Decadal Surface and Subsurface Salinity Changes in the Oceanic Subtropical Gyres
[16-Dec-2016] Subrahmanyam, B. and Melzer, B.A.
Presented at the 2016 AGU Fall Meeting
Global salinity data from Simple Ocean Data Assimilation (SODA) reanalysis highlights surface and subsurface ocean salinity trends in evaporative-dominated subtropical gyre systems over the period of 1950-2010. The SODA reanalysis provides an assimilated view of interannual and decadal salinity variability in the oceans. Subtropical sea surface salinity trends over the past six decades were analyzed, as salinity can be a potential diagnostic of the acceleration pattern of the global water cycle. Our results indicate an increase in salinity within subtropical gyre systems, although our trend is more conservative than previous estimates. A comparison of satellite, in situ, and model simulations was conducted in an effort to resolve the near-surface salinity stratification as it pertains specifically to the subtropical gyre regions and also to show the growing relevance of satellite data in global water cycle studies. Freshwater fluxes at the air-sea interface have been established as the primary drivers of the sea surface salinity signature over open ocean regions, and are the most significant component within the oceanic branch of the water cycle. A mixed layer salinity budget was created in each subtropical gyre, based on the vertically integrated lateral advection of salt with the mean current. Despite negligible changes in the mixed layer velocity fields, we observed a net export of salt in the southern hemisphere gyres. In conclusion the observed increase in upper ocean salinity is primarily attributed to changes in non-conservative surface forcing rather than conservative advective or diffusive processes.