Lowermost layer of ocean water that can be distinguished by its characteristic low temperature, high density, and low oxygen content compared with surface waters.
Most bottom waters are formed near Antarctica during the southern winter. The partial freezing of seawater over the Antarctic continental shelf produces salt-free ice and residual brine with a high density, which causes it to sink; it then flows northward along the seafloor. The Arctic Ocean is less important as a source of bottom water because it is isolated by barriers such as the Bering Sill and submarine ridges and banks between Greenland and the British Isles.