The effects of subgrid-scale parameterizations in a zonally averaged oceanmodel

Isopycnal diffusion and an additional transport velocity parameterizing the effect of mesoscale eddies are implemented in the ocean component of a 2.5 -dimensional zonally averaged coupled ocean-atmosphere model. The equilibri um states of the coupled ocean-atmosphere model, resulting from the differe nt mixing parameterizations, are compared, and extensive parameter sensitiv ity studies are presented. For the equilibrium base states, the new mixing schemes result in changes in the distributions of temperature and salinity that are significant in the Southern Ocean, where the isopycnal surfaces ar e steep and the eddy-induced transport velocity approximately cancels the D eacon cell. The temperature and salinity changes are relatively small in th e rest of the ocean. Furthermore, the implementation of the new mixing sche mes results in significant changes in the strength and the pattern of the t hermohaline circulation. Transient responses of the coupled ocean-atmospher e system in global warming scenarios are compared for the different mixing parameterizations. It is demonstrated that large changes in the stability o f the thermohaline circulation occur and that the observed changes in stabi lity are highly parameter dependent.