Mechanisms of interannual steric sea level variability

Processes contributing to interannual steric sea level variability are studied over the period 1993\textendash2004 using an observationally-constrained ocean state estimate produced by the ECCO (\textquotedblleftEstimating the Circulation and Climate of the Ocean\textquotedblright) consortium. The estimate\textquoterights dynamical consistency allows for the comprehensive attribution of steric changes in terms of advection, diffusion, and surface buoyancy exchange processes. Steric variations are found to be owing more to oceanic transports than to local surface buoyancy fluxes. Advection is responsible for steric variability in the tropical Indian and Pacific oceans. At extratropical latitudes, advection and diffusion appear to be equally important. Local surface buoyancy fluxes can contribute in some regions (e.g., the tropical Atlantic). Analysis of the anomalous wind stress curl shows that extra-equatorial vertical advection is driven primarily by Ekman pumping. The complexity of the interannual steric budget suggests that anomalous sea level is probably not predictable on the basis of ocean memory alone. Furthermore, proper parameterizations of mixing processes and good estimates of wind-driven transports both appear to be very important to reliable projections of interannual sea level.