Ice dynamics in McMurdo Sound, Antarctica, based on precise synthetic aperture radar interferometry analysis

Abstract. The embayment at the end of Ross Island's Hut Point Peninsula is often covered by a patch of landfast sea ice (henceforth fast ice), which can remain attached to the McMurdo Ice Shelf (MIS) for a few years at a time, rather than breaking out every summer. Over recent years, later fast ice formation and increased fast ice breakout have been observed, but the influence on ice shelf stability is unclear. We examined historical MIS front positions, as well as the summer 2025 fast ice breakout and MIS calving, using Landsat optical imagery and historical USGS aerial photography.

A precise interferometric satellite analysis was conducted for spring 2024 based on ascending-descending combinations of TerraSAR-X image acquisitions. Two non-orthogonal horizontal component velocity fields were calculated, and ground-referenced with precise movement data acquired with three automated GNSS stations that had been placed on the ice. This allowed us to calibrate three simply connected subsets to each of the velocity field components: the MIS itself, the multi-year fast ice, and the first-year fast ice. These component fields then enabled us to calculate a near-complete 2D horizontal velocity field of ice motion in the area. This analysis was the basis for calculating the divergence field of the velocity as well as principal strain rate fields. The overall ice dynamics were then related to the areas where we expect a stabilizing effect of the fast ice on the ice shelf front, or where the ice shelf geometry suggests stabilizing effects.

Once the January–February 2025 fast ice breakout was complete, the MIS front began calving almost immediately, leading to a net retreat of the MIS front to a minimum beyond any other found in the Landsat 4–9 record. The dynamics of the fast ice were largely dependent on age, with the behavior of the multi-year fast ice resembling in most ways that of the adjoining MIS rather than the first-year fast ice, due to strong coupling at the MIS–multi-year fast ice interface. The divergence of the velocity field and the principal strain rates show convergence and compression of the fast ice in the embayment, providing evidence of a stabilizing effect and possible buttressing of the MIS by fast ice.