Decadal steric and sea surface height changes in the Southern Hemisphere

Abstract

Sea surface height (SSH) changes result from changes in steric height (SH) and mass. We investigate total SH and mass from co-located measurements of SSH and SH in the upper 1500 dbar (SH 0-1500). SSH changes are decomposed into SH 0-1500 and other contributions, where other includes SH changes below 1500 dbar and mass changes. This is done using satellite altimeter measurements of SSH available since late 1992 in combination with WOCE-era hydrography and Argo. A hemispheric analysis of co-located WOCE and Argo profiles gives robust δSH/δSSH relationships, varying with latitude. The δSH/δSSH ratio together with satellite SSH yields an estimate of decadal SH increase. It is found that ∼0.5 of the hemispheric decadal SSH rise is steric, with this proportion increasing southwards. The relatively large rate of SSH increase south of 30°S, the high proportion attributable to SH (i.e., ocean warming) and the great area of the southern ocean, mean the total heat gain south of 20S is comparable to estimates of global 0-700 m heat gain for this period. Copyright 2011 by the American Geophysical Union.