Multiple equilibria in a global ocean general circulation model

A global ocean general circulation model is forced using various upper boundary conditions (BCs) on temperature and salinity. Solutions are obtained under restoring and mixed BCs (i.e., a restoring condition on the upper-level temperature but using a fixed, specified surface salt flux). Salt flux anomalies are temporarily applied under mixed BCs, and solutions are obtained in which overturning associated with deep-water formation is either present or absent in the North Atlantic and either vigorous or weak in the North Pacific. A comparison between these solutions helps to clarify the role North Atlantic deep-water formation plays in maintaining the current climate. The surface heat fluxes differ substantially between the solutions, and their very existence is dependent upon these differences. As a result they are not multiple equilibra of the ocean model alone. Instead, they should be regarded as multiple equilibria of a very crude coupled atmosphere-ocean system. -from Authors