A holistic model of outlet calving, dynamic acceleration and drawdown for the Greenland Ice Sheet

The body of scientific evidence for significant anthropogenic impacts on the global climate is growing and public concern underscores a need for better assessments of contemporary environmental changes in polar regions. The greatest store of fresh water in the northern hemisphere - equivalent to 7m of eustatic sea level rise - is held within the Greenland Ice Sheet (GIS), and yet its present and future contribution to sea level is poorly constrained (IPCC, 2007). Recent observations suggest that mass loss near the margin of the GIS is accelerating through a combination of increased surface melting (e.g. Steffen et al, 2004) and dynamic thinning (e.g. Rignot and Kanagaratnam, 2006). However, the key processes controlling interior drawdown have yet to be fully identified, and in consequence, are not incorporated in the ice-sheet models which form the basis of the IPCC sea level projections. This in part reflects the fact that the satellite data that has revealed the widespread speed-up of glaciers cannot be acquired at the temporal resolution needed to resolve the causal mechanisms. This project focuses on second and third largest outlet glaciers of western GIS in order to help understand the processes by which these glaciers increase their speed and lose ice to the ocean by means of iceberg calving. Calving is the process of mechanical fracture where ice breaks off from the edge of glaciers and floating ice shelves. It accounts for the majority of loss from the Antarctic and over 50% of that from the GIS. Calving is a very efficient mass-loss mechanism which provides a rapid connection between the ice stored on land and the ocean where it is turned into sea level rise. Despite its fundamental importance, our understanding of the controls on iceberg calving and the associated process of dynamic drawdown are poorly understood and the present generation of coupled ice sheet models (ISMs) do not simulate these processes at all which severely handicaps their predictive ability. We aim to collect detailed oceanic, climatic, geodetic and geophysical datasets at two outlet glaciers which will enable us to: 1) investigate the main processes and linkages controlling iceberg calving and its effect on upstream glacier flow and thinning, and, 2) to use this data to refine a new process-based calving/flow dynamics criterion that can be easily included within models coupled to simulate the future climate and polar ice cover and its contribution on rising sea levels.