The North Atlantic Subtropical Surface Salinity Maximum As Observed by Aquarius

Aquarius satellite-derived sea surface salinity (SSS) data from August 2011 through September 2013 reveals significant seasonal migration and freshening of the subtropical surface salinity maximum (SSS-max) area in the North Atlantic, in good agreement with in situ observations, including those obtained as part of the SPURS (Salinity Processes in the Upper Ocean Regional Study) field experiment in 2012–2013. The SSS-max fluctuated in surface area—as defined by the 37.4 surface isohaline—during the course of the Aquarius time series by about 67%. The SSS-max has a surprisingly large amount of non-seasonal variability, including a general decrease in salinity throughout the eastern subtropical North Atlantic between 2011–2012 and 2012–2013 of about 0.1–0.2. The documented seasonal variability is weakest in the maximum salinity area and increases toward the north and south, respectively. This is consistent with the important role played by Ekman transport and regional excess of evaporation over precipitation in the formation of the SSS-max.