Abstract
AbstractTo better understand recent rapid recession of marine-terminating glaciers in Greenland, we performed satellite and field observations near the calving front of Bowdoin Glacier, a 3 km wide outlet glacier in northwestern Greenland. Satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for >20 years. Ice radar measurements showed that the glacier front is grounded, but very close to the floating condition. These results, in combination with the results of ocean depth soundings, suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat. Presumably, glacier thinning due to atmospheric and/or ocean warming triggered the initial retreat. In situ measurements showed complex short-term ice speed variations, which were correlated with air temperature, precipitation and ocean tides. Ice speed quickly responded to temperature rise and a heavy rain event, indicating rapid drainage of surface water to the bed. Semi-diurnal speed peaks coincided with low tides, suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance. These observations demonstrate that the dynamics of Bowdoin Glacier are sensitive to small perturbations occurring near the calving front.
Highlights
The Greenland ice sheet has been losing mass at accelerating rates since the 1990s (Rignot and others, 2011; Shepherd and others, 2012)
We suggest the importance of bed geometry in the observed rapid retreat, but we suspect climatic and/or oceanic forcings as a trigger
In order to better understand the processes driving recent rapid changes in marine-terminating outlet glaciers in Greenland, we carried out satellite and field measurements near the calving front of Bowdoin Glacier and the fjord in front of the glacier
Summary
The Greenland ice sheet has been losing mass at accelerating rates since the 1990s (Rignot and others, 2011; Shepherd and others, 2012). Satellite measurements and numerical modeling results have shown that the current mass loss of the Greenland ice sheet is primarily due to increased surface melt and ice discharge from accelerated marine-terminating outlet glaciers (Sasgen and others, 2012; Enderlin and others, 2014; Khan and others, 2014). The overview of the ongoing changes has been revealed by previous studies based on an increasing number of data available from satellite measurements and numerical modeling. Field observations on tidewater glaciers are limited to several glaciers, so the driving mechanism of glacier acceleration is poorly constrained. Acceleration, thinning and retreat of outlet glaciers are playing key roles in recent rapid ice loss in Greenland. The system is complex, as the ocean temperature is influenced by meltwater discharge from the glaciers into the ocean (e.g. Murray and others, 2010; Straneo and Heimbach, 2013)
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