The equivalent salinity of sea water at a particular depth is defined as the salinity, that water at a potential temperature of 0°C would have to have to be neutrally stable with respect to the sea water. The equivalent salinity at a depth of 5 km in the World Ocean decreases northward from the Antartic. Because of the nonlinearity of the equation of state of sea water, water of a given equivalent salinity at the sea surface will attain a variable equivalent salinity as it sinks and will set up a normal potential temperature gradient. As water spills over a sill into a basin, water of equal equivalent salinity at the sill depth will become segregated vertically as it fills the basin with the coldest, least saline water at the bottom. A vertical equivalent salinity section of the Western Atlantic Ocean indicates that bottom waters in the section converge from the Antartic and the Arctic at about 37°N. © 1969.
