In this special issue of Oceanography, we explore the results of SPURS-1, the first part of the ocean process study Salinity Processes in the Upper-ocean Regional Study (SPURS). The experiment was conducted between August 2012 and October 2013 in the subtropical North Atlantic and was the first of two experiments (SPURS come in pairs!). SPURS-2 is planned for 2016–2017 in the tropical eastern Pacific Ocean.
The scientific motivation behind SPURS arises from the desire to understand the patterns and variations of salinity at the ocean’s surface. To first order, surface salinity patterns reflect the overlying patterns of evaporation and precipitation that force the freshwater balance in the upper ocean (Wüst, 1936). Maps of the net difference between evaporation and precipitation (E–P) appear to be quite similar in pattern to surface salinity. If the surface salinity is determined only by (E–P), then the ocean itself might serve as crude “rain gauge.” In fact, it is already known that ocean circulation in the form of wind-driven surface currents must be accounted for in understanding surface salinity patterns (surface salinity maxima are offset poleward of subtropical E–P maxima due to Ekman currents induced by the trade winds). In addition, ocean mixing processes also affect the temporal evolution of surface salinity. SPURS was designed to examine the salinity balance in the upper ocean through observation of salinity and ocean circulation on a variety of scales.