Accounting for Gravitational Attraction and Loading Effects from Land Ice on Absolute Sea Level

Abstract

AbstractGravitational 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 ζ, as measured by satellite altimeters. The largest spatial gradients in ζ 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 ζ 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 ζ 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. Thus, accounting for static GAL effects on ζ records, which are commonly neglected in oceanographic studies, seems important for a quantitative interpretation of the observed ζ trends.