Control of salinity on the mixed layer depth in the world ocean: 2. Tropical areas

Abstract

A new global climatology of the barrier layer (BL) thickness based on the analysis of instantaneous temperature and salinity profiles was presented in the first part of this paper. It is used here to revisit the mean properties of the phenomenon in the tropics. Consistent with previous studies, thick and persistent BLs are detected in the deep tropics of each ocean. Their formation involves various mechanisms such as intense precipitations, oceanic circulation, wind seasonality, and river runoff, in relation with the specific geography and climatology of each basin. The weak seasonal cycle of the BL in the equatorial Pacific is analyzed in particular. Thick BLs are also detected in winter on the equatorial flank of each of the subtropical salinity maxima. They are due to the specific salinity stratification in this area and to the seasonal homogenization of temperature over the vertical under the action of atmospheric heat fluxes. Thick BLs in the western tropical Atlantic that are partly associated with important vertical temperature inversions are furthermore identified and described. More generally, agreement of the BLs mean properties in these areas with previous literature confirms the robustness of the features and validates this new product that uses most available data including the most recent ones issued from the ARGO floats. Copyright 2007 by the American Geophysical Union.