Quote:
Originally Posted by Average Joe
Actually thats incorrect. The polar ice is not frozen fresh water with liquid sea water below.
Sea water WILL freeze if it is cold enough at the surface, it won't freeze at 0 degrees like freshwater, but will freeze at many degrees below zero - which it is at the poles.
The reason the ice cap has liquid water underneath is because once you go further below the surface the water is warmer and not cold enough to freeze - remember the severely sub zero temperatures are air temperatures at the surface and the water itself provides an insulation against those temperatures when you start going down. plus you have to factor in warm ocean currents. But of course the surface of the sea, in contact with frigid air, will freeze.
Think of it this way, you get a very cold snap and the local lake freezes over, does it ever freeze all the way to the bottom? No. Even freshwater will not freeze absolutely solid.
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Salty water freezes below 0°C (32°F): this is why salt is used to melt the snow or ice on a road pavement. The saltier the brine, the lower its freezing point. This is also why salt traditionally was added to the water–ice mixture used to make ice cream.
Ocean water with a typical salinity of 35 parts per thousand freezes only at −1.8°C (28.9°F). So if there were no halocline in the polar oceans, then the cooled top ocean layer, being denser, would sink into the deep ocean, in the same way as thunderstorm clouds rise in the atmosphere, and the entire ocean column would have to cool to −1.8°C before its surface could freeze.