Three water masses account for most of the deepwater masses in the oceans— Antarctic Bottom Water, North Atlantic Deep Water, and Antarctic Intermediate Water.
"Antarctic Bottom Water forms when antarctic seas freeze during the winter. With temperatures below 0°C, this deepwater mass is the coldest and densest in all the oceans."
"North Atlantic Deep Water forms in a similar manner offshore from Greenland."
"Antarctic Bottom Water is colder and denser than North Atlantic Deep Water, so it sinks below it.
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I could summarize it for you but that wouldn't be a proper answer so heres the material you need to summarize it.
