Structure and form of grounding lines of modern ice sheets

Abstract:

The form of the bed at the grounding line of a glacier and the character of the underlying rock can be critical to the stability of the glacier. Aerogravity measurements offer a unique insight in to the character of the grounding line environment. By combining depth measurements from further onshore radar and geological information from magnetic surveys, gravity-based models can reveal both the depth and slope of the bed at the grounding line. Where bed elevation is known at the grounding line, gravity models can show the density structure of the underlying rock.

Operation IceBridge has flown coincident radar, lidar, photography, gravity and magnetic airborne surveys along fjords and over ice shelves in both Greenland and Antarctica. Aerogravity measurements have been used extensively to model the bathymetry of the sea floor in front of the grounding line, and to identify the depth of the grounding line in areas where radar measurements have proven challenging.

These models have also been used to reveal the range of conditions at present day grounding lines, as well as those experienced in the past and predicted for future grounding line positions. In some regions, we have identified low-density sediment accumulations, at both present day grounding lines and within fjords, that we interpret to be terminal moraines deposited by the glacier itself during hiatuses in retreat. In other regions, we find that the present day grounding line is stalled on a ridge of high-density rock. Ridges such as these remain in the same position through many cycles of advance and retreat of the glacier.

Our synthesis of gravity data from a wide range of glacial environments can be used to identify likely drivers of change at the grounding line, whether this is the depth, the slope, or the geological character of the glacier bed.