Global mean sea level: what's ocean circulation got to do with it?

Global mean sea level rise partly reflects volumetric expansion due to ocean density change, otherwise known as steric sea level change. Owing to the nonlinear nature of the equation of state of seawater, causes for observed global mean steric sea level change have not been well understood. Using a data-constrained state estimate, we revisit global mean steric sea level change over 1993-2003, quantifying contributions from ocean transports and surface exchanges using closed temperature and salinity budgets. Analyses demonstrate that estimated decadal global mean steric sea level change (1 mm/yr) represents a relatively small deviation from a near balance between atmospheric forcing and ocean transports: surface heat and freshwater exchanges produce a positive trend in global mean steric sea level (9 mm/yr) that is mainly compensated by redistribution of temperature and salinity through small-scale diffusion (-7 mm/yr) and large-scale advection (-1 mm/yr). Global trends effected by ocean transport processes reflect the nonlinear nature of the equation of state of seawater. Results contradict the notion that global mean sea level is not affected by advection of temperature and salinity by ocean currents. Inherent difficulties associated with simulating global mean sea level in general circulation models will be highlighted.