Atlantic Ocean Leakage/Rings, which brings salty Indian Ocean waters into the South Atlantic, and the "Atmospheric Bridge", which evaporates subtropical Atlantic waters and exports it to the Pacific. The Atlantic Ocean consists of four major, upper water masses with distinct temperature and salinity. The Atlantic Subarctic Upper Water in the northern-most North Atlantic is the source for Subarctic Intermediate Water and North Atlantic Intermediate Water. North Atlantic Central Water can be divided into the Eastern and Western North Atlantic central Water since the western part is strongly affected by the Gulf Stream and therefore the upper layer is closer to underlying fresher
Atlantic Ocean and the Southern Ocean in the south (other definitions describe the Atlantic as extending southward to Antarctica). The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean at about 8°N. Scientific explorations of the Atlantic include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont-Doherty Earth Observatory and the United States Navy Hydrographic Office. The oldest known mentions of an "Atlantic" sea come from Stesichorus around mid-sixth century BC (Sch. A. R. 1. 211): "Atlantikoi pelágei" (Greek: Ἀτλαντικῷ πελάγει; English: 'the Atlantic sea'; etym. 'Sea of Atlantis') and in "The Histories" of Herodotus