• Question: Why don't the oceans freeze? is it to do with salt in the water?

    Asked by sodiumpolyacrylate to David, James, Mike, Suze, Will on 15 Jun 2011.
    • Photo: Mike Dodd

      Mike Dodd answered on 15 Jun 2011:

      I think it is a mixture of salt in the water and the movement. The north pole is actually a frozen sea. So it can freeze, but it is unlikely. When you add salt to water it changes the freezing point from the normal 0 degrees to around -10 degrees. So only if the temperature drops below -10 and the ocean is still, is it going to freeze.

    • Photo: David Ingram

      David Ingram answered on 15 Jun 2011:

      Oceans do freeze but only when it’s very cold and then only the surface layers. We have sometimes had frozen sea near the shore in the UK, but the polar seas are frozen for much of the time.

      If it wasn’t for the Gulf Stream (a warm water current which flows passed the UK) our oceans would be frozen more often in winter and the English Channel would be crossable by sledge or ice-breaking ship!

    • Photo: James Marrow

      James Marrow answered on 15 Jun 2011:

      The salt is the main reason – it’s why we sprinkle salt on the roads and pavements in the winter. The freezing point of pure water is 0C, but the freezing point of salty water is lower, so unless it gets really cold (like this winter), the water won’t freeze.

      The same thing happens when we make metal alloys – in many cases the melting temperature (same as the freezing temperature!) is lower for the alloy (mix) of two elements than it is for the pure elements. Solder is a good example – it has a very low melting point which is useful for making electrical circuits without damaging the delicate electronic components.

    • Photo: Suze Kundu

      Suze Kundu answered on 15 Jun 2011:

      Salt does lower the freezing point of the water, but as they are so HUGE, it would take a lot to freeze the lot. You get surface ice in very cold areas, but to freeze everything would take something awful happening to the Earth, and we don’t want that!

      As water gets bigger when frozen, I wonder where all the ice / water would go, if the oceans did freeze… I don’t think we’d be around to find out!

Comments

  • Photo: sodiumpolyacrylate

    sodiumpolyacrylate commented on :

    I have done a practical once and place 2 jars of water in a freezer, one of it had salt mixed with it and the other had just water and so i kept it in the freezer for hours … after i took it out, the jar with just water froze completely and the other jar which had salt in it didnt completely freeze.. why was it like that when you told me that the tempreture of the salty water drops and the salty water didnt completely freeze?

  • Photo: Mike

    Mike commented on :

    I’m not sure to be honest. Although only a small amount of the ocean actually freezes. It’s possible that you would have to wait a long time for the whole jar of salty water to freeze. As the two types of water will have different freezing points, they will take different times to freeze at the set temperature. So if you have salty water and fresh water at -10, then the fresh water will freeze quicker, as it is 10 degrees below it’s freezing point. However the salty water would take longer, as it is just at it’s freezing point. I guess you could test this by having the salty water jar at -10 and the other water jar at 0 degrees and see if they take the same time to freeze. I don’t know the answer but would be interesting.

    On a slightly different note, did you know that water is densest at 4 degrees? When water reaches 4 degrees it will sink, until it starts to freeze and will then rise and can float. It is an odd property for a solid, as you think of most solids being denser (or sinking) than when they are a liquid.