A multirheology ice model: Formulation and application to the Greenland ice sheet

Abstract

Accurate prediction of future sea level rises requires models which can reproduce recent observed change in ice sheet behavior. This study describes a new multiphase, multiple-rheology ice dynamics model (SEGMENT-ice), which is used to examine Greenland ice sheet (GrIS) responses both to past and to possible future warming climate conditions. When applied to the GrIS, SEGMENT-ice exhibits skill in reproducing the mass loss rate derived from the Gravity Recovery and Climate Experiment (GRACE), the interferometric synthetic aperture radar (InSAR) measured surface flow speed, and the microwave remotely sensed surface melt area over the past decade. When forced by the NCEP/NCAR reanalysis atmospheric parameters, the ice model simulates closely the GrIS mass loss rate obtained from GRACE. An increase of summer maximum melt area extent (SME) is indicative of an expansion of the ablation zone. The modeled SME from 1979 to 2006 also simulates well the observed interannual variability of SME, with a high correlation of 0.88 between the two time series. The geographical distributions of the modeled and observed SME also agree well.Comparison of modeled and observed velocity over three regions, covering the west, northeast, and north sides of the GrIS, respectively, indicates a satisfactory model performance in delineating flow direction and magnitudes for regions with flow speed less than 500 m/y, with no region-specific systematic errors. However, the model cannot simulate extremes in the observations, mainly because it is limited by spatial resolution. The SEGMENT-ice simulations are sufficiently close to the observations to employ the model to project the future behavior of the GrIS. By the end of this century, if the moderate A1B scenario is realized, the total mass lossrate will reach ~ 220 km3/y. The ice divergence contribution will be about 60%, outweighing the contribution from surface processes.