Ice sheets matter because they can change sea level---fast. When ice sheets grow, ocean level sinks. This usually happens very slowly because ice sheet growth is limited by the amount of snow that falls. When ice sheets shrink, sea level rises and records of past sea level show this happens generally faster than ice sheet growth, with periods of very rapid sea level rise indicating very rapid loss of ice.
The type of ice sheet believed most susceptible to rapid ice loss is a "marine-based" ice sheet, that is, one that rests on a bed below sea level. West Antarctica is the last of this type of ice sheet on earth and has been in the science spotlight for the past 20 years. Sure enough, satellite observations have shown a portion of the West Antarctic ice sheet is acting up. It’s the portion that flows into the Amundsen Sea, one sector of the Southern Ocean that surrounds Antarctica. This ice is thinning, the flow rate is increasing and the junction between the grounded ice and floating ice is retreating inland. The thickness and speed changes are most dramatic at the near the grounding line and decrease inland. This signals scientists that the trigger for these changes is at or near the grounding line.
A favored theory to explain these changes is that the ice shelf provides resistance against the seaward flow of the grounded ice sheet and as the size (thickness in this case) decreases, so does the resistance and the ice sheet can flow seaward faster. Warm water is believed to be the cause of the thinning ice shelf.
Our project is aimed at testing this hypothesis. We are motivated by the urgent need to predict future ice sheet behavior so that future rates of sea level change can be anticipated. Progress toward this goal is impossible without the quantitative understanding of the processes controlling the exchange of mass, heat and salt beneath the Amundsen Sea ice shelves and the incorporation of that knowledge into prognostic coupled models of ocean and ice dynamics.