The immense Antarctic ice sheet, on average two kilometers thick and almost twice the size of Australia, holds enough fresh water to raise global sea level by 58 metres. However, ice loss from this layer is projected to be the main driver of sea level rise by 2100, although its exact contribution remains uncertain. The projections vary from an increase of 44 centimeters to a drop of 22 centimeters, which highlights the complexity of the processes that regulate it.
Much of this uncertainty lies in the fact that the ocean processes that affect the ice sheet occur at extremely small scales, which are difficult to measure and model. However, recent scientific advances have allowed us to delve deeper into what is called the “ice-ocean boundary layer”, a fundamental aspect in the study of Antarctic melting, which has been the subject of a new review article published in Annual Reviews.
Glacial weathering and melting
Antarctic glaciers flow into the Southern Ocean and form floating ice shelves that act as stabilizers for the ice sheet. However, these platforms are in decline. Basal melting, a process in which the ocean melts ice from below, has led to a thinning and retreat of the ice sheet in certain regions, contributing to sea level rise. In addition, this phenomenon has slowed down the deepest current of the ocean circulation system, which transports water around the planet.
Interactions in the ice-ocean boundary layer are complex and occur in a cold and remote environment, which has made their study difficult. However, advances in computer simulations have begun to offer new insights into how the ocean melts Antarctic ice shelves. Researchers in different parts of the world are analyzing the microscale ocean flow that supplies heat to the ice and therefore determines its melting rate.
So far, multiple relationships have been identified between ocean conditions (temperature, salinity and current speed) and different melting regimes. The shape of the ice sheet plays a crucial role, as meltwater is lighter than the surrounding ocean water, causing fresh water to accumulate in depressions at the bottom of the ice sheet. slowing down their fusion. In the case of steep slopes, this insulating effect is much lower, which facilitates the contact of meltwater with warmer ocean waters and accelerates melting.
Recently, the use of underwater robots equipped with sonar and cameras has provided unprecedented data on the environment beneath ice shelves. These robots have revealed a striking frozen landscape, made up of various ice features ranging from centimeters to kilometers in size. Among these, there are crevasses and depressions, formed both by fractures in the ice and by melting processes.
Despite advances in understanding basal melt and ice landscape dynamics, uncertainties remain. New computer models that allow us to simulate the evolution of the interface between ice and water are beginning to show self-sculpting behaviors of melting ice, similar to how dunes form and move in a desert. However, additional models are required to simulate the formation and evolution of the entire frozen landscape.
These recent advances are helping to reduce uncertainty in understanding the impact of the Antarctic ice sheet on global sea level rise. However, integrating this new knowledge about basal melt into climate and ice sheet models remains a significant challenge. Overcoming this hurdle is urgent, as accurate representation of melt in models will help reduce profound uncertainty in sea level rise projections, especially as ocean conditions and ice shelf melt regimes change. change in the future.
