiment was conducted on gully slopes with slopes ranging from 80° to 90° to investigate the relationship between erosion rates, spatial and temporal changes in microtopography, and drivers of erosion on gully slopes in different seasons. To precisely characterize the microtopography of slopes where debris slides occur, we used the RIEGL VZ-400 3D laser scanner to scan the observation site and acquire point cloud data on the slope's microtopography. Using the "data conversion module" of ArcGIS software, the point cloud data were transformed into raster data. Through the "3D analysis," "hydrological analysis," and "grid calculator" modules, the basic microgeomorphological indicators were extracted from the gully slope grid data, and the erosion rate and microterrain evolution mechanism of the gully slope in different seasons were also determined. The results revealed the following: (1) in the Pisha sandstone area, erosion was relatively strong in the first quarter, with 65% of the area being eroded. The average erosion rates over the four quarters followed the order of first quarter > fourth quarter > second quarter > third quarter, from fastest to slowest. (2) As the soil on the gully slope thawed, melt water increased soil moisture. This phenomenon sharply increased surface roughness in the first quarter. The correlation coefficients between the erosion rate and temperature in the first and fourth quarters were 0.75 and 0.82, respectively. Temperature mainly affected the erosion rate through surface roughness. The direct path coefficient of this effect was 0.72. (3) In the first and fourth quarters, temperature and wind speed were the main factors influencing the erosion rate; the relationship between surface roughness and other factors was evident, making surface roughness the best topographic factor for assessing slope erosion in the Pisha sandstone area. The results of this study aim to provide theoretical references for understanding the gravity erosion mechanism of gully slopes in the Pisha sandstone area and contribute to the high-quality development of the Yellow River Basin. [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]

Arc magmas have higher water contents (2-6 wt.% H2O) than magmas generated in other tectonic environments, with a growing body of evidence suggesting that some deep arc magmas may be 'super-wet' (>6 wt.% H2O). Here, we use thermodynamic modelling to show that the behaviour of zirconium during magmatic differentiation is strongly sensitive to melt water contents. We demonstrate that super-wet magmas crystallise zircon with low, homogeneous titanium concentrations (75th percentile <10 ppm) due to a decrease in zircon saturation temperatures with increasing melt H2O. We find that zircon titanium concentrations record a transition to super-wet magmatism in Central Chile immediately before the formation of the world's largest porphyry copper deposit cluster at Río Blanco-Los Bronces. Broader analysis shows that low, homogeneous zircon titanium concentrations are present in many magmatic systems. Our study suggests that super-wet magmas are more common than previously envisaged and are fundamental to porphyry copper deposit mineralisation. Titanium concentrations in zircon crystals reveal a link between the world's largest copper resources and magmas with very high-water contents. [ABSTRACT FROM AUTHOR]

The Mount Brown South ice core (MBS 69.111° S 86.312° E) is a new, high resolution ice core drilled in coastal East Antarctica. With mean annual accumulation estimated to be 20–30 cm ice equivalent accumulation throughout the length of the core (∼295 m), MBS represents a high resolution archive of ice core data spanning 1137 years (873–2009 CE), from an area previously underrepresented by high resolution ice core data. Here, we present a high-resolution dataset of chemistry and impurities obtained via continuous flow analysis (CFA). The dataset consists of meltwater electrolytic conductivity, sodium (Na+), ammonium (NH4+), hydrogen peroxide (H2O2), and insoluble microparticle measurements. The data are presented in three datasets: as a 1 mm depth resolution record, 3 cm averaged record, and decadal average record. The 1 mm record represents an oversampling of the true resolution, as due to smoothing effects the actual resolution is closer to 3 cm for some species. Therefore, the 3 cm resolution dataset is considered to be the minimum true resolution given the system setup. We also describe the current Copenhagen CFA system, and provide a detailed assessment of data quality, precision, and functional resolution. The 1 mm averaged, 3 cm averaged, and MBS2023 decadal averaged datasets are available at the Australian Antarctic Data Center: http://dx.doi.org/doi:10.26179/9tke-0s16 (Harlan et al., 2024). [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]

This study aimed to synthesise and interpret stable isotopic data (δ2H and δ18O) from various sources to understand the isotope hydrology around coal mine operations in Elk Valley, B.C., Canada. The data, including precipitation, groundwaters, seeps, and mine rock drains, were used to construct a local meteoric water line (LMWL) for the Elk Valley, evaluate the spatiotemporal isotopic composition of its groundwater, and assess mine seepage and mine rock drain discharge. The study revealed a robust LMWL relation (δ2H = 7.4 ± 0.2 · δ18O – 4.3 ± 4.1). The groundwater and seep data indicated a winter season bias and a north–south latitudinal gradient, suggesting rapid near-surface groundwater flow without significant post-precipitation evaporation. Porewater isotope samples from unsaturated mine rock piles (MRPs) showed site-specific evaporation patterns, potentially due to convective air flows or exothermic sulphide oxidation. This research revealed the influence of groundwater and meltwater on rock drain discharge. Based on evaporative mass balance calculations, MRPs seasonally contributed ca. 5 %(December base flow) and 22 % (snowmelt) to drain discharge. The findings underscore the value of stable isotope data collections in the Elk Valley to help better define and quantify the hydrology–hydrogeology, including a better understanding of evaporative conditions in MRPs. [ABSTRACT FROM AUTHOR]

The incorporation of sulfate anions in a suitable host matrix has proven to be a challenging task for glass technologists around the world. Therefore, the present work reports on the solubility and retention of sulfate species, as an invaluable macronutrient for plants, in a multicomponent silicate-phosphate glasses from the SiO2–P2O5–K2O–MgO–CaO–XSO3 system. Glasses containing target [SO4]2− concentrations 0–5 mol.% were synthesized via high-temperature melt-quenching technique, the last stage of which constituted fritting the acquired melt in water. It was observed that this synthesis route broadened the glass-forming range of materials from the studied system, the sulfate capacity of which was determined to be ∼ 2 mol.%. At higher [SO4]2− concentrations, additional sulfur was retained in glasses as crystalline inclusions of sulfate salt. An in-depth insight into the materials' structure revealed that sulfate species exist in the vitreous matrix as units not bonded to either the silico-oxygen or phosphor-oxygen subnetworks, and their addition leads to a gradual increase in the polymerization degree of the former, and to the opposite effect as regards the latter. Thermal analysis of the tested glasses supported the structural studies and demonstrated that the addition of sulfur initially reduces materials' glass stability, leading to its increase after SO3 content reaches 1 mol.%. It was also shown that [SO4]2− species affect local environments of Si and Mg atoms indirectly, inducing changes in the medium-range structure beyond their first coordination spheres presumably involving the rearrangement of potassium cations within the vitreous matrix. [ABSTRACT FROM AUTHOR]

Glacial fjords often contain ice mélange, a frozen conglomeration of icebergs and sea ice, which has been postulated to influence both glacier dynamics and fjord circulation through coupled mechanical and thermodynamic processes. Ice mélange meltwater can alter stratification of the water column by releasing cool fresh water across a range of depths in the upper layer of the fjord. This meltwater input can subsequently modify the depth at which the subglacial discharge plume reaches neutral buoyancy and therefore the underlying buoyancy-driven fjord circulation and heat exchange with warm ocean shelf waters. Despite a spate of recent modeling studies exploring these proposed feedbacks, we lack in situ observations quantifying changes to the water column induced by ice mélange meltwater. Here we use a novel dataset collected before and after the melt, breakup, and down-fjord transport of ephemeral ice mélange in front of Kangilliup Sermia (Rink Isbræ) to directly investigate the extent to which ice mélange meltwater can modify glacier-adjacent water properties. We find that even a short-lived ice mélange event (4 d) can cause substantial cooling (0.18 °C) and freshening (0.25 g kg−1) of the water column that leads to stratification change down to the depth of the outflowing discharge plume. We compare our observations to an adjacent fjord, Kangerlussuup Sermia, where ice mélange seldom forms in the summertime and show that the presence or absence of ice mélange melt creates fundamental differences in the upper-layer hydrography of the two areas. These observations provide critical constraints for and agreement with recent modeling studies that have suggested ice mélange meltwater needs to be included in ocean circulation models for glaciers with deep grounding lines and high ice fluxes, which are precisely the glaciers exhibiting the largest-magnitude terminus retreats at present. [ABSTRACT FROM AUTHOR]

This research develops a conceptual model of a karst system subject to mountain permafrost. The transient thermal response of a frozen rock cleft after the rise in the atmospheric temperature above the melting temperature of water is investigated using numerical simulations. Free convection in liquid water (i.e. buoyancy-driven flow) is considered. The density increase in water from 0 to 4 °C causes warmer meltwater to flow downwards and colder upwards, resulting in significant enhancement of the heat transferred from the ground surface to the melting front. Free convection increases the melting rate by approximately an order of magnitude compared to a model based on thermal conduction in stagnant water. The model outcomes are compared qualitatively with field data from the Monlesi ice cave (Switzerland) and confirm the agreement between real-world observations and the proposed model when free convection is considered. [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]

Globally, there is now a growing evidence for a low velocity layer in the deeper parts of the upper mantle, above the 410 km discontinuity (hereafter called LVL-410). The origin of this layer is primarily attributed to interaction of slabs or plumes with a hydrous mantle transition zone (MTZ) that results in dehydration melting induced by water transport upward out of the MTZ. However, the ubiquitous nature of this layer and its causative remain contentious. In this study, we use high quality receiver functions (RFs) sampling diverse tectonic units of the Indian subcontinent to identify Ps conversions from the LVL-410. Bootstrap and differential slowness stacking of RFs migrated to depth using a 3-D velocity model reveal unequivocal presence of a deep low velocity layer at depths varying from 290 to 400 km. This layer appears more pervasive and deeper beneath the Himalaya, where detached subducted slabs in the MTZ have been previously reported. Interestingly, the layer is shallower in plume affected regions like the Deccan Volcanic Province and Southern Granulite Terrane. Even though a common explanation does not appear currently feasible, our observations reaffirm deep low velocity layers in the bottom part of the upper mantle and add to the list of regions that show strong presence of such layers above the 410 km discontinuity. [ABSTRACT FROM AUTHOR]

The configuration of the Northern Hemisphere ice sheets during the Penultimate Glacial Maximum differed to the Last Glacial Maximum. However, the reasons for this are not yet fully understood. These differences likely contributed to the varied deglaciation pathways experienced following the glacial maxima and may have had consequences for the interglacial sea level rise. To understand the differences between the North American Ice Sheet at the Last and Penultimate glacial maxima (21 and 140 ka), we perform two perturbed-physics ensembles of 62 simulations using a coupled atmosphere–ice sheet model, FAMOUS-ice, with prescribed surface ocean conditions, in which the North American and Greenland ice sheets are dynamically simulated with the Glimmer ice sheet model. We apply an implausibility metric to find ensemble members that match reconstructed ice extent and volumes at the Last and Penultimate glacial maxima. We use a resulting set of "plausible" parameters to perform sensitivity experiments to decompose the role of climate forcings (orbit, greenhouse gases) and initial conditions on the final ice sheet configurations. This confirms that the initial ice sheet conditions used in the model are extremely important in determining the difference in final ice volumes between both periods due to the large effect of the ice–albedo feedback. In contrast to evidence of a smaller Penultimate North American Ice Sheet, our results show that the climate boundary conditions at these glacial maxima, if considered in isolation, imply a larger Penultimate Glacial Maximum North American Ice Sheet than at the Last Glacial Maximum by around 6 m sea level equivalent. This supports the notion that the growth of the ice sheet prior to the glacial maxima is key in explaining the differences in North American ice volume. [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]

Photosynthesis by phytoplankton reduces partial pressure CO2 of at the surface of the ocean and is therefore a potential means of action for a marine CO2 removal technology. Here we study how glacial rock flour may influence photosynthesis in the open ocean. Glacial rock flour is a fine-grained silicate mineral from the bedrock grinded by the Greenland Ice Sheet and enters the ocean via fjords and coastal waters. It is therefore a natural source of nutrients and trace metals to the ocean. It is easily accessible in large quantities and could be a suitable source for large-scale CO2 removal. The impact of suspended glacial rock flour was analyzed through 14 incubation experiments with natural phytoplankton communities sampled in the subtropical Atlantic. A significant increase in photosynthesis was found in 12 experiments where variable fluorescence Fv/Fm increased 12% and the average concentration of chlorophyll a increased significantly in comparison with control treatments during a 6-day period. Incubations with glacial rock flour showed a significant uptake of phosphorus whereas the average concentrations of silicate and dissolved inorganic nitrogen increased. Nutrient changes could be explained by increasing phytoplankton and microbial biomass, remineralization of organic matter, and weathering (mobilization) of glacial rock flour. These short time experiments indicated that trace metals from glacial rock flour stimulated phytoplankton growth. Thus, glacial rock flour has the potential to increase photosynthesis and phytoplankton growth, and therefore may be a potential means of action for marine CO2 removal. [ABSTRACT FROM AUTHOR]

We provide a detailed description of the ice-sheet layer age tracer Englacial Layer Simulation Architecture (ELSA) – a model that uses a straightforward method to simulate the englacial stratification of large ice sheets – as an alternative to Eulerian or Lagrangian tracer schemes. ELSA's vertical axis is time, and individual layers of accumulation are modeled explicitly and are isochronal. ELSA is not a standalone ice-sheet model but requires unidirectional coupling to another model providing ice physics and dynamics (the "host model"). Via ELSA's layer tracing, the host model's output can be evaluated throughout the interior using ice core or radiostratigraphy data. We describe the stability and resolution dependence of this coupled modeling system using simulations of the last glacial cycle of the Greenland ice sheet using one specific host model. Key questions concern ELSA's design to maximize usability, which includes making it computationally efficient enough for ensemble runs, as well as exploring the requirements for offline forcing of ELSA with output from a range of existing ice-sheet models. ELSA is an open source and collaborative project, and this work provides the foundation for a well-documented, flexible, and easily adaptable model code to effectively force ELSA with (any) existing full ice-sheet model via a clear interface. [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]

Glacier pattern changes directly indicate variability in local climatic circumstances. The present study dealt with the proposition and estimation of spatiotemporal glacier movement using a synthetic aperture radar-derived polarimetric tracking method which revealed improved estimates over four selected large tributary-bearing glaciers (Siachen, Bara Shigri, Gangotri, and Zemu) in the Indian Himalayas. The average estimated velocities in 2021–2022 for the four glaciers were 0.13, 0.06, 0.08 and 0.09 m/day. The thick debris cover hindered the movement temporally in the middle and lower reaches of the glaciers. The effect of meltwater influx along the tributary confluence zone was also witnessed over the glaciers. Comparison and validation with the US National Aeronautics and Space Administration (NASA) Inter-mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) products has shown the utility of the proposed method in studying the contributions of active feeding tributaries of the glaciers in the ablation zone. [ABSTRACT FROM AUTHOR]

An isolation basin is a geomorphological landform that enables the precise reconstruction of the former height and age of relative sea level. A series of isolation basins at different elevations within a small geographical area can provide a high-resolution record of the timing and magnitude of relative sea-level change. Arisaig, on the west coast of Scotland, provides the longest post-Last Glacial Maximum record of relative sea-level change in the UK, produced from the analysis of a series of 16 isolation basins. The records produced from these basins continue to provide important constraints that inform understanding of processes acting from local to global scales, such as glacial and climatic transitions, glacio-isostatic adjustment and global meltwater pulses. [ABSTRACT FROM AUTHOR]

Reductions in winter snowpack over the last few decades have affected water resource availability in the western United States. In regions where glaciers exist, local communities have an advantage over nonglaciated regions as water continues to flow once the snowpack has melted. Despite this advantage, relatively little is understood about the contributions of glacial meltwater quantity and quality to streamflow. Torrey Creek watershed in the Wind River Range, Wyoming, contains several glaciers that provide meltwater to supplement late summer streamflow to the Wind River. Despite its importance as a contributor to water resources in the region, Torrey Creek discharge is not regularly monitored. Field research conducted in August 2019 for this study, along with previous field work completed in August 2012 and 2014, provides some understanding of late summer meltwater quantity and quality within the Torrey Creek watershed. Measured Torrey Creek discharge during mid-August 2019 averaged 3.80 m³ s−1 with 37 percent of the discharge attributed to glacial ice melt from stable isotope analysis. Nutrient loading to Torrey Creek from glacial meltwater was dominated by NO2–NO3 at 179.99 kg per month followed by 21.86 kg of total P for August 2019. [ABSTRACT FROM AUTHOR]

Cerro Machín, a volcano located in the northern segment of the Andes, is considered one of the most dangerous volcanoes in Colombia with an explosive record that involves at least five plinian events. Prior studies focused on the last dome-building eruption have suggested the presence of a water-rich mid-crustal magma reservoir. However, no direct volatile measurements have been published and little work has been completed on the explosive products of the volcano. Here, we study the largest known eruption of Cerro Machín volcano which occurred 3600 years BP producing dacitic pyroclastic fall deposits that can be traced up to 40 km from the vent. Lapilli pumice clasts have a mineral assemblage of plagioclase, amphibole, quartz, and biotite phenocrysts, with accessory olivine, Fe–Ti oxides, and apatite. The occurrence of Fo89–92 olivine rimmed by high Mg# amphibole and the established high-water contents in the magma imply the presence of magma near or at water saturation at pressures > ~ 500 MPa. Measurements of up to 10.7 wt % H2O in melt inclusions hosted in plagioclase and quartz in the 3600 years BP eruption products support the idea that Cerro Machín is a remarkably water-rich volcanic system. Moreover, this is supported by measurements of ~103 to 161 ppm H2O in plagioclase phenocrysts. The application of two parameterizations of water partitioning between plagioclase and silicate melt allows us to use our water in plagioclase measurements to estimate equilibrium melt water contents of 5 ± 1 wt % to 11 ± 2 wt % H2O, which are in good agreement with the water contents we measured in melt inclusions. Results of amphibole geobarometry are consistent with a magma reservoir stored in the mid-to-lower crust at a modal pressure of 700 ± 250 MPa, corresponding to a depth of ~25 km. Minor crystallization in the shallow crust is also recorded by amphibole barometry and calculated entrapment pressures in melt inclusions. Amphibole is present as unzoned and zoned crystals. Two populations of unzoned amphibole crystals are present, the most abundant indicate crystallization conditions of 853 ± 26°C (1 se; standard error), and the less abundant crystallized at an average temperature of 944 ± 24°C (1 se). Approximately 18% of the amphibole crystals are normally or reversely zoned, providing evidence for a minor recharge event that could have been the trigger mechanism for the explosive eruption. Plagioclase crystals also show normal and reverse zoning. The moderate Ni concentrations (<1600 μg/g) in the high-Fo olivine xenocrysts suggest that Cerro Machín primary magmas are generated by inefficient interaction of mantle peridotite with a high-silica melt produced by slab melting of basaltic material. Some sediment input is also suggested by the high Pb/Th (>2.2) and Th/La (0.3–0.4) ratios. Whole rock chemistry reveals heavy rare earth element (HREE) depletion and Sr enrichment that likely formed during the crystallization of garnet and amphibole in the upper part of the mantle or lower portion of the crust, promoting the formation of water-rich dacitic magma that was then injected into the middle-to-lower crust. Textural and compositional differences in the crystal cargo that erupted during dome-building and plinian events support the idea that large volumes of magma recharge lead to effusive eruptions, while only small recharge events are needed to trigger plinian eruptions at Cerro Machín. [ABSTRACT FROM AUTHOR]

In a warming world, the input of glacier meltwater to inland water ecosystems is predicted to change, potentially affecting their productivity. Meta-ecosystem theory, which posits that the nutrient availability in the recipient ecosystem can determine the extent of cross-ecosystem boundary utilization, can be useful for studying landscape-scale influences of glacier meltwater on inland waters. Here, we investigate how the input of glacier meltwater in a river system in Southern Greenland influences the utilization of marine subsidies in freshwater fish. Our study system comprised four sites, with controls for glacial meltwater and marine subsidies, harboring a partially migrating population of arctic char, meaning that some individuals migrate to the ocean and others remain in freshwaters, and two fully resident populations as a freshwater reference. We assessed the incorporation of marine carbon in freshwater resident char using both bulk and amino acid stable isotope analysis of muscle tissue. In the population with partial migration, marine subsidies were a significant resource for resident char individuals, and estimates of trophic position suggest that egg cannibalism is an important mechanism underlying the assimilation of these marine subsidies. In proglacial streams, namely those with high glacial meltwater, the total dependence on marine subsidies increased and reached 83% because char become cannibals at smaller sizes. In the configuration of our focal meta-ecosystem, our results suggest that the importance of marine subsidies to freshwater fish strengthens within increasing meltwater flux from upstream glaciers. [ABSTRACT FROM AUTHOR]

Tufa deposits have significant potential for reconstructing past lake-level fluctuations. Here, we conducted U-Th dating of tufa deposits exposed along the shoreline of Longmu Co Lake in the northwestern Tibetan Plateau to reconstruct its water level history during the middle-late Holocene. Our data demonstrate that Longmu Co Lake reached its highest level (61 m above the present level) at around 7.4 ka in response to the strengthened Indian Summer Monsoon and increased glacial meltwater; its lake level subsequently decreased due to solar insolation-induced decline in summer monsoon and glacial meltwater. Moreover, we find that the lake level experienced an abrupt decline at ~2.2 ka with a maximum amplitude of 13 m, probably owing to the rapid cooling of the local climate. The δ18O and δ13C of Longmu Co tufa also show a covariance trend, which supports the regional climate change reflected by the lake level fluctuation of Longmu Co. Additionally, we observed an inverse correlation between initial δ234U content in tufa and lake level variation, suggesting that initial calcium δ234U can serve as a proxy for reconstructing environmental changes. Our study therefore implies that lake tufa as a reliable archive for accurately reconstructing lake level changes. [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]

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 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]

The collapse of ice shelves could expose tall ice cliffs at ice sheet margins. The marine ice cliff instability (MICI) is a hypothesis that predicts that, if these cliffs are tall enough, ice may fail structurally leading to self-sustained retreat. To date, projections that include MICI have been performed with a single model based on a simple parameterization. Here, we implement a physically motivated parameterization in three ice sheet models and simulate the response of the Amundsen Sea Embayment after a hypothetical collapse of floating ice. All models show that Thwaites Glacier would not retreat further in the 21st century. In another set of simulations, we force the grounding line to retreat into Thwaites' deeper basin to expose a taller cliff. In these simulations, rapid thinning and velocity increase reduce the calving rate, stabilizing the cliff. These experiments show that Thwaites may be less vulnerable to MICI than previously thought, and model projections that include this process should be re-evaluated. [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]

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]

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]

In polar regions, glaciers are retreating onto land, gradually widening ice-free coastal waters, which are known to act as new sinks of atmospheric carbon. However, the increasing delivery of inorganic suspended particulate matter (iSPM) with meltwater might significantly impact their capacity to contribute to carbon sequestration. Here, we present an analysis of satellite, meteorological, and SPM data as well as results of a coupled physical–biogeochemical model (1D GOTM-ECOSMO-E2E-Polar) with a newly implemented iSPM group to show the impact of iSPM on the ecosystem dynamics in a warming polar fjord (Hornsund, European Arctic) with numerous shallow-grounded marine-terminating glaciers. Our results indicate that with a longer melt season (9 d per decade, 1979–2022), the loss of sea ice cover (44 d per decade, 1982–2021) and the formation of new marine habitats after the retreat of marine-terminating glaciers (around 100 km 2 in 1976–2022, a 38 % increase in the total area), glacial meltwater has transported increasing loads of iSPM from land (3.7 g m -3 per decade, reconstructed for 1979–2022). The simulated light limitation induced by the iSPM input delayed and decreased the peaks in phytoplankton, zooplankton, and macrobenthos. The newly ice-free areas still markedly contributed to plankton primary and secondary production and carbon burial in sediments (5.1, 2.0, and 0.9 Gg C yr -1 , respectively, on average for 2005–2009 in the iSPM scenario). However, these values would have been 5.0, 2.1, and 0.1 Gg C yr -1 higher, respectively, without the iSPM input. Since carbon burial was the least affected by iSPM (a decrease of around 16 %, in comparison to 50 % for plankton primary and secondary production), the impact of marine ice loss and enhanced land–ocean connectivity should be investigated further in the context of carbon fluxes in expanding polar fjords. [ABSTRACT FROM AUTHOR]

We report neutron-scattering measurements of the density of states (DOS) of water and liquid Fomblin in a wide range of temperatures. In the liquid phase, we confirm the presence of a universal low-energy linear scaling of the experimental DOS as a function of the frequency, g (ω) = a (T) ω , which persists at all temperatures. The low-frequency scaling of the DOS exhibits a sharp jump at the melting point of water, below which the standard Debye's law, g (ω) ∝ ω 2 , is recovered. On the contrary, in Fomblin, we observe a continuous transition between the two exponents reflecting its glassy dynamics, which is confirmed by structure measurements. More importantly, in both systems, we find that the slope a(T) grows with temperature following an exponential Arrhenius-like form, a (T) ∝ exp (- ⟨ E ⟩ / T) . We confirm this experimental trend using molecular dynamics simulations and show that the prediction of instantaneous normal mode (INM) theory for a(T) is in qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Ocean stratification on Arctic shelves critically influences nutrient availability, essential for primary production. However, discerning the changes in stratification and their drivers is challenging. Through the use of a highresolution ocean-sea-ice model, this study investigates the variability in stratification within the northeastern Chukchi Sea over the period from 1987 to 2016. Our analysis, validated against available observations, reveals that summers with weak stratification are marked by a warmer water column that features a saltier upper layer and a fresher lower layer, thereby diminishing the vertical density gradient. In contrast, summers with strong stratification are characterized by a cooler column with a fresher upper layer and a saltier lower layer, resulting in an increased density gradient. This variability is primarily driven by the timing of sea-ice retreat and the consequent variations in meltwater flux, with early retreat leading to less meltwater and saltier surface conditions. This factor significantly outweighs the influence of changes in circulation and associated lateral freshwater transport driven by the Bering Strait inflow. We also find that the synchronization of sea-ice retreat and Bering Strait inflow intensity is linked to the timing and strength of the Aleutian Low's westward shift from the Gulf of Alaska to the Aleutian Basin in the early winter. These insights are crucial for understanding nutrient dynamics and primary production in the region. Furthermore, monitoring sea-ice retreat timing could serve as a useful proxy for predicting subsequent summer stratification changes. [ABSTRACT FROM AUTHOR]

Arctic air temperatures have increased about four times faster than the global average since about 1980. Consequently the Greenland Ice Sheet has lost about twice as much ice as the Antarctic Ice Sheet between 2003 and 2019, and mass loss from glaciers and ice caps is also dominated by those that lie in the Arctic. Thus, Arctic land ice loss is currently a major contributor to global sea level rise. This increasing freshwater flux into the Arctic and North Atlantic oceans, will also impact physical, chemical and biological processes across a range of domains and spatiotemporal scales. Although, meltwater discharge data at Arctic coastlines are available from two existing datasets, these are limited by their spatial resolution and/or coverage. Here, we improve upon previous work and provide a high-resolution coastal meltwater discharge data product that covers all Arctic regions, where land ice is present, i.e. the Canadian Arctic Archipelago, Greenland, Iceland, Svalbard, Russian Arctic Islands. Coastal meltwater discharge data were derived from Modεave;le Atmosphérique Régional daily ice and land runoff products between 1950 and 2021, which we statistically downscaled from their original ~6 km resolution to 250 m. The complete data processing algorithm, including downscaling, is fully documented and relies on open-source software. The coastal discharge database is disseminated in easily accessible and storage efficient netCDF files. [ABSTRACT FROM AUTHOR]

Glacial Lake Outburst Flood (GLOF) events, particularly prevalent in Asia's High Mountain regions, pose a significant threat to downstream regions. However, limited understanding of triggering mechanisms and inadequate observations pose significant barriers for early warnings of impending GLOFs. The 2018 Nyalam GLOF event in southern Tibet offers a valuable opportunity for retrospective analysis. By combining optical and radar remote sensing images, meteorological data, and seismicity catalogs, we examined the spatiotemporal evolution, triggering factors, and the outburst mechanism of this event. Our analysis reveals a progressive retreat of 400–800 m for the parent glaciers between 1991 and 2018, increasing the runoff areas at glacier termini by 167% from 2015 to 2018 and contributing abundant meltwater to the glacial lake. In contrast, the lake size shrunk, potentially due to a weakening moraine dam confirmed by SAR interferometry, which detected continuous subsidence with a maximum line-of-sight (LOS) rate of ~120 mm/a over the preceding ~2.5 years. Additionally, temperature and precipitation in 2018 exceeded the prior decade's average. Notably, no major earthquakes preceded the event. Based on these observations, we propose a likely joint mechanism involving high temperatures, heavy precipitation, and dam instability. An elevated temperature and precipitation accelerated glacial melt, increasing lake water volume and seepage through the moraine dam. This ultimately compromised dam stability and led to its failure between 3 August 2018 and 6 August 2018. Our findings demonstrate the existence of precursory signs for impending GLOFs. By monitoring the spatiotemporal evolution of environmental factors and deformation, it is possible to evaluate glacial lake risk levels. This work contributes to a more comprehensive understanding of GLOF mechanisms and is of significant importance for future glacial lake risk assessments. [ABSTRACT FROM AUTHOR]

Despite extensive investigation, the nature and causes of the Mid-Pleistocene Transition remain enigmatic. In this work, we assess its linkage to asynchronous development of bipolar ice sheets by synthesizing Pleistocene mid- to high-latitude proxy records linked to hemispheric ice sheet evolution. Our results indicate substantial growth of the Antarctic Ice Sheets (AISs) at 2.0 to 1.25 million years ago, preceding the rapid expansion of Northern Hemisphere Ice Sheets after ~1.25 million years ago. Proxy-model comparisons suggest that AIS and associated Southern Ocean sea ice expansion can induce northern high-latitude cooling and enhanced moisture transport to the Northern Hemisphere, thus triggering the Mid-Pleistocene Transition. The dynamic processes involved are crucial for assessing modern global warming that is already inducing asynchronous bipolar melting of ice sheets. [ABSTRACT FROM AUTHOR]

Changes in global mean sea level are a clear indicator of a warming climate, but local factors including land subsidence or uplift, cause changes in relative sea level that drive shoreline shifts. These local changes and their impact on coastal hazards matter to coastal communities. NZ SeaRise produced relative sea level projections for Aotearoa to include the latest global climate and Antarctic Ice Sheet research and estimates of vertical land movement at high spatial resolution. Research-informed communication to the public and planners included a web-based projections tool supplemented by written and visual narratives, and a media engagement plan. This communication, and analysis of media impact, provided a case study for audience-relevant information on sea-level rise. Information regarding shoreline change and evolving hazards, required for risk assessment, was not included in the NZ SeaRise projections. New research is needed to reduce uncertainty in future Antarctic Ice Sheet contribution to sea level, link changes in sea surface height to our dynamic land surface and enhance communication approaches. Several examples of the required research are presented here but ongoing efforts must refine the timing and magnitude of coastline change, better define coastal hazards and risks, and develop appropriate adaptation strategies for unavoidable climate change impacts. [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]

Microbes residing in cryoconite holes (debris, water, and nutrient-rich ecosystems) on the glacier surface actively participate in carbon and nutrient cycling. Not much is known about how these communities and their functions change during the summer melt-season when intense ablation and runoff alter the influx and outflux of nutrients and microbes. Here, we use high-throughput-amplicon sequencing, predictive metabolic tools and Phenotype MicroArray techniques to track changes in bacterial communities and functions in cryoconite holes in a coastal Antarctic site and the surrounding fjord, during the summer season. The bacterial diversity in cryoconite hole meltwater was predominantly composed of heterotrophs (Proteobacteria) throughout the season. The associated functional potentials were related to heterotrophic-assimilatory and -dissimilatory pathways. Autotrophic Cyanobacterial lineages dominated the debris community at the beginning and end of summer, while heterotrophic Bacteroidota- and Proteobacteria-related phyla increased during the peak melt period. Predictive functional analyses based on taxonomy show a shift from predominantly phototrophy-related functions to heterotrophic assimilatory pathways as the melt-season progressed. This shift from autotrophic to heterotrophic communities within cryoconite holes can affect carbon drawdown and nutrient liberation from the glacier surface during the summer. In addition, the flushing out and export of cryoconite hole communities to the fjord could influence the biogeochemical dynamics of the fjord ecosystem. [ABSTRACT FROM AUTHOR]

Ice-core records from the interior of the Greenland ice sheet suggest widespread thinning during the Holocene. However, the recurring underestimation of this thinning in numerical models raises concerns about both the veracity of such reconstructions and the reliability of glaciological models. Recent work suggests the 8000-year-old Northeast Greenland Ice Stream (NEGIS), including a now-extinct northern tributary, may have been an early influence on Greenland ice-sheet dynamics. Yet, the inaccurate reproduction of NEGIS-like dynamics in most models hampers investigation of whether this feature played a role in Holocene ice-sheet thinning. Here we show that grounding-line retreat in northeast Greenland triggers elevation changes at the northern summit via ice-dynamic effects modulated by the paleo NEGIS system. In our simulations, fast ice-stream flow caused by transiently imposed reduced basal shear stress following the northeast retreat explains 55% (± 18%) of the estimated ice thinning, showing that ice-stream dynamics is one of the main drivers of the NGRIP Holocene surface elevation drop. Our findings show that the ice-flow in northeast Greenland plays a large role in ice-surface elevation changes in central Greenland. Using a three-dimensional ice sheet model, this work demonstrates that more than half of the Holocene surface elevation drop recorded in ice cores from north-central Greenland can be attributed to ice dynamic changes in northeast Greenland following ice-sheet retreat during the last deglaciation. [ABSTRACT FROM AUTHOR]

The optical characteristics of coastal Antarctic waters exhibit complexity due to the dynamic hydrography influenced by meltwater intrusion, which alters nutrient levels, thermohaline structure, and optically active substances (OAS) regimes. Studies on bio-optical variability and its implications on phytoplankton productivity (PP) are scanty in coastal polar regions. On this backdrop, timeseries measurements (72 h at 6 h intervals) of bio-optical properties such as phytoplankton biomass (chlorophyll-a), absorption (aph), and total suspended matter (TSM) concurrently with PP were measured to understand their interplay and variability in relation to the ambient physicochemical settings in the undersampled Prydz Bay, coastal Antarctica. Our findings revealed thermohaline stratification within the bay, likely attributed to the inflow of less saline meltwater from nearby glaciers and minimal wind activity. The consistent presence of subsurface chlorophyll maximum (SCM) beneath the stratified layer underscored the light-acclimatization response of shade-adapted phytoplankton. Surface waters exhibited higher TSM compared to deeper layers, indicating glacial melt influence, while the depth of the sunlit layer remained relatively stable, suggesting limited watermassmovement and/or variability in OAS at the study site. An inverse relation between chlorophyll-a and chlorophyll-a-specific phytoplankton light absorption (a*ph(λ)) manifested 'pigment package effect' within the prevailing phytoplankton community, implying reduced light-absorption efficiency and consequent lower PP. Compared to chlorophyll-a, the phytoplankton light absorption (aph(l)) emerged as a better proxy for explaining PP variability. Nutrient availability was not limiting, which was conducive to micro (large) phytoplankton growth. Classification of phytoplankton size classes (micro, nano, and pico) based on the B/R ratio (aph at Blue (443 nm)/Red (676 nm) region) confirmed the dominance of larger (micro) phytoplankton that aremore susceptible to package effect, thus have implications on reduced PP potential of this polar marine ecosystem. [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 Atlantic Meridional Overturning Circulation (AMOC) has recently been categorized as a core tipping element as, under climate change, it is believed to be prone to critical transition implying drastic consequences on a planetary scale. Moreover, the AMOC is strongly coupled to polar ice sheets via meltwater fluxes. On the one hand, most studies agree on the fact that a collapse of the Greenland Ice Sheet would result in a weakening of AMOC. On the other hand, the consequences of a collapse of the West Antarctica Ice Sheet are less well understood. However, some studies suggest that meltwater originating from the Southern Hemisphere is able to stabilize the AMOC. Using a conceptual model of the AMOC and a minimal parameterization of ice sheet collapse, we investigate the origin and relevance of this stabilization effect in both the deterministic and stochastic cases. While a substantial stabilization is found in both cases, we find that rate- and noise-induced effects have substantial impact on the AMOC stability, as those imply that leaving the AMOC bistable regime is neither necessary nor sufficient for the AMOC to tip. Also, we find that rate-induced effects tend to allow a stabilization of the AMOC in cases where the peak of the West Antarctica Ice Sheet meltwater flux occurs before the peak of the Greenland Ice Sheet meltwater flux. [ABSTRACT FROM AUTHOR]

On December 4, 2020, a massive high-locality landslide occurred at Qingliu Village, Li County, Sichuan Province, China (UTC + 8). This event resulted in a landslide deposit of approximately 34.8 × 104 m3, causing the destruction of two roads and several houses on the hillslope and blocking a downstream river. Extensive field investigations, UAV photography, borehole drilling, and GNSS monitoring were conducted after the landslide. Additionally, a PFC3D numerical simulation was used to reproduce the movement of the landslide after calibrating its meso-strength parameters. Based on the motion and deposit characteristics, the landslide is divided into a major sliding zone (comprising the source zone, impact-shoveling zone, and deposition zone) and a landslide-affected zone. The primary triggering factor for the Qingliu landslide is the slope mass damage caused by frequent preceding earthquakes. On the other side, the direct triggers are continuous rainfall and upslope meltwater, which increased the weight and further weakened the strength of the slope mass. The landslide initiation involves the formation of a tensile crack in the major sliding zones, followed by the shoveling of loose debris by the displaced landslide mass, and then termination with the striking at the slope foot and damming a river. This study offers valuable insights into the evolutionary processes of high-locality landslides. [ABSTRACT FROM AUTHOR]