Calving of a Large Greenlandic Tidewater Glacier has Complex Links to Meltwater Plumes and Mélange. Issue 4 (9th April 2021) - Cook, Samuel J.
Abstract: 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 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. Plain Language Summary: We observe the release of icebergs by calving at a large glacier in Greenland for 3 weeks, during which we find 8, 026 calving events across a wide range of environmental conditions. We show that our observation method (radar interferometry) agrees well with an independent method (aerial drone photography). We find that the type of calving varies significantly over time, but there is no single mechanism that controls this variation; instead, it is due to multiple factors. This leads to two kinds of calving events: small blocks falling off the visible part of the front of the glacier and large blocks of the entire thickness of the front (including the area underwater) breaking off. Previous study has assumed that glaciers can be grouped by which of these types of calving is more important, but we show that this is an over‐simplification at large glaciers such as store, as both these mechanisms are observed and both are the more important mechanism at different times. Key Points: We derive a record of 8, 026 calving events and sizes at Store Glacier in July 2017 using a terrestrial radar interferometer We find no single clear control on calving and clear variations in calving behavior over time, producing a bimodal calving event‐size distribution Our findings suggest that grouping glaciers by their dominant calving mechanism is not tenable, as this mechanism can change over time