Global sea level rise and glacial isostatic adjustment

The fact that the ongoing global process of glacial isostatic adjustment (GIA) contributes significantly to present-day observed rates of secular sea level change that are recorded on tide gauges is now rather well established. There is a continuing discussion, however, of the magnitude of the globally averaged rate of relative sea level rise that is residual to this GIA related 'contamination'. Accurate estimation of this residual is clearly important to the understanding of ongoing global change in the earth system. In the analyses presented herein, following a review of the global theory of the GIA process that focuses on the issue of rotational feedback, I begin by revisiting the issue of estimating this residual on the basis of secular sea level change measurements derived from long time series of annually averaged tide gauge recordings. These observations, all from the US east coast, are then decontaminated by subtracting estimates of the GIA effect determined on the basis of analysis of C-14 dated relative sea level histories to infer a (climate related?) residual signal. Also discussed herein, from a global modelling perspective, is the issue of the extent to which a globally averaged rate of sea level rise based upon TOPEX/POSEIDON type altimetric data (or secular gravity field data from the future GRACE mission) is expected to be contaminated by the GIA process. This issue has not been addressed previously and our analyses show that this contamination of the satellite altimeter estimated rate of global sea level rise will also be significantly influenced, locally, by ongoing glacial isostatic adjustment. However, when this signal is averaged over the surface track of TOPEX/POSEIDON we find that the extent to which this instrument's measure of the globally averaged rate of sea level rise is contaminated by the GIA process is small. (C) 1999 Elsevier Science B.V. All rights reserved.