Modelling interactions between Antarctica and the Southern Ocean

Ice berg with striations, known as a 'jade berg'
This jade berg was once part of the Antarctic ice sheet. (Photo: Andrew Meijers)
Southern Ocean bathymetry and Antarctic bedrock topography overlain with the model.Mid-winter snapshot of the surface ice growth rate (metres per year), where red is ice growth.

Ice sheets have a complicated relationship with oceans. The margins of Antarctica are shrinking due to warmer climate, causing sea levels to rise and the oceans to freshen. The increased loss of ice from Antarctica is mostly due to the rapid thinning and retreat of glaciers, driven by the enhanced melting of ice shelves that fringe the continent. These massive floating ice shelves are continually eroded by melting that occurs at their base and the calving of icebergs from their front. The enhanced supply of cool and fresh glacial meltwater into the Southern Ocean is the most likely cause of the observed changes seen in the dense (cold and salty) water that feeds the global overturning circulation. However, we do not yet fully understand the processes that link ocean warming to ice-shelf melting and the retreat of glaciers and dense water formation.

Research at the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) will improve our understanding of the interaction between the Southern Ocean and the Antarctic ice sheet using state-of-the-art modelling. The model solves mathematical equations that describe the physics of the ocean and its interaction with ice shelves (see graphics below). This model is based on the Regional Ocean Modelling System, which is widely regarded as the best model for coastal oceanographic process studies. The model is able to simulate interactions between ocean flows and topography, such as the buoyant plumes of glacial meltwater that can rise under ice shelves and the dense water that flows from the continental shelves to the deep ocean. Realistic simulations rely on comprehensive descriptions of the various physical components (the sea floor, ice sheet, ocean and atmosphere) and the way that these interact with each other. These inputs, collectively known as ‘boundary conditions’ are, in part, derived from a suite of observations. However, many inputs are often poorly understood, such as the shape of the ocean cavity beneath ice shelves.

Oceanographic observations like those collected by the AMISOR project are extremely valuable for defining boundary conditions and testing the level of realism that the model can produce. Continued collection of such data is important to further improve the models. Conversely, the development of realistic simulations can help to extend our interpretation of the few observations we do have, to times and places where there are currently none. In addition, the planning of future field campaigns can be guided by results from these types of realistic simulations. Future research needs strong interdisciplinary collaboration between modellers and observers to rapidly progress our understanding of the role of the cryosphere in the global climate system. Realistic simulations can be a valuable research tool for all sciences interested in the Southern Ocean and coastal oceanic environment around Antarctica. If you wish to learn more about the modelling outlined here please contact Ben at Ben.Galton-Fenzi@utas.edu.au.

BEN GALTON-FENZI

ACE CRC