Sea Surface Salinity budget in the North Atlantic subtropical gyre during the 2012-2013 Strasse/SPURS experiment and from the SMOS salinity mission.

Sea surface salinity (SSS) is investigated in the subtropical North Atlantic Ocean during the Subtropical Atlantic Surface Salinity Experiment Strasse/SPURS in August 2012 - September 2013. During this experiment, more than 100 drifters were deployed providing measurements of temperature, salinity and 15m depth currents. In addition, Level3 salinity products of the Soil Moisture and Ocean Salinity (SMOS) mission corrected from large scale bias and noise are used to retrieve meso-scale salinity features. The comparison between corrected SMOS SSS data and drifter's in situ measurements shows a reasonable agreement, especially during winter time and when enough drifter data are available; the RMS differences are on the order of 0.15 pss.

The contribution of meso-scale eddies to mixed layer salinity seasonal budget is estimated both from drifter in situ data and from the combination of SMOS SSS and AVISO regional surface currents. The meso-scales eddies salinity flux contribute to a substantial freshening in the central high salinity region of the subtropical gyre, albeit often smaller than Ekman and atmospheric freshwater seasonal flux components, the leading terms of the surface salinity budget in this region. The influence of the errors from different products used to compute the salinity budget is estimated, and residuals in these SSS and SST budgets are discussed. They can arise both from the errors in the advection fields and freshwater flux, or from neglected small scale and local processes (salt fingering, vertical mixing and small scale subduction, etc.). Mercator simulation are also used to estimate the variability of the different components of the salinity budget, in particular horizontal and vertical advection.