Summer-time salinity variability in the North Atlantic subtropical gyre; comparison of freshening events observed in June 2006 and in July-August 2012

The largest surface salinity in the world ocean away from semi-enclosed seas is found in late summer in the North Atlantic subtropical gyre near 25-26°N 35-40°W, where it often exceeds 37.7 psu. This region is the site of the SPURS experiment. We examined all thermosalinograph data between 2002 and 2012 from two ships regularly crossing this region, the MN Colibri and MN Toucan. The data show that this region presents a minimum of spatial variability in summer, but is interspersed by occasional tongues of lower salinity, the best observed instance having happened in June 2006. In this case, we interpret the feature as advected from the north by southward currents in front of a high feature propagating to the west as Rossby waves. In the same region, recent salinity observations from instrumented drifters indicate occasional drops (by 0.3) in July and August 2012. We will discuss how advection and vertical stirring contribute to the surface salinity budget of these features. Data from the Strasse cruise surveys in August 2012 will be used to further diagnose the summer-time surface salinity budget in this region.