The density of seawater is a complex function of temperature,
salinity, and pressure. Because of the non-linearity of the equation of
state of seawater, the densities of sea waters having the same temperature
and the same salinity differences (with respect to the mean salinity of
the ocean) will vary with the mean salinity of the ocean. Although this
strange property of seawater is evident in a plot of the equation of state,
it has never been considered in trying to reconstruct ancient ocean circulation.
These differences in the density field may have caused the ocean
to respond differently to atmospheric forcing in the past. The different
response may hold the key to understanding "ocean anoxic events" and
episodes of large-scale burial of organic carbon and production of petroleum
source rocks
