Investigating the recent dynamic evolution of the Larsen B tributary glaciers

– Naomi Ochwat, University of Colorado –

Résumé :

Glaciers in the Antarctic Peninsula have had a dynamic history over the last thirty years as the large floating extensions of the ice cap have begun to collapse. For example, the Larsen B ice shelf on the Eastern Antarctic Peninsula broke up in 2002 initiating decades of instability for the tributary glaciers that fed it. In 2011, sea ice that fastened to the shoreline (‘fast ice’) temporarily stabilized these glaciers and allowed them to partially readvance into the embayment. In 2022, the fast ice broke-up thus exposing the glaciers to a new stress regime yet again. Using remote sensing methods, we have studied the potential triggers for the fast ice break-out as well as the initial glacier responses. Our results suggest that the fast ice loss was linked to strong wave action (>1.5 m amplitude) with long period swells (>5 s) that reached the embayment on the day of the appearance of multiple new rifts in the fast ice. This coincided with a 12-year low in sea ice concentration in the northwestern Weddell Sea creating a corridor for open ocean wave trains to reach the Larsen B fast ice. The tributary glaciers responded almost immediately. Crane Glacier lost its floating ice tongue and has retreated 11 km as of March 2024, farther upstream than its lowest extent prior to the fast ice formation. Hektoria and Green glaciers lost their 300 m thick floating tongue and retreated 25 km between February 2022 and January 2024, of which at least 8-13 km was grounded ice. Hektoria underwent several short periods of rapid retreat at rates faster than any other glacier in the modern record. We link these observations to known causes of glacier instability, such as Marine Ice Sheet Instability and Marine Ice Cliff Instability, as well as the classical tidewater glacier retreat cycle.