Geothermal heat flow (GHF) influences ice sheet thermal conditions, affecting ice flow by sliding and deformation. However, GHF distribution under polar ice sheets remains poorly constrained, with few direct borehole-derived estimates and large discrepancies between glaciological and geophysical models caused by methodological differences and data limitations. As a result, many ice sheet models rely on uniform GHF estimates, ensemble averages or outdated fields that oversimplify reality. The choice of GHF product can lead to significantly different thermal conditions simulated at the ice-bed interface, which affects the projected evolution of ice sheets under climate warming. Therefore, we conducted an expert elicitation survey to identify the most suitable GHF fields for use as basal boundary conditions in ice sheet modelling, particularly for the Ice Sheet Modelling Intercomparison Project for CMIP7 (ISMIP7). GHF fields generally fall into three categories: (1) outdated due to improved data availability, (2) overly simplified parameterisations and (3) current and preferred. For GHF fields that rank highly in the survey, we discuss uncertainty and data dependency and guide their use in different applications. Finally, we recommend two Antarctic and one Greenlandic GHF fields for ISMIP7.

We present a new version of the PROMICE | GC-NET automatic weather station (AWS) data product, combining observations from two Greenland AWS networks; PROMICE and GC-NET. As of late 2025, the dataset integrates records from 52 active and historical AWS sites across the Greenland Ice Sheet, peripheral glaciers and land areas. This new version includes improvements in station design, sensor configuration, and data processing. Two primary station types are used: dual-boom masts in the accumulation area, and free-standing tripods with a single instrument boom in the ablation area. Data are processed with pypromice, an open-source Python package designed for standardized, transparent, and reproducible workflows, including calibration, filtering, variable derivation, and correction. The resulting products are distributed in CF-compliant NetCDF and CSV formats and include both measured and derived variables for applications in polar meteorology, climatology, and glaciology. Access is open under license CC-BY 4.0. A GitHub-based issue tracker (https://github.com/GEUS-Glaciology-and-Climate/PROMICE-AWS-data-issues, last access: 12 November 2025) supports community-driven quality control within a living data framework. The datasets are openly available at 10.22008/FK2/IW73UU .

Abstract. High-altitude lakes across High Mountain Asia (HMA) are one of the critical freshwater reservoirs and sensitive indicators of climate change due to their remote locations and limited human disturbances. This study presents continuous water level estimates for 232 lakes across HMA from 2010 to 2024 using CryoSat-2 and ICESat-2 data. We analyzed temporal and spatial variations and inter-mission consistency in the lake water level across HMA. Our results reveal an overall increasing trend (median rate: +0.1 ± 0.01 m yr−1), with 77 % of lakes experiencing rising levels and 91 % exhibiting statistically significant trends. We find a substantial regional heterogeneity with the Tibetan Plateau contributing dominantly to regional increase (0.07 ± 0.001 m yr−1), while Himalayan lakes show persistent decline (0.04 ± 0.001 m yr−1). Water level times series observed with the satellite altimetry missions CryoSat-2 and ICESat-2 intercomparison demonstrates strong consistency (80 % sign agreement, p = 0.013). Lake catchment scale analysis identifies precipitation as the dominant deriver of lakes water level variability (r = 0.42, p < 0.001), whereas lakes in glaciated catchments exhibit weak climate correlations despite significant increases in temperature, indicating nonlinear cryosphere buffering. We find systematic relationships between lake characteristics (area, elevation) and increasing water levels, with larger lakes generally showing more rapid growth. The contrasting hydrological responses with continued rising water levels in cryosphere influenced lakes and accelerating declines in precipitation sensitive lakes in Himalaya highlight divergent lake hydrological regimes. These findings underscore the critical importance of regional differentiation in understanding lake water storage changes and informing climate adaptation strategies for population vulnerable to these changes in the regions.

Outlet glaciers of the Greenland Ice Sheet typically undergo a seasonal cycle in ice flow, yet the magnitude and timing of peak annual velocities vary substantially among glacier systems, across years, and with distance away from the terminus. At tidewater glaciers, this variability reflects mainly the competing influences of surface meltwater-driven basal lubrication and flexural perturbations associated with calving-front dynamics. Because observations alone cannot readily separate these processes, we develop a physics-based framework that integrates ice-flow simulations with high-resolution surface velocity observations to decompose seasonal ice motion into basal and frontal components.We apply this approach to 61 tidewater glacier basins in western Greenland and show that seasonal velocity variations are primarily controlled by evolving basal hydrologic conditions. Frontal perturbations nonetheless exert a secondary but persistent influence on seasonal ice flow. Near glacier termini, mixed basal–frontal control occurs 49.6–62.3% of the time, and although the influence of frontal forcing generally diminishes inland, it can extend to elevations of up to 2000 metres above sea level at fast-flowing glaciers such as Sermeq Kujalleq (Jakobshavn Isbræ). Our method further isolates signals that are subdued in raw velocity observations and closer aligned with expected patterns of seasonal basal drainage development. Importantly, results from three independent transient model configurations demonstrate that our conclusions are robust to the choice of sliding law, with consistent identification of the dominant controlling process in 97.1% of cases. We therefore propose that this framework provides a reliable basis for process-level interpretation of seasonal ice-flow variability across Greenland.

Geothermal heat flow (GHF) plays a fundamental role in regulating basal thermal conditions of ice sheets, influencing basal sliding, internal deformation, and lithospheric rheology. Despite its importance, GHF in polar regions remains poorly constrained due to the scarcity of borehole measurements and substantial divergence among existing geophysical and glaciological estimates. These discrepancies stem from differences in methodology, data availability, and underlying assumptions, leading many ice sheet models to rely on spatially uniform values, ensemble means, or legacy products that inadequately represent spatial variability. We review all available continent-wide GHF fields, analysing their methodologies and data sources, and provide recommendations on their use. GHF fields generally fall into three categories: (1) outdated due to improved data availability, (2) overly simplified parametrization, and (3) preferred fields. To further assess applicability, we conducted an online expert elicitation survey to identify the most suitable fields for ice sheet modeling, particularly for ISMIP7. For preferred fields, we discuss uncertainty and data dependency to guide their use in different applications.In Antarctica, all fields agree on the broad division between low heat flow in East and higher heat flow in West Antarctica, though spatial patterns vary. Preferred fields serve as a baseline for local studies, which can incorporate additional datasets like magnetic depth estimates or regional geological constraints. In Greenland, uncertainty is particularly high at NGRIP, where estimation and observations are difficult to reconcile. Local heterogeneity impacts heat flow observations in ways that regional fields cannot yet fully address. Nonetheless, recent estimates suggest low to moderate heat flow under the Greenland ice sheet, indicating that the Iceland hot spot has a limited impact, while subglacial geology plays a dominant role in controlling local variations.Results from the expert survey indicate broad support for multivariate, data-driven approaches that integrate geological and geophysical constraints, including recent fields by Stål et al. (2021), Lösing & Ebbing (2021), and Colgan et al. (2022). These methods are generally regarded as better equipped to use all existing information, represent spatial heterogeneity, provide uncertainty information, and remain consistent with inferred basal conditions. Importantly, the survey captures, as objectively as possible, the reasons why a given GHF field is a good choice as a representation to be used for ice sheet modelling, and hence, model intercomparisons.Continued progress in GHF estimation will require both methodological innovation and improved data coverage. Integrating machine learning with physics-based models, fostering cross-disciplinary data integration, and increasing spatial resolution are key priorities. In the context of ISMIP7, we recommend moving beyond outdated or purely interpolated GHF products and adopting modern, data-driven fields that better reflect current understanding.

In 2016, we established the first network of GNSS stations on the Northeast Greenland Ice Stream (NEGIS), enabling continuous monitoring of ice flow motion and surface elevation changes. These stations have revealed both short-term variability and longer-term accelerations that propagate far inland from the terminus (Khan 2022; Khan 2024), highlighting the dynamic coupling between the glacier front and the interior of the ice sheet. Building on this effort, in 2024 we deployed four additional GNSS stations on Jakobshavn Isbræ, one of Greenland’s fastest-flowing outlet glaciers. All stations on both Jakobshavn and NEGIS are located along the main glacier trunks, spanning distances of ~20 to ~200 km from the terminus, thereby capturing spatial gradients in flow and deformation.The GNSS sites also enable direct validation of satellite-derived surface elevation products (ICESat-2 and CryoSat-2). Whereas satellite altimetry provides repeat measurements of ice-surface elevation once per month, GNSS observations deliver continuous, hourly records of both vertical and horizontal ice motion. This high temporal resolution allows us to resolve short-lived dynamic events, seasonal signals, and longer-term trends that are not detectable from spaceborne sensors alone. Together, these complementary datasets provide powerful constraints for improving ice-flow models and for assessing the future evolution and stability of the Greenland Ice Sheet.In addition, we apply GNSS interferometric reflectometry (GNSS-IR) to the ice-sheet environment, using reflected GNSS signals to infer changes in ice-surface height and physical properties such as roughness and snow accumulation. This technique adds a new observational dimension to the GNSS network, further enhancing its value for characterizing glacier–atmosphere interactions and surface processes.

Thermal springs are rare but diverse features of Greenland’s ice-free margins, with observed temperatures ranging from near freezing to over 60°C. Greenland’s thermal springs host distinctive biological communities, from thermophilic microbial mats to unique vascular plant assemblages, representing important Arctic biodiversity hotspots. They hold cultural, ecological and scientific importance, yet records are mostly scattered across historical literature, local knowledge and isolated field reports. Here, we present the first comprehensive review and quality-controlled geodatabase of Greenland’s thermal springs, compiled from more than a century of scientific and historical sources, botanical surveys, Greenlandic place names, satellite imagery and field observations. The present database contains entries for 382 individual spring localities, providing names, coordinates, geological setting, thermal characteristics and metadata on source reliability. We describe their geographic distribution, geological setting and possible heat sources, which include radiogenic decay, residual magmatic heat and exothermic chemical weathering. Besides a lack of recent visits and photo documentation of many thermal springs, this synthesis highlights substantial gaps in temperature, chemistry and discharge measurements, underlining the need for systematic sampling and community-based monitoring. The open access database offers a foundation for future interdisciplinary research, supports conservation planning and provides a baseline for assessing climate-driven changes in Greenland’s geothermal systems.

Communities dependent on snow and ice melt need to face escalating challenges due to glacier depletion, particularly in High Mountain Asia (HMA). Understanding glacier changes is thus crucial for addressing these impacts. Employing Ice, Cloud, and land Elevation Satellite (ICESat) and ICESat-2, we estimate glacier mass balance from 2003 to 2023 using three independent geodetic methods to reduce methodological biases. We find an acceleration in ice loss from 27.48 +/- 7.96 Gt a(-1) (2003-2009) to 36.58 +/- 8.08 Gt a(-1) (2018-2023). Mass loss is now evident at all elevations in several HMA regions, with few exceptions above 6000 m a.s.l. Climate data indicate that increased warming and reduced precipitation have intensified mass loss in recent years. These findings highlight a transition toward a widespread negative mass balance in the region. Increased glacier melt elevates the risk of seasonal water security and glacial hazards across HMA.

The surface elevation of the Greenland Ice Sheet is constantly changing due to the interplay between surface mass balance processes and ice dynamics, each exhibiting distinct spatiotemporal patterns. Here, we employ satellite and airborne altimetry data with fine spatial (1 km) and temporal (monthly) resolutions to document this spatiotemporal evolution from January 2003 to August 2023. To estimate elevation changes of the Greenland Ice Sheet (GIS), we utilize radar altimetry data from CryoSat-2 and EnviSat, laser altimetry data from the ICESat and ICESat-2, and laser altimetry data from NASA's Operation IceBridge Airborne Topographic Mapper. We produce continuous monthly ice surface elevation changes from January 2003 to August 2023 on a 1 km grid covering the entire GIS. We estimate cumulative ice loss of 4352 Gt +/- 315 Gt (12.1 +/- 0.9 mm sea level equivalent) during this period, excluding peripheral glaciers. Between 2003 and 2023, the ice sheet land-terminating margin underwent a significant cumulative thinning of several meters. Ocean-terminating glaciers exhibited thinning between 20-40 m, with Jakobshavn Isbr ae experiencing an exceptional thinning of nearly 70 m. This dataset of fine-resolution altimetry data in both space and time will support studies of ice mass loss and will be useful for GIS modeling. To validate our monthly mass changes of the Greenland ice sheet, we use mass change from satellite gravimetry and mass change from the input-output method. On multiannual timescales, there is a strong correlation between the time series, with R values ranging from 0.88 to 0.92 (10.5061/dryad.s4mw6m9dh, Khan et al., 2025)

Greenland and Antarctica's peripheral glaciers are an important but often overlooked element in the global sea-level rise budget. Here, we use satellite laser altimetry from ICESat and ICESat-2 to assess the mass loss from Greenland's and Antarctica's peripheral glaciers for three periods: February 2003 to October 2009, October 2009 to April 2018, and October 2018 to April 2023. Over these periods, Greenland's peripheral glacier mass loss has increased from 27.3 +/- 7.9 Gt yr-1 during 2003-2009, to 35.8 +/- 5.3 Gt yr-1 during 2018-2023. The ice loss from Antarctica's peripheral glaciers underwent a more complex change during this time, with a mass loss -4.2 +/- 1.3 Gt yr-1 during 2003-2009, sharply rising to -16.0 +/- 5.9 Gt yr-1 during 2009-2018, and subsequently declining to -9.0 +/- 0.7 Gt yr-1 during 2018-2023. This temporal pattern of mass loss is observed across all Antarctic regions. Notably, the Antarctic Peninsula experienced a mass loss of 2.6 +/- 3.1 Gt yr-1 during 2003-2009 followed by gains of 2.7 +/- 3.8 Gt yr-1 and 11.9 +/- 1.7 Gt yr-1 during 2009-2018 and 2018-2023, respectively. This shift toward mass gain during 2018-2023 can be attributed to exceptional levels of precipitation during the winters of 2019 and 2020. We conclude that increased snowfall played a crucial role in mitigating glacier mass loss during this later period. Overall, our findings show accelerating mass loss of Greenland and Antarctica's peripheral glaciers with complex variability, both spatially and temporally, with certain regions experiencing mass gains through increased snowfall.

The rapid demise of ice sheets and glaciers worldwide has increased the need for mass balance observations at a temporal and spatial resolution, where they can both help us understand the physical processes and also serve as validation or calibration for remote sensing data products or regional climate model output. Here we present the latest developments in measuring crucial components of the surface mass balance at automatic weather stations, including snow water equivalent, snow height in the vicinity of the station, sufficiently accurate transmitted position and elevation of the station, snow compaction and non-stake ice sheet ablation. Immediate access to the observations is key to certain applications, such as numerical weather forecasts. Hence, we also present the complications of providing near real-time data transmission and quality-checking as well as obstacles to a wider distribution on the WMO Global Telecommunication System (GTS).

We examine the feasibility of an overland motorised traverse from Pituffik to Greenland’s oldest ice outcrop in Warming Land, North Greenland. We assess a 778 km overland traverse that departs Pituffik via the Nunatarssuaq Take-Off Ramp, which is an alternative to the more frequently used, but more heavily crevassed, Thule Take-Off Ramp. The traverse route includes brief sea ice and primitive road conditions, each c. 4% of the route length, and a lengthy ice sheet segment (c. 92% of the route length). This study outlines challenges for each of these traverse segments, including primitive road conditions and snow cover, seasonality of extreme cold conditions (air temperatures below –30°C), seasonality of surface melting and softening (air temperatures above 0°C), sea-ice thickness and potential ridging hazards and ice dynamics and potential crevasse hazards. Ongoing work is required for annual vetting of the traverse route to ensure operational safety. The optimal operational window for such a traverse is departing Pituffik in mid-April and returning in mid-May. In comparison to aircraft-supported ice-sheet fieldwork, scientific traverses offer the opportunity for more intensive ground-based science, while significantly reducing carbon emissions. Based on previously reported traverse fuel consumptions, a ground traverse from Pituffik to Warming Land would use 90% less fuel than aircraft-supported fieldwork. This assessment underscores the potential for sustainable ground-based access to Greenland’s oldest ice outcrop and other science sites within the region.

Abstract Greenland's bedrock responds to ongoing ice loss with an elastic vertical land motion (VLM) that is measured by Greenland's Global Navigation Satellite System (GNSS) Network (GNET). The measured VLM also contains other contributions, including the long‐term viscoelastic response of the Earth to the deglaciation of the last glacial period. Greenland's ice sheet (GrIS) produces the most significant contribution to the total VLM. The contribution of peripheral glaciers (PGs) from both Greenland (GrPGs) and Arctic Canada (CanPGs) has not carefully been accounted for in previous GNSS analyses. This is a significant concern, since GNET stations are often closer to PGs than to the ice sheet. We find that, PGs produce significant elastic rebound, especially in North and East Greenland. Across these regions, the PGs produce up to 32% of the elastic rebound. For a few stations in the North, the VLM from PGs is larger than that due to the GrIS.

Glacier catchments, refer to the upstream area of an ice sheet that is being drained by a single glacier. Delineated catchments are used to study the mass balance of individual glaciers or conglomerates of glaciers. Single glacier basin mass balance studies allow us to gain an understanding of the controlling processes and monitor changes of individual glaciers. Such studies, however, are highly sensitive to how the surface mass balance collection area is delineated for comparison with the grounding line ice discharge. Frequently, catchments are assumed to be temporally invariant, which can impact studies of basin wide mass balance on longer time scales. We have explored variations in present day delineated area, and potential temporal variability, in the catchment of Sermeq Kujalleq, or Jakobshavn Isbræ, Greenland. Five observation based, ‘present day’ catchment delineations are evaluated along with delineations based on modeled surface velocities from a sixteen-member ensemble of ice-sheet models within the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). The ISMIP6 ensemble mean area was found to be ~5.4% larger than the mean of the observed catchments. Observed and modeled ensemble spreads were comparable, ±12.3% and ±15.4%. Hence, models are able to delineate the present day catchment with the same degree of uncertainty as observational methods. The ISMIP6 ensemble mean catchment area shows temporal variation, increasing ~4% from 2015-2100, primarily as the southern catchment boundary migrates southward. This is interpreted as Jakobshavn Isbræ exhibiting dynamic piracy, redirecting ice away from adjacent land terminating glaciers. Repeat velocity observations in the catchment suggest a recent acceleration in ice flow ~100 km inland from the terminus of Jakobshavn Isbræ. This observed acceleration is not believed to be attributable to changes in meltwater lubrication nor driving stress changes. Instead it is theorized that changes in the basal temperate ice layer could be the cause of the acceleration. The trend in simulated ensemble velocity and azimuth values over the 2015-2100 period is evaluated against trends from the recent velocity observations. The ISMIP6 ensemble is underestimating the observed regional acceleration, not fully capturing the deep inland dynamic response of the ice sheet to the recent climatic changes.

Knowledge of ice-sheet catchments is critical for mass-balance assessments, especially glacier- scale input-output budgets. This study explores variations in the catchment of Sermeq Kujalleq, or Jakobshavn Isbr empty set, Greenland. Six observation-based catchment delineations are evaluated along with a 16-member catchment ensemble calculated from ice-sheet models within the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). The ' present-day ' ISMIP6 ensemble mean area was found to be similar to 6.3% larger than the mean of the observed catchments. Ensemble spreads were comparable in size, +/- 12 . 3 % and +/- 15 . 4 % , suggesting models are able to delineate the present-day catchment with the same degree of uncertainty as observational methods. The mean catchment area of a 13-member ISMIP6 ensemble shows temporal variation, increasing similar to[2.7, 5.7, 9.1]% under three ocean forcing scenarios and a RCP8.5 projection based on one GCM from 2015 to 2100, primarily as the southern catchment boundary migrates southward. This is interpreted as Sermeq Kujalleq exhibiting dynamic piracy, re-directing ice away from adjacent land terminating glaciers. For mass-balance assessments, present-day catchment delineation is more important than capturing the temporal evolution of individual catchments. However, the modeled temporal changes in catchment area are potentially underestimated, as the models exhibit insufficient acceleration of inland ice flow.

There is currently poor scientific agreement on whether the ice–bed interface is frozen or thawed beneath approximately one third of the Greenland ice sheet. This disagreement in basal thermal state results, at least partly, from differences in the subglacial geothermal heat-flow basal boundary condition used in different ice-flow models. Here, we employ seven widely used Greenland geothermal heat-flow maps in 10 000-year spin-ups of the Community Ice Sheet Model (CISM). We perform two spin-ups: one nudged toward thickness observations and the other unconstrained. Across the seven heat-flow maps, and regardless of unconstrained or nudged spin-up, the spread in basal ice temperatures exceeds 10 ∘C over large areas of the ice–bed interface. For a given heat-flow map, the thawed-bed ice-sheet area is consistently larger under unconstrained spin-ups than nudged spin-ups. Under the unconstrained spin-up, thawed-bed area ranges from 33.5 % to 60.0 % across the seven heat-flow maps. Perhaps counterintuitively, the highest iceberg calving fluxes are associated with the lowest heat flows (and vice versa) for both unconstrained and nudged spin-ups. These results highlight the direct, and non-trivial, influence of the heat-flow boundary condition on the simulated equilibrium thermal state of the ice sheet. We suggest that future ice-flow model intercomparisons should employ a range of basal heat-flow maps, and limit direct intercomparisons with simulations using a common heat-flow map.

AbstractPresent 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.

AbstractIn the past two decades, mass loss from the Greenland ice sheet has accelerated, partly due to the speedup of glaciers. However, uncertainty in speed derived from satellite products hampers the detection of inland changes. In-situ measurements using stake surveys or GPS have lower uncertainties. To detect inland changes, we repeated in-situ measurements of ice-sheet surface velocities at 11 historical locations first measured in 1959, located upstream of Jakobshavn Isbræ, west Greenland. Here, we show ice velocities have increased by 5–15% across all deep inland sites. Several sites show a northward deflection of 3–4.5° in their flow azimuth. The recent appearance of a network of large transverse surface crevasses, bisecting historical overland traverse routes, may indicate a fundamental shift in local ice dynamics. We suggest that creep instability—a coincident warming and softening of near-bed ice layers—may explain recent acceleration and rotation, in the absence of an appreciable change in local driving stress.