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Greenland's main outlet glaciers have more than doubled their contribution to global sea level rise over the last decade. Recent work has shown that Greenland's mass loss is still increasing. Here we show that the ice loss, which has been well-documented over southern portions of Greenland, is now spreading up along the northwest coast, with this acceleration likely starting in late 2005. We support this with two lines of evidence. One is based on measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission, launched in March 2002. The other comes from continuous Global Positioning System (GPS) measurements from three long-term sites on bedrock adjacent to the ice sheet. The GRACE results provide a direct measure of mass loss averaged over scales of a few hundred km. The GPS data are used to monitor crustal uplift caused by ice mass loss close to the sites. The GRACE results can be used to predict crustal uplift, which can be compared with the GPS data. In addition to showing that the northwest ice sheet margin is now losing mass, the uplift results from both the GPS measurements and the GRACE predictions show rapid acceleration in southeast Greenland in late 2003, followed by a moderate deceleration in 2006. Because that latter deceleration is weak, southeast Greenland still appears to be losing ice mass at a much higher rate than it was prior to fall 2003. In a more general sense, the analysis described here demonstrates that GPS uplift measurements can be used in combination with GRACE mass estimates to provide a better understanding of ongoing Greenland mass loss; an analysis approach that will become increasingly useful as long time spans of data accumulate from the 51 permanent GPS stations recently deployed around the edge of the ice sheet as part of the Greenland GPS Network (GNET). Copyright © 2010 by the American Geophysical Union.

In Greenland, 87% of the glacierized area terminates in the ocean, but mass lost at the ice‐ocean interface, or frontal ablation, has not yet been fully quantified. Using measurements and models we calculate frontal ablation of Greenland's 213 outlet and 537 peripheral glaciers and find a total frontal ablation of 481.8 ± 24.0 for 2000–2010 and 510.2 ± 18.6 Gt a−1 for 2010–2020. Ice discharge accounted for ∼90% of frontal ablation during both periods, while mass loss due to terminus retreat comprised the remainder. Only 16 glaciers were responsible for the majority (>50%) of frontal ablation from 2010 to 2020. These estimates, along with the climatic‐basal balance, allow for a more complete accounting of Greenland Ice Sheet and peripheral glacier mass balance. In total, Greenland accounted for ∼90% of Northern Hemisphere frontal ablation for 2000–2010 and 2010–2020. Plain Language Summary: We estimate the mass of ice lost from all Greenland glaciers that entered the ocean during each of the last two decades. This ice loss at the front of these marine‐terminating glaciers is called frontal ablation and is approximately equal to the mass of icebergs entering the ocean. Frontal ablation is important because 87% of glacier area in Greenland ends in the ocean, through 750 outlets, and previous work has only approximated frontal ablation. This study quantifies it for the first time, helping to close the mass budget for the Greenland Ice Sheet and better partition its mass balance into components. We find that Greenland accounts for ∼90% of all Northern Hemisphere frontal ablation and, of that contribution, just 17 glaciers for 2000–2010 and 16 glaciers for 2010–2020 account for more than half of total Greenland frontal ablation. Key Points: Frontal ablation of the Greenland Ice Sheet averaged 510.2 ± 18.6 Gt a−1 for 2010–2020, ∼90% of which came from ice dischargeThe frontal ablation we measured is larger than the total mass loss from the ice sheet, indicating a positive climatic‐basal balanceOnly 16 glaciers account for 50% of the total frontal ablation from the Greenland Ice Sheet [ABSTRACT FROM AUTHOR]

The largest floating tongue of Greenland's ice sheet, Nioghalvfjerdsbræ, has so far been relatively stable with respect to areal retreat. Curiously, it experienced significant less thinning and ice flow acceleration than its neighbour Zacharias Isbræ. Draining more than 6% of the ice sheet, Nioghalvfjerdsbræ might become a large contributor to sea level rise in the future. Therefore, the stability of the floating tongue is a focus of this study. We employ a suite of observational methods to detect recent changes. We found that the calving style has changed at the southern part of the eastern calving front from normal tongue-type calving to a crack evolution initiated at frontal ice rises reaching 5-7km and progressing further upstream compared to 2010. The calving front area is further weakened by a substantial increase of a zone of fragments and open water at the tongue's southern margin, leading to the formation of a narrow ice bridge. These geometric and mechanical changes are a precursor of instability of the floating tongue. We complement our study by numerical ice flow simulations to estimate the impact of future break-up or disintegration events on the ice discharge. These idealised scenarios reveal that a loss of the south-eastern area would lead to 1% of increase of ice discharge at the grounding line, while a sudden collapse of the frontal area (46% of the floating tongue area) will enhance the ice discharge by 8.3% due to loss in buttressing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Glacial lake outburst floods (GLOFs) or 'jökulhlaups' from ice-dammed lakes are frequent in Greenland and can influence local ice dynamics, bedrock displacement, geomorphological changes and flooding hazards. Multidecadal time series of lake drainage dates, drainage volumes and flood outlets are rare but essential for understanding the impact on and interaction with the surroundings, identifying drainage mechanisms, and for mitigating downstream flood effects. In this study, we use ultra-high-resolution structure-from-motion (SfM) digital elevation models (DEM) and orthophotos from unmanned aerial vehicle field surveys in combination with optical satellite imagery to reconstruct robust lake volume changes associated with 14 GLOFs between 2007 and 2021 at Russell Glacier, West Greenland. This makes it, one of the most comprehensive and longest records of ice-dammed lake drainages in Greenland. We find a mean difference of 10 % between the lake drainage volumes compared with estimates derived from a gauged hydrograph 27 km downstream. Due to ice dam thinning, the potential maximum drainage volume in 2021 is c. 60 % smaller than that estimated to have drained in 2007. Our time series reveals variations in the drainage dates ranging from late May to mid-September and moreover that drained volumes range between 0.9–37.7 M m3. We attribute these fluctuations between short periods of relatively high and low drainage volumes to a weakening of the ice dam and an incomplete sealing of the englacial tunnel following the large GLOFs. The syphoning drainage mechanism is triggered by a reduction in englacial meltwater, likely driven by late seasonal drainages and sudden temperature reductions, as well as annual variations in the glacial drainage system. Furthermore, we provide geomorphological evidence of an additional drainage route first observed following the 2021 GLOF with a sub- or englacial and supraglacial water flow across the ice margin. It seems probable that the new drainage route will become dominant in the future which will drive changes in the downstream geomorphology and raise the risk of flooding-related hazards as the existing buffering outlet lakes will be bypassed. [ABSTRACT FROM AUTHOR]