Melting and Freezing Beneath Larsen C Ice Shelf

The calving of a trillion tonne iceberg from Larsen C Ice Shelf (LCIS) in July 2017 has led to concern about whether the ice shelf is heading for collapse. Satellite radar altimetry measurements have shown that the surface of LCIS lowered between 1992 and 2011. It has been suggested that oceanic basal melting had caused the ice to thin, resulting in the observed lowering. To determine the extent to which ocean melting has driven ice loss, simulations of varying ocean conditions in this region have been run using the MITgcm numerical ocean model. The model has a new high-resolution bathymetry created from 113 seismic soundings taken through the ice shelf, which reveal the presence of a seabed trough running from the calving front to the grounding line. In model ocean warming experiments, the overall increase in local melting is concentrated in this region of the ice shelf. The formation of ‘marine ice’, deposited when ocean water freezes to the base of the ice shelf, slows significantly when ocean temperatures are warmed. This reduces the extent of stabilising bands of marine ice within the ice shelf. As marine ice is one of the main mechanisms thought to stabilise LCIS, this may indicate that the stability of LCIS is particularly sensitive to ocean warming.