An assessment of basic processes controlling mean surface salinity over the global ocean

A data‐constrained ocean state estimate that permits closed property budget diagnostics is used to examine the balance between surface forcing ( F¯), advective ( A¯), and diffusive ( D¯) fluxes in maintaining the large‐scale time‐mean surface salinity Ss¯. Time‐mean budgets (1993–2010) are considered for the 10 m thick top layer. In general, D¯ tends to counteract F¯, but A¯ is important almost everywhere, and some regions show a main balance between A¯ and D¯ (Bay of Bengal, Arctic) or A¯ and F¯ (tropical Atlantic and Pacific). Advection tends to freshen the surface in the tropics and high latitudes, with opposite tendencies in midlatitudes. For various Ss¯ tropical extrema, A¯ adds to the F¯ tendencies in precipitation regions and opposes F¯ in evaporation regions. Long‐term Ss¯ conditions thus reflect more than a simple diffusive adjustment to F¯, likely involving close interaction between wind‐ and buoyancy‐driven circulation and mixing processes. Key Points A global ocean state estimate yields closed budget diagnostics of the mean surface salinity balance Surface advection plays a key role in balancing forcing and diffusion tendencies in most regions Advection tends to freshen the tropics and high latitudes and add salt to midlatitudes