The Freshwater Balance Over the North Atlantic SPURS Domain from Aquarius Satellite Salinity, OSCAR Satellite Surface Currents, and Some Simplified Approaches

Within the North Atlantic subtropical gyre lies a salinity maximum region, relatively constant in time, yet forced by a seasonally varying strong evaporation zone located several degrees south and advected by wind-driven Ekman currents and geostrophic gyre currents and eddies. Large-scale calculations using in situ salinities to quantify salt divergence in the mixed layer, together with freshwater flux products, cannot account for the observed surface salinity signature. Small-scale and vertical processes must complete the budget. The Aquarius satellite system, launched in June 2011, now provides sea surface salinity observations every seven days at approximately 100 km spacing. Here, we reexamine the surface freshwater balance in the salinity maximum region, the location of the Salinity Processes in the Upper-ocean Regional Study (SPURS) campaign, from a satellite-sensed perspective. Advection of surface salinity by Ocean Surface Current Analyses Real-time (OSCAR) satellite-based surface currents is investigated for the whole region as well as within two boxes that isolate the salinity maximum and the maximum evaporation regions. Locations of imbalance, variability of surface salinity forcing terms, and areas of potential transport and redistribution are explored using satellite observations. A discussion then considers the vertical pathways by which surface waters reach and exchange salinity with the deep ocean, thus contributing to the signal seen at the surface.