Ben Galton-Fenzi

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

Supervisors: Dr John Hunter, Prof. Richard Coleman, Dr John Church, and Dr Simon Marsland

Project Overview:

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 x 10^6 square kilometres. It comprises 25.7 x 10^6 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 peninsular disappeared in 1995 and 2002 respectively.

The melting of ice-shelves cannot in themselves 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 in the rate of sea-level rise of about 4%.

Project Outline and Objectives:

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 modeling 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.

Recipient of Tasmanian Marine Science Fellowship:

Ben Galton-Fenzi is working towards a PhD in Quantitative Marine Science with the Centre of Marine Science, at the University of Tasmania, CSIRO and the Antarctic Climate and Ecosystems CRC. Ben was one of first recipients of the Inaugural Marine Science Fellowship awards, to travel to Toulouse, France to visit the Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS). See full report.