Sensitivity of the Greenland ice sheet evolution and flow on basal conditions – a parameter study with the PISM model

Friday, 19 December 2014
Lisbeth Tangaa Nielsen, Centre for Ice and Climate, Copenhagen, Denmark and Christine S. Hvidberg, Niels Bohr Institute - University of Copenhagen, Center for Ice and Climate, Copenhagen, Denmark
The basal boundary conditions of the Greenland ice sheet have an important control on the ice flow pattern and dynamical evolution of the ice sheet. Basal melting and sliding conditions cannot be observed directly, but observables such as ice thickness, surface velocity and the internal radar layer structure contain indirect information of the basal conditions. The northeast ice stream extend to the interior parts indicating that basal conditions are also important in the interior parts.

The purpose of this study is to investigate the sensitivity of the large-scale evolution of the Greenland Ice Sheet on millennial to glacial/interglacial time scales to parameters controlling basal sliding and ice flow. In the study, we use the Parallel Ice Sheet Model (PISM) to examine the response of the ice sheet evolution to the choices of dynamic parameters. The investigated parameters relates to the parameterization of the basal processes and ice viscosity, these includes the enhancement factor, the exponent in the basal sliding relation employed in the model and the parameterization of the basal material. We run the PISM model through the last glacial/interglacial cycle for an ensemble of model parameters sets to obtain the evolution of the ice sheet using the same climate reconstruction as surface boundary conditions in all experiments in order to estimate the sensitivity of the ice sheet evolution to the choices of dynamic parameters alone. The paleo-climatic spinup of the seaRISE experiment is used as surface boundary conditions.

The results of the ensemble experiments are compared using time series of global variables and by comparing snapshots of the ice sheet at predefined times. We discuss the regional differences and sensitivity to the model parameters, and further discuss the evaluation of the parameter combinations by comparing the modelled ice flow pattern to observed present day velocities.