Laura A. Stevens

Supraglacial lakes on the Greenland Ice Sheet drain through physically distinct pathways: hydrofracture, moulins, lateral stream routing, and crevasse-fields. Each drainage mechanism carries unique implications for ice sheet dynamics. Existing automated classifications reduce each lake’s drainage behavior to a time-series of scalar values representing the observed water surface-area and classify each lake based on drainage rate (e.g., rapid vs. slow). This scalar reduction conflates physically different drainage mechanisms, which can only be determined through consideration of full spatio-temporal tracking. Here we introduce a human-benchmarked, machine learning-ready benchmark dataset that pairs full Sentinel-2 multispectral satellite imagery time series with human-expert-labels assigned for N = 1679 supraglacial lakes in the central-west basin of the Greenland Ice Sheet during the 2018 (n = 679) and 2019 (n = 1000) melt seasons. The dataset is formatted as per-lake CF-1.8 NetCDF files each containing: six Sentinel-2 reflectance bands at 10 meter spatial resolution and daily cadence over the 153 day melt season (1 May to 30 September); a per-pixel binary cloud mask; co-registered lake water masks (both static and dynamic); and the human-assigned drainage classification labels. We accompany the dataset with a baseline deep learning classifier, demonstrating the utility of the dataset both in deep learning workflows and in extending lake drainage classification from rate-based to mechanism-based. The dataset is released through the Stanford Digital Repository under a CC BY 4.0 license, and the accompanying open-source sat-tile-stack preprocessing software under an MIT license.

Drainage of supraglacial lakes via hydro-fracture is widely argued to be a mechanism for destabilization of grounded ice sheets under climate-warming scenarios because it may accelerate surface meltwater access to the ice-sheet bed. Progress in interrogating this hypothesis has been hindered by the lack of regional observations of hydro-fracture event occurrence, and the lack of observations of regional ice-sheet response to hydro-fracture events. Here, we remedy both deficiencies using a 22-station Global Navigation Satellite System array to discern inter-lake, hydro-fracture-event triggering potential between lakes spanning the mid-to-upper Greenland Ice Sheet ablation zone. In four separate instances, multiple lake hydro-fracture events occur close in time at similar elevations; meanwhile, strain rates across higher-elevation lake basins are unperturbed. Our findings support a simple model for the inland progression of surface-to-bed meltwater pathways beneath lakes: pathway initiation migrates alongside advancing surface melt, but is not accelerated by drainage activity at distant, lower-elevation lakes.

Cryospheric retreat associated with deglaciation and permafrost thaw exposes previously stable carbon reservoirs to active biogeochemical cycling. While substantial effort has focused on constraining greenhouse gas emissions from thawing soil organic matter, many cryospheric environments also host large carbon stocks within bedrock and regolith, whose contribution to carbon-climate feedbacks remains poorly quantified. Mobilisation of these carbon stocks can enhance CO2 release to the atmosphere via an acceleration of sulphide mineral and rock-derived organic carbon oxidation. Multi-decadal increases in riverine sulphate concentrations across the Arctic, together with growing reports of “rusting rivers”, provide compelling evidence for a direct link between permafrost degradation and enhanced oxidative weathering. However, the magnitude, spatial distribution, and climatic significance of this feedback remain poorly constrained.Here, we quantify the impact of cryospheric retreat on oxidative weathering through a field investigation spanning five valleys in Svalbard underlain by contrasting lithologies. Surface water geochemistry and discharge measurements collected from glacier termini to valley bottoms reveal that CO2 release from geological carbon stocks is sustained—and in some cases amplified—downstream of glacier margins. These observations indicate that enhanced oxidative weathering is not confined to subglacial environments but persists across regions subject to paraglacial processes. This improved spatial understanding of oxidative weathering is used to inform a forward model of carbon release from geological reservoirs resulting from permafrost thaw and and ice-sheet retreat, focused on the last deglaciation. Together, our results demonstrate that cryospheric retreat can enhance carbon release from geological reservoirs, representing a previously under-constrained positive feedback on the Earth system with implications for both past climate transitions and ongoing cryospheric retreat.

On the Greenland Ice Sheet, drainage of supraglacial lakes via hydrofracture can transport substantial volumes of meltwater into the subglacial drainage system within hours, generating subglacial “blisters” that transiently accelerate adjacent ice flow. The blisters subsequently dissipate, with their thickness diminishing as water spreads laterally, propagates, and leaks into adjacent components of the subglacial drainage system. Although field observations reveal surface-elevation and velocity anomalies associated with blisters, existing subglacial hydrology models—typically comprised of linked cavities and channels—do not include the physics of elastic ice uplift, and therefore cannot reproduce the observed flood propagation or ice-flow anomalies.We present a modelling framework that integrates elastic ice uplift with an established subglacial hydrology model of linked cavities and channels to model subglacial blisters and their interactions with the surrounding hydrological network. We further couple this framework to a depth-integrated ice-flow model, and simulate the resulting, transient surface-uplift and velocity anomalies following lake drainages. This unified model provides a new tool for interpreting remote-sensing and in situ observations of drainage events on short timescales, and for assessing how lake-drainage processes influence ice dynamics and the long-term mass balance of the Greenland Ice Sheet.

Continuous monitoring of Antarctic ice shelf fronts is essential for understanding ice sheet dynamics, detecting iceberg calving events, supporting operational logistics, and generating up-to-date continental maps. However, the automated and continuous delineation of ice shelf fronts has been held back by a lack of suitable training data for deep learning models. We present Shelf-Bench, a comprehensive benchmark dataset comprising 161 manually annotated SAR scenes from three satellite sensors (ERS, Envisat, and Sentinel-1), providing spatial coverage of the Antarctic coastline with multi-temporal seasonal acquisitions spanning 1992–2021. The dataset features manually delineated masks paired with pre-processed imagery at moderate spatial resolution. Through complexity analysis, we characterize delineation challenges, including fast ice, crevassed surfaces, dense iceberg mélange, and limited spatial context. We evaluate five state-of-the-art semantic segmentation architectures, establishing baseline performance metrics. Baseline models showed strongly contrasting behaviour on Shelf-Bench: architectures that achieved higher pixel-wise accuracy tended to produce larger boundary errors, while models with better geometric precision obtained lower semantic scores. This trade-off indicates that the dataset jointly challenges ice-ocean classification and fine-scale calving front delineation, revealing complementary challenges which make it a profound benchmark for automated ice front mapping. By providing this open-access, standardized benchmark, Shelf-Bench enables accelerated development of deep learning methodologies for automated Antarctic coastline detection and supports continuous monitoring across current and future SAR satellite missions. The Shelf-Bench dataset is available at https://doi.org/10.5281/zenodo.17610870.

The transport of meltwater from the surface to the bed of the Greenland Ice Sheet is well understood to result in elevated surface velocities, although this relationship remains poorly resolved on a seasonal scale. Transient speed-ups associated with supraglacial lake drainages, which generally occur in the early-to-mid summer melt season, have been studied in detail. However, the connection between basal hydrology and ice dynamics is less well understood in the late melt season, after most lakes have ceased draining and meltwater input to the bed is through widely distributed moulins. Here, we use a Global Positioning System (GPS) array to investigate transient speed-up events in response to runoff across the 2011 and 2012 melt seasons and use these data to infer the evolution of subglacial conditions beneath the ice sheet in western Greenland. We find no relationship between the magnitude of runoff and the amplitude of speed-up events; we do observe a general trend of increasing velocity responses and decreasing variability in the velocity response across the GPS array as the melt season progresses. Early-season transient speed-ups (frequently associated with lake drainages) produce highly variable speed-up and pronounced uplift across the array. The variability across the array during a lake drainage corresponds with the bedrock topography and persists on annual timescales. By contrast, late-season melt events produce longer, higher amplitude, and more uniform velocity responses, but do not produce large or coherent uplift patterns. We interpret our results to imply that by the late melt season, most subglacial channels and/or connective flow pathways between cavities are closing or have closed, sharply lowering basal transmissivity. At the same time, moulins formed throughout the melt season remain open, producing pervasive and widely distributed surface-to-bed pathways. The result is that small magnitude, late-season melt events can rapidly supply meltwater to the bed and overwhelm the subglacial system, decreasing frictional coupling. This late-season response contrasts with early-season lake drainage events when surface-to-bed pathways are not yet open, and therefore, similarly small magnitude melt events do not have the same impact. Finally, we show that due to their extended duration and amplitude, late-season melt events accommodate a larger fraction of the annual ice motion than early-season lake drainages but their net influence on ice-sheet motion remains small (2 %–3 % of annual displacement).

Drainage of supraglacial lakes to the ice-sheet bed can occur when a hydrofracture propagates downward, driven by the weight of the water in the lake. For supraglacial lakes in the grounding zones of Antarctic glaciers, drainage mechanics are complicated by the glaciers' proximity to the grounding line. Recently, a series of supraglacial lake drainage events through hydrofractures were observed in the Amery Ice Shelf grounding zone, East Antarctica. The lake depth at drainage varied considerably between events, raising questions about the mechanisms that induce hydrofractures even at low lake depth. Here, we use a modelling approach to investigate the contribution of tidally driven flexure to hydrofracture propagation in the grounding zone. We model the viscoelastic response of a laterally unconfined marine ice sheet to tides, the tidally induced stress, and the contribution of this stress to hydrofracture propagation. A sensitivity analysis is used to explore the dependence of viscoelastic grounding-line dynamics on the material properties of ice and local bedrock bathymetry. We propose a model-based criterion that predicts hydrofracture and supraglacial lake drainage as a function of daily maximum tidal amplitude and pre-drainage lake depth in laterally unconfined grounding zones. Although lateral confinement may contribute to the dynamics of lake drainage at Amery, our model predictions are consistent with observations of hydrofracture events from this grounding zone.

The transport of meltwater from the surface to the bed of the Greenland Ice Sheet is well understood to result in elevated surface velocities, although this relationship remains poorly resolved on a seasonal scale. Transient speed-ups associated with supraglacial lake drainages, which generally occur in the early- to mid-summer melt season, have been studied in detail. However, the connection between basal hydrology and ice dynamics is less well understood in the late melt season, after most lakes have ceased draining and meltwater input to the bed is through widely distributed moulins. Here, we use a Global Positioning System (GPS) array to investigate transient speed-up events in response to runoff across the 2011 and 2012 melt seasons and use these data to infer the evolution of subglacial conditions beneath the ice sheet in western Greenland. We find no relationship between the magnitude of runoff and the amplitude of speed-up events; we do observe a general trend of increasing velocity responses and decreasing variability in the velocity response across the GPS array as the melt season progresses. Early-season velocity transients (frequently associated with lake drainages) produce highly variable speed-up and pronounced uplift across the array. Late-season events produce longer, higher amplitude, and more uniform velocity responses, but do not produce large or coherent uplift patterns. We interpret our results to imply that by the late melt season, most subglacial channels and/or connective flow pathways between cavities are closing or have closed, sharply lowering basal transmissivity. At the same time, moulins formed throughout the melt season remain open, producing pervasive and widely distributed surface-to-bed pathways. The result is that small magnitude runoff events can rapidly supply meltwater to the bed and overwhelm the subglacial system, decreasing frictional coupling. This response contrasts with early-season runoff events when surface-to-bed pathways are not yet open, and therefore, similarly small magnitude runoff events do not have the same impact. Finally, we show that due to their extended duration and amplitude, late-season events accommodate a larger fraction of the annual ice motion than lake drainages but their net influence on ice sheet motion remains small (2–3 % of annual displacement).

The transport of meltwater from the surface to the bed of the Greenland Ice Sheet is well understood to result in elevated surface velocities, although this relationship remains poorly resolved on a seasonal scale. Transient speed-ups associated with supraglacial lake drainages, which generally occur in the early- to mid-summer melt season, have been studied in detail. However, the connection between basal hydrology and ice dynamics is less well understood in the late melt season, after most lakes have ceased draining and meltwater input to the bed is through widely distributed moulins. Here, we use a Global Positioning System (GPS) array to investigate transient speed-up events in response to runoff across the 2011 and 2012 melt seasons and use these data to infer the evolution of subglacial conditions beneath the ice sheet in western Greenland. We find no relationship between the magnitude of runoff and the amplitude of speed-up events; we do observe a general trend of increasing velocity responses and decreasing variability in the velocity response across the GPS array as the melt season progresses. Early-season velocity transients (frequently associated with lake drainages) produce highly variable speed-up and pronounced uplift across the array. Late-season events produce longer, higher amplitude, and more uniform velocity responses, but do not produce large or coherent uplift patterns. We interpret our results to imply that by the late melt season, most subglacial channels and/or connective flow pathways between cavities are closing or have closed, sharply lowering basal transmissivity. At the same time, moulins formed throughout the melt season remain open, producing pervasive and widely distributed surface-to-bed pathways. The result is that small magnitude runoff events can rapidly supply meltwater to the bed and overwhelm the subglacial system, decreasing frictional coupling. This response contrasts with early-season runoff events when surface-to-bed pathways are not yet open, and therefore, similarly small magnitude runoff events do not have the same impact. Finally, we show that due to their extended duration and amplitude, late-season events accommodate a larger fraction of the annual ice motion than lake drainages but their net influence on ice sheet motion remains small (2–3 % of annual displacement).

The hydrofracture-driven drainage of supraglacial lakes rapidly introduces large volumes of meltwater to the ice-sheet bed, influencing ice-sheet dynamics on multiple timescales. Immediate ice deformation mainly arises from three sources: the opening of the hydrofracture crack, separation of the ice from the bed, and additional slip at the bed. An understanding of the ice response to drainage requires knowledge of these spatially and temporally varying sources, ideally constrained by observations obtained both on the ice surface and within the ice column. Previous work examining ice dynamics during supraglacial lake drainage relies on ice-surface observations only: aerial and satellite imagery, Global Navigation Satellite System (GNSS) data, and pressure-sensor records from draining lakes. We deployed three autonomous phase-sensitive radio echo sounders (ApRES) near a set of three supraglacial lakes at ~950 m elevation, in the mid-ablation zone of the western Greenland Ice Sheet, to record englacial deformation during lake drainage. The ApRES stations were embedded within a geophysical network including GNSS stations, air-temperature sensors, and a lake pressure logger, and were configured to make repeat measurements every 15 minutes from May 2022 to September 2023. In 2022, two of the lakes adjacent to the ApRES stations drained abruptly via hydrofracture, exhibiting characteristics of inter-lake static-stress triggering; in 2023, all three lakes drained in a similar manner. We demonstrate the capability of the ApRES system to provide estimates of the time-varying change in englacial vertical strain rate that accompanies hydrofracture-driven lake drainage, despite the short durations of the drainages and the wet and variable ice surface that is inevitable during the melt season. At station locations ~1 km away from the hydrofracture cracks, we observe vertical strain rates of magnitude up to ~1 yr-1 during lake drainages, averaged over the top 500 m of ice and over 15 minutes; background vertical strain rates have magnitudes of ~10-3 yr-1 at these locations. As a first step towards incorporating these englacial observations of deformation as constraints on an inverse problem to obtain the spatial and temporal history of the deformation source, we compare the englacial observations to predictions from a source model constructed using only GNSS data. Following previous work, we use an elastic dislocation model and invert the GNSS data to obtain time- and space-varying estimates of the opening of the hydrofracture crack, opening at the ice-bed interface, and excess slip at the bed during lake drainage. We then use this model to predict changes in strain in the ice under the ApRES stations, and compare the resulting timeseries with our observations. We evaluate the additional sensitivity provided by our englacial observations to the deformation source.