The density is calculated using the UNESCO equation of state
for seawater, assuming that input variables are defined
according to modern calibrations.
In conventional Oceanographic notation, the calculated quantity is
$\rho(S,t,p)$
References
Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for computation of
fundamental properties of seawater. Unesco Technical Papers in Marine
Science, 44, 53 pp
Gill, A.E., 1982. Atmosphere-ocean Dynamics,
Academic Press, New York, 662 pp.