| Summary: | [1] The presence of low-latitude circumglobal passage from the late Jurassic (160 Ma) through the Miocene (14 Ma) provides a possible mechanism for increased poleward ocean heat transport during periods of warm climate and may help explain low meridional temperature gradients of the past. Experiments using an ocean general circulation model (GCM) with an energy-balance atmosphere and idealized bathymetry reveal that, like the modern Drake Passage, a circumglobal Tethyan Passage might have induced high rates of wind-driven upwelling of relatively cold and deep water, but at low latitudes. With no change in radiative forcing, a low-latitude circumglobal passage increases simulated northern high-latitude temperatures by 3–7C, while tropical temperatures cool by up to 2C relative to a scenario with solid meridional boundaries. Combining this mechanism of heat transport with increased radiative forcing allows substantial warming of northern high latitudes by 7–11C, while tropical temperatures remain within 3C of present-day temperatures. INDEX
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