From Ross Ice Shelf to Pine Island, studying the most stable and the most changing places in Antarctica
École Normale Supérieure
Abstract: Ice mass loss from Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. The Antarctic Ice Sheet loses mass via its ice shelves (the floating extensions of the ice sheet) predominantly through two processes: basal melting and iceberg calving. The large Ross Ice Shelf, is presently stable but buttresses grounded ice equivalent to about 12 m of global sea level, and for which geological evidence points to large and sometimes rapid past changes. Recent ocean modeling and observations show that seasonal inflows of warmed upper-ocean water under a thin-ice corridor under the ice shelf and at the ice front can produce locally high melt rates each summer, suggesting that future increases in summer upper-ocean ocean warming north of the ice front could accelerate ice-shelf flow speeds and mass loss. GPS observations of Ross Ice Shelf velocity have shown seasonal flow variations of several meters per year over a large part of the ice shelf, accelerating in summer and decelerating in winter. However, ice-sheet simulations driven by realistic annual cycles of basal melt rates near the ice front produce much smaller seasonal variations than observed, suggesting that other processes could be at play. In a follow-up study, we investigate a new potential mechanism for a seasonal signal in ice flow: variations of sea surface height (SSH) driven by seasonal changes in thermodynamic and atmospheric forcing of ocean state under the ice shelf. In the Amundsen Sea sector, we find some of the fastest changing glaciers. Recent observations of rapid ice-shelf thinning and grounding line retreat have been attributed to increased basal melting driven by inflows of warm Circumpolar Deep Water. However, recent studies have shown that basal melting alone might not be sufficient to explain the recent acceleration, retreat and thinning of the outlet glaciers in the sector. In an attempt to better understand the mechanisms at play in the region, we conduct numerical simulations to determine the role of damage on changes observed over the last two decades in the Amundsen Sea Sector. More particularly, we combine the classical Stokes flow formulation with a Continuum Damage Mechanics model to simulate the ice flow evolution over the last 20 years.