Question: Why dont the oceans freeze?

Michael Nolan answered on 14 Nov 2013:

Hi,

I think I had tried to answer this somewhere else.
Parts of the Arctic Ocean do freeze in Winter and there would also be winter freezing around Antartica.
However the interesting point is that ice forms only at the surface, rather than in the depths. As you freeze water into ice, its density (mass divided by volume) decreases, so that ice will float on water.
So, if you imagine freezing a bucket of water – the first bit to freeze is the surface of the water and the ice formed will float on the water. Now if you try to freeze deeper parts, well once you form the ice, it being less dense, will float up to sit on the water. There comes a point where you cannot freeze any deeper, so the depths of the oceans do not freeze.

Couple of points to think about
1. IF the ice were MORE dense than water, then as it forms it would sink into the depths – therefore the oceans would freeze.
2. We live in a relatively warm period – if the planet were a lot colder, then you could imagine oceans freezing to much greater depths.

Hope this helps

M