Bottom Water

Bottom water is the densest water mass filling the deepest layer of an ocean basin, directly above the sea floor. The principal source is Antarctic Bottom Water, AABW, formed by brine rejection during sea-ice growth in the Weddell and Ross seas, the coldest and densest water in the open ocean, which spreads north along the deep basins. North Atlantic Deep Water overlies it. Bottom water is cold, near 0 degrees Celsius, oxygen-bearing where recently ventilated, and slow-moving, but its currents rework deep sediment into contourite drifts. It is a primary limb of the global overturning circulation and a tracer of deep ventilation.