• Question: Why don`t the ocean freeze in the winter?

    Asked by PartyPoison123 to Anne, Florence, Mark, Neil, Sinead on 6 Nov 2015.
    • Photo: Florence McCarthy

      Florence McCarthy answered on 6 Nov 2015:

      Good question, in many polar regions it does but freezing is much less common in sea water than in fresh water. The level of salt in sea water effectively lowers the freezing point (which is why we salt/grit the roads in winter). Also the constant motion of the ocean makes it difficult for ice to form in comparison to a standing lake (why do small puddles freeze before rivers?).

    • Photo: Neil Day

      Neil Day answered on 8 Nov 2015:

      It’s a combination of the presence of salt lowering the freezing point of water and also the continual motion of the ocean. The earth’s climate has changed in recent times so that the sea freezing happens less and less in our area of the planet. I had heard tales of Portsmouth Harbour freezing over in winterback in the 19th Century but it has never happened in my life-time.If global temperatures lower in the future this may become a fixture again…we’ll see!

    • Photo: Mark Collins

      Mark Collins answered on 8 Nov 2015:

      This is a great question! It does partially in the Arctic regions and all year round in that area! For the rest of the globe, it is the continuous flow of the oceans caused by the gravitational pull of the moon that gives us our weather systems and the tides, there is also the sheer volume of water and that is much warmer between the tropics and this warm water always flows around. There is also just the sheer size and volume of the water mass, it is enormous! We may see at some stage in many centuries the Irish Sea freezing or a smaller body but even if it did, if we went a few metres beneath the water would not be frozen. In order for the water to freeze completely we would need to move our planet out of its orbit and also the due to the specific gravity of ice being lower than water, it will expand so the earth would just become a giant flying ice ball flying through the cosmos! I’m quite happy the oceans do not all freeze!

    • Photo: Sinead Balgobin

      Sinead Balgobin answered on 11 Nov 2015:

      The ocean does freeze- but only if it’s really really cold, and only a little bit. There are several reasons for this: first, the salt in ocean water lowers the freezing point of water so it has to get a lot colder for the water to freeze (this is why we put salt on the roads in winter to stop them getting icy). Another reason is the sheer volume of water in the ocean- heat is lost from the surface of the water, and with a volume as big as the ocean (because it’s deep) it doesn’t have a lot of surface to lose heat from (try putting a teaspoon of water in the freezer, next to a bottle, and see which freezes first). The ocean is also always moving which makes it harder to freeze (a pond freezes faster than a river). Another reason altogether is that the earth is actually hot in the middle- so the deeper you go, the hotter it gets, so heat isn’t lost from the ocean at the bottom.