Abstract
AbstractCalving 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 spatiotemporal nature of calving, we use a terrestrial radar interferometer to derive a 3‐week record of 8,026 calving events from Sermeq Kujalleq (Store Glacier, West Greenland), 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 unmanned aerial vehicle 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 blocks breaking off the subaerial part of the glacier front and large capsizing icebergs forming by full‐thickness failure. Whereas previous work has hypothesized 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.
Highlights
Tidewater outlet glaciers drain 88% of the area of the Greenland ice sheet (GrIS) (Rignot & Mouginot, 2012)
The unmanned aerial vehicles (UAVs)-derived digital elevation models (DEMs) (Figures 3a–3c) show a distinct change in the terminus position, but cannot specify whether calving occurred as a single large event or multiple smaller events for the total ≈1,400,000 m3 in subaerial volume loss calculated by differencing the two DEMs
When we sum up all the events within the same area detected by the terrestrial radar interferometer (TRI), we obtain a total subaerial ice volume loss of 1,240,000 m3, which is a discrepancy of only 12% compared to the independent UAV method
Summary
Tidewater outlet glaciers (i.e., glaciers that flow into the sea) drain 88% of the area of the Greenland ice sheet (GrIS) (Rignot & Mouginot, 2012). Ice discharge due to calving from these glaciers is currently responsible for 40% of the GrIS annual net mass loss (equivalent to 0.33 mm a−1 global sea-level rise) (Mouginot et al, 2019). Understanding how calving occurs and its relationship to other processes in the tidewater-glacier system and external forcing becomes of central importance in forecasting the evolution of the GrIS in the coming decades and century. Calving is an important glaciological process in tidewater environments in which glaciers discharge ice into fjords and coastal seas. It occurs when extensional stresses at the terminus produce fractures that intersect
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