Hi, I read that in Antarctica, water under ice is warmer than the atmosphere above the ice, and many animals hide underwater to stay warm. Sea lions and what not. Why is that? Thanks!
In: Planetary Science
Liquid water can’t get a whole lot colder than 0° C / 32° F otherwise, it would turn into ice. It can get a little bit colder if it’s under pressure or it’s salt water, both of which lower the freezing point, but only by a couple of degrees.
On the other hand, depending on where you are in Antarctica, the air is either always colder than that, or colder than that during almost all of the year except for the peak of summer.
If you’re confused about why water that’s underneath ice is warmer than the ice, it’s because water has the convenient (for us) property that liquid water is actually densest at around 4° C, and the density decreases as it gets colder than that. That means if you have a bunch of water that’s very close to freezing, and some other water that’s at 4° C, the warmer water will sink down, away from the surface, and that means it gets insulated from the very cold air by all the water above it. In an ocean, there’s enough water that it’s impossible for all of the water to freeze except where the ocean is very shallow. And the water below the ice will always be warmer than the ice, because otherwise it would be part of the ice.
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