Greenland's Elastic and Viscoelastic Adjustments to Ice Mass Changes

Abstract:

We present the latest geodetic time series from the Greenland GPS Network (GNET), assess the relative importance of instantanous elastic and delayed viscoelastic adjustments to the crustal displacement field, and discuss the complementary nature of GNET's and GRACE's sensing of ice mass changes. Clearly the most robust and best informed inversions for modern ice mass changes will utilize the GNET displacement history, GRACE's mass fields, and ice surface height changes derived from repeat altimetry and repeat optical DEMs. These inversions will also be guided by measured changes in ice flow rates, surface mass balance estimates from numerical weather models, and models of glacial isostatic adjustment. Designing an optimal inverse method requires us to asses and exploit the strengths of each class of observation in order to offset the main weaknesses in the others. GPS and GRACE are the only techniques that directly sense ice mass changes, and we present an analysis of accerations in both time series which demonstrates that GNET senses the lateral variability of ice mass accelerations in SE Greenland with much better resolution than does GRACE. When an optimal model for modern ice mass changes is achieved, and the associated elastic adjustments are subtracted from the GPS displacements, the residual displacements can be used to characterize visoelastic adjusments. These should promote an improved 'PGR correction' for GRACE.