New Gravity-Derived Grounding Line Depths Highlight Role Bathymetry Plays in Ongoing Greenland Ice Sheet Change

Abstract:

Bathymetry has been a missing piece in understanding ice-ocean interactions of marine-terminating glaciers in Greenland. As bathymetry in fjords often controls the flow of warm water to the terminus of the glacier, and the grounding line depth of the glacier can modulate the effect of this warm water on the glacier. Study of Tracy and Heilprin Glaciers, a pair of neighboring glaciers in northwest Greenland, has indicated that when exposed to similar external forcings, the glacier with the deeper grounding line will retreat more rapidly. The new comprehensive mapping of grounding line depths with Operation IceBridge gravity inversions provides the basis for examining this question for all of Greenland’s glaciers. 

We consider 54 distinct glaciers in our analysis. Grounding line depths for these 54 come from data collected by Operation IceBridge from 2010-2012. New grounding line depths for 36 glaciers are derived from gravity measurements in locations where radar is unable to retrieve grounding line depths. 18 grounding line depths come from CReSIS Multichannel Coherent Depth Sounder radar data. Offshore bathymetry in all 54 fjords is gravity-derived. The gravity-derived bathymetry is always constrained onshore by radar, and when possible pinned offshore to acoustic bathymetric measurements.

Here we present the gravity-derived grounding line depths along with recent glacier behavior, including surface lowering and terminus retreat, of these 54 glaciers. In general, the glaciers with deeper grounding lines are experiencing greater mass loss. This relationship between grounding line depth and mass balance extends to much of Greenland. We systematically discuss this relationship in the different major regions of Greenland, and note that the relationship is strongest in the southeast, and weakest in the north.