Ocean heat transport and a climate paradox

Paleoclimate data indicate a climate paradox. In warmer climates the equato r to pole temperature gradient is typically less than that of the current c limate. However, more northward heat transport is required to maintain this weaker gradient, particularly in tropical, subtropical and midlatitude reg ions where the ice-albedo feedback and polar stratification of the atmosphe re have little effect. Most heat transport mechanisms decrease with decreas ed temperature gradient. Two oceanic mechanisms that might contribute to a resolution of this paradox are examined, one relies upon salinity re-distri bution, while the other relies upon the non-linearity of the equation of st ate. These are tested in a simply configured ocean general circulation mode l of the North Atlantic. Both are shown to increase northward heat transpor t without increasing the meridional temperature gradient. The nonlinearity mechanism is the more significant of the two, but neither of the mechanisms can conclusively resolve the paradox.