The Dotson Ice Shelf has resisted acceleration and ice-front retreat despite high basal-melt rates and rapid disaggregation of the neighboring Crosson Ice Shelf. Because of this lack of acceleration, previous studies have assumed that Dotson is stable. Here we show clear evidence of Dotson's destabilization as it decelerates, contrary to the common assumption that ice-flow deceleration is synonymous with stability. Ungrounding of a series of pinning points initiated acceleration in the Upper Dotson in the early 2000s, which subsequently slowed ice flow in the Lower Dotson. Discharge from the tributary Kohler Glacier into Crosson increased, but non-proportionally. Using ICESat and ICESat-2 altimetry data we show that ungrounding of the remaining pinning points is linked to a tripling in basal melt rates between 2006-2016 and 2016-2020. Basal melt rates on Crosson doubled over the same period. The higher basal melt at Lower Dotson is consistent with the cyclonic ocean circulation in the Dotson cavity, which tends to lift isopycnals and allow warmer deep water to interact with the ice. Given current surface-lowering rates, we estimate that several remaining pinning points in the Upper Dotson will unground within one to three decades. The grounding line of Kohler Glacier will retreat past a bathymetric saddle by the late 2030s and merge into the Smith West Glacier catchment, raising concern that reconfiguration of regional ice-flow dynamics and new pathways for the intrusion of warm modified Circumpolar Deep Water could further accelerate grounding-line retreat in the Dotson-Crosson Ice Shelf System.

Calving and solid ice discharge into fjords account for approximately half of the annual net ice loss from the Greenland Ice Sheet, but these processes are rarely observed. To gain insights into the spatio-temporal nature of calving, we use a terrestrial radar interferometer to derive a three-week record of 8,026 calving events from Store Glacier, including the transition between a mélange-filled and ice-free fjord. We show that calving rates double across this transition and that the interferometer record is in good agreement with volumetric estimates of calving losses from contemporaneous UAV surveys. We report significant variations in calving activity over time, which obfuscate any simple power-law relationship. While there is a statistically significant relationship between surface melt and the number of calving events, no such relationship exists between surface melt and the volume of these events. Similarly, we find a 70% increase in the number of calving events in the presence of visible meltwater plumes, but only a 3% increase in calving volumes. While calving losses appear to have no clear single control, we find a bimodal distribution of iceberg sizes due to small sections of ice breaking off the subaerial part of the front and large capsizing icebergs forming by full-thickness failure. Whereas previous work has hypothesised that tidewater glaciers can be grouped according to whether they calve predominantly by the former or latter mechanism, our observations indicate that calving here inherently comprises both, and that the dominant process can change over relatively short periods.

Calving and solid ice discharge into fjords account for approximately half of the annual net ice loss from the Greenland Ice Sheet, but these processes are rarely observed. To gain insights into the spatio-temporal nature of calving, we use a terrestrial radar interferometer to derive a three-week record of 8,026 calving events from Store Glacier, including the transition between a mélange-filled and ice-free fjord. We show that calving rates double across this transition and that the interferometer record is in good agreement with volumetric estimates of calving losses from contemporaneous UAV surveys. We report significant variations in calving activity over time, which obfuscate any simple power-law relationship. While there is a statistically significant relationship between surface melt and the number of calving events, no such relationship exists between surface melt and the volume of these events. Similarly, we find a 70% increase in the number of calving events in the presence of visible meltwater plumes, but only a 3% increase in calving volumes. While calving losses appear to have no clear single control, we find a bimodal distribution of iceberg sizes due to small sections of ice breaking off the subaerial part of the front and large capsizing icebergs forming by full-thickness failure. Whereas previous work has hypothesised that tidewater glaciers can be grouped according to whether they calve predominantly by the former or latter mechanism, our observations indicate that calving here inherently comprises both, and that the dominant process can change over relatively short periods.