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The magnitude and azimuth of horizontal ice flow at Camp Century, Greenland have been measured several times since 1963. Here, we provide a further two independent measurements over the 2017–21 period. Our consensus estimate of horizontal ice flow from four independent satellite-positioning solutions is 3.65 ± 0.13 m a−1 at an azimuth of 236 ± 2°. A portion of the small, but significant, differences in ice velocity and azimuth reported between studies likely results from spatial gradients in ice flow. This highlights the importance of restricting inter-study comparisons of ice flow estimates to measurements surveyed within a horizontal distance of one ice thickness from each other. We suggest that ice flow at Camp Century is stable on seasonal to multi-decadal timescales. The airborne and satellite laser altimetry record indicates an ice thickening trend of 1.1 ± 0.3 cm a−1 since 1994. This thickening trend is qualitatively consistent with previously inferred ongoing millennial-scale ice thickening at Camp Century. The ice flow divide immediately north of Camp Century may now be migrating southward, although the reasons for this divide migration are poorly understood. The Camp Century flowlines presently terminate in the vicinity of Innaqqissorsuup Oqquani Sermeq (Gade Gletsjer) on the Melville Bay coast.

There is currently poor scientific agreement 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 a diversity of opinion in the subglacial geothermal heat flow basal boundary condition employed in different ice-flow models. Here, we employ seven Greenland geothermal heat flow maps in widespread use to 10,000-year spin ups of the Community Ice Sheet Model (CISM). We perform both a fully unconstrained transient spin up, as well as a nudged spin up that conforms to Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) protocol. 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, thawed-bedded ice-sheet area is consistently larger under unconstrained spin ups than nudged spin ups. Under the unconstrained spin up, thawed-bedded 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. This highlights the direct, and non-trivial, influence of choice of 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 to simulations employing a common heat flow map.

The Greenland ice sheet mass loss is one of the main sources of contemporary sea-level rise. The mass loss is primarily caused by surface melt and the resulting runoff. During the melt season, the ice sheet’s surface receives energy from sunlight absorption and sensible heating, which subsequently heats the subsurface snow and ice. The energy from the previous melt season can also enhance melting in the following summer as less heating is required to bring the snow and ice to the melting point. Subsurface temperatures are therefore both a result and a driver of the timing and magnitude of surface melt on the ice sheet. We present a dataset of more than 3900 measurements of ice, snow and firn temperature at 10 m depth across the Greenland ice sheet spanning the years from 1912 to 2022. We construct an artificial neural network (ANN) model that takes as input the ERA5 reanalysis monthly near-surface air temperature and snowfall for the 1954-2022 period and train it on our compilation of observed 10-meter temperature. We use our dataset and the ANN to evaluate three broadly used regional climate models (RACMO, MAR and HIRHAM). Our ANN model provides an unprecedented and observation-based description of the recent warming of the ice sheet’s near-surface and our evaluation of the three climate models highlights future development for the models. Overall, these findings improve our understanding of the ice sheet’s response to recent atmospheric warming and will help reduce uncertainties of ice sheet surface mass balance estimates.

The rise of satellite survey techniques over the last few decades has allowed more detailed measurement of ice flow velocities and directions. Although satellite measurements are generating ice-flow maps of increasingly higher resolution, both temporally and spatially, these records only span a period of less than two decades. During this time, however, ice dynamics have generally been dominated by anomalous changes. This makes it challenging to observe multi-decadal trends in glacier dynamics.In 1959, the Expédition Glaciologique Internationale Groenland (EGIG) surveys were launched in Central West Greenland. Stakes positions and elevations were surveyed East-West across the Greenland ice sheet between c. 70 and 72°N. The positions of these stakes were subsequently re-measured in 1967. We calculate changes in position between these precise surveys into ice flow velocity and direction during the 1959/67 periods. These calculations assess uncertainties in both ice flow magnitude and azimuth.This re-analysis is focused on 11 of the EGIG stakes located closest to Jakobshavn Isbræ, and is part of a present day effort to re-measure ice flow velocity and direction. Comparison of the 1959/1967 to current day observations shows an increase in velocity between the two periods ranging from approximately 8 to 15% increase. A subtle but systematic northward shift in azimuth is observed with the increase in values ranging from approximately 0.9 to 1.9%. These in situ observations offer a glimpse into the state of ice flow before the satellite era and provide a better understanding of trends in the form and flow of the Greenland Ice Sheet.

In the past two decades, mass loss from the Greenland ice sheet has accelerated, partly due to speedup of glaciers. However, uncertainty in speed derived from satellite products hampers 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 historical locations first measured in 1959. Here, we show ice velocities have increased 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 suggest 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 a change in local driving stress. This mechanism, if included in simulations may improve projections of future ice loss.

Here, we present a compilation of 85 ice temperature profiles from 79 boreholes from the Greenland Ice Sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Only 25 profiles (32 %) were previously available in open-access data repositories. The remaining 54 profiles (68 %) are being made digitally available here for the first time. These newly available profiles, which are associated with pre-2010 boreholes, have been submitted by community members or digitized from published graphics and/or data tables. All 85 profiles are now made available in both absolute (meters) and normalized (0 to 1 ice thickness) depth scales, and are accompanied by extensive metadata. This metadata includes a transparent description of data provenance. The ice temperature profiles span 70 years, with the earliest profile being from 1950 at Camp VI, West Greenland. To highlight the value of this database in evaluating ice flow simulations, we compare the ice temperature profiles from the Greenland Ice Sheet with an ice flow simulation by the Parallel Ice Sheet Model (PISM). We find a cold bias in modeled near-surface ice temperatures within the ablation area, a warm bias in modeled basal ice temperatures at inland cold-bedded sites, and an apparent underestimation of deformational heating in high-strain settings. These biases provide process-level insight on simulated ice temperatures., The Cryosphere Discussions, ISSN:1994-0432, ISSN:1994-0440

We compile and analyze all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This database also includes 129 new sites, which have not been previously reported by the IHFC. These new sites consist of 88 offshore measurements and 41 onshore measurements, of which 24 are subglacial. We employ machine learning to synthesize these in situ measurements into a gridded geothermal heat flow model that is consistent across both continental and marine areas in and around Greenland. This model has a native horizontal resolution of 55 km. In comparison to five existing Greenland geothermal heat flow models, our model has the lowest mean geothermal heat flow for Greenland onshore areas. Our modeled heat flow in central North Greenland is highly sensitive to whether the NGRIP (North GReenland Ice core Project) elevated heat flow anomaly is included in the training dataset. Our model's most distinctive spatial feature is pronounced low geothermal heat flow (

The Greenland Ice Sheet is the largest land ice contributor to sea level rise. This will continue in the future but at an uncertain rate and observational estimates are limited to the last few decades. Understanding the long-term glacier response to external forcing is key to improving projections. Here we use historical photographs to calculate ice loss from 1880–2012 for Jakobshavn, Helheim, and Kangerlussuaq glacier. We estimate ice loss corresponding to a sea level rise of 8.1 ± 1.1 millimetres from these three glaciers. Projections of mass loss for these glaciers, using the worst-case scenario, Representative Concentration Pathways 8.5, suggest a sea level contribution of 9.1–14.9 mm by 2100. RCP8.5 implies an additional global temperature increase of 3.7 °C by 2100, approximately four times larger than that which has taken place since 1880. We infer that projections forced by RCP8.5 underestimate glacier mass loss which could exceed this worst-case scenario., The Greenland Ice Sheet is the largest land ice contributor to sea level rise and understanding the long-term glacier response to external forcing is key to improved projections. Here the authors show Greenland’s three largest outlet glaciers will likely exceed current worst-case scenario

The Greenland Ice Sheet is the largest land ice contributor to sea level rise. This will continue in the future but at an uncertain rate and observational estimates are limited to the last few decades. Understanding the long-term glacier response to external forcing is key to improving projections. Here we use historical photographs to calculate ice loss from 1880–2012 for Jakobshavn, Helheim, and Kangerlussuaq glacier. We estimate ice loss corresponding to a sea level rise of 8.1 ± 1.1 millimetres from these three glaciers. Projections of mass loss for these glaciers, using the worst-case scenario, Representative Concentration Pathways 8.5, suggest a sea level contribution of 9.1–14.9 mm by 2100. RCP8.5 implies an additional global temperature increase of 3.7 °C by 2100, approximately four times larger than that which has taken place since 1880. We infer that projections forced by RCP8.5 underestimate glacier mass loss which could exceed this worst-case scenario.