Tracing West Antarctic Iceberg Origins through Scour Depth Analyses

Abstract:

Icebergs form along coasts at the glacier ice-ocean interface through calving. It is critical that we understand the effects of Antarctic calving in a changing climate. One such effect is that of iceberg scouring: If icebergs are thick enough, they can run aground, leaving scours in the seabed. One recent study relied on radar altimetry to construct hypothetical Antarctic iceberg keel depths, linking them to three different types of parent ice. The purpose of this study is to determine the average water depths at which real scours—digitized from multibeam sonar bathymetry data—occur for several sections of the seafloor off of West Antarctica and compare the depths with those generated by the earlier study. Depth analyses for scours seaward of the Ross Ice Shelf, Getz Ice Shelf, and Pine Island and Thwaites glaciers and in the northeast Bellingshausen Sea indicate a substantial difference from the projected radar altimetry results. All six areas register average depths greater than 450 meters. For five of the six areas examined, the observed scours occur at deeper water depths on average than would the scours projected by the radar altimetry study. This difference holds for four of those five areas even after the application of a 130-meter sea-level correction—an upper-bound estimate for the sea-level drop associated with the Last Glacial Maximum. This suggests a fundamental dissimilarity between the projected calving dimensions and those of the icebergs responsible for the scours examined here. As iceberg geometry is primarily controlled by parent ice mass thickness, we can also extend this difference to the source ice in each study. These results allow us to make inferences about iceberg life cycles, trajectories, and grounding patterns off of West Antarctica. They can help scientists better understand patterns of mass loss and freshwater input into the Southern Ocean, processes that ultimately lead to sea-level rise.