Caspian Sea of around 149,200 square miles (386,400 square km)— bigger than the region of Japan—and its surface lies somewhere in the range of 90 feet (27 meters) below sea level. The sea bed in the southern part reaches as low as 1,023 m (3,356 ft) below sea level, which is the second lowest natural depression on earth after Lake Baikal (−1,180 m, −3,871 ft). The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size. The sea has a surface area of 371,000 km (143,200 sq mi) (not including the detached
Water column Water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment. Descriptively, the deep sea water column is divided into five parts—"pelagic zones" (from Greek πέλαγος (pélagos), 'open sea')—from the surface to below the floor, as follows: "epipelagic", from the surface to 200 meters below the surface; "mesopelagic", from 200 to 1000 meters below the surface; "bathypelagic", from 1000 to 4000 meters below the surface; "abyssopelagic", from 4000 meters below the surface to the level sea floor; "hadopelagic", depressions and crevices below the level sea floor. The