At thousands of kilometres long and hundreds of metres deep, Antarctic ice shelves are massive. Yet scientists say it is the small-scale physical processes that occur at the boundary between the ice and ocean that determine their fate, including how fast they melt.
In this millimetre-thick 'boundary layer', salt and heat from the ocean interact with the base of floating ice shelves that fringe the Antarctic continent, triggering melting that contributes to sea level rise.
However Dr Madelaine Rosevear, from the Australian Centre for Excellence in Antarctic Science (ACEAS) and the University of Melbourne, said precisely how the ocean melts ice shelves is unresolved, due to the difficulty of taking measurements beneath ice shelves, and simulating such small-scale ocean processes.
"Ice loss from the Antarctic Ice Sheet is projected to be the leading driver of sea level rise by 2100, yet its contribution remains highly uncertain," Dr Rosevear said.
"Projections of Antarctic-driven sea level rise range from a 22 centimetre fall to a 44 centimetre rise over this century, largely due to a knowledge gap in understanding how ocean heat melts floating ice shelves."
Now Dr Rosevear and other Australian Antarctic Program scientists, including Dr Ben Galton-Fenzi from the Australian Antarctic Division, Dr Bishakhdatta Gayen from ACEAS, and Dr Catherine Vreugdenhil from the University of Melbourne, have reviewed the current understanding of ice-ocean boundary-layer dynamics, published this month in the Annual Review of Marine Science.
Their review focuses on recent progress from laboratory experiments, numerical simulations of the small-scale movements of water, salt and heat within the boundary layer, novel observations beneath ice shelves, and the application of new knowledge to large-scale simulations.
"Recent advances in computer simulations have allowed scientists to model the boundary layer for the first time and uncover new melting patterns depending on ocean conditions and ice geometry," Dr Rosevear said.
"At the same time, scientists have used cutting-edge, ocean-observing robots, to reveal a highly complicated 'ice-scape' on the underside of ice shelves, with metre-scale ice dimples, steep terraces, and kilometre-scale scoops, which influence melting and freezing."
Dr Galton-Fenzi said these discoveries point to a tightly coupled ice-ocean system where melt, circulation, and ice geometry evolve together.
"Incorporating these processes into climate and sea level models presents a major challenge for scientists, but it is essential for reducing uncertainty in sea level predictions," he said.
Learn more in the authors' article in The Conversation and the scientific paper 'How does the ocean melt ice shelves'.
