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How dense are the waters around Antarctica?
According to its Wikipedia entry: "The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from -0.8 to 2 °C (31 °F), salinities from 34.6 to 34.7 psu. Being the densest water mass of the World Ocean, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level." From Windows to the Universe: "The density of pure water is 1000 kg/m3. Ocean water is more dense because of the salt in it. Density of ocean water at the sea surface is about 1027 kg/m3."
Why doesnt Antarctic bottom water freeze?
From its Wikipedia page: "Being the densest water mass of the World Ocean, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level." The Southern Ocean freezes at about a depth of eight to 12 feet during the winter months, which is not deep enough to freeze the bottom water.
How cold is it in the deepest part of the ocean?
Density rules. The heaviest, or most dense, water will always be on the bottom. Pure water is densest at 4 C . To make it heavier, it has to get saltier. As the surface of the Arctic ocean freezes, the left-behind part is very salty water at 3 to 4 C. This North Atlantic Deep Water sinks to the bottom and flows worldwide. Warmer less salty water sits on top of it. In the Antarctic, there is no warmer fresher water to sit on top of it, so NADW is exposed at the surface. When fresh water freezes out at the surface, this already salty and cold water gets even saltier and can cool to about -0.8C before sinking. This is Antarctic Bottom Water - the deepest, coldest water layer in the world. An interesting point is that the Marianas Trench, the deepest spot in the oceans, is only at about plus 2 C. This is because it is completely surrounded by water shallow enough (at only a mile or so deep) that AABW would have to flow uphill to get to it.
