• Question: how come at the bottom of oceans the water is cold ? because it is closer to the core which is meant to be hot

    Asked by theo to Adam, Chris, Eleanor, Jessamyn, Sinead on 11 Nov 2013.
    • Photo: Adam Murphy

      Adam Murphy answered on 11 Nov 2013:

      There are two reasons why it’s cold. Cold water is denser than hot water, so the water molecules are closer together, making it heavier, so it sinks to the bottom.

      (Weird thing about water is once it cools past 4 degrees celsuis it starts to expand again, which is why pipes burst when it freezes)

      The other reason is that once it’s down there there’s nothing to heat it, so it stays cold. There’s no light to warm it up, and it’s still too far away from the core to feel it’s effects.

      BUT! There are things called hydrothermic vents, which are places where the molten mantle is exposed, and the water around these can be more than 400 degrees c! There are some weird animals that live around these things, like a new type of armored snail called the scaly foot gastropod!

      Deep sea stuff is really cool!

    • Photo: Christian Wirtz

      Christian Wirtz answered on 11 Nov 2013:

      I think Adam has answered it nicely. The fact that water is most dense at 4 degrees Celsius means the bottom of the ocean is 4 degrees Celsius warm. This strange density anomaly is what makes water so special and allows for it to support life. If ice was denser than water (for almost all substances the solid phase is denser than the liquid) the bottom of the oceans would be made of ice that would never melt as the sun cannot heat it up in those depths.

      The deepest point of the ocean is about 11 km below sea level. That is not very much closer to the core than we are on the surface here so the main source of heat for the oceans is the sun, not the core.

    • Photo: Eleanor Holmes

      Eleanor Holmes answered on 11 Nov 2013:

      It is cold down there at the bottom of the ocean. And that is because the colder something is the denser it is (generally) and denser stuff sinks.

      The water at the bottom may well be heated by the earth’s core and by the hydrothermic vents that Adam talked about. But you have to remember the sheer volume of water there is in the ocean. It takes 4.2 Joules (or 1 Calorie) of energy to heat 1 litre of water by 1 degree celsius.

      The combined oceans of the world contain about 5.46 x10^21 litres of water. So to heat all that water up from the bottom would take 5,460,000,000,000,000,000,000 (5.46 sextillion) Joules of energy. And that’s just to be 1 degree warmer.

      Now the sun heats from the top down, which is much easier because the heated water tends to stay near the top and get even hotter. So it takes much less energy to make the oceans around Greece warm enough to swim in down to about 3 metres.

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