Upper Ocean Salinity Stratification in the Tropics As Derived from the Buoyancy Frequency N2

Abstract:

The idea that salinity contributes to ocean dynamics is simply common sense in physical oceanography. Along with temperature, salinity determines the ocean mass and hence, through geostrophy, influences ocean dynamics and currents. But, in the Tropics, salinity effects have generally been neglected. Nevertheless, observational studies of the western Pacific Ocean have suggested since the mid-1980s that the barrier layer resulting from the ocean salinity stratification within the mixed layer could influence significantly the ocean-atmosphere interactions. The present study aims to isolate the specific role of the salinity stratification in the layers above the main pycnocline by taking into account the respective thermal and saline dependencies in the Brunt-Vaisala frequency, N2. Results will show that the haline stabilizing effect may contribute to 40–50% in N2 as compared to the thermal stratification and, in some specific regions, exceeds it for a few months of the seasonal cycle. At the contrary, the centers of action of the subtropical gyres are characterized by the permanent absence of such effect. The relationships between the stabilizing effect and the sea surface fields such as SSS and SST are shown to be well defined and quasilinear in the Tropics, providing some indication that in the future, analyses that consider both satellite surface salinity measurements at the surface and vertical profiles at depth will result in a better determination of the role of the salinity stratification in climate prediction systems.