Glacial isostatic adjustment and nonstationary signals observed by GRACE

Changes in hydrologic surface loads, glacier mass balance, and glacial isostatic adjustment (GIA) have been observed using data from the Gravity Recovery and Climate Experiment (GRACE) mission. In some cases, the estimates have been made by calculating a combination of the linear rate of change of the time series and periodic seasonal variations of GRACE estimates, yet the geophysical phenomena are often not stationary in nature or are dominated by other nonstationary signals. We investigate the variation in linear rate estimates that arise when selecting different time intervals of GRACE solutions and show that more accurate estimates of stationary signals such as GIA can be obtained after the removal of model-based hydrologic effects. We focus on North America, where numerical hydrological models exist, and East Antarctica, where such models are not readily available. The root mean square of vertical velocities in North America are reduced by ∼20% in a comparison of GRACE- and GPS-derived uplift rates when the GRACE products are corrected for hydrological effects using the GLDAS model. The correlation between the rate estimates of the two techniques increases from 0.58 to 0.73. While acknowledging that the GLDAS model does not model all aspects of the hydrological cycle, it is sufficiently accurate to demonstrate the importance of accounting for hydrological effects before estimating linear trends from GRACE signals. We also show from a comparison of predicted GIA models and observed GPS uplift rates that the positive anomaly seen in Enderby Land, East Antarctica, is not a stationary signal related to GIA.