Sea Surface Temperature-Evaporation Feedback and the Ocean's Thermohaline Circulation

Abstract

A simple surface boundary condition that allows evaporation to depend on sea surface temperature is developed for use in uncoupled ocean models. A positive feedback with the thermohaline circulation is produced, whereby accelerated overturning warms the high latitudes by advection, increasing evaporation and hence the sea surface salinity, which then feeds back upon the overturning circulation. Nonlinear interaction with convection complicates the response in some cases; however, in general the time-dependent component of the evaporation tends to be small so that the evolution is similar between parallel experiments with SST-dependent evaporation and under fixed freshwater fluxes. In agreement with this, two examples with internal variability of the thermohaline circulation on decadal and millennial timescales respectively are not fundamentally altered under the new feedback compared to the control runs under mixed boundary conditions, although both the period and the duration of the variability am shortened in some instances.