Effect of isostasy on dynamical ice sheet modeling: A case study for Eurasia

摘要

Isostatic adjustment is an important process when modeling dynamical ice sheet evolution. A number of different types of Earth model are used to model this process, ranging from models with local or elastic lithospheres with a single relaxation time to account for temporal behavior to self-gravitating spherically symmetric models of the crust-mantle system. We performed sensitivity tests to assess the dynamical response of ice sheets to isostatic adjustment. The resulting ice sheet geometries depend on the response times of the system, including the growth rate of ice sheets versus the relaxation time of the Earth. Differences in lithospheric strength cause large differences in the modeled ice sheets, with the largest differences in isostatic adjustment in the vicinity of the ice margins. In addition, we compared predictions based on an often used flexural model with an elastic plate and a single relaxation time to a spherically symmetric self-gravitating viscoelastic approach. No flexural model was able to reproduce the viscoelastic response completely, due to the fact that the models have an intrinsically different spatial and temporal response. When applied to a full transient glacial cycle in Eurasia, even the best fitting flexural model underestimated the ice volume at the LGM by 30 percent. Our results indicate that the commonly used value of 3000 years for the relaxation time in flexural models is too short for Eurasia by at least 3000 years.