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Formation of salinity maximum water and its contribution to the overturning circulation in the North Atlantic as revealed by a global general circulation model
Author(s) -
Qu Tangdong,
Gao Shan,
Fukumori Ichiro
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20152
Subject(s) - ocean gyre , salinity , oceanography , thermohaline circulation , geology , north atlantic deep water , thermocline , ekman transport , water mass , subtropics , subtropical front , mode water , temperature salinity diagrams , precipitation , boundary current , surface water , halocline , deep ocean water , ocean current , environmental science , upwelling , geography , environmental engineering , fishery , meteorology , biology
The formation of salinity maximum water in the North Atlantic is investigated using a simulated passive tracer and its adjoint. The results reveal that most salinity maximum water in the North Atlantic comes from the northwestern part of the subtropical gyre, and direct contribution from the evaporation‐precipitation maximum region via the surface Ekman current is minor. Water originating from the evaporation‐precipitation maximum region has to recirculate in the subtropical gyre before entering the sea surface salinity maximum region from the northwest. Once subducted, some portion (~10%) of the salinity maximum water enters the equatorial region in the shallow subtropical cell, but most (~70%) of it appears to turn northward to join the North Atlantic Deep Water. The latter pathway involves a three‐dimensional circulation. When the warm, fresh surface water flows northward along the western boundary, it turns eastward in the northern subtropical gyre. As a result of the large excess of evaporation over precipitation, this water gradually gains its salinity on the route, until it reaches the sea surface salinity maximum region in the central subtropical gyre. From there, the salinity maximum water is subducted and flows back to the western boundary in the depth range of the thermocline. With its high‐salinity nature, a major portion of this water penetrates into the subpolar region and directly contributes to the deep thermohaline circulation.