I don’t subscribe to this AGW crap, but an interesting property of water is that as the temperature decreases, there is a point where its density increase stops, then reverses. If I remember correctly, that point is 39*F.
So technically there is a window close to the freezing point where the warmer water will sink.
But the AGW theory is still crap.
Great point. Some fantastic design work which prevents water from freezing from the bottom up which would be a bit of a problem here on Gaia.