Ice shelves, the Southern Ocean, and the future

Ice shelves, the floating extensions of the Antarctic Ice Sheet, are melted from below by the ocean. Increased ice shelf basal melting is the main mechanism by which Antarctica currently contributes to global sea level rise. As melt rates are sensitive to temperature, salinity, and circulation in tiny pockets of the Southern Ocean, predicting how they might respond to climate change is not straightforward. Projecting future ice shelf melting is at the forefront of coupled Earth system modelling, as most climate and ocean models still do not include ice shelves at all. This talk will summarise my research since 2020 on the future of ice shelf basal melting, focusing on three regions of Antarctica. In the Amundsen Sea, in West Antarctica, relatively warm ocean water already accesses the ice shelves. However, climate change is projected to make these regions warmer still, by increasing the volume of warm water flowing onshore. In contrast, Antarctica’s two largest ice shelves, the Ross and Filchner-Ronne, are currently bathed in cold water and melt rates are stable. However, numerous models predict that with sufficient climate change, these cavities could abruptly flip into a warm state similar to the Amundsen Sea. Sea level rise from Antarctica, therefore, is not all-or-nothing. Ice loss from some regions may already be committed, but in other regions abrupt changes may or may not be triggered, depending on how much the climate warms. Therefore, the trajectory of carbon emissions over the coming century will likely have a large impact on Antarctica’s long-term contribution to sea level rise.