Climate Drift in a Global Ocean General Circulation Model

Abstract

Abstract A global version of the GFDL modular ocean model is forced using conventional restoring boundary conditions (BCs), mixed BCs (i.e., restoring the upper-level temperature but specifying a fixed salt flux), and stochastic fluxes of both heat and freshwater. The climatology of the model is found to drift if stochastic freshwater fluxes are applied at high latitudes under mixed BCs. The drift is global in extent: the ocean is generally warmer in the North Pacific and Weddell Sea but cooler and fresher at depths elsewhere in the Southern Ocean and in the North Atlantic. There is a slight reduction (by about 5%) in the meridional overturning of the Southern Ocean and the North Atlantic. The drift of the barotropic flow is most pronounced in the Southern Ocean and is associated with a permanent meandering of the Antarctic Circumpolar Current. The drift occurs within a few decades, suggesting that it may be important in enhanced greenhouse scenarios for early next century that have been obtained using co...