PhD in Quantitative Marine Science

Thesis Title: Numerical Study of the Circulation and Melt/Freeze Under Ice Shelves

Supervisors: Dr John Hunter (ACE CRC), Prof Richard Coleman (Quantitative Marine Studies), and Dr John Church (CSIRO Marine and Atmospheric Research)

Ice shelves around Antarctica form an important part of the global climate system. Approximately 40% of the Antarctic coastline is composed of large ice shelves in coastal embayments, such as the Filchner, Ronne, Ross and Amery, and fringing shelves on the periphery of the ice sheet, such as the Shackleton, Fimbulisen, Ekstromisen, and Larsen shelves. They provide a direct connection between the Antarctic ice sheet and the Southern Ocean.

Antarctica's ice sheet covers 12.4 million square kilometres. It comprises 25.7 million cubic kilometres of ice or 70% of the world's freshwater. Mass is continually added to the ice sheet from snowfall, and removed via ablation, melt and iceberg calving; particularly from ice shelves. Any change in the ice sheet's `mass-budget' caused by imbalance between these mass input and output terms can affect sea level.

Changes in ocean temperatures can dramatically change the state of ice shelves. Ocean interaction beneath the shelves is complicated, and regions of basal refreezing as well as melt occur. These processes are important not only because they are a major component of the Antarctic mass budget, but because they modify the characteristics of the surrounding ocean. Since ice shelves are floating on ocean waters at the freezing point, even a small change in ocean temperature can significantly affect the shelves' basal melt rate and cause them to thin quickly. For example, Larsen A and B Ice Shelves on the Antarctic Peninsula disappeared in 1995 and 2002 respectively.

The melting of ice shelves cannot in itself cause a significant rise in the oceans; however, recent evidence suggests that ice shelves have a buttressing effect on continental ice sheets. A significant increase in the discharge of the glaciers that previously fed Larsen A and B has been recently observed, leading to an increase of about 4% in the rate of sea level rise.

Of primary interest is the way in which the melting and freezing depends on the ocean temperature, which is increasing (and will continue to increase) with global warming. During the past few years there has been a large program of data collection on and under the Amery Ice Shelf (the latter using hot water drilling techniques) and in the adjacent area of Prydz Bay. These and future observations will form the basis of numerical modelling of this ocean system.

The model is based on the well-known Princeton Ocean Model, which was originally developed in the late 1970s and has had thousands of users worldwide. The model is also a contributor to the Ice Shelf - Ocean Model Intercomparison Project (ISOMIP), which is an international comparison of existing ice shelf cavity models. There is also an interest in modelling the cavities under other ice shelves. Each specific application of the model would indicate the sensitivity of that particular ice shelf to a warming ocean.

For more information:

Telephone: +61 3 6226 2251

Email: bkgalton@utas.edu.au