Abstract
Abstract. Calving is a crucial process for the recently observed dynamic mass loss changes of the Greenland ice sheet. Despite its importance for global sea level change, major limitations in understanding the process of calving remain. This study presents high-resolution calving event data and statistics recorded with a terrestrial radar interferometer at the front of Eqip Sermia, a marine-terminating outlet glacier in Greenland. The derived digital elevation models with a spatial resolution of several metres recorded at 1 min intervals were processed to provide source areas and volumes of 906 individual calving events during a 6 d period. The calving front can be divided into sectors ending in shallow and deep water with different calving statistics and styles. For the shallow sector, characterized by an inclined and very high front, calving events are more frequent and larger than for the vertical ice cliff of the deep sector. We suggest that the calving volume deficiency of 90 % relative to the estimated ice flux in our observations of the deep sector is removed by oceanic melt, subaquatic calving, and small aerial calving events. Assuming a similar ice thickness for both sectors implies that subaqueous mass loss must be substantial for this sector with a contribution of up to 65 % to the frontal mass loss. The size distribution of the shallow sector is represented by a log-normal model, while for the deep sector the log-normal and power-law model fit well, but none of them are significantly better. Variations in calving activity and style between the sectors seem to be controlled by the bed topography and the front geometry. Within the short observation period no simple relationship between environmental forcings and calving frequency or event volume could be detected.
Highlights
Over the past decade rapid retreat, thinning, and flow acceleration of many outlet glaciers contributed substantially to the observed increasing mass loss of the Greenland ice sheet (Moon et al, 2012; Enderlin et al, 2014; King et al, 2018) and to global sea level rise (Rignot et al, 2011; IPCC, 2014)
By differencing high-resolution digital elevation models (DEMs) generated from the terrestrial radar interferometer (TRI) data, a detailed calving event catalogue was established, providing timing, source area, and calving volume of aerial calving events
During the 6 d observation period, a total of 906 calving events were detected, of which 80 % occurred in the shallow sector where mean calving volumes were 35 % larger than in the deep sector
Summary
Over the past decade rapid retreat, thinning, and flow acceleration of many outlet glaciers contributed substantially to the observed increasing mass loss of the Greenland ice sheet (Moon et al, 2012; Enderlin et al, 2014; King et al, 2018) and to global sea level rise (Rignot et al, 2011; IPCC, 2014). These dynamic changes seem to be related to a general warming of air temperature and water masses around Greenland (Straneo et al, 2013). Mechanisms causing fractures to propagate are (1) spatial gradients in the glacier velocity, (2) changes in frontal geometry (front position, height), (3) undercutting of the glacier front by melting at or below the water line, and (4) buoy-
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