Abstract
The effects of temporal changes in the marine geoid on estimates of the
ocean dynamic topography is being investigated. Influences from changes
of land hydrology, ice sheets, Post-Glacial Rebound (PGR), and ocean and
atmospheric dynamics are considered and the associated crustal
deformation is included. The strongest signals are associated with the
seasonal cycle caused by changes in terrestrial water content and ice
sheets as well as the redistribution of atmospheric mass. Second to this
is the importance of an overall trend caused by PGR and decreasing ice
sheets over Greenland and Antarctica. On long spatial scales, the
amplitude of regional trends estimated for the geoid height have a
sizable fraction of those from Sea Level Anomaly (SLA) for the period
1993–2016, also after subtraction of steric height of the upper 1000m
to analyze trends in deep ocean geostrophic currents. The estimated
strong negative geoid height trend south of Greenland for the period
1993–2016 opposes changes in dynamic sea level for the same period
thereby affecting past studies on changes of both the strength of the
Subpolar Gyre based on SLA and the meridional overturning circulation on
a section between Cape Farewell and Portugal applying ocean dynamic
topography and hydrography. We conclude that temporal geoid height
trends should be considered in studies of (multi-)decadal trends in sea
level and circulation on large spatial scales based on altimetry data
referenced to a geoid field.