The polar warmth of the greenhouse climates in the Earth's past represents a fundamentally different climate state to that of today, with a strongly reduced temperature difference between the Equator and the poles. It is commonly thought that this would lead to a more quiescent ocean, with much reduced ventilation of the abyss. Surprisingly, using a Cretaceous cimate model, we find that ocean overturning is not weaker under a reduced temperature gradient arising from amplified polar heat.