Toward a macroscopic parameterization of iceberg calving

Tuesday, 16 December 2014
Jason M Amundson, University of Alaska Southeast, Juneau, AK, United States
Parameterization of iceberg calving for prognostic glacier and ice sheet models remains a major challenge due to a poor understanding of the physical processes governing calving. Here, I propose a semi-empirical, macroscopic parameterization of calving that ignores the complex physics of the glacier-ocean interface, can be applied to any calving margin, and is easy to implement with very little computational cost. To test the parameterization, I apply it to a one-dimensional flowline model of an Alaskan-style tidewater glacier and subject the model to various climatic forcings. The model produces results that are roughly consistent with observations, i.e., rapid retreat and flow acceleration through an overdeepening over decades and slow re-advance over millenia. Model results are compared to the previously proposed water depth, height above flotation, and crevasse-depth calving parameterizations to show that they are consistent with the macroscopic parameterization under certain conditions. Although there remains a great deal of uncertainty in the exact form of the macroscopic parameterization, it does appear to be a promising and simple way to model the glacier-ocean boundary.