Due to the spin of the earth, things are actually slightly heavier nearer to the poles than at the Equator, meaning that cooler, denser ocean water will tend to want to “sink” towards the equator while warmer, less dense ocean water will tend to “float” towards the poles.
This results in a circulation effect in large water bodies, like the Atlantic and Pacific oceans, where water heats up at the equator, flows north and cools as it goes, releasing that heat into the nearby enviornment (and eventually radiating into space), and thus keeping those areas relatively warm, before flowing back south.
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