A low-resolution coupled ocean-atmosphere general circulation model (OAGCM) is used to study the characteristics of the large-scale ocean circulation and its climatic impacts in a series of global coupled aquaplanet experiments. Three configurations, designed to produce fundamentally different ocean circulation regimes, are considered. The first has no obstruction to zonal flow, the second contains a low barrier that blocks zonal flow in the ocean at all latitudes, creating a single enclosed

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... in, while the third contains a gap in the barrier to allow circumglobal flow at high southern latitudes. Warm greenhouse climates with a global average air surface temperature of around 27°C result in all cases. Equator-to-pole temperature gradients are shallower than that of a current climate simulation. While changes in the land configuration cause regional changes in temperature, winds, and rainfall, heat transports within the system are little affected. Inhibition of all ocean transport on the aquaplanet leads to a reduction in global mean surface temperature of 8°C, along with a sharpening of the meridional temperature gradient. This results from a reduction in global atmospheric water vapor content and an increase in tropical albedo, both of which act to reduce global surface temperatures. Fitting a simple radiative model to the atmospheric characteristics of the OAGCM solutions suggests that a simpler atmosphere model, with radiative parameters chosen a priori based on the changing surface configuration, would have produced qualitatively different results. This implies that studies with reduced complexity atmospheres need to be guided by more complex OAGCM results on a case-by-case basis. FIG. 2. Twice-yearly average of the maximum strength of the oceanic meridional overturning streamfunction (Sv) for the last 300 yr of the climate spinups, the first 200 of which are integrated with periodic coupling scheme: WaterWorld (light, solid line); RidgeWorld (heavy, solid line); and (dashed line) DrakeWorld. 4722