Anatomy of Interannual to Decadal Sea Level Changes in the GECCO3 Ocean Synthesis

Abstract

The GECCO3 synthesis is used to infer a dynamically consistent decomposition of sea level changes (variability and trends) on interannual to decadal time scales. Over most parts of the global ocean equatorward of 60° latitude, sea level variability and trends can be explained almost completely by the upper ocean (above 2,000 m) steric component alone. On decadal and longer time scales, we find strong but negative relations between the deep steric component (below 2,000 m) and the manometric changes. Such a relation, albeit weaker, can also be identified on annual to decadal timescales in the MPI‐ESM climate model. Sea level variability over all shallow shelf regions (water depth <500 m) and some fraction of the Southern Ocean appear to be dominated by manometric changes. Enhanced but short spatial scale manometric contributions exist also in boundary current regions, such as the North Atlantic or the Antarctic Circumpolar Current region. Our findings suggest that without a full depth steric sea level information available, observed sea level change on decadal and longer time scales might best be explained by just using the steric estimate available from the top 2,000 m depth as provided by Argo. Adding additionally information from the GRACE bottom pressure fields without knowing the deep steric changes will likely degrade the decomposition of sea level in many regions of the world ocean. We encountered large differences between the GECCO3 reanalysis manometric component and what the GRACE project provides, suggesting remaining uncertainties to exist in the GRACE ocean products and/or GECCO3 fields.