I was curious about the density of seawater depending on temperature and salinity, and found the following stuff. The salinity corrections in the cited paper use some other freshwater density equation than the one given here (the only one for which I found a paper), so the results might be somewhat inprecise. The salinity can be defined by different standards ("Reference Salinity", "Practical Salinity", "Conductive Salinity", "Chlorinity" - I did not study the details), some information is in the paper by Millero/Huang.
Essentially it is the salt content in mass promille.
# density in kg/m^3, Temp. in Celsius
# Salinity in mass promille
# freshwater density: Tanaka et al., cited in
# Becerra: "Water density"
# Salinity correction
# Millero+Huang, "The density of saltwater as a function ...",
# Ocean Sci. 5, 91-100, 2009
# 0≤t≤40, other ranges see table 2. in Millero/Hunag
Ergebnisse/Results (click on pictures to embiggen)
Fig. 1: Density. The effect of the salinity dominates, the anomaly is invisible