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The chemistry of H2O, CO, and other small molecular species in an isolated pre-stellar core, L1544, has been assessed in the context of a comprehensive gas-grain chemical model, coupled to an empirically constrained physical/dynamical model. Our main findings are (i) that the chemical network remains in near equilibrium as the core evolves towards star formation and the molecular abundances change in response to the evolving physical conditions. The gas-phase abundances at any time can be calculated accurately with equilibrium chemistry, and the concept of chemical clocks is meaningless in molecular clouds with similar conditions and dynamical time-scales, and (ii) A comparison of the results of complex and simple chemical networks indicates that the abundances of the dominant oxygen and carbon species, H2O, CO, C, and C+ are reasonably approximated by simple networks. In chemical equilibrium, the time-dependent differential terms vanish, and a simple network reduces to a few algebraic equations. This allows rapid calculation of the abundances most responsible for spectral line radiative cooling in molecular clouds with long dynamical time-scales. The dust ice mantles are highly structured and the ice layers retain a memory of the gas-phase abundances at the time of their deposition. A complex (gas-phase and gas-grain) chemical structure therefore exists, with cosmic-ray induced processes dominating in the inner regions. The inferred H2O abundance profiles for L1544 require that the outer parts of the core and also any medium exterior to the core are essentially transparent to the interstellar radiation field. [ABSTRACT FROM AUTHOR]

The formation of solid macroscopic grains (pebbles) in protoplanetary discs is the first step towards planet formation. We aim to study the distribution of pebbles and the chemical composition of their ice mantles in a young protoplanetary disc. We use the two-dimensional hydrodynamical code feosad in the thin-disc approximation, which is designed to model the global evolution of a self-gravitating viscous protoplanetary disc taking into account dust coagulation and fragmentation, thermal balance, and phase transitions and transport of the main volatiles (H2O, CO2, CH4, and CO), which can reside in the gas, on small dust (⁠|$\lt 1\, \mu\mathrm{ m}$|⁠), on grown dust (⁠|$\gt 1\, \mu\mathrm{ m}$|⁠) and on pebbles. We model the dynamics of the protoplanetary disc from the cloud collapse to the 500 kyr moment. We determine the spatial distribution of pebbles and composition of their ice mantles and estimate the mass of volatiles on pebbles, grown dust, and small dust. We show that pebbles form as early as 50 kyr after the disc formation and exist until the end of simulation (500 kyr), providing prerequisites for planet formation. All pebbles formed in the model are covered by icy mantles. Using a model considering accretion and desorption of volatiles on to dust/pebbles, we find that the ice mantles on pebbles consist mainly of H2O and CO2, and are carbon-depleted compared to gas and ices on small and grown dust, which contain more CO and CH4. This suggests a possible dominance of oxygen in the composition of planets formed from pebbles under these conditions. [ABSTRACT FROM AUTHOR]

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

This research was carried out in north-central Poland, which was occupied by the ice sheet of the Saalian (Marine Isotope Stage [MIS] 6) and Upper Stadial of the Weichselian (MIS 2) glaciation. The application of the anisotropy of magnetic susceptibility (AMS) method supported by a digital elevation model (DEM) analysis of the orientation of glacial landforms allowed for the reconstruction of ice-sheet extent and ice movement directions of these two Pleistocene glaciations. The research used an innovative method of collecting AMS till samples from the glacial plateau areas. Based on the research, it was found that during the general recession of the ice sheet of the Saalian glaciation, a previously undescribed glacial transgression occurred, characterized by a different direction of ice-sheet movement. On the basis of detailed geomorphological studies of the area of terminal moraines, previously described in fragments, the maximum extent of the ice sheet during the Weichselian glaciation was clarified. The recession of the ice sheet of the Weichselian glaciation from the area of north-central Poland took place in four regressive or transgressive–regressive stages with variable directions of ice-sheet movement. The results obtained indicate the great potential of the AMS method in paleoenvironmental studies of glaciated areas. [ABSTRACT FROM AUTHOR]

Predicting coastal change depends upon our knowledge of postglacial relative sea-level variability, partly controlled by glacio-isostatic responses to ice-sheet melting. Here, we reconstruct the postglacial relative sea-level changes along the Caribbean and Pacific coasts of northwestern South America by numerically solving the sea-level equation with two scenarios of mantle viscosity: global standard average and high viscosity. Our results with the standard model (applicable to the Pacific coast) agree with earlier studies by indicating a mid-Northgrippian high stand of ~2 m. The high-viscosity simulation (relevant to the Caribbean coast) shows that the transition from far- to intermediate-field influence of the Laurentide Ice Sheet occurs between Manzanillo del Mar and the Gulf of Morrosquillo. South of this location, the Colombian Caribbean coast has exhibited a still stand with a nearly constant Holocene relative sea level. By analyzing our simulations considering sea-level indicators, we argue that tectonics is more prominent than previously assumed, especially along the Caribbean coast. This influence prevents a simplified view of regional relative sea-level changes on the northwestern South American coast. [ABSTRACT FROM AUTHOR]

Van Vliet-Lanoë, B.; Andrieu, V.; Cliquet, D.; Authemayou, C.; Le Roy, P., and Renouf, J.C., 2024. Sea ice and the Middle to Recent Quaternary: Marine highstands in Western Europe. Journal of Coastal Research, 40(3), 445–473. Charlotte (North Carolina), ISSN 0749-0208. This study analyzes the raised beaches of less than 700 kilo annum (ka) above present sea level along the English Channel, which are associated with negative anomalies in δ18O and evidence for anchor ice. The dated coastal events were compared in terms of recent storminess, sea-ice extents, and permafrost with regional paleoclimates. In western France, late Eemian and early interstadial highstands (HSs) indicate an extended annual sea-ice duration during early transgressions, with orbitally forced cold winters and a still-cool Southern Ocean. During regressions, storminess developed with a still-warm intertropical ocean but Arctic cooling. The Northern Atlantic ice sheets starved during early stadials, with aridity because of the seasonal sea-ice extent. (1) A delayed sea-level drop resulted from some ice storage in permafrost and sea ice, which caused depleted δ18O seawater (δ18Osw) values and limited ice caps. (2) The large ice sheets along the Northern Atlantic spread progressively and were delayed until marine isotope stage 4 (MIS 4). Their development resulted from summer precipitation rise caused by the cyclic restoration of thermohaline circulation during Dansgaard–Oechger (DO) events alternating with multiyear sea-ice cover. This led to a more unstable North Atlantic Current, which was repeatedly destabilized. (3) Early glacial storage partly or fully vanished during early DO or interstadial HSs, with climate conditions close to those of the present day. [ABSTRACT FROM AUTHOR]

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

Elevated ice shelf melt rates in West Antarctica have been attributed to transport of warm Circumpolar Deep Water (CDW) onto the continental shelf via bathymetric troughs. These inflows are supplied by an eastward, subsurface slope current (referred to as the Antarctic Slope Undercurrent) that opposes the westward momentum input from local winds and tides. Despite its importance to basal melt, the mechanism via which the undercurrent forms, and thus what controls the shoreward heat transport, remains unclear. In this study, the dynamics of the undercurrent are investigated using high-resolution process-oriented simulations with coupled ocean, sea ice, and ice shelf components. It is shown that the bathymetric steering of the undercurrent toward the ice shelf is driven by upwelling of meltwater within the ice shelf cavity. Increased basal melt therefore strengthens the undercurrent and enhances onshore CDW transport, which indicates a positive feedback that may accelerate future melt of ice shelves, potentially further destabilizing the West Antarctic Ice Sheet. [ABSTRACT FROM AUTHOR]

Here, we show that the Last Glacial Maximum (LGM) provides a stronger constraint on equilibrium climate sensitivity (ECS), the global warming from increasing greenhouse gases, after accounting for temperature patterns. Feedbacks governing ECS depend on spatial patterns of surface temperature ("pattern effects"); hence, using the LGM to constrain future warming requires quantifying how temperature patterns produce different feedbacks during LGM cooling versus modern-day warming. Combining data assimilation reconstructions with atmospheric models, we show that the climate is more sensitive to LGM forcing because ice sheets amplify extratropical cooling where feedbacks are destabilizing. Accounting for LGM pattern effects yields a median modern-day ECS of 2.4°C, 66% range 1.7° to 3.5°C (1.4° to 5.0°C, 5 to 95%), from LGM evidence alone. Combining the LGM with other lines of evidence, the best estimate becomes 2.9°C, 66% range 2.4° to 3.5°C (2.1° to 4.1°C, 5 to 95%), substantially narrowing uncertainty compared to recent assessments. [ABSTRACT FROM AUTHOR]

The explicit representation of cryospheric components in Earth system models has become more and more important over the last years. However, there are few advanced coupled Earth system models that employ interactive icebergs, and most iceberg model studies focus on iceberg trajectories or ocean surface conditions. Here, we present multi-centennial simulations with a fully coupled Earth system model including interactive icebergs to assess the effects of heat and freshwater fluxes by iceberg melting on deep-ocean characteristics. The icebergs are modeled as Lagrangian point particles and exchange heat and freshwater fluxes with the ocean. They are seeded in the Southern Ocean, following a realistic present-day size distribution. Total calving fluxes and the locations of discharge are derived from an ice sheet model output which allows for implementation in coupled climate–ice sheet models. The simulations show a cooling of up to 0.2 K of deep-ocean water masses in all ocean basins that propagates from the southern high latitudes northward. We also find enhanced deep-water formation in the continental shelf area of the Ross Sea, a process commonly underestimated by current climate models. The vertical stratification is weakened by enhanced sea ice formation and duration due to the cooling effect of iceberg melting, leading to a 10 % reduction of the buoyancy frequency in the Ross Sea. The deep-water formation in this region is increased by up to 10 %. By assessing the effects of heat and freshwater fluxes individually, we find latent heat flux to be the main driver of these water mass changes. The altered freshwater distribution by freshwater fluxes and synergetic effects play only a minor role. Our results emphasize the importance of realistically representing both heat and freshwater fluxes in the high southern latitudes. [ABSTRACT FROM AUTHOR]

In recent decades, the Greenland ice sheet has been losing mass through glacier retreat and ice flow acceleration. This mass loss is linked with variations in submarine melt, yet existing ocean models are either coarse global simulations focused on decadal‐scale variability or fine‐scale simulations for process‐based investigations. Here, we unite these scales with a framework to downscale from a global state estimate (15 km) into a regional model (3 km) that resolves circulation on the continental shelf. We further downscale into a fjord‐scale model (500 m) that resolves circulation inside fjords and quantifies melt. We demonstrate this approach in Scoresby Sund, East Greenland, and find that interannual variations in submarine melt at Daugaard‐Jensen glacier induced by ocean temperature variability are consistent with the decadal changes in glacier ice dynamics. This study provides a framework by which coarse‐resolution models can be refined to quantify glacier submarine melt for future ice sheet projections. Plain Language Summary: Over the past several decades, the Greenland ice sheet has been losing ice and contributing to sea‐level rise. About half of this ice loss is induced by melt that occurs where glaciers meet the ocean. Using coarse‐scale ocean models that simulate circulation around the globe, previous studies have noted a strong link between ocean temperature and enhanced glacier ice loss. However, due to the small scale of Greenland's fjords, coarse models are unable to directly quantify circulation in these fjords and melt on submerged glaciers. In this study, we develop a new framework to "zoom in" on a fjord, using high‐resolution models driven by larger coarse‐resolution models. In this approach, we simulate melt on one of Greenland's biggest glaciers and find that periods of higher melt coincide with more ice loss as observed from satellites. Since this framework is adaptable to other regions, it could also be used to simulate melt on other glaciers and support estimates of future sea‐level rise. Key Points: Subsurface temperature variability is simulated in a narrow fjord network using regional models downscaled from a global state estimateModeled increases in ocean melt at Daugaard‐Jensen glacier coincide with the onset of acceleration in 2005 and retreat and thinning in 2011Model variations in shelf‐to‐fjord ocean properties match with observations, providing a basis to estimate ocean forcing in ice projections [ABSTRACT FROM AUTHOR]

Using the climate model CLIMBER-X, we present an efficient method for assimilating the temporal evolution of surface temperatures for the last deglaciation covering the period 22000 to 6500 years before the present. The data assimilation methodology combines the data and the underlying dynamical principles governing the climate system to provide a state estimate of the system, which is better than that which could be obtained using just the data or the model alone. In applying an ensemble Kalman filter approach, we make use of the advances in the parallel data assimilation framework (PDAF), which provides parallel data assimilation functionality with a relatively small increase in computation time. We find that the data assimilation solution depends strongly on the background evolution of the decaying ice sheets rather than the assimilated temperatures. Two different ice sheet reconstructions result in a different deglacial meltwater history, affecting the large-scale ocean circulation and, consequently, the surface temperature. We find that the influence of data assimilation is more pronounced on regional scales than on the global mean. In particular, data assimilation has a stronger effect during millennial warming and cooling phases, such as the Bølling-Allerød and Younger Dryas, especially at high latitudes with heterogeneous temperature patterns. Our approach is a step toward a comprehensive paleo-reanalysis on multi-millennial time scales, including incorporating available paleoclimate data and accounting for their uncertainties in representing regional climates. [ABSTRACT FROM AUTHOR]

Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m -2. In this study, we first investigate the agreement between such pointwise heat flow observations and solid Earth models, applying a 1D steady-state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) point in central Greenland. For further testing, we perform a conditional simulation with focus on Greenland in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates but leads to less variation than existing geophysical models. [ABSTRACT FROM AUTHOR]

We propose an asymptotic method to solve the problem of flexural-gravity wave scattering by an ice sheet of variable geometry in the presence of uniform currents. The significance of the article resides in the development of first and second-order solutions via the use of asymptotic expansion and the Fourier transform technique. We consider two different shape functions for the plate geometry, namely, Gaussian and Gaussian oscillatory. For both shape functions, the first and second-order solutions result in a major impact of depth Froude numbers in hydrodynamic coefficients, emphasizing the crucial function of the higher-order solutions in understanding the current responsiveness. We also observe the occurrence of Bragg resonance for the Gaussian oscillatory shape. The depth Froude number alters the frequency of wave components that are most reflected, and wave action conservation causes a rise in the energy of reflected waves. The depth Froude numbers can induce a unique minimum in reflection coefficient, which is close to 0. An examination of plate deflection reveals that the elevation amplitude is substantially higher near the point where there is a peak of elastic plate's shape. The pressure exerted by the plate is also concentrated near this point, highlighting the significance of the elastic plate's shape. The collective numerical observations for both shapes provide insight into resonance phenomena, the role of plate shape, and the intricate relationship between wave characteristics and varying plate properties. The findings from this study could assist geologists and marine engineers in designing and managing ice sheets, ports, and harbor infrastructure. [ABSTRACT FROM AUTHOR]

Given the high number and diversity of events in a typical cryoseismic dataset, in particular those recorded on ice sheet margins, it is desirable to use a semi-automated method of grouping similar events for reconnaissance and ongoing analysis. We present a workflow for employing semi-unsupervised cluster analysis to inform investigations of the processes occurring in glaciers and ice sheets. In this demonstration study, we make use of a seismic event catalogue previously compiled for the Whillans Ice Stream, for the 2010–2011 austral summer outlined in Part 1,. We address the challenges of seismic event analysis for a complex wave field by clustering similar seismic events into groups using characteristic temporal, spectral, and polarization attributes of seismic time series with the k -means++ algorithm. This provides the basis for a reconnaissance analysis of a seismic wave field that contains local events (from the ice stream) set in an ambient wave field that itself contains a diversity of signals (mostly from the Ross Ice Shelf). As one result, we find that two clusters include stick-slip events that diverge in terms of length and initiation locality (i.e., central sticky spot and/or the grounding line). We also identify a swarm of high-frequency signals on 16–17 January 2011 that are potentially associated with a surface melt event from the Ross Ice Shelf. Used together with the event detection presented in Part 1, the semi-automated workflow could readily be generalized to other locations and, as a possible benchmark procedure, could enable the monitoring of remote glaciers over time and comparisons between locations. [ABSTRACT FROM AUTHOR]

Cryoseismology is a powerful toolset for progressing the understanding of the structure and dynamics of glaciers and ice sheets. It can enable the detection of hidden processes such as brittle fracture, basal sliding, transient hydrological processes, and calving. Addressing the challenge of detecting signals from many different processes, we present a novel approach for the semi-automated detection of events and event-like noise, which is well-suited for use as Part 1 of a workflow where unsupervised machine learning will be used as Part 2 to facilitate the main reconnaissance of diverse detected event types. Implemented in the open-source and widely used ObsPy Python package, the multi-STA/LTA algorithm constructs a hybrid characteristic function from a set of short-term average (sta)–long-term average (lta) pairs (refer to Sect. in the main text for an explanation of how uppercase and lowercase STA/sta and LTA/lta abbreviations are differentiated). We apply the algorithm to data from a seismic array deployed on the Whillans Ice Stream (WIS) in West Antarctica (austral summer 2010–2011) to form a "catch-all" catalogue of events and event-like noise. The new algorithm compares favorably with standard approaches, yielding a diversity of seismic events, including all previously identified stick-slip events , teleseisms, and other noise-type signals. In terms of a catalogue overview, we investigate a partial association of seismicity with the tidal cycle and a slight association with ice temperature changes of the Antarctic summer. The new algorithm and workflow will assist in the comparison of different glacier environments using seismology, the identification of process change over time, and the targeting of possible subsequent high-resolution studies. [ABSTRACT FROM AUTHOR]

The paper presents the first terrestrial record of millennial-scale palaeo-ice margin oscillations at the southern fringe of the last Fennoscandian Ice Sheet (FIS) during the last glacial cycle. The study area is located in northern Poland close to the last FIS maximum limit. The chronology and dynamics of palaeo-ice margin oscillations at the southern fringe of the FIS are based on combined luminescence and 10 Be surface exposure dating. Optically stimulated luminescence (OSL) was used to date sandy deposits (fluvioglacial sediments and aeolian deposits filling fossil periglacial wedges) intercalating basal till layers. The most likely age of the tills was constrained by Bayesian modelling of the sequence of OSL ages and lithostratigraphy. 10 Be surface exposure dating was used on erratic boulders left during the final retreat of the last FIS and resting on the surface of glacial landforms. Our results, which are mainly based on OSL chronology and Bayesian modelling, indicate millennial-scale oscillations of the last FIS in northern Poland between ∼19 and ∼17 ka. The last FIS retreated and re-advanced over a relatively short period of time (2–3 ka), leaving lithostratigraphic records (basal tills) of three ice re-advances over a millennial-scale cycle: 19.2±1.1 , 17.8±0.5 and 16.9±0.5 ka. Despite 10 Be surface exposure ages obtained for 14 erratic boulders being poorly clustered, the main mode of age distribution occurs at ∼18 ka and indicates a possible signal of the ice sheet retreat after one of the re-advances. We explore the dynamics of these oscillations and compare the proposed cycles of the southern FIS advances and retreats with existing patterns of the last deglaciation and millennial-scale fluctuations of the last FIS inferred from marine records. [ABSTRACT FROM AUTHOR]

Landscapes buried beneath the Antarctic Ice Sheet preserve information about the geologic and geomorphic evolution of the continent both before and during the wide-scale glaciation that began roughly 34×106 years ago. Since the inception of this ice sheet, some areas have remained cold-based and non-erosive, preserving ancient landscapes remarkably intact. The Gamburtsev Subglacial Mountains in central East Antarctica are one such landscape, maintaining evidence of tectonic, fluvial and glacial controls on their distinctly alpine morphology. The central Gamburtsev Mountains have previously been surveyed using airborne ice-penetrating radar; however, many questions remain as to their evolution and their influence on the East Antarctic Ice Sheet, including where in the region to drill for a 1.5×106 year-long "oldest-ice" core. Here, we derive new maps of the planform geometry of the Gamburtsev Subglacial Mountains from satellite remote sensing datasets of the ice sheet surface, based on the relationship between bed roughness and ice surface morphology. Automated and manual approaches to mapping were tested and validated against existing radar data and elevation models. Manual mapping was more effective than automated approaches at reproducing bed features observed in radar data, but a hybrid approach is suggested for future work. The maps produced here show the detail of mountain ridges and valleys on wavelengths significantly smaller than the spacing of existing radar flightlines, and mapping has extended well beyond the confines of existing radar surveys. Morphometric analysis of the mapped landscape reveals that it constitutes a preserved (>34 Ma) dendritic valley network, with some evidence for modification by topographically confined glaciation prior to ice sheet inception. The planform geometry of the landscape is a significant control on locations of basal melting, subglacial hydrological flows and the stability of the ice sheet over time, so the maps presented here may help to guide decisions about where to search for oldest ice. [ABSTRACT FROM AUTHOR]

The shift in climate that occurred between the Last Glacial Maximum (LGM) and the Early Holocene (ca. 18–12 kyr BP) displayed rates of temperature increase similar to present-day warming trends. The most rapid recorded changes in temperature occurred during the abrupt climate oscillations known as the Bølling–Allerød interstadial (14.7–12.9 kyr BP) and the Younger Dryas stadial (12.9–11.7 kyr BP). Reconstructing ice sheet dynamics during these climate oscillations provides the opportunity to assess long-term ice sheet evolution in reaction to a rapidly changing climate. Here, we use glacial geomorphological inversion methods (flowsets) to reconstruct the ice flow dynamics and the marginal retreat pattern of the southwestern sector of the Laurentide Ice Sheet (SWLIS). We combine our reconstruction with a recently compiled regional deglaciation chronology to depict ice flow dynamics that encompass the time period from pre-LGM to the Early Holocene. Our reconstruction portrays three macroscale reorganizations in the orientation and dynamics of ice streaming followed by regional deglaciation associated with rapid warming during the Bølling–Allerød interstadial. Initial westward flow is documented, likely associated with an early set of ice streams that formed during the advance to the LGM. During the LGM ice streaming displays a dominant north to south orientation. Ice sheet thinning at ∼15 ka is associated with a macroscale reorganization in ice stream flow, with a complex of ice streams recording south-eastward flow. A second macroscale reorganization in ice flow is then observed at ∼14 ka, in which southwestern ice flow is restricted to the Hay, Peace, Athabasca, and Churchill river lowlands. Rates of ice sheet retreat then slowed considerably during the Younger Dryas stadial; at this time, the ice margin was situated north of the Canadian Shield boundary and ice flow continued to be sourced from the northeast. Resulting from these changes in ice sheet dynamics, we recognize a three-part pattern of deglacial landform zonation within the SWLIS characterized by active ice margin recession, stagnation and downwasting punctuated by local surging (terrestrial ice sheet collapse): the outer deglacial zone contains large recessional moraines aligned with the direction of active ice margin retreat; the intermediate deglacial zone contains large regions of hummocky and stagnation terrain, in some areas crosscut by the signature of local surges, reflecting punctuated stagnation and downwasting; and the inner deglacial zone contains inset recessional moraines demarcating progressive regional ice margin retreat. We attribute these macroscale changes in ice flow geometry and associated deglacial behaviour to external climatic controls during the Bølling–Allerød and Younger Dryas but also recognize the role of internal (glaciological, lithological and topographic) controls in SWLIS dynamics. [ABSTRACT FROM AUTHOR]

The Scandinavian topography and bathymetry have been shaped by ice through numerous glacial cycles in the Quaternary. In this study, we investigate how the changing morphology has influenced the Scandinavian ice sheet (SIS) in return. We use a higher-order ice-sheet model to simulate the SIS through a glacial period on three different topographies, representing different stages of glacial landscape evolution in the Quaternary. By forcing the three experiments with the same climate conditions, we isolate the effects of a changing landscape morphology on the evolution and dynamics of the ice sheet. We find that early Quaternary glaciations in Scandinavia were limited in extent and volume by the pre-glacial bathymetry until glacial deposits filled depressions in the North Sea and built out the Norwegian shelf. From middle–late Quaternary (∼0.5 Ma) the bathymetry was sufficiently filled to allow for a faster southward expansion of the ice sheet causing a relative increase in ice-sheet volume and extent. Furthermore, we show that the formation of The Norwegian Channel during recent glacial periods restricted southward ice-sheet expansion, only allowing for the ice sheet to advance into the southern North Sea close to glacial maxima. Finally, our experiments indicate that different stretches of The Norwegian Channel may have formed in distinct stages during glacial periods since ∼0.5 Ma. These results highlight the importance of accounting for changes in landscape morphology through time when inferring ice-sheet history from ice-volume proxies and when interpreting climate variability from past ice-sheet extents. [ABSTRACT FROM AUTHOR]

Genetic variation in Arctic species is often influenced by vicariance during the Pleistocene, as ice sheets fragmented the landscape and displaced populations to low‐ and high‐latitude refugia. The formation of secondary contact or suture zones during periods of ice sheet retraction has important consequences on genetic diversity by facilitating genetic connectivity between formerly isolated populations. Brant geese (Branta bernicla) are a maritime migratory waterfowl (Anseriformes) species that almost exclusively uses coastal habitats. Within North America, brant geese are characterized by two phenotypically distinct subspecies that utilize disjunct breeding and wintering areas in the northern Pacific and Atlantic. In the Western High Arctic of Canada, brant geese consist of individuals with an intermediate phenotype that are rarely observed nesting outside this region. We examined the genetic structure of brant geese populations from each subspecies and areas consisting of intermediate phenotypes using mitochondrial DNA (mtDNA) control region sequence data and microsatellite loci. We found a strong east–west partition in both marker types consistent with refugial populations. Within subspecies, structure was also observed at mtDNA while microsatellite data suggested the presence of only two distinct genetic clusters. The Western High Arctic (WHA) appears to be a secondary contact zone for both Atlantic and Pacific lineages as mtDNA and nuclear genotypes were assigned to both subspecies, and admixed individuals were observed in this region. The mtDNA sequence data outside WHA suggests no or very restricted intermixing between Atlantic and Pacific wintering populations which is consistent with published banding and telemetry data. Our study indicates that, although brant geese in the WHA are not a genetically distinct lineage, this region may act as a reservoir of genetic diversity and may be an area of high conservation value given the potential of low reproductive output in this species. [ABSTRACT FROM AUTHOR]

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

Surface exposure–age dating was applied to rock surfaces associated with ice‐marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here 10Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio‐isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar 10Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt‐hammer R‐values and independent Schmidt‐hammer exposure‐age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine‐ridge morphology and estimates of equilibrium‐line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short‐lived re‐advances of active glaciers, at least the lower reaches of which were warm‐based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway. [ABSTRACT FROM AUTHOR]

The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice sheet dynamics within the Quebec–Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (>175 km). However, major oxide data from till matrix geochemistry show a correlation with underlying bedrock, and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice flow, followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS. [ABSTRACT FROM AUTHOR]

Aim: To assess the relative relevance of dispersal limitation and species sorting as drivers of spatial turnover between spider faunas of European territories. Location: Continental Europe. Time period: Present. Major taxa studied: Spiders (Order Araneae). Methods: We analysed how distance‐decay patterns differ between northern and southern Europe (broadly, territories covered vs. not covered by ice sheets during the last glacial maximum, respectively) in 15 spider families, using standardized distances to allow a direct comparison between parameters (i.e. slope and intercept) of climatic and spatial distance‐decay models. Thus, we assessed North–South differences in parameters of spatial and, independently, climatic distance‐decay models, and whether those differences are explained by family‐specific traits related to dispersal ability. Results: Climatic and spatial distance‐decay patterns are very similar in northern Europe, where climatic and spatial distances are highly correlated. In contrast, slopes are steeper in spatial than in climatic distance‐decay curves in southern Europe, where climatic and spatial distances are decoupled. Moreover, family traits related to dispersal ability explained the North–South difference in spatial distance‐decay slopes, as well as the amount of nestedness‐resultant dissimilarity between southern and northern spider faunas. Main conclusions: Our results suggest that differences in beta diversity patterns between northern and southern Europe reflect the strength of dispersal limitation in spiders, which varies across families and leads to different degrees of disequilibrium with current climatic conditions depending on the taxon. Moreover, in the South of Europe, where spatial and climatic distances are uncorrelated, spatial distance‐decay models are steeper and have larger explanatory power than climatic distance‐decay models, which suggests that dispersal limitation is the main factor shaping current beta diversity patterns of European spiders at the continental scale. [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]

Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice‐sheet dynamics. Yet, direct data are sparse and difficult to acquire. Here, we employ ultra‐wideband radar to map high‐backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. Our backscatter analysis reveals that the basal ice in an area of ∼10,000 km2 is composed of along‐flow oriented sediment‐laden basal ice units connected to the basal substrate, extending up to several hundred meters thick. Three‐dimensional thermomechanical modeling supports that these units form via basal freeze‐on of subglacial water that originated from further upstream. Our findings suggest that basal freeze‐on, and the entrainment and transport of subglacial material play a significant role in an accurate representation of material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice‐sheet modeling. Plain Language Summary: We investigate the lowermost portion of the ice column of the Antarctic ice sheet, known as basal ice. This part holds crucial information about how the ice sheet behaves when it flows. Using the principle of echo‐location, we use radar technology to scan the ice in East Antarctica's Jutulstraumen drainage basin. We discover that a significant portion of the basal ice in this region is filled with sediment and can be several hundred meters thick. To better understand how this distinctive type of ice forms, we used a mathematical model that suggested that these ice units likely form when water underneath the ice is transported and refreezes at particular locations. Our findings highlight the importance of these freezing and mixing of materials from beneath the ice. Understanding where these ice units are located provides important information for ice‐flow models to ultimately better understand how the Antarctic ice sheet behaves in the future. Key Points: We have identified high‐scattering basal ice in Jutulstraumen Glacier's onset region using radar, reaching several hundred meters from the bedBackscatter analysis suggests that the basal ice units contain unstratified point scatters and cause little radio‐glaciological loss3D thermo‐mechanical modeling implies that freeze‐on of basal meltwater generated upstream likely initially formed the basal ice units [ABSTRACT FROM AUTHOR]

Terrestrial glacial records from the Patagonian Andes and New Zealand Alps document quasi-synchronous Southern Hemisphere-wide glacier advances during the late Quaternary. However, these records are inherently incomplete. Here, we provide a continuous marine record of western-central Patagonian ice sheet (PIS) extent over a complete glacial-interglacial cycle back into the penultimate glacial (~140 ka). Sediment core MR16-09 PC03, located at 46°S and ~150 km offshore Chile, received high terrestrial sediment and meltwater input when the central PIS extended westward. We use biomarkers, foraminiferal oxygen isotopes, and major elemental data to reconstruct terrestrial sediment and freshwater input related to PIS variations. Our sediment record documents three intervals of general PIS marginal fluctuations, during Marine Isotope Stage (MIS) 6 (140 to 135 ka), MIS 4 (~70 to 60 ka), and late MIS 3 to MIS 2 (~40 to 18 ka). These higher terrigenous input intervals occurred during sea-level low stands, when the western PIS covered most of the Chilean fjords, which today retain glaciofluvial sediments. During these intervals, high-amplitude phases of enhanced sediment supply occur at millennial timescales, reflecting increased ice discharge most likely due to a growing PIS. We assign the late MIS 3 to MIS 2 phases and, by inference, older advances to Antarctic cold stages. We conclude that the increased sediment/meltwater release during Southern Hemisphere millennial-scale cold phases was likely related to higher precipitation caused by enhanced westerly winds at the northwestern margin of the PIS. Our records complement terrestrial archives and provide evidence for PIS climate sensitivity. [ABSTRACT FROM AUTHOR]

Provenance records from sediments deposited offshore of the West Antarctic Ice Sheet (WAIS) can help identify past major ice retreat, thus constraining ice‐sheet models projecting future sea‐level rise. Interpretations from such records are, however, hampered by the ice obscuring Antarctica's geology. Here, we explore central West Antarctica's subglacial geology using basal debris from within the Byrd ice core, drilled to the bed in 1968. Sand grain microtextures and a high kaolinite content (∼38–42%) reveal the debris consists predominantly of eroded sedimentary detritus, likely deposited initially in a warm, pre‐Oligocene, subaerial environment. Detrital hornblende 40Ar/39Ar ages suggest proximal late Cenozoic subglacial volcanism. The debris has a distinct provenance signature, with: common Permian‐Early Jurassic mineral grains; absent early Ross Orogeny grains; a high kaolinite content; and high 143Nd/144Nd and low 87Sr/86Sr ratios. Detecting this "fingerprint" in Antarctic sedimentary records could imply major WAIS retreat, revealing the WAIS's sensitivity to future warming. Plain Language Summary: Ice loss from the West Antarctic Ice Sheet (WAIS) could potentially raise global sea level by up to 4 m over the coming decades to centuries. However, projections of sea‐level contributions from the WAIS are highly uncertain. Understanding when the WAIS was smaller in warm times in the Earth's more recent history would reduce these uncertainties, but direct evidence for the most recent large‐scale WAIS retreat is lacking. Tracing the source of sediments deposited offshore will help detect WAIS retreat because, under a smaller WAIS, there would be more erosion of presently ice‐covered areas in central West Antarctica. However, the subglacial geology of central West Antarctica is poorly known, making it difficult to identify a WAIS retreat signal in sedimentary records. Here, we present new results from debris in the Byrd ice core, drilled in the center of the WAIS to its base in 1968. The mineralogical, geochemical and age compositions of the debris provide a distinct geological "fingerprint" that should be identifiable in sedimentary records. This fingerprint can be searched for in existing and upcoming Antarctic drill core records, which will ultimately help constrain the environmental conditions that would lead to future WAIS retreat and the resulting sea‐level rise. Key Points: Debris from the base of the Byrd ice core comprises predominantly of sedimentary strata weathered before the onset of Antarctic glaciation40Ar/39Ar dated hornblende grains support evidence for recent subglacial volcanismByrd geochemical data reveal the provenance signature expected in marine sediments following major West Antarctic Ice Sheet retreat [ABSTRACT FROM AUTHOR]

Ground-based high resolution observations of downward longwave irradiance (DLI), surface air temperature, water vapor surface partial pressure and column amount, zenith sky infrared (IR) radiance in the atmospheric window, and all-sky camera images are regularly obtained at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W), northwestern Greenland. The datasets for the years 2017 and 2018 have been used to assess the performance of different empirical formulas used to infer clear sky DLI. An algorithm to identify clear sky observations has been developed, based on value, variability, and persistence of zenith sky IR radiance. Seventeen different formulas to estimate DLI have been tested against the THAAO dataset, using the originally determined coefficients. The formulas that combine information on total column water vapor and surface air temperature appear to perform better than others, with a mean bias with respect to the measured DLI smaller than 1 W m -2 and a root mean squared error (RMSE) around 6 W m -2. Unexpectedly, some formulas specifically developed for the Arctic are found to produce poor statistical results. This is attributed partly to limitations in the originally used dataset, which does not cover a whole year or is relative to very specific condition (i.e., the presence of an ice sheet). As expected, the bias displays a significant improvement when the coefficients of the different formulas are calculated using the THAAO dataset. The presence of 2 full years of data allows the determination and the applicability of the coefficients for singular years and the evaluation of results. The smallest values of the bias and RMSE reach 0.1 and 5 W m -2 , respectively. Overall, the best results are found for formulas that use both surface parameters and total water vapor column content, and have been developed from global datasets. Conversely, formulas that express the atmospheric emissivity as a linear function of the logarithm of the column integrated water vapor appear to reproduce poorly the observations at THAAO. [ABSTRACT FROM AUTHOR]

High subglacial heat flow and volcanic activity in West Antarctica contribute to instability and accelerated flow into the ocean of the West Antarctic ice sheet. In this case, a catastrophic rise in sea level by tens of centimeters – the first meters can occur in a very short geological time (years-decades) due to the rapid sliding of large masses of ice in West Antarctica into the ocean. If the Pine Island (50 cm sea level rise) or Thwaites (65 cm sea level rise) glaciers slide into the ocean, the West Antarctic Ice Sheet will lose support from these glaciers and may begin to collapse. In this case, the sea level will rise by a few meters. Based on Glen's rheological law for a two-dimensional model of the movement of ice as a nonlinear viscous fluid, the flow velocities of a 3000 m thick glacier were calculated under conditions of adhesion to the bed (~20 m/year) and under conditions of sliding along the bedrock when the lower edge of the glacier melts due to increased heat flow from below (~3000 m/year). These velocities are in good agreement with the velocities of the Pine Island, Thwaites, Amery, Denman and Totten glaciers. The rapid movement of some outlet glaciers in East Antarctica is also likely caused by melting of their bases, suggesting increased subglacial heat flow in these areas of East Antarctica. [ABSTRACT FROM AUTHOR]

Salt structures and their surroundings can play an important role in the energy transition related to a number of storage and energy applications. Thus, it is important to assess the current and future stability of salt bodies in their specific geological settings. We investigate the influence of ice sheet loading and unloading on subsurface salt structures using physical models based on the geological setting of northern Germany, which was repeatedly glaciated by the Scandinavian Ice Sheet during the Pleistocene. Apparent spatial correlations between subsurface salt structures in northern Germany and Weichselian ice marginal positions have been observed before, and the topic is a matter of ongoing debate. Recently described geomorphological features – termed surface cracks – have been interpreted as a direct result of ice-sheet-induced salt movement resulting in surface expansion. The spatial clustering and orientation of these surface cracks has not been well understood so far, owing to only a limited number of available studies dealing with the related salt tectonic processes. Thus, we use four increasingly complex physical models to test the basic loading and unloading principle, to analyze flow patterns within the salt source layer and within salt structures, and to examine the influence of the shape and orientation of the salt structures with respect to a lobate ice margin in a three-dimensional laboratory environment. Three salt structures of the northern German basin were selected as examples that were replicated in the laboratory. Salt structures were initially grown by differential loading and buried before loading. The ice load was simulated by a weight that was temporarily placed on a portion of the surface of the models. The replicated salt structures were either completely covered by the load, partly covered by the load, or situated outside the load extent. In all scenarios, a dynamic response of the system to the load could be observed; while the load was applied, the structures outside the load margin started to rise, with a decreasing tendency with distance from the load margin, and, at the same time, the structures under the load subsided. After the load was removed, a flow reversal set in, and previously loaded structures started to rise, whereas the structures outside the former load margin began to subside. The vertical displacements during the unloading stage were not as strong as during the load stage, and thus the system did not return to its pre-glaciation status. Modeled salt domes that were located at distance from the load margin showed a comparably weak reaction. A more extreme response was shown by modeled salt pillows whose margins varied from sub-parallel to sub-perpendicular to the load margin and were partly covered by the load. Under these conditions, the structures showed a strong reaction in terms of strain and vertical displacement. The observed strain patterns at the surface were influenced by the shape of the load margin and the shape of the salt structure at depth, resulting in complex deformation patterns. These physical modeling results provide more evidence for a possible interplay between ice sheets and subsurface salt structures, highlighting the significance of three-dimensional effects in dynamic geological settings. Our results lead to a better understanding of spatial patterns of the surface cracks that were mapped at the surface above salt structures and offer further room for interpretation of the influence of salt movements on the present-day landscape. [ABSTRACT FROM AUTHOR]

The Greenland Ice Sheet is a key contributor to contemporary global sea level rise, but its long-term history and response to episodes of warming in Earth's geological past remain uncertain. The terrain covered by the ice sheet comprises ∼ 79 % of Greenland and ∼ 1.1 % of the Earth's land surface and contains geomorphological records that may provide valuable insights into past ice-sheet behaviour. Here we use ice surface morphology and radio-echo sounding data to identify ice-covered valleys within the highlands of southern and eastern Greenland and use numerical ice-sheet modelling to constrain the climatological and glaciological conditions responsible for valley incision. Our mapping reveals intricate subglacial valley networks with morphologies that are indicative of substantial glacial modification of an inherited fluvial landscape, yet many of these valleys are presently situated beneath cold-based, slow-moving (i.e. non-erosive) ice. We use the morphology of the valleys and our simple ice-sheet model experiments to infer that incision likely occurred beneath erosive mountain valley glaciers during one or more phases of Greenland's glacial history when ice was restricted to the southern and eastern highlands and when Greenland's contribution to barystatic sea level was up to + 7 m relative to today. We infer that this valley incision primarily occurred prior to the growth of a continental-scale ice sheet, most likely during the late Miocene (ca. 7–5 Ma) and/or late Pliocene (ca. 3.6–2.6 Ma). Our findings therefore provide new data-based constraints on early Greenland Ice Sheet extent and dynamics that can serve as valuable boundary conditions in models of regional and global palaeoclimate during past warm periods that are important analogues for climate change in the 21st century and beyond. [ABSTRACT FROM AUTHOR]

Studying the retreat of the Patagonian Ice Sheet (PIS) during the last deglaciation represents an important opportunity to understand how ice sheets outside the polar regions have responded to deglacial changes in temperature and large-scale atmospheric circulation. At the northernmost extension of the PIS during the Last Glacial Maximum (LGM), the Chilean Lake District (CLD) was influenced by the southern westerly winds (SWW), which strongly modulated the hydrologic and heat budgets of the region. Despite progress in constraining the nature and timing of deglacial ice retreat across this area, considerable uncertainty in the glacial history still exists due to a lack of geologic constraints on past ice margin change. Where the glacial chronology is lacking, ice sheet models can provide important insight into our understanding of the characteristics and drivers of deglacial ice retreat. Here we apply the Ice Sheet and Sea-level System Model (ISSM) to simulate the LGM and last deglacial ice history of the PIS across the CLD at high spatial resolution (450 m). We present a transient simulation of ice margin change across the last deglaciation using climate inputs from the National Center for Atmospheric Research Community Climate System Model (CCSM3) Trace-21ka experiment. At the LGM, the simulated ice extent across the CLD agrees well with the most comprehensive reconstruction of PIS ice history (PATICE). Coincident with deglacial warming, ice retreat ensues after 19 ka, with large-scale ice retreat occurring across the CLD between 18 and 16.5 ka. By 17 ka, the northern portion of the CLD becomes ice free, and by 15 ka, ice only persists at high elevations as mountain glaciers and small ice caps. Our simulated ice history agrees well with PATICE for early deglacial ice retreat but diverges at and after 15 ka, where the geologic reconstruction suggests the persistence of an ice cap across the southern CLD until 10 ka. However, given the high uncertainty in the geologic reconstruction of the PIS across the CLD during the later deglaciation, this work emphasizes a need for improved geologic constraints on past ice margin change. While deglacial warming drove the ice retreat across this region, sensitivity tests reveal that modest variations in wintertime precipitation (∼10%) can modulate the pacing of ice retreat by up to 2 ka, which has implications when comparing simulated outputs of ice margin change to geologic reconstructions. While we find that TraCE-21ka simulates large-scale changes in the SWW across the CLD that are consistent with regional paleoclimate reconstructions, the magnitude of the simulated precipitation changes is smaller than what is found in proxy records. From our sensitivity analysis, we can deduce that larger anomalies in precipitation, as found in paleoclimate proxies, may have had a large impact on modulating the magnitude and timing of deglacial ice retreat. This fact highlights an additional need for better constraints on the deglacial change in strength, position, and extent of the SWW as it relates to understanding the drivers of deglacial PIS behavior. [ABSTRACT FROM AUTHOR]

Ice-penetrating radar (IPR) imaging is a valuable tool for observing the internal structure and bottom of ice sheets. Subglacial water bodies, also known as subglacial lakes, generally appear as distinct, bright, flat, and continuous reflections in IPR images. In this study, we use available IPR images from the Gamburtsev Subglacial Mountains to extract one-dimensional reflector waveform features of the ice–bedrock interface. We apply a deep-learning method to reduce the dimension of the reflector features. An unsupervised clustering method is then used to separate different types of reflector features, including a reflector type corresponding to subglacial lakes. The derived clustering labels are then used to detect features of subglacial lakes in IPR images. Using this method, we compare the new detections with a known-lakes inventory. The results indicate that this new method identified additional subglacial lakes that were not previously detected, and some previously known lakes are found to correspond to other reflector clusters. This method can offer automatic detections of subglacial lakes and provide new insight for subglacial studies. [ABSTRACT FROM AUTHOR]

A realistic initialization of ice flow models is critical for predicting future changes in ice sheet mass balance and their associated contribution to sea level rise. The initial thermal state of an ice sheet is particularly important, as it controls ice viscosity and basal conditions, thereby influencing the overall ice velocity. Englacial and subglacial conditions, however, remain poorly understood due to insufficient direct measurements, which complicate the initialization and validation of thermal models. Here, we investigate the impact of using different geothermal heat flux (GHF) datasets and vertical velocity profiles on the thermal state of the Antarctic ice sheet and compare our modeled temperatures to in situ measurements from 15 boreholes. We find that the temperature profile is more sensitive to vertical velocity than to GHF. The basal temperature of grounded ice and the amount of basal melting are influenced by both selection of GHF and vertical velocity. More importantly, we find that the standard approach, which consists of combining basal sliding speed and incompressibility to derive vertical velocities, provides reasonably good results in fast-flow regions (ice velocity >50 m yr -1) but performs poorly in slow-flow regions (ice velocity <50 m yr -1). Furthermore, the modeled temperature profiles in ice streams, where bed geometry is generated using a mass conservation approach, show better agreement with observed borehole temperatures compared to kriging-based bed geometry. [ABSTRACT FROM AUTHOR]

The retreat of the West Antarctic Ice Sheet (WAIS) in the Ross Sea after the Last Glacial Maximum (LGM) was more significant than for any other Antarctic sector. Here we combined the available chronology of retreat with new mapping of seismically resolvable grounding zone wedges (GZWs). Mapping GZWs is important because they record the locations of former stillstands in the extent of grounded ice for individual ice streams during the overall retreat. Our analysis shows that the longest stillstands occurred early in the deglacial period and had millennial durations. Stillstands ended abruptly with retreat distances measured in the tens to hundreds of kilometers creating deep embayments in the extent of grounded ice across the Ross Sea. The location of embayments shifted through time. The available chronological data show that cessation of WAIS and East Antarctic Ice Sheet (EAIS) stillstands was highly asynchronous across at least 5000 years. There was a general shift to shorter stillstands throughout the deglacial period. The asynchronous collapse of individual catchments during the deglacial period suggests that the Ross Sea sector would have contributed to multiple episodes of relatively small-amplitude sea-level rise as the WAIS and EAIS retreated from the region. The high sinuosity of the modern grounding zone in the Ross Sea suggests that this style of retreat persists. [ABSTRACT FROM AUTHOR]

The latitudinal diversity gradient (LDG) hypothesis has been validated for many taxon groups, but so far, stream diatoms have not conformed to this pattern. Research on diatoms that includes data from South America is lacking, and our study aims to address this knowledge gap. Previous studies have successfully explained stream diatom species richness by considering niche dimensionality of physicochemical variables. Moreover, in southwestern South America, the observed biogeographical pattern differs from LDG and has been shown to be determined by historical factors. We used a dataset comprising 373 records of stream diatom communities located between 35° S and 52° S latitude, southwestern South America. The dataset included physicochemical river water variables, climate data, and ice sheet cover from the Last Glacial Maximum. We explored geographical patterns of diatom species richness and evaluated 12 different causal mechanisms, including climate‐related theories, physicochemical and climatical exploratory analyses, historical factors, and niche dimensionality. A metacommunity analysis was conducted to evaluate the possible nested structure due to historical factors. We observed an increase in diatom species richness from south to north. Models containing both physicochemical and climatic predictors explained the highest proportion of variation in the data. Silica, which was correlated with latitude, and flow velocity, which did not show any spatial pattern, were the most important predictors. Historical factors and nested structure did not play any role. Contrary to what has been reported in the literature, we found no support for climate‐related explanations of species richness. Instead, theories related to niche dimensionality and local factors provided better explanations, consistent with previous related research. We suggest that the increase in diatom richness in the north of our study region is due to a higher nutrient supply in these rivers, rather than a due to larger species pool in the area. [ABSTRACT FROM AUTHOR]

The penultimate deglaciation was characterized by a sub-millennial-scale warm event in the Heinrich Stadial 11(HS11), termed the 134-ka event. However, its precise timing and structure remain poorly constrained due to the lack of high-resolution and precisely dated records. We present an oxygen isotope record of a speleothem with well-developed annual lamina from Zhangjia Cave, located on the north margin of the Sichuan Basin, characterizing Asian summer monsoon (ASM) changes in the 134-ka event, which included an increase excursion of ca. 149 years and decrease excursion of ca. 200 years, inferred from 3.3‰ δ18O variations. This event also divided the weak ASM interval-II (WMI-II), corresponding to HS11, into two stages, the WMI-IIa 132.8–134.1 ka and WMI-IIb 134.4–136.4 ka. With a comparable climatic pattern globally, the 134-ka event is essentially similar to the millennial-scale events in last glacial–deglacial period. Particularly, the observed weak-strong-weak ASM sequence (138.8–132.8 ka) is largely controlled by changes in the Atlantic Meridional Overturning Circulation (AMOC) forced by the meltwater of northern high-latitude ice sheets. Moreover, our results underpin that AMOC, rather than the global ice volume, is more critical to ASM variations during the last two deglaciations. [ABSTRACT FROM AUTHOR]

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

Kangerlussuaq Glacier (KG) is a major contributor to central‐eastern Greenland mass loss, but existing estimates of its mass balance over the last century are inconsistent, and specific drivers of change remain poorly understood. We present a novel approach that combines numerical modeling and a 1933–2021 climate forcing to reconstruct its mass balance over the past century. The model's final state aligns remarkably well with present‐day observations. The model reveals a total ice mass loss of 285 Gt over the past century, equivalent to 0.68 mm global sea level rise, 51% of which occurred since 2003 alone. Dynamic thinning from ice front retreat is responsible for 88% of mass change since 1933, with short‐term ice front variations having minimal impact on centennial mass loss. Compared to earlier studies, our findings suggest that KG lost 59% (or 301 Gt) less mass over the century than previously thought. Plain Language Summary: Kangerlussuaq Glacier (KG) is a primary source of mass loss from the central‐eastern sector of the Greenland Ice Sheet. Despite various efforts, there is still disagreement on how much mass KG has lost over the past century and the reason for the mass loss. We used computer models and climate data to determine that the glacier has lost 285 billion metric tons of ice over the last 100 years. That is enough to raise global sea levels by about two‐thirds of a millimeter. Over half of this ice loss has happened in the last 20 years, and the rates of mass loss in the past two decades were significantly higher than for most of the last century. While the ice front of the glacier can retreat without losing mass, if the snowfall is significant enough, we found that most ice loss was related to the glacier retreating. This new estimate of ice loss is 59% lower than previous studies suggested, showing that the glacier's decline is less severe than we thought. Key Points: Dynamic thinning due to the retreat of the ice front explains 88% of the mass loss since 1933Short‐term variability in the ice front has a lesser impact on the mass balance on centennial time scalesKangerlussuaq Glacier lost 59% (or 301 Gt) less mass over the century than previously thought [ABSTRACT FROM AUTHOR]

The Baltic Sea basins, some of which only submerged in the mid-Holocene, preserve Stone Age structures that did not survive on land. Yet, the discovery of these features is challenging and requires cross-disciplinary approaches between archeology and marine geosciences. Here, we combine shipborne and autonomousunderwater vehicle hydroacoustic data with up to a centimeter range resolution, sedimentological samples, and optical images to explore a Stone Age megastructure located in 21 m water depth in the Bay of Mecklenburg, Germany. The structure is made of 1,673 individual stones which are usually less than 1 m in height, placed side by side over a distance of 971 m in a way that argues against a natural origin by glacial transport or ice push ridges. Running adjacent to the sunken shoreline of a paleolake (or bog), whose youngest phase was dated to 9,143 ±36 ka B.P., the stonewall was likely used for hunting the Eurasian reindeer (Rangifer tarandus) during the Younger Dryas or early Pre-Boreal. It was built by hunter-gatherer groups that roamed the region after the retreat of the Weichselian Ice Sheet. Comparable Stone Age megastructures have become known worldwide in recent times but are almost unknown in Europe. The site represents one of the oldest documented man-made hunting structures on Earth, and ranges among the largest known Stone Age structure in Europe. It will become important for understanding subsistence strategies, mobility patterns, and inspire discussions concerning the territorial development in the Western Baltic Sea region. [ABSTRACT FROM AUTHOR]

The timing of the initial peopling of the Americas is unresolved. Because the archaeological record necessitates discussion of human entry from Beringia into southern North America during the last glaciation, addressing this problem routinely involves evaluating environmental parameters then targeting areas suitable for human settlement. Vertebrate remains indicate landscape quality and are a key dataset for assessing coastal migration theories and the viability of coastal routes. Here, radiocarbon dates on vertebrate specimens and archaeological sites are calibrated to document species occurrences and the ages of human settlements across the western expansion and decay of the Cordilleran Ice Sheet (CIS) during the Late Wisconsin Fraser Glaciation in four subregions of the north Pacific coast of North America. The results show archaeological sites occur after glacial maxima and are generally consistent with the age of other securely dated earliest sites in southern North America. They also highlight gaps in the vertebrate chronologies around CIS maxima in each of the subregions that point to species redistributions and extirpations and signal times of low potential for human settlement and subsistence in a key portion of the proposed coastal migration route. This study, therefore, defines new age constraints for human coastal migration theories in the peopling of the Americas debate. [ABSTRACT FROM AUTHOR]

Ice chemistry in the dense, cold interstellar medium (ISM) is probably responsible for the formation of interstellar complex organic molecules (COMs). Recent laboratory experiments performed at T ∼ 4 K have shown that irradiation of CO:N2 ice samples analog to the CO-rich interstellar ice layer can contribute to the formation of COMs when H2 molecules are present. We have tested this organic chemistry under a broader range of conditions relevant to the interior of dense clouds by irradiating CO:15N2:H2 ice samples with 2 keV electrons in the 4–15 K temperature range. The H2 ice abundance depended on both, the ice formation temperature and the thermal evolution of the samples. Formation of H-bearing organics such as formaldehyde (H2CO), ketene (C2H2O), and isocyanic acid (H15NCO) was observed upon irradiation of ice samples formed at temperatures up to 10 K, and also in ices formed at 6 K and subsequently warmed up and irradiated at temperatures up to 15 K. These results suggest that a fraction of the H2 molecules in dense cloud interiors might be entrapped in the CO-rich layer of interstellar ice mantles, and that energetic processing of this layer could entail an additional contribution to the formation of COMs in the coldest regions of the ISM. [ABSTRACT FROM AUTHOR]

The Southern Ocean plays a major role in controlling the evolution of Antarctic glaciers and in turn their impact on sea level rise. We present the Southern Ocean high‐resolution (SOhi) simulation of the MITgcm ocean model to reproduce ice‐ocean interaction at 1/24° around Antarctica, including all ice shelf cavities and oceanic tides. We evaluate the model accuracy on the continental shelf using Marine Mammals Exploring the Oceans Pole to Pole data and compare the results with three other MITgcm ocean models (ECCO4, SOSE, and LLC4320) and the ISMIP6 temperature reconstruction. Below 400 m, all the models exhibit a warm bias on the continental shelf, but the bias is reduced in the high‐resolution simulations. We hypothesize some of the bias is due to an overestimation of sea ice cover, which reduces heat loss to the atmosphere. Both high‐resolution and accurate bathymetry are required to improve model accuracy around Antarctica. Plain Language Summary: Warm water from the Southern Ocean melts the glaciers and ice shelves around the Antarctic margin, leading to glacier de‐stabilization, and sea level rise. We present the Southern Ocean high‐resolution (SOhi) model to better represent ocean circulation and ice‐ocean interaction around Antarctica. We assess the accuracy of SOhi with in situ data from marine mammals and compare the results with three other ocean model simulations and to a baseline reference. All model results are slightly too warm on the continental shelf, but the higher‐resolution models yield colder waters in better agreement with observations. We attribute the warm bias to an overestimation of the sea ice cover in the ocean models. An improved bathymetry also significantly improves model accuracy in Antarctica. Key Points: High‐resolution ocean models with more complete physics are in better agreement with in situ ocean data than coarser resolution modelsAccurate bathymetry is essential to capture circulation pathways and warm water intrusions on the Antarctic continental shelfHigh‐resolution ocean models may remain too warm on the continental shelf because they over‐predict the sea ice cover [ABSTRACT FROM AUTHOR]

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

Changes in grain size of two firn (density from ∼550 to ∼820–840 kg m−3) samples, extracted at Summit Greenland during their stress relaxation over 3 days were observed using optical micrographs. These changes were confirmed by both 3-D microstructural reconstruction images and plots of microstructural parameters vs. time, viz., the grain size increased with the decrease of pore size, the specific surface area, and the index of prevalent ice curvature. Building on studies of both the viscoelastic behaviour of firn deformation and the measured changes in grain size, a quadratic-based model is constructed to describe the evolution of grain size during the stress relaxation stage, where the grain growth is in relation to the microstructure, the relaxation time, and the threshold stress (an equilibrium residual stress at the grain size maximum, which forces the grain growth before the arrival of the grain size maximum). This model can be scaled up from laboratory samples to the glaciers and ice sheets, e.g. the time at the grain size maximum spanning across days to thousands of days, even to a geological age. In addition to the firn samples which have undergone the stress relaxation prior to laboratory tests, especially sensitive to the effect of grain size, should be calibrated, this work also sheds light on learning more about the mechanical behaviours and changes in grain size during the deformation of firn or other porous materials under interrupted or cycle load, particularly from the stress relaxation, irrespective of the compression, tension, or shear. [ABSTRACT FROM AUTHOR]

[Display omitted] Understanding the impact of meltwater discharge during the final stage of the Laurentide Ice Sheet (LIS) has important implications for predicting sea level rise and climate change. Here we present a high-resolution ice-core isotopic record from the central Tibetan Plateau (TP), where the climate is sensitive to the meltwater forcing, and explore possible signals of the climate response to potential LIS meltwater discharges in the early to mid-Holocene. The record shows four abrupt large fluctuations during the 7–9 ka BP (kiloannum before present), reflecting large shifts of the mid-latitude westerlies and the Indian summer monsoon (ISM) over this period, and they corresponded to possible LIS freshwater events documented in other paleoclimate records. Our study suggests that multiple rapid meltwater discharge events might have occurred during the final stage of LIS. The finding implies the possibility of rapid sea level rise and unstable climate in the transition zone between the mid-latitude westerlies and the ISM due to fast polar ice retreat under the anthropogenic global warming. [ABSTRACT FROM AUTHOR]