CoAuthors

Katherine Quinn (AER, United States); Christopher Piecuch (WHOI, United States)

Gravitational attraction and loading (GAL) effects associated with ongoing long-term changes in land ice are expected to cause spatially varying trends in absolute sea level (ASL) measured by satellite altimetry. The largest spatial gradients in ASL trends, predicted from solving the Sea Level Equation using GRACE retrievals of mass distribution over land for the period 2005-15, occur near Greenland and West Antarctica, consistent with a strong local land ice loss. Misinterpreting the estimated static GAL trends in ASL as dynamic pressure gradients can lead to substantial errors in large-scale geostrophic transports across the Southern Ocean and the subpolar North Atlantic over the analyzed decade. South of Greenland, where altimeter sea level and hydrography (Argo) data coverage is good, the residual ASL minus steric height trends are similar in magnitude and sign to the gravitationally based predictions. In addition, estimated GAL-related trends are as large, if not larger than other factors such as deep steric height, dynamic bottom pressure, and glacial isostatic rebound.

The results indicate that accounting for static GAL effects on altimeter records, just as one routinely corrects for static inverted barometer effects, can be important for quantitative interpretation of the observed ASL trends. The issue will only become more crucial as altimeter records are extended in the future and effects of land ice become relatively larger, compared to other dynamical trends in ASL. Initial discussion is pursued on some of the pros and cons of implementing a GAL correction and the uncertainties involved, in the broader context of altimeter error budgets.