Stabilization of thermohaline circulation by wind-driven and vertical diffusive salt transport

The stability of the thermohaline circulation is investigated using an ocea n general circulation model coupled to a simple atmospheric model. The atmo spheric model is so developed that it represents the wind stress and the fr eshwater flux more realistically than existing energy balance models. The c oupled model can reproduce the realistic deep ocean circulation without any flux adjustment. Effects of the wind stress and the vertical diffusion on the thermohaline circulation are studied by conducting various experiments with the coupled model. The Ekman upwelling between 60 degreesN and 90 degr eesN brings up salt to the sea surface, while the compensation flow of the Ekman transport and the wind-driven gyro circulation between 30 degreesN an d 60 degreesN carry salt horizontally to the high latitudes. By carrying ou t experiments where the wind stress is completely or partly removed, it is demonstrated that either of the vertical or the horizontal salt transport p revents the halocline formation at high latitudes and maintains the thermoh aline circulation. For an experiment in which the vertical diffusivity is e nhanced at high latitudes, it is shown that the vertical diffusion at high latitudes also prevents the halocline formation and stabilizes the thermoha line circulation. It is also shown that the value of the vertical diffusivi ty at high latitude affects the existence of the multiple equilibria of the thermohaline circulation.