Antarctic Diving 8 - Flakes of Ice Forming at 5m

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When the temperature drops in the sea, sometimes in the shallows ice starts to form below the surface as it is here. It starts as a nucleation point which can happen on submerged sea weed as here as delicate flakes of ice randomly forming ice crystals. In the shallows of 1-2m, ice may form on the sea bed from below as above.

Normally ice freezes from the surface of the water down as ice has a very unusual property amongst all substances in that as it turns from liquid to a solid, so it expands rather than contacts which is normal for cooling materials. This is why sea-ice floats rather than sinks as it would if it was almost anything else. The effect on the planet is profound, if water behaved "normally" then the oceans would be mainly solid ice other than the upper reaches and warmer climates.

Water has its maximum density at 4C and so all of the depths of the worlds oceans are at or around 4C as this temperature water descends due to it being denser than water around it of other temperatures.

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