if heat rises, why do bodies of water freeze from the top down?

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If I had to guess, it’s because the temperature above the water is constantly colder than the water itself – but that is what I actually don’t understand.

If the surface temperate is extremely colder than the temperature of the water itself, wouldn’t the cold “sink” that much faster, making the warm water “rise” at an equivalent rate, and thus forcing more of the cold water to the bottom?

Maybe a better post for stupid questions, but I’m very curious what causes this – perhaps this just applies to air, and not water? And if that’s the case, then also why?

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Anonymous 0 Comments

Heat rises because heat tends to make things less dense and so they float in the same fluid medium. Water, however, is different, while water does follow the same rule because of the crystalline structure formed water reaches its maximum density under normal atmospheric conditions at 4°C. So water at freezing temperatures is less dense than the relatively warmer waters underneath it, as a result water tends to freeze from the top down and act as an insulator for the liquid water underneath, this is an important factor for aquatic species surviving the freezing winters.

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