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Constraining past West Antarctic Ice Sheet (WAIS) change helps validate numerical models simulating future ice sheet dynamics. Following rapid deglaciation during the mid‐Holocene, ice near Thwaites Glacier was ∼35 m thinner than present; however, the timing of ice regrowth to its present configuration remains unknown. To fill this knowledge gap, we present cosmogenic nuclide exposure ages of cobbles from the surface of a moraine situated between Thwaites and Pope glaciers. We infer that the moraine formed and stabilized in the Late Holocene (∼1.4 ka) when a small glacier thickened. We also present a novel reconstruction of WAIS volume constrained by sea‐level data, which demonstrates that moraine formation coincided with a large‐scale WAIS readvance. Our new geologic constraints will help inform models of the solid Earth response to surface mass loading, improving our understanding of ice sheet dynamics in a vulnerable part of WAIS. Plain Language Summary: The Antarctic ice sheets are melting and adding to sea‐level rise, with the rate at which they lose mass expected to increase in the coming decades to centuries. However, recent studies have shown that, only a few thousand years ago, the Antarctic ice sheets were smaller than they are now, and subsequently regrew to their present size. Understanding how the Antarctic ice sheets regrew to their present size, as well as the rate it happened, helps us understand whether ongoing loss of ice sheet mass is reversible. In this study, we identify a glacial landform (a moraine) that was deposited as an Antarctic glacier grew in size after the Antarctic ice sheets were smaller than they are today. We collected rocks from the surface of the glacial landform and measured isotopes in them. These isotopes tell us the landform was created by the glacier about 1,400 years ago. The new information from this study on the past of the Antarctic ice sheets can be used to improve our understanding of how the Antarctic ice sheets will change, and add to sea‐level rise, in the future. Key Points: Direct evidence is found for a Late Holocene episode of glacier thickening in the Amundsen Sea Embayment, West AntarcticaIce thickening is evidenced by a moraine between Thwaites and Pope glaciers and is dated with surface exposure dating of erratic cobblesThe moraine may help to constrain the end of a mid‐Holocene contracted ice sheet configuration in the Amundsen Sea sector [ABSTRACT FROM AUTHOR]

Although fluctuations in ice sheet surface mass balance lead to seasonal and interannual elevation changes, it is unclear if they are resolved differently by radar and laser satellite altimeters. We compare methods of computing elevation change from CryoSat‐2 and ICESat‐2 over the Greenland Ice Sheet to assess their consistency and to quantify recent change. Solutions exist such that interannual trends in the interior and the ablation zone agree to within −0.2 ± 1.5 and 3.3 ± 6.0 cm/yr, respectively, and that seasonal cycle amplitudes within the ablation zone agree to within 3.5 ± 38.0 cm. The agreement is best in the north where the measurements are relatively dense and worst in the southeast where the terrain is rugged. Using both missions, we estimate Greenland lost 196 ± 37 km3/yr of volume between 2010 and 2022 with an interannual variability of 129 km3/yr. Plain Language Summary: The polar ice sheets are reacting to climate warming. Changes in their height can be used to study changes in their snowfall, surface melting, glacier flow, and sea level contribution. Although satellite altimeters are able to detect changes in ice sheet height, it is not clear whether these changes are sensed differently by laser and radar systems. Using four years of coincident measurements recorded by ESA's CryoSat‐2 and NASA's ICESat‐2, we show that radar‐laser differences at the ice sheet scale are, in fact, a small proportion (<10%) of the changes in height that are taking place. This means that either system can be used with confidence to study the effects of climate change on the polar ice sheets. At smaller spatial scales, the remaining differences are still important and should be investigated further so that we can understand their causes. Key Points: Greenland Ice Sheet elevation change between 2018 and 2022 from CryoSat‐2 and ICESat‐2 was −11.4 ± 0.8 and −11.7 ± 1.3 cm/yr, respectivelyAblation zone seasonal cycle amplitude between 2018 and 2022 from CryoSat‐2 and ICESat‐2 was 62.9 ± 26.5 and 59.4 ± 24.4 cm, respectivelyVolume change between 2010 and 2022 was −196 ± 37 km3/yr with an interannual variability of 129 km3/yr [ABSTRACT FROM AUTHOR]

Investigations of the geomorphological fingerprints of palaeo‐ice streams are essential for enhancing our understanding of ice‐stream behaviour. Cross‐cutting flowsets of palaeo‐ice streams, during and following the Last Glacial Maximum, have been suggested in northeast Iceland based on the mapping of streamlined subglacial bedforms (SSBs). To increase our understanding of the dynamics of the Icelandic Ice Sheet (IIS) during deglaciation, we investigate transverse ridges, together with glacifluvial and ice‐marginal landforms, within the largest flowset. The main emphasis is on the transverse ridges, which are primarily interpreted as ribbed moraines – the first to be described in Iceland. Morphological data are combined with sedimentological analyses of the ribbed moraines. Our results show that the ribbed moraines are composed of pre‐existing material, often exhibiting a base of stratified glacifluvial sediments draped with subglacial till. Deformation and thrust structures within both units suggest compressional flow during the formation of the ridges. Our results suggest the ribbed moraines develop due to velocity gradients under the lateral shear margin of an ice stream based on their distribution and often oblique orientation in relation to SSBs. The ribbed moraines superimpose and thus post‐date the SSBs, signifying the waning stage of ice streaming. We suggest that the ridges formed during ice‐stream shutdown following the Younger Dryas and/or Preboreal re‐advances. Eskers and ice‐marginal landforms imply channelized water drainage during the final deglaciation interrupted by short‐lived re‐advances. This study has implications for the style of deglaciation associated with ice streaming in the northeastern part of the IIS. We characterize the role of ribbed moraines within the ice sheet and identify directions for future work. [ABSTRACT FROM AUTHOR]

Paleoclimate information has played an instrumental role in showing how fast climate can vary and how large these changes can be. It provided the first vivid demonstration of the relationships between atmospheric greenhouse gas concentrations and surface air temperatures, as well as striking representations of climate change impacts and possible feedbacks within the climate system, such as those associated with vegetation or ice sheet changes. Here, a short review of recent advances in paleoclimate studies is provided, with the objective of showing what this information on past climates and environments can bring to research on current and possible future climates. We advocate that (1) paleoclimatic and paleoenvironmental information can be leveraged for narratives about climate change, in particular at the local and regional levels, (2) paleoclimate data is essential for out-of-range tests of climate models, since future climates are also out of the range of recent climate information used for calibrating climate models, (3) paleoclimate data, in particular for the last millennia, is essential for taking multi-centennial and multi-millennial variability into account when describing trends related to anthropogenic forcings and attributing climate change signals, in particular for extreme and rare events, and (4) paleoclimates also provide extremely valuable information for initializing the slow components of climate models. In addition, we show how paleoclimate studies can be beneficial to put recent and future climate change into context and improve our knowledge on key processes. They can both benefit from and contribute to models and knowledge based on the study of recent and future climates. [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]

Ancient Native American ancestors (Clovis) have been interpreted as either specialized megafauna hunters or generalist foragers. Supporting data are typically indirect (toolkits, associated fauna) or speculative (models, actualistic experiments). Here, we present stable isotope analyses of the only known Clovis individual, the 18-month-old Anzick child, to directly infer maternal protein diet. Using comparative fauna from this region and period, we find that mammoth was the largest contributor to Clovis diet, followed by elk and bison/camel, while the contribution of small mammals was negligible, broadly consistent with the Clovis zooarchaeological record. When compared with second-order consumers, the Anzick-1 maternal diet is closest to that of scimitar cat, a mammoth specialist. Our findings are consistent with the Clovis megafaunal specialist model, using sophisticated technology and high residential mobility to subsist on the highest ranked prey, an adaptation allowing them to rapidly expand across the Americas south of the Pleistocene ice sheets. [ABSTRACT FROM AUTHOR]

The dominant periodicity of the late Pleistocene glacial cycles is roughly 100 kyr, rather than other major astronomical periods such as 19, 23, 41, and 400 kyr. Various models explain this fact through distinct dynamical mechanisms, including synchronization of self-sustained oscillations and resonance in mono- or multi-stable systems. However, the variety of proposed models and dynamical mechanisms could obscure the essential factor for realizing the 100-kyr periodicity. We propose the hypothesis that the ice-sheet climate system responds to astronomical forcing at the ~100-kyr periodicity because the intrinsic timescale of the system is closer to 100 kyr than to other major astronomical periods. We support this idea with analyses and sensitivity studies of several simple ice age models with contrasting mechanisms. [ABSTRACT FROM AUTHOR]

Cosmogenic-nuclide surface exposure ages provide empirical data for testing the accuracy of models simulating the timing and pace of ice sheet response to a warming climate. Increasing emphasis is being placed on obtaining exposure ages that both accurately constrain Holocene deglaciation and are precise enough to capture ice sheet change at the sub-millennial scale. However, the accuracy of Holocene deglacial chronologies can be compromised by nuclide inheritance when measuring longer-lived nuclides, such as 10Be. Short-lived in situ-produced 14C is unique because it is largely insensitive to nuclide inheritance pre-dating the last glacial maximum (LGM), and when combined with longer-lived nuclides can be used to constrain complex ice sheet histories over Holocene timescales. Here, we present new in situ 14C exposure ages from Mt Murphy, West Antarctica. Many of the new in situ 14C ages are inconsistent with published 10Be ages, suggesting samples collected from the same elevation above the modern ice were exposed at different times. We investigate potential explanations for such conflicting exposure histories by analysing paired 14C-10Be data of Holocene age presently archived in the informal cosmogenic-nuclide exposure-age database (ICE-D, https://version2.ice-d.org/). Our analysis reveal that neither geologic sources of uncertainty due to variations in geologic setting nor modelled scenarios of subsurface nuclide production explain conflicting paired 14C-10Be exposure ages observed at Mt Murphy. Furthermore, we observe that repeat in situ 14C concentrations measured in 15 of 31 samples do not replicate within their nominal 6 % (2σ) analytical uncertainty and identify ~ 2 kyr of excess unquantified scatter from Mt Murphy in situ 14C exposure ages. Taken together, these results suggest analytical uncertainty for in situ 14C measurements may currently be underestimated. We provide recommendations for improving measurement precision that will benefit future Holocene deglaciation studies including analysis and publication of more replicate measurements, and the continuation of efforts to quantify and minimise sources of scatter in blank measurements. [ABSTRACT FROM AUTHOR]

Recent silicoflagellate distributions have been examined in 195 surface sediment samples from the North Pacific to establish the silicoflagellate assemblage dataset from surface sediments across the North Pacific for paleo sea surface temperature (SST) reconstruction. The relative abundance data of all seven silicoflagellate taxa identified in this study were used for the modern analog method to reconstruct past SST. The SST reconstruction based on the silicoflagellate modern analog technique was applied to the two sediment cores from the Japan Sea. With the development of ice sheets, the Japan Sea experienced a low salinity isolation event during the Last Glacial Maximum (LGM: 19 ka–26.5 ka), which hampers the SST reconstruction employing geochemical proxies such as alkenone and Mg/Ca thermometry. The reconstructed glacial SST between 25 and 15 ka was ~ 5 °C in the northern and southern Japan Sea, indicating significant southward migration of the glacial subpolar front. The timings of the deglacial SST rises were ~ 14 ka at the south core site and ~ 10 ka at the north core site, indicating a latitudinal lag. This lag likely reflects a gradual increase in the fluxes of the Tsushima Warm Current from the East China Sea through the Tsushima Strait. Compilation of the silicoflagellate assemblages in the North Pacific surface sediments used for the modern analog technique to reconstruct past sea surface temperature (SST), revealing the Japan Sea SST during the last glacial maximum ~20 ka ago. [ABSTRACT FROM AUTHOR]

Models of glacial isostatic adjustment (GIA) play a central role in the interpretation of various geologic and geodetic data to understand and simulate past and future changes in ice sheets and sea level, as well as to infer rheological properties of the deep Earth. During the past few decades, a major advance has been the development of models that include 3D Earth structure, as opposed to 1D spherically symmetric (SS) structure. However, a major limitation in employing 3D GIA models is their high computational expense. As such, we have developed a method using artificial neural networks (ANNs) and the Tensorflow library to predict the influence of 3D Earth models with the goal of more affordably exploring the parameter space of these models, specifically the radial (1D) viscosity profile to which the lateral variations are added. Our goal is to test whether the use of an ANN to produce a fast surrogate model can accurately predict the difference in GIA model outputs (i.e., relative sea level (RSL) and uplift rates) for the 3D case relative to the SS case. If so, the surrogate model can be used with a computationally efficient SS (Earth) GIA model to generate output that replicates that from a 3D (Earth) GIA model. Evaluation of the surrogate model performance for deglacial RSL indicates that it is able to provide useful estimates of this field throughout the parameter space when trained on only ≈15% (≈50) of the parameter vectors considered (330 in total). We applied the surrogate model in a model–data comparison exercise using RSL data distributed along the North American coasts from the Canadian Arctic to the US Gulf Coast. We found that the surrogate model is able to successfully reproduce the model–data misfit values such that the region of minimum misfit either generally overlaps the 3D GIA model results or is within two increments of the radial viscosity model parameter space (defined here as lithosphere thickness, upper-mantle viscosity, and lower-mantle viscosity). The surrogate model can, therefore, be used to accurately explore this aspect of the 3D Earth model parameter space. In summary, this work demonstrates the utility of machine learning in 3D Earth GIA modelling, and so future work to expand on this initial proof-of-concept analysis is warranted. [ABSTRACT FROM AUTHOR]

Quaternary glaciations have significantly impacted the midcontinental North American landscape, leaving behind a proglacial sediment record of glacial lake deposits, glacio-fluvial sand and gravel, and windblown loess. This paper aims to expand upon a previous study using detrital zircon provenance analysis to investigate midcontinental North American loess provenance in relation to the glacial history of the southern Laurentide ice sheet during the middle to late Pleistocene. The study incorporates previously published detrital zircon data from last glacial tills (representing the Huron-Erie Lobe, Lake Michigan Lobe, Green Bay Lobe, Superior Lobe, Des Moines Lobe, and James Lobe), middle to late Pleistocene loess from several sites along the Illinois and Mississippi River valleys, and suspended sediment load inputs from the Missouri River and Arkansas River. A statistical mixing model (DzMix version 2.2) was used to estimate the relative proportions of glacial and nonglacial sources to Wisconsin Episode, Illinois Episode, and pre-Illinois Episode age loess. We show that mixing models that include the modern suspended sediment loads of the Missouri and Arkansas Rivers significantly improve (up to 23% increase in cross-correlation value) the source characterization of Wisconsin Episode (last glacial) and Illinois Episode (penultimate glacial) loess deposits within the Mississippi River drainage basin. These river sources are dominant inputs for certain loess sites (as much as 51%), but their relative contributions are not static across time and space, which has implications for temporal and spatial differences in relative sediment source estimates and glacial and fluvial sediment transport evolution. Specifically, differences in relative sediment proportion estimates among Wisconsin, Illinois, and pre-Illinois Episode loess support previous evidence for the persistence of a Quebec-Labrador ice dome source through multiple glacial cycles, even with the inclusion of river sources in updated mixing models. Illinois and pre-Illinois Episode loess in the southern portion of our study area received ~20% detrital zircon input from sources similar to the present-day Missouri and Arkansas Rivers, suggesting that these river systems were contributing a significant amount of detritus to the lower Mississippi River valley region during the middle Pleistocene. [ABSTRACT FROM AUTHOR]

Icing poses significant threats to the safety and reliability of structures in cold regions, thus prompting researchers to explore deicing methods. This paper establishes a bubble deicing system and investigates the utilization of bubble pulsation energy for removing ice from frozen structures. Traditional deicing methods suffer from issues such as high energy consumption, severe environmental pollution, and secondary icing. To address these challenges and advance the development of deicing technology, harnessing the substantial energy generated by bubble pulsation can be employed for effective deicing purposes. Through experimental analysis, this study successfully demonstrates the feasibility of employing cavitation for deicing applications. Several experimental cases are conducted to elucidate the mechanism behind bubble-energy-based deicing, varying parameters including the distance between bubbles and targets as well as ice sheet thickness within a range of 5~35 mm. The findings indicate that bubbles can effectively facilitate deicing processes. Further exploration is required to fully understand the potential of bubble deicing technology and its prospects in engineering applications. [ABSTRACT FROM AUTHOR]

A probabilistic projection of sea‐level rise uses a probability distribution to represent scientific uncertainty. However, alternative probabilistic projections of sea‐level rise differ markedly, revealing ambiguity, which poses a challenge to scientific assessment and decision‐making. To address the challenge of ambiguity, we propose a new approach to quantify a best estimate of the scientific uncertainty associated with sea‐level rise. Our proposed fusion combines the complementary strengths of the ice sheet models and expert elicitations that were used in the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC). Under a low‐emissions scenario, the fusion's very likely range (5th–95th percentiles) of global mean sea‐level rise is 0.3–1.0 m by 2100. Under a high‐emissions scenario, the very likely range is 0.5–1.9 m. The 95th percentile projection of 1.9 m can inform a high‐end storyline, supporting decision‐making for activities with low uncertainty tolerance. By quantifying a best estimate of scientific uncertainty, the fusion caters to diverse users. Plain Language Summary: A probabilistic projection of sea‐level rise uses a probability distribution to represent uncertainty. Using differing methods, scientists have constructed several alternative probabilistic projections of sea‐level rise. By considering their complementary strengths, we propose to combine the alternative projections into a single fusion. The fusion quantifies our best estimate of the uncertainty associated with future sea‐level rise. Under a low‐emissions scenario, the fusion's very likely range of global mean sea‐level rise is 0.3–1.0 m by 2100. Under a high‐emissions scenario, the very likely range is 0.5–1.9 m. The fusion is easy to interpret and caters to diverse users. Key Points: We fuse the complementary strengths of alternative projections of sea‐level riseThe fusion is a single probabilistic projection that quantifies a best estimate of scientific uncertaintyThe fusion provides a meaningful very likely range and an associated high‐end projection [ABSTRACT FROM AUTHOR]

Volcanic activity has been shown to affect Earth's climate in a myriad of ways. One such example is that eruptions proximate to surface ice will promote ice melting. In turn, the crustal unloading associated with melting an ice sheet affects the internal dynamics of the underlying magma plumbing system. Geochronologic data from the Andes over the last two glacial cycles suggest that glaciation and volcanism may interact via a positive feedback loop. At present, accurate sea‐level predictions hinge on our ability to forecast the stability of the West Antarctic Ice Sheet, and thus require consideration of two‐way subglacial volcano‐deglaciation processes. The West Antarctic Ice Sheet is particularly vulnerable to collapse, yet its position atop an active volcanic rift is seldom considered. Ice unloading deepens the zone of melting and alters the crustal stress field, impacting conditions for dike initiation, propagation, and arrest. However, the consequences for internal magma chamber dynamics and long‐term eruption behavior remain elusive. Given that unloading‐triggered volcanism in West Antarctica may contribute to the uncertainty of ice loss projections, we adapt a previously published thermomechanical magma chamber model and simulate a shrinking ice load through a prescribed lithostatic pressure decrease. We investigate the impacts of varying unloading scenarios on magma volatile partitioning and eruptive trajectory. Considering the removal of km‐thick ice sheets, we demonstrate that the rate of unloading influences the cumulative mass erupted and consequently the heat released into the ice. These findings provide fundamental insights into the complex volcano‐ice interactions in West Antarctica and other subglacial volcanic settings. Plain Language Summary: In regions like West Antarctica, volcanic eruptions occur underneath ice sheets. When hot magma comes in contact with ice, it can accelerate the melting of the ice cover. Beyond this, as climate change causes ice sheets to shrink, the decreasing weight on a volcano may affect its likelihood of erupting. The effects of ice loss above volcanoes on the underlying volcanic activity are not well understood. We conducted computer simulations to explore how gradual ice loss affects magma stored in the Earth's crust. We find that volcanoes beneath shrinking ice sheets are sensitive to the rate at which the ice sheet shrinks. As the ice melts away, the reduced weight on the volcano allows the magma to expand, applying pressure upon the surrounding rock that may facilitate eruptions. Additionally, the reduced weight from the melting ice above also allows dissolved water and carbon dioxide to form gas bubbles, which causes pressure to build up in the magma chamber and may eventually trigger an eruption. Under these conditions, we find that the removal of an ice sheet above a volcano results in more abundant and larger eruptions, which may potentially hasten the melting of overlying ice through complex feedback mechanisms. Key Points: During deglaciation, the evolution of a crustal magma chamber beneath kilometers of ice is sensitive to the rate at which ice is removedA critical rate of unloading can trigger additional eruption eventsIce unloading expedites the onset of volatile exsolution, with consequences for magma chamber pressurization and eruption size [ABSTRACT FROM AUTHOR]

Global warming has changed both the amount of global precipitation and the atmospheric capacity to retain water. In this paper, a novel definition of the long‐term Capturability of Atmospheric Water (CAW) based on horizontal atmospheric water transport is proposed, describing the ability of a certain area to intercept and convert the atmospheric water transported by horizontal moisture flux into local precipitation. The significant decrease of the CAW in Amazon and Congo rainforests and Inside Greenland indicates that these areas were having less precipitation with the same water vapor in the past 42 years, while in Asia (especially China), CAW is showing a large‐scale increasing trend, verifying the regional humidifying. Considering the change of both the CAW and the background atmospheric water simultaneously, their mismatch degree is also investigated. The positive mismatch in Qinghai Tibet Plateau, Greenland, and the Andes, suggests higher susceptibility to climate change, and in the areas of negative mismatch (Amazon, Maritime Continent, southeastern China, the Eastern United States, India, and Japan), a more stable precipitation response to climate change is expected. The proposed concept of CAW provides a novel perspective to analyze the precipitation response to climate change on a global scale. Key Points: A novel definition of long‐term Capturability of Atmospheric Water (CAW) based on horizontal transport is proposedIn the past 42 years, the CAW in the Amazon and Congo rainforests and the Greenland ice sheet has degraded significantlyThe findings provide a perspective to analyze the precipitation response to global climate change [ABSTRACT FROM AUTHOR]

Wind activity is a powerful force that shapes the landscapes of deserts, coastal areas, and regions adjacent to ice sheets, and it has significant implications for human settlement. In southern Greenland, it has been proposed that the increased wind and soil erosion observed around Norse settlements (~985–1450 CE) were caused by overgrazing by animals, which ultimately contributed to the decline of the Norse culture. Alternatively, some studies have linked the observed intensification of aeolian activity to changes in large‐scale atmospheric circulation patterns in the North Atlantic. However, the timing and impact of this increased aeolian activity in southern Greenland remain uncertain due to a lack of well‐dated records. In this study, we use a lake record and optically stimulated luminescence (OSL) dating of adjacent dunes to reconstruct the Holocene history of aeolian activity at Igaliku Kujalleq (Søndre Igaliku) in southern Greenland. Our findings indicate two periods of intensified aeolian activity over the past 10 000 years: from ~500 to 1200 CE and ~1450 CE. Importantly, the peak aeolian activity observed in the Igaliku Kujalleq records was unrelated to Norse activities and their decline. Instead, we suggest that changes in the North Atlantic atmospheric circulation pattern combined with Neoglacial glacier advances led to increased katabatic wind activity and triggered increased aeolian activity from large outwash plains. [ABSTRACT FROM AUTHOR]

Understanding the formation of carbonyl sulfide (OCS) in interstellar ices is key to constrain the sulfur chemistry in the interstellar medium (ISM), since it is the only ice S-bearing molecule securely detected thus far. Two general pathways for OCS formation have been proposed: sulfurization of CO (CO + S) and oxidation of CS (CS + O), but their relative contribution in interstellar ices remains unconstrained. We have evaluated the contribution of both pathways to OCS formation upon energetic processing in isotopically labelled CO |$_2$|⁠ :CS |$_2$| and CO:CS |$_2$| ice samples at 7 |$-$| 50 K. Our results indicated that formation of OCS through the CS + O pathway was more favourable than through the CO + S pathway, as previously suggested by theoretical calculations. In addition, its relative contribution increased at higher temperatures. Therefore, this pathway could play a role in the ice formation of OCS, especially in warm regions where CO is expected to be preferentially in the gas phase. At the same time, we have explored the chemistry of CS |$_2$| -bearing, CO |$_2$| -, CO-, and also H |$_2$| O-rich ices, that could be relevant to the sulfur interstellar chemistry. We observed formation of a variety of S-bearing products in addition to OCS, including SO |$_2$|⁠ , C |$_3$| S |$_2$|⁠ , and S |$_2$|⁠. However, a significant fraction of sulfur was not detected at the end of the experiments, and could be locked in long, undetectable sulfur allotropes, one of the potential carriers of the missing sulfur in the dense ISM. [ABSTRACT FROM AUTHOR]

The Arctic is warming rapidly, significantly reducing the Greenland ice sheet (GrIS) surface mass balance (SMB) and raising its contribution to global sea‐level rise. Since these trends are expected to continue, it is essential to explore the GrIS SMB response to projected climate warming. We compare projections from three polar regional climate models, RACMO, MAR, and HIRHAM, forced by the Community Earth System Model CESM2 under a high‐end warming scenario (SSP5‐8.5, 1970–2099). We reveal different modeled SMB by 2100, including a twofold larger annual surface mass loss in MAR (−1735 Gt/yr) and HIRHAM (−1698 Gt/yr) relative to RACMO (−964 Gt/yr). Discrepancies primarily stem from differences in projected runoff, triggering melt‐albedo positive feedback and subsequent modeled ablation zone expansion. In addition, we find different responses of modeled meltwater production to similar atmospheric warming. Our analysis suggests clear avenues for model developments to further improve SMB projections and contribution to sea‐level rise. Plain Language Summary: We explore how three different polar climate models predict the future surface mass balance (SMB) of the Greenland ice sheet (GrIS), a major contributor to global sea‐level rise. Our results show that SMB projections among these models differ significantly by the end of the century. Differences primarily stem from how models convert meltwater into surface runoff toward the ocean, a crucial SMB component that directly contributes to sea‐level rise. Another key factor is the response of these models to climate warming, substantially affecting future melting rates. Our research highlights the need for further improvements of these climate models. By identifying and understanding the drivers behind model differences, we can improve SMB predictions and better estimate future global sea‐level rise. Key Points: With identical forcing, Greenland Ice Sheet surface mass balance from 3 regional climate models shows a two‐fold difference by 2100Different runoff projections stem from substantial discrepancies in projected ablation zone expansion, and reciprocallyThe response of meltwater production to similar atmospheric warming differs significantly among regional climate models [ABSTRACT FROM AUTHOR]

Beginning in March 2022, the Antarctic Peninsula's Hektoria Glacier experienced an unprecedented retreat of ∼23 km over 1.5 years, one of the fastest observed glacier retreats on record. Improving constraints on the drivers of such extreme events is key to understanding glacier change around the continent and future sea‐level rise. We use satellite remote sensing and reanalysis data to characterize changes in Hektoria, a former Larsen B Ice Shelf tributary, over the last ∼20 years and document a period of retreat from 2002 to 2011, and readvancement from 2011 to 2022. We find that the long‐term ice front and velocity response (2002–2022) correlated more strongly with changes in modeled ocean temperatures compared to surface air temperatures. However, the acute loss of buttressing support following fast ice collapse paired with a near‐contemporaneous extreme atmospheric river in the region likely catalyzed the unprecedented 2022–2023 retreat. Plain Language Summary: The Antarctic Ice Sheet is one of the largest sources for future sea level rise, yet how much and how fast ice is lost to the ocean here remains relatively unknown. Ice shelves can buttress glaciers from flowing quickly into the ocean, stabilizing their movement and limiting mass discharge. As ice shelves retreat or break up, glaciers accelerate, adding mass to the ocean. In this study, we use imagery and elevation data collected from airborne studies and satellites to characterize how Hektoria Glacier—a marine‐terminating glacier located on the Eastern Antarctic Peninsula that was previously a Larsen B Ice Shelf tributary—has changed over the past 20 years. We compare these changes with available ocean and air temperatures in the region to determine how they influenced the observed fluctuations over time. We find that Hektoria retreated from 2002 to 2011 and readvanced from 2011 to 2022, followed by an unprecedented retreat of ∼23 km between March 2022 and August 2023. We find that abrupt changes in stress following buttressing loss drives glacier change, while modeled ocean temperatures wield influence on Hektoria's long‐term fluctuations and atmospheric temperatures drive shorter term changes in glacier response. Key Points: Hektoria Glacier retreated ∼23 km between March 2022 and August 2023—one of the fastest observed marine‐terminating glacier retreatsChanges in buttressing support and mid‐depth ocean temperatures served as primary drivers for change at Hektoria between 2002 and 2022Understanding long‐ and short‐term glacier response to ocean and atmospheric variability is key to improved sea level rise predictions [ABSTRACT FROM AUTHOR]

The surface elevation of the Greenland Ice Sheet is constantly changing due to the interplay between surface mass balance processes and ice dynamics, each exhibiting distinct spatiotemporal patterns. Here, we employ satellite and airborne altimetry data with fine spatial (1 km) and temporal (monthly) resolutions to document this spatiotemporal evolution from January 2003 to August 2023. To estimate elevation changes of the Greenland Ice Sheet (GIS), we utilize radar altimetry data from CryoSat-2 and EnviSat, laser altimetry data from the ICESat and ICESat-2, and laser altimetry data from NASA's Operation IceBridge Airborne Topographic Mapper. We produce continuous monthly ice surface elevation changes from January 2003 to August 2023 on a 1 km grid covering the entire GIS. We estimate cumulative ice loss of 4,352 Gt ± 315 Gt (12.1 ± 0.9 mm sea level equivalent) during this period, excluding peripheral glaciers. Between 2003 and 2023, the ice sheet land-terminating margin underwent a significant cumulative thinning of several meters. Ocean-terminating glaciers exhibited thinning between 20–40 m, with Jakobshavn Isbræ experiencing an exceptional thinning of nearly 70 m. This dataset of fine-resolution altimetry data in both space and time will support studies of ice mass loss and useful for GIS ice sheet modelling. To validate our monthly mass changes of the Greenland ice sheet, we use mass change from satellite gravimetry and mass change from the Input-Output method. On multiannual timescales, there is a strong correlation between the time series, with R values ranging from 0.88 to 0.92. [ABSTRACT FROM AUTHOR]

The Greenland Ice Sheet is highly sensitive to climate change, leading to significant retreat along its edges. This rapid ice loss contributes to rising sea levels and impacts the Earth's climate stability. Understanding the extent of recent glacier retreat is crucial in order to determine if it is unprecedented or within ranges of natural variability. Palaeoenvironmental studies aim to identify past glacial phases and landscape changes using advanced dating methods such as cosmic ray exposure (CRE) dating. In NE Greenland, CRE dating has helped establish the timing of glacial oscillations, yet a comprehensive understanding of glacial fluctuations during specific periods still needs to be developed. This study aims to chronologically constrain the postglacial landscape evolution of two NE Greenland valleys from the Young Sund–Tyrolerfjord area (74°N, 20–25°E) from the onset of deglaciation and throughout the Holocene to better understand glacial and postglacial changes. The chronological framework relies on 27 10Be cosmic‐ray exposure ages that constrain our interpretation of the geomorphological features in both valleys. Inconsistencies were observed in the ages dataset, highlighting potential bias associated with nuclide inheritance and post‐glacial dynamics. Despite limitations, the CRE results confirm the general pattern observed in NE Greenland: (i) major deglaciation and disconnection of glaciers from the main glacial systems during the Lateglacial and Early Holocene with a rapid but not homogeneous deglaciation within the range from ~14.3 to 11.9 ka; (ii) no evidence of glacial activity during the Middle Holocene, probably associated with the withdrawn position of the ice masses’ fronts; and (iii) glacier expansion during the Late Holocene, with a Little Ice Age advance as the last significant period of glacial regrowth. [ABSTRACT FROM AUTHOR]

Internal solitary waves in polar regions have attracted much interest recently. It is important to understand how sea ice affects them as this may have a profound influence on human activities and the environment. In this study, experiments on internal solitary waves with and without two types of sea ice (ice sheet and ice keel) are presented, as well as corresponding simulations using the Korteweg-de Vries (KdV) equation, the Benjamin-Ono (BO) equation, and the variable-coefficient Korteweg-de Vries (vKdV) equation, which is a derivation of the KdV equation. Comparison between experiments without sea ice and simulations using the KdV and BO equations proves the suitability of the former over the latter for this study. The experiments with sea ice and theoretical simulations using the vKdV equation provide evidence for wave deformation, oscillation occurring in the rear of the wave, and a decrease in amplitude. The latter suggests possibilities of energy dissipation or the emission of small amplitude linear waves. The sharp vertices of the ice result in occasional inconsistency with the vKdV predictions. Nonetheless, the vKdV equation is still suitable for modeling internal solitary waves under sea ice, giving generally accurate results that can assist further studies. This is the first time the vKdV equation has been applied to investigate the impacts of sea ice on internal solitary waves. [ABSTRACT FROM AUTHOR]

At least three primary iceberg calving styles have been identified in Greenland: serac collapse, which produces falling icebergs tens of meters in length; slab capsize, which produces rotating icebergs hundreds of meters in length; and tabular rifting, which produces kilometer‐scale icebergs. However, calving styles are mostly undocumented across Greenland. Here, we develop a method to disentangle the sizes of individual calving events and map the dominant calving style at glaciers, using the characteristic properties of step retreats in satellite‐derived terminus positions. At glaciers known to frequently produce calving teleseisms, step retreats greater than 200 m account for >80% ${ >} 80\%$ of net calved length since 2018. In contrast, at glaciers known to calve by serac failure, 200 m step retreats account <20% ${< } 20\%$ of net calving. Thus, terminus change timeseries can offer promising insight into the dominant calving styles at marine‐terminating glaciers. Plain Language Summary: Iceberg calving is ubiquitous at the ocean‐bounded edges of ice sheets. However, not all iceberg calving is the same: at least three distinct mechanisms govern the discharge of solid ice from the Greenland Ice Sheet. We show these are associated with a characteristic range of iceberg sizes. Because calving constitutes a major component of Greenland's continued mass loss, it is important that these distinct mechanisms be understood. We develop a method to identify which calving mechanisms are important at various glaciers. We do so by using satellite observations to estimate the lengths of terminus retreats producing icebergs at individual glaciers. Key Points: Greenland outlet glaciers with different calving styles have different characteristic retreat magnitudes in consecutive satellite imagesAt glaciers which frequently produce calving teleseisms, step retreats in terminus position are dominated by retreats >200 mThe distinct processes underlying different calving styles will likely necessitate several distinct calving laws [ABSTRACT FROM AUTHOR]

Southeast Greenland contributes significantly to global sea level rise, with mass loss having increased by about 600% over the past 30 years due to enhanced melt and dynamic instabilities of marine-terminating glaciers. Accurate modelling of glacier dynamics is crucial to minimise uncertainties in predictions of future sea level rise, necessitating detailed reconstructions of long-term glacial histories. One key complexity in these models that is not well understood or documented is ice flow piracy, where ice is redirected between catchment basins, significantly influencing regional glacier dynamics and mass balance. Here, we document and characterise the collapse of Midgaard Glacier in Southeast Greenland using a multi-data approach, providing a 90-year record of the area's complex glacial history. Initiated over 80 years ago, this collapse triggered catchment-scale dynamic changes in several neighbouring glaciers, impacting local glacial stability throughout the 20th century and into the present. Our analysis reveals that catchment-scale ice flow piracy can cause substantial disturbances in mass balance evolution and catchment reconfigurations, independent of climatic conditions. These findings underscore the importance of understanding long-term changes in complex glacier systems to make accurate predictions of future glacial mass loss and associated sea-level rise. This study explores the 90-year collapse of the Midgaard Glacier, one of the greatest mass losers in the entire Greenland ice sheet. The study reveals complex ice flow piracy and demonstrates the impact of Midgaard's collapse on the dynamics of glaciers at a regional scale. [ABSTRACT FROM AUTHOR]

Coupled ice sheet–ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, which play a pivotal role in ice sheet stability and sea level rise projections. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics. This discrepancy, combined with the high computational cost of ocean models due to their finer temporal resolution, limits the time frame that can be modelled. In this study, we introduce an "accelerated forcing" approach to address the timescale discrepancy and thus improve computational efficiency in a framework designed to couple evolving ice geometry to ice shelf cavity circulation. This approach is based on the assumption that the ocean adjusts faster to imposed changes than the ice sheet, so the ocean can be viewed as being in a quasi-steady state that varies slowly over timescales of ice geometry change. By assuming that the mean basal melt rate during one coupling interval can be reflected by a quasi-steady-state melt rate during a shortened coupling interval (equal to the regular coupling interval divided by a constant factor), we can reduce the ocean model simulation duration. We first demonstrate that the mean cavity residence time, derived from standalone ocean simulations, can guide the selection of suitable scenarios for this approach. We then evaluate the accelerated forcing approach by comparing basal melting response under the accelerated forcing with that under the regular forcing (without the accelerated forcing) based on idealized coupled ice sheet–ocean model experiments. Our results suggest that the accelerated approach can yield comparable melting responses to those under the regular forcing approach when the model is subjected to steady far-field ocean conditions or time-varying conditions with timescales much shorter than the cavity residence time. However, it may not be suitable when the timescale of the accelerated ocean conditions is not significantly different from the cavity residence time. We have also discussed the limitations of applying the accelerated forcing approach to real-world scenarios, as it may not be applicable in coupled modelling studies addressing climate variability on sub-decadal, decadal, and mixed timescales or in fully coupled climate models with interactive ice sheets. Nevertheless, when appropriately applied, the accelerated approach can be a useful tool in process-oriented coupled ice sheet–ocean modelling or for downscaling climate simulations with a coupled ice sheet–ocean model. [ABSTRACT FROM AUTHOR]

The coastal circulation around Southern Greenland transports fresh, buoyant water masses from the Arctic and Greenland Ice Sheet near regions of convection, sinking, and deep-water formation in the Irminger and Labrador Seas. Here, we track the pathways and fate of these fresh water masses by initializing synthetic particles in the East Greenland Coastal Current on the Southeast Greenland shelf and running them through altimetry-derived surface currents from 1993 to 2021. We report that the majority of waters (83%) remain on the shelf around the southern tip of Greenland. Variability in the shelf-basin exchange of the remaining particles closely follows the number of tip jet wind events on seasonal and interannual timescales. The probability of a particle exiting the shelf increases almost fivefold during a tip jet event. These results indicate that the number of tip jets is a close proxy of the shelf-basin exchange around Southern Greenland. [ABSTRACT FROM AUTHOR]

Two-thirds of all glaciers worldwide are projected to disappear by 2100 CE. Large uncertainties however remain in maritime settings, where some glaciers have recently gained mass in response to increased snowfall. One of these regions is southern Patagonia, where increased precipitation since the 1980s seems to have attenuated glacier retreat. Whether this exceptional behavior will continue in a warmer future is unclear. Here, we use a numerical ice-flow model constrained by paleoglaciological data to simulate how climate variability influenced the evolution of three maritime outlet glaciers of the Southern Patagonian Icefield during the last 6000 years. Our experiments suggest that precipitation drove 67% of the centennial-scale fluctuations in the volume of the modeled glaciers. When applied to the temperature projected by 2100 CE, our simulations show that precipitation needs to increase by 10–50% to maintain present-day glacier volumes, depending on the climate scenario (SSP1-2.6 to SSP5-8.5). This implies that if greenhouse-gas emission cuts fail, these glaciers will enter a warmer regime unseen over the last 6000 years, where precipitation cannot offset glacier mass loss. Conversely, if emissions are curtailed, increased precipitation could halt mass loss of some of Patagonia's largest glaciers, and potentially of other maritime glaciers worldwide. [ABSTRACT FROM AUTHOR]

Globally elevated temperatures during the Cretaceous extreme greenhouse climate interval were punctuated by the Valanginian cooling event, which was characterized by a positive carbon isotope excursion, global cooling, and a glacial event approximately at 135 Ma. Disentangling ocean temperature and continental ice volume trends enables us to better understand climate fluctuations over deep time. We investigated the ocean temperature--ice sheet dynamics of glaciation events that occurred in the Cretaceous greenhouse world. New clumped isotope and δ18 O data from sites in the Tethyan Ocean show that seawater temperatures decreased by 5-6 °C, consistent with the development of glacial periods, and maximum ice volumes about half the size of present-day Antarctica. This cooling event provides a counter-example to other Mesozoic climate transitions driven by changes in atmospheric greenhouse gas contents. Our results emphasize the importance of quantitatively reconstructing continental ice volume, providing further support for exploring deep-time Earth climate dynamics. [ABSTRACT FROM AUTHOR]

Surface topography across the marginal zone of the Greenland Ice Sheet is constantly evolving in response to changing weather, season, climate, and ice dynamics. However, current digital elevation models (DEMs) for the ice sheet are usually based on data from a multi-year period, thus obscuring these changes over time. Here we present four 500 m resolution summer DEMs (PRODEMs) of the Greenland Ice Sheet marginal zone for 2019 through 2022. The PRODEMs cover the marginal zone from the ice edge to 50 km inland, hence capturing all Greenland outlet glaciers. Each PRODEM is based on data fusion of CryoSat-2 radar altimetry and ICESat-2 laser altimetry using regionally varying kriging of elevation anomalies relative to ArcticDEM. The PRODEMs are validated using leave-one-out cross-validation, and PRODEM19 is further validated against an external data set, showcasing their ability to correctly represent surface elevations within the associated spatially varying prediction uncertainties. We observe a general lowering of surface elevations during the 4-year PRODEM period, but the spatial pattern of change is highly complex and with annual changes superimposed. The PRODEMs enable detailed studies of the marginal ice sheet elevation changes. With their high spatio-temporal resolution, the PRODEMs will be of value to a wide range of researchers and users studying ice sheet dynamics and monitoring how the ice sheet responds to changing environmental conditions. PRODEMs from summer 2019 through 2022 are available at 10.22008/FK2/52WWHG (Winstrup, 2024), and we plan to annually update the product henceforth. [ABSTRACT FROM AUTHOR]

This study investigates the uncertain future contribution to sea-level rise in response to global warming of Upernavik Isstrøm, a tidewater glacier in Greenland. We analyse multiple sources of uncertainty, including Shared Socioeconomic Pathways (SSPs), climate models (global and regional), ice–ocean interactions, and ice sheet model (ISM) parameters. We use weighting methods based on spatio-temporal velocity and elevation data to reduce ice flow model uncertainty and evaluate their ability to prevent overconfidence. Our developed initialization method demonstrates the capability of Elmer/Ice to accurately replicate the hindcast mass loss of Upernavik Isstrøm. Future mass loss predictions in 2100 range from a contribution to sea-level rise from 1.5 to 7.2 mm, with an already committed sea-level contribution projection from 0.6 to 1.3 mm. At the end of the century, SSP-related uncertainty constitutes the predominant component of total uncertainty, accounting for 40 %, while uncertainty linked to the ISM represents 15 % of the overall uncertainty. We find that calibration does not reduce uncertainty in the future mass loss between today and 2100 (+ 2 %) but significantly reduces uncertainty in the hindcast mass loss between 1985 and 2015 (- 32 % to - 61 % depending on the weighting method). Combining calibration of the ice sheet model with SSP weighting yields uncertainty reductions in future mass loss in 2050 (- 1.5 %) and in 2100 (- 32 %). [ABSTRACT FROM AUTHOR]

Ice-sheet models used to predict sea-level rise often neglect subglacial hydrology. However, theory and observations suggest that ice flow and subglacial water flow are bidirectionally coupled: ice geometry affects hydraulic potential, hydraulic potential modulates basal shear stress via the basal water pressure, and ice flow advects the subglacial drainage system. This coupling could impact rates of ice mass change but remains poorly understood. We develop a coupled ice–subglacial-hydrology model to investigate the effects of coupling on the long-term evolution of marine-terminating ice sheets. We combine a one-dimensional channelized subglacial hydrology model with a depth-integrated marine-ice-sheet model, incorporating each component of the coupling listed above, yielding a set of differential equations that we solve using a finite-difference, implicit time-stepping approach. We conduct a series of experiments with this model, using either bidirectional or unidirectional coupling. These experiments generate profiles of channel cross-sectional area, channel flow rate, channel effective pressure, ice thickness, and ice velocity. We discuss how the profiles shape one another, resulting in the effective pressure reaching a local maximum in a region near the grounding line. We also describe the impact of bidirectional coupling on the transient retreat of ice sheets through a comparison of our coupled model with ice-flow models that have imposed static basal conditions. We find that including coupled subglacial hydrology leads to grounding-line retreat that is virtually absent when static basal conditions are assumed. This work highlights the role time-evolving subglacial drainage may have in ice-sheet change and informs efforts to include it in ice-sheet models. This work also supplies a physical basis for a commonly used parameterization which assumes that the subglacial water pressure is set by the bed's depth beneath the sea surface. [ABSTRACT FROM AUTHOR]

Antarctica's Lambert Glacier drains about one-sixth of the ice from the East Antarctic Ice Sheet and is considered stable due to the strong buttressing provided by the Amery Ice Shelf. While previous projections of the sea-level contribution from this sector of the ice sheet have predicted significant mass loss only with near-complete removal of the ice shelf, the ocean warming necessary for this was deemed unlikely. Recent climate projections through 2300 indicate that sufficient ocean warming is a distinct possibility after 2100. This work explores the impact of parametric uncertainty on projections of the response of the Lambert–Amery system (hereafter "the Amery sector") to abrupt ocean warming through Bayesian calibration of a perturbed-parameter ice-sheet model ensemble. We address the computational cost of uncertainty quantification for ice-sheet model projections via statistical emulation, which employs surrogate models for fast and inexpensive parameter space exploration while retaining critical features of the high-fidelity simulations. To this end, we build Gaussian process (GP) emulators from simulations of the Amery sector at a medium resolution (4–20 km mesh) using the Model for Prediction Across Scales (MPAS)-Albany Land Ice (MALI) model. We consider six input parameters that control basal friction, ice stiffness, calving, and ice-shelf basal melting. From these, we generate 200 perturbed input parameter initializations using space filling Sobol sampling. For our end-to-end probabilistic modeling workflow, we first train emulators on the simulation ensemble and then calibrate the input parameters using observations of the mass balance, grounding line movement, and calving front movement with priors assigned via expert knowledge. Next, we use MALI to project a subset of simulations to 2300 using ocean and atmosphere forcings from a climate model for both low- and high-greenhouse-gas-emission scenarios. From these simulation outputs, we build multivariate emulators by combining GP regression with principal component dimension reduction to emulate multivariate sea-level contribution time series data from the MALI simulations. We then use these emulators to propagate uncertainty from model input parameters to predictions of glacier mass loss through 2300, demonstrating that the calibrated posterior distributions have both greater mass loss and reduced variance compared to the uncalibrated prior distributions. Parametric uncertainty is large enough through about 2130 that the two projections under different emission scenarios are indistinguishable from one another. However, after rapid ocean warming in the first half of the 22nd century, the projections become statistically distinct within decades. Overall, this study demonstrates an efficient Bayesian calibration and uncertainty propagation workflow for ice-sheet model projections and identifies the potential for large sea-level rise contributions from the Amery sector of the Antarctic Ice Sheet after 2100 under high-greenhouse-gas-emission scenarios. [ABSTRACT FROM AUTHOR]

Water depths of supraglacial lakes on the ice sheets are difficult to monitor continuously due the lakes' ephemeral nature and inaccessible locations. Supraglacial lakes have been linked to ice shelf collapse in Antarctica and accelerated flow of grounded ice in Greenland. However, the impact of supraglacial lakes on ice dynamics has not been quantified accurately enough to predict their contribution to future mass loss and sea level rise. This is largely because ice-sheet-wide assessments of meltwater volumes rely on models that are poorly constrained due to a lack of accurate depth measurements. Various recent case studies have demonstrated that accurate supraglacial lake depths can be obtained from NASA's Ice, Cloud and land Elevation Satellite (ICESat-2) ATL03 photon-level data product. ATL03 comprises hundreds of terabytes of unstructured point cloud data, which has made it challenging to use this bathymetric capability at scale. Here, we present two new algorithms – Flat Lake and Underlying Ice Detection (FLUID) and Surface Removal and Robust Fit (SuRRF) – which together provide a fully automated and scalable method for lake detection and along-track depth determination from ATL03 data and establish a framework for its large-scale implementation using distributed high-throughput computing. We report FLUID–SuRRF algorithm performance over two regions known to have significant surface melt – central West Greenland and the Amery Ice Shelf catchment in East Antarctica – during two melt seasons. FLUID–SuRRF reveals a total of 1249 ICESat-2 lake segments up to 25 m deep, with more water during higher-melt years. In the absence of ground-truth data, manual annotation of test data suggests that our method reliably detects melt lakes along ICESat-2's ground tracks whenever the lake bed is visible or partially visible and estimates water depths with a mean absolute error <0.27 m. These results imply that our proposed framework has the potential to generate a comprehensive data product of accurate meltwater depths across both ice sheets. [ABSTRACT FROM AUTHOR]

Projections of Antarctic Ice Sheet mass loss and therefore global sea level rise are hugely uncertain, partly due to how mass loss of the ice sheet occurs at the grounding line. The Wilkes Subglacial Basin (WSB), a vast region of the East Antarctic Ice Sheet, is thought to be particularly vulnerable to deglaciation under future climate warming scenarios. However, future projections of ice loss, driven by grounding-line migration, are known to be sensitive to the parameterization of ocean-induced basal melt of the floating ice shelves and, specifically, to the adjacent grounding line – termed grounding-line melt parameterizations (GLMPs). This study investigates future ice sheet dynamics in the WSB with respect to four GLMPs under both the upper and lower bounds of climate warming scenarios from the present to 2500, with different model resolutions, ice shelf melt parameterizations (ISMPs) and choices of sliding relationships. The variation in these GLMPs determines the distribution and the amount of melt applied in the finite-element assembly procedure on partially grounded elements (i.e. elements containing the grounding line). Our findings indicate that the GLMPs significantly affect both the trigger timings of tipping points and the overall magnitude of ice mass loss. We conclude that applying full melting to the partially grounded elements, which causes melting on the grounded side of the grounding line, should be avoided under all circumstances due to its poor numerical convergence and substantial overestimation of ice mass loss. We recommend preferring options that depend on the specific model context, by either (1) not applying any melt immediately adjacent to the grounding line or (2) employing a sub-element parameterization. [ABSTRACT FROM AUTHOR]

Reliable projections of future sea level rise from the polar ice sheets depend on the ability of ice sheet models to accurately reproduce flow dynamics in an evolving ice sheet system. Ice sheet models are sensitive to the choice of the basal sliding law, which remains a significant source of uncertainty. In this study we apply a range of sliding laws to a hindcast model of Jakobshavn Isbræ, western Greenland, from 2009 to 2018. We demonstrate that a linear viscous sliding law requires the assimilation of regular velocity observations into the model in order to reproduce the observed large seasonal and inter-annual variations in flow speed. This requirement introduces a major limitation for producing accurate future projections. A regularised Coulomb friction law, in which basal traction has an upper limit, is able to more accurately reproduce the range of speeds from 2012 to 2015, the period of peak flow and maximal retreat, without the requirement for assimilating regular observations. Additionally, we find evidence that the speed at which sliding transitions between power-law and Coulomb regimes may vary spatially and temporally. These results point towards the possible form of an ideal sliding parameterisation for accurately modelling fast-flowing glaciers and ice streams, although determining this is beyond the scope of this study. [ABSTRACT FROM AUTHOR]

Current climate warming is accelerating mass loss from glaciers and ice sheets. In Greenland, the rates of mass changes are now dominated by changes in surface mass balance (SMB) due to increased surface melting. To improve the future sea-level rise projections, it is therefore critical to have an accurate estimate of the SMB, which depends on the representation of the processes occurring within the snowpack. The Explicit Snow (ES) scheme implemented in the land surface model Organising Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) has not yet been adapted to ice-covered areas. Here, we present the preliminary developments we made to apply the ES model to glaciers and ice sheets. Our analysis mainly concerns the model's ability to represent ablation-related processes. At the regional scale, our results are compared to the MAR regional atmospheric model outputs and to MODIS albedo retrievals. Using different albedo parameterizations, we performed offline ES simulations forced by the MAR model over the 2000–2019 period. Our results reveal a strong sensitivity of the modelled SMB components to the albedo parameterization. Results inferred with albedo parameters obtained using a manual tuning approach present very good agreement with the MAR outputs. Conversely, with the albedo parameterization used in the standard ORCHIDEE version, runoff and sublimation were underestimated. We also tested parameters found in a previous data assimilation experiment, calibrating the ablation processes using MODIS snow albedo. While these parameters greatly improve the modelled albedo over the entire ice sheet, they degrade the other model outputs compared to those obtained with the manually tuned approach. This is likely due to the model overfitting to the calibration albedo dataset without any constraint applied to the other processes controlling the state of the snowpack. This underlines the need to perform a "multi-objective" optimization using auxiliary observations related to internal snowpack processes. Although there is still room for further improvements, the developments reported in the present study constitute an important advance in assessing the Greenland SMB with possible extension to mountain glaciers or the Antarctic ice sheet. [ABSTRACT FROM AUTHOR]

Antarctic ice shelves buttress the flow of the ice sheet but are vulnerable to increased basal melting from contact with a warming ocean and increased mass loss from calving due to changing flow patterns. Channels and similar features at the bases of ice shelves have been linked to enhanced basal melting and observed to intersect the grounding zone, where the greatest melt rates are often observed. The ice shelf of Thwaites Glacier is especially vulnerable to basal melt and grounding zone retreat because the glacier has a retrograde bed leading to a deep trough below the grounded ice sheet. We use digital surface models from 2010–2022 to investigate the evolution of its ice-shelf channels, grounding zone position, and the interactions between them. We find that the highest sustained rates of grounding zone retreat (up to 0.7 kmyr-1) are associated with high basal melt rates (up to ∼250 myr-1) and are found where ice-shelf channels intersect the grounding zone, especially atop steep local retrograde slopes where subglacial channel discharge is expected. We find no areas with sustained grounding zone advance, although some secular retreat was distal from ice-shelf channels. Pinpointing other locations with similar risk factors could focus assessments of vulnerability to grounding zone retreat. [ABSTRACT FROM AUTHOR]

Blowing-snow sublimation is a key boundary layer process in polar regions and is the major ablation term in the surface mass balance (SMB) of the Antarctic ice sheet. This study updates the blowing-snow model in the Regional Atmospheric Climate Model (RACMO), version 2.3p3, incorporating blowing-snow sublimation into the prognostic equations for temperature and water vapour. These updates address numerical artefacts in the previous model version by replacing the uniformly discretised ice particle radius distribution, which limited the maximum ice particle radius to ≤ 50 µm , with a non-uniform distribution covering radii from 2 to 300 µm without additional computational overhead. The improved model is validated against meteorological observations from site D47 in Adélie Land, East Antarctica. The updates fix the numerical artefacts, successfully predicting the power-law variation in the blowing-snow flux with wind speed while improving the prediction of its magnitude. Additionally, a qualitative comparison with CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite data shows that RACMO accurately forecasts the spatial pattern of monthly blowing-snow frequencies. The model also yields an average blowing-snow layer depth of 230±116 m at D47, matching typical satellite observation values. Results reveal that, without blowing snow, sublimation in Antarctica mainly occurs in summer (October–March), with minimal surface sublimation in winter (April–September). Introducing the blowing-snow model creates an additional sublimation mechanism primarily contributing in winter. From 2000–2012, model-integrated blowing-snow sublimation averaged 175±7 Gt yr−1, a 52 % increase from the previous version. Total sublimation, summing blowing-snow and surface sublimation, reached 234±10 Gtyr-1 , 47 % higher than in simulations without the blowing-snow model. This increase leads to a 1.2 % reduction in the Antarctic ice sheet's integrated SMB. Additionally, changes in sublimation in coastal and lower escarpment zones underscore the importance of the model updates for Antarctic climatology. [ABSTRACT FROM AUTHOR]

The work presented here marks a further advance in expert uncertainty quantification. In a recent probabilistic evaluation of ice sheet process contributions to sea level rise, tail dependence was elicited and propagated through an uncertainty analysis for the first time. The elicited correlations and tail dependencies concerned pairings of three processes: Accumulation, Discharge and Run-off, which operate on major ice sheets in the West and East Antarctic and in Greenland. The elicitation enumerated dependencies between these processes under selected global temperature change scenarios over different future time horizons. These expert judgments allowed us to populate a Paired Copula Bayesian network model to obtain the estimated contributions of these ice sheets for future sea level rise. Including positive central tendency dependence and tail dependence increases the fatness of the upper tails of projected sea level rise distributions, an amplification important for designing and evaluating possible mitigation strategies. Detailing and jointly computing distributional dependencies and tail dependencies can be crucial components of good practice for assessing the influence of uncertainties on extreme values when modelling stochastic multifactorial processes. [ABSTRACT FROM AUTHOR]

Late Pennsylvanian cyclothems are documented from the carbonate platform margin in Guizhou, South China, providing a unique opportunity to study glacio-eustatic fluctuations and their impact on reef development. This paper focuses on a shallow-water, reef-bearing succession and a deep-water succession in the Houchang area of Guizhou. Fourteen microfacies, grouped into seven associations, represent distinct depositional environments. These microfacies associations exhibit vertical cyclicity, interpreted as cyclothems, similar to those observed globally, which are attributed to the waxing and waning of the Gondwana ice sheet. The cyclothems are primarily composed of sediments below the wave base within a shallow-water platform margin and deep-water settings. Those cyclothems show strong correlations with those observed in South China, Ukraine, and the North American Midcontinent, suggesting a potential connection to global glacio-eustatic processes. A brief and rapid sea-level rise during the late Kasimovian may correspond to a recently recognized global warming event. A microfacies analysis indicates that these cyclothems reflect glacial-type sea-level fluctuations ranging from 15 to 35 m. Notably, the reef-bearing cyclothems correspond to intermediate, major cyclothems identified in South China and the Midcontinent from the late Moscovian to early Kasimovian stages. The global cyclothem correlations and reef development patterns in South China suggest that intermediate, major cycles were the primary controls on reef growth and demise, while minor cycles influenced biostromes and community succession within the reefs. These findings underscore the pivotal role of the Late Paleozoic Ice Age (LPIA) in shaping reef development in far-field regions during the Late Pennsylvanian. [ABSTRACT FROM AUTHOR]

The stratigraphic principle of superposition assumes that sediments at surface are youngest. And yet, patches of older preserved landscapes continue to be identified in the regions formerly covered by the Laurentide Ice Sheet. Two gravel pits, at the edge of the western Hudson Bay Lowland near the geographic centre of the North American Ice Sheet Complex, reveal additional patches where older glacial and nonglacial sediment is preserved. These sites expose 1–4 m of a darker, highly overconsolidated, clayier till, and 0–2 m of a lighter, less consolidated, sandier till over glaciofluvial and post-glacial gravels and sands; the waning stages of deposition occurred at 214 ± 22 ka (1σ minimum age model quartz grain optical age estimates, n = 2). This was during the latter end of the cool Marine Isotope Stage (MIS) 7-d (within 1σ range) or near the end of MIS-8 (within 2σ range). Next followed a warmer period similar to, or warmer than, present day with higher precipitation; inferred from pollen and macrofossils deposited in nonglacial low-energy floodplain or pond sediments. Our study highlights the need to accurately date Quaternary sediments, given that the shallowest nonglacial sediments at both gravel pits were deposited during an old (MIS 7) interglacial; there is likely no record of the youngest interglacial (MIS 5). Preservation of older sediment also means that in Quaternary stratigraphy, disjoint regional nonglacial "organic marker beds" should not automatically be considered correlative. Identification of similar "old" patches, together with till stratigraphy and composition, is essential to accurately model glacial sediment transport over time. [ABSTRACT FROM AUTHOR]

Laurentide Ice Sheet (LIS) reconstructions beyond the last glacial maximum (LGM) are difficult due to the incomplete stratigraphic record that has largely been eroded by the most recent glaciation. The Hudson Bay Lowland (HBL) is a key region to understanding the long-term evolution of the LIS, as it contains an extensive pre-LGM stratigraphic record of glacial and nonglacial events. This study uses a hybrid lithostratigraphy–allostratigraphy approach to decipher the stratigraphic record in the Kaskattama highland region of the western HBL, Manitoba, Canada. We identify five glacial (till) units and three nonglacial (sorted sediment) units that were deposited during at least three glacial–interglacial cycles, which are constrained by radiocarbon and optical ages. The provenance of till units is identified using clast-lithology and detrital hornblende 40Ar/39Ar ages and supported by matrix geochemistry. The new stratigraphic framework for this western HBL region indicates that the ice emanating from the Quebec–Labrador dome advanced into the region at the start of the last two glaciations, suggesting accelerated early growth of the Quebec–Labrador dome relative to the Keewatin Dome. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change will drive extensive mass loss across both the Antarctic (AIS) and Greenland Ice Sheets (GrIS), with the potential for global climate system feedbacks, especially in polar regions. Historically, the high‐latitude North Atlantic and Southern Ocean have been critical regions for anthropogenic heat and carbon uptake, but our understanding of how this uptake will be altered by future freshwater discharge is incomplete. We assess each ice sheet's impact on global ocean anthropogenic heat and carbon storage for a high‐emission scenario over the 21st ${21}^{\text{st}}$‐century using a coupled Earth system model. We explore the impact of contemporaneous mass loss from both ice sheets on anthropogenic heat and carbon storage and quantify their linear and nonlinear contributions. Notably, added freshwater reduces ocean heat and carbon storage by 2,100, and the sum of individual freshwater effects differ from those induced by simultaneous freshwater discharge from both ice sheets. Combined AIS and GrIS freshwater engenders distinct anthropogenic storage anomalies—particularly in the high‐latitude Southern Ocean and North Atlantic. From 2080 to 2100, GrIS freshwater exerts primary control on the temporal evolution of global ocean heat storage, while global ocean carbon storage is modulated by the linear AIS and GrIS freshwater impacts. Nonlinear impacts of simultaneous ice sheet discharge have a non‐negligible contribution to the evolution of global ocean heat storage. Further, anthropogenic heat changes are realized more quickly in response to ice sheet discharge than anthropogenic carbon. Our results highlight the need to incorporate both ice sheets actively in climate models to accurately project future global climate. Plain Language Summary: As the globe continues to warm in the next 100 years, the Antarctic and Greenland Ice sheets will continue to melt, adding freshwater to the surrounding ocean regions. This process is often poorly (if at all) represented in global climate models used to make projections about future climate change. Here, we simulate the climate response to melting ice sheets in a global climate model by adding freshwater to the model ocean near the edges of ice sheets. We focus our analysis on the impact of this freshwater addition on the future evolution of heat and carbon in the ocean, because both heat and carbon have the potential to feed back on the climate system (less heat/carbon in the ocean means more heat/carbon in the atmosphere and a warmer climate). By the end of the century, we find that the ocean stores less heat and carbon because of the melting ice sheets. We also find that summing the effects from melt on Antarctica and Greenland separately is not equal to the effect of melting both ice sheets simultaneously. Finally, we show that ocean heat and carbon respond differently to the same amount of ice sheet melt. Key Points: We disentangle the linear and nonlinear effects of Greenland and Antarctic Ice Sheet melt on ocean heat content and anthropogenic carbonFuture anthropogenic carbon storage and ocean heat content have disparate responses to separate and combined ice sheet melt in polar regionsGreenland freshwater is more influential than Antarctic freshwater in driving future changes in anthropogenic carbon and ocean heat content [ABSTRACT FROM AUTHOR]

The properties of laser signals are affected by deformation of the optical fibre through which they are transmitted. While this deformation dependence is undesirable in telecommunication, it can be exploited for the construction of novel seismic sensors that fill a niche in data acquisition where traditional seismometer arrays would be difficult to deploy. This includes densely populated urban centers, the oceans, volcanoes and the Earth's polar regions. These notes complement a presentation on recent methodological developments and applications in fibre-optic seismology. The first part is focused on the use of distributed fibreoptic sensing in cryosphere research, and specifically the investigation of the internal structure and seismicity of glaciers and ice sheets. The second part is dedicated to recent advances in integrated fibre-optic sensing, with emphasis on novel measurement principles and sensitivity. [ABSTRACT FROM AUTHOR]

The document is a reply to a comment regarding research on the Magallanes Fault System (MFS) in Tierra del Fuego, Patagonia. The authors address criticisms of their work and discuss overlapping results with another study on fault slip rates in Argentina. They highlight the importance of fieldwork, drone photography, and data integration in determining fault slip rates. The study emphasizes the need for further research on other active faults in the MFS and the implications for seismic hazard and neotectonics. [Extracted from the article]

The Vimmerby Moraine is the only significant ice‐marginal moraine on the eastern side of southern Sweden, but no detailed studies exist on its formation during the final deglaciation of the Fennoscandian Ice Sheet. Through ground‐penetrating radar surveys and detailed sediment logging, we provide evidence for an active, oscillating ice margin during the formation of the Vimmerby Moraine, suggesting that the deglaciation of the South Swedish Uplands was, at least in some regions, dynamic. Ground‐penetrating radar surveys enabled imaging of internal sediment and delineation of the bedrock surface. These were complemented by common mid‐point surveys and sediment logging, as well as lithofacies analysis at three exposures in agravel pit. This approach revealed multiple subglacial till units partially separated by intercalated glacifluvial deposits. The glacifluvial sediments exhibit evidence of glaciotectonism, suggesting active overriding by the last ice sheet. Further evidence of an active ice margin is provided by the ground‐penetrating radar profiles collected perpendicular to the moraine crest. These contain a series of northerly dipping reflectors, which we interpret as evidence of repeated basal freeze‐on and melt‐out of sediment slabs during ice margin oscillations, as has been observed at contemporary glacier margins in Iceland, Norway, and the Alps. The data presented here demonstrate that the last Fennoscandian Ice Sheet remained active around the time of the Vimmerby Moraine formation. This work highlights the benefits of including detailed sediment logging and near‐surface geophysical surveys in the interpretation of deglaciation dynamics. [ABSTRACT FROM AUTHOR]

The integration of data from multiple satellite altimetry missions, each offering unique observational characteristics, has enabled us to discern both short-term variability and long-term climate trends affecting Greenland's peripheral glaciers and the Greenland Ice Sheet (GrIS). Our methodology, adapted and informed by lessons learned from our similar efforts in Antarctica, ensures the consistency and reliability of the derived elevation change dataset. The data covers the years 1992–2023 and is made publicly available as part of the NASA's Making Earth System Data Records for Use in Research Environments (MEaSUREs) Inter-Mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) project. Our analysis of the dataset reveals significant patterns of mass loss across the GrIS. We find that the ice sheet and peripheral glaciers have experienced an average mass loss of -173 ± 19 Gt a-1 and -23 ± 5 Gt a-1 respectively over the 1992–2022 time period (given temporal availability of selected firn models), with notable variations over time. Specifically, the early years of the record exhibit a positive mass balance, likely due to anomalously positive surface mass balance. However, this trend shifts in subsequent years, with a pronounced increase in mass loss rates, highlighting the accelerating impact of a changing climate on ice sheet dynamics and surface mass balance. Moreover, our analysis underscores the importance of considering peripheral glaciers in addition to the continental ice sheet when assessing overall mass trends. By incorporating data from peripheral glaciers, we provide a more comprehensive understanding of Greenland's total contributions to global sea level rise. Our findings reveal not only the magnitude of mass loss but also its evolution over time, emphasizing the need for continued monitoring and research to better understand the impacts of climate change on Earth's cryosphere. [ABSTRACT FROM AUTHOR]

Assessing changes of the mass balance in the Antarctic ice sheet in the context of global warming is a key focus in polar study. This study analyzed the spatiotemporal variation in the Antarctic ice sheet's mass balance, both as a whole and by individual basins, from 2003 to 2016 and from 2018 to 2022 using GRACE RL06 data published by the Center for Space Research (CSR) and ERA-5 meteorological data. It explored the lagged relationships between mass balance and precipitation, net surface solar radiation, and temperature, and applied the random forest method to examine the relative contributions of these factors to the ice sheet's mass balance within a nonlinear framework. The results showed that the mass loss rates of the Antarctic ice sheet during the study periods were −123.3 ± 6.2 Gt/a and −24.8 ± 52.1 Gt/a. The region with the greatest mass loss was the Amundsen Sea in West Antarctica (−488.8 ± 5.3 Gt/a and −447.9 ± 14.7 Gt/a), while Queen Maud Land experienced the most significant mass accumulation (44.9 ± 1.0 Gt/a and 30.0 ± 3.2 Gt/a). The main factors contributing to surface ablation of the Antarctic ice sheet are rising temperatures and increased surface net solar radiation, each showing a lag effect of 1 month and 2 months, respectively. Precipitation also affects the loss of the ice sheet to some extent. Over time, the contribution of precipitation to the changes in the ice sheet's mass balance increases. [ABSTRACT FROM AUTHOR]