Climatic inferences from the ventilated thermocline

Abstract

Several computed cases of a model of the subtropical gyre with a partially ventilated thermocline (Luytenet al., 1982) are presented to illustrate the sensitivity of the field of density stratification, mean flow and location of unventilated regions to slight changes in surface boundary conditions. The structure of the low latitude thermocline is less sensitive to climatic change in amount of water forced down by convergence of wind-driven surface layers at higher latitudes than might be expected, even allowing for the well-known localness of vertically integrated meridional transport. On the other hand changes in structure at low latitudes do arise from changes in boundary conditions on the surface density at higher latitudes.

The main climatic inference for transient tracers injected into a thermocline in steady state is that there are two time-scales in the subtropical thermocline: an advective time scale associated with distance from regions of direct ventilation of a density layer at the surface, and a subsurface diffusive time scale from ventilated to unventilated region.