# Oxygen-18 in saline water and freshwater

Which has higher $$\delta {}^{18} \text{O}$$, saline water or freshwater? I searched for this question and found many researches about the relationship between $$\delta {}^{18} \text{O}$$ and salinity. But, I'm not sure why δ18O differs by salinity. Some researches say that $$\delta {}^{18} \text{O}$$ is high in saline water and low in freshwater.

Why would $$\delta {}^{18} \text{O}$$ differs by salinity, especially of seawater and freshwater?

EDIT: I was just curious if I can determine whether a diadromous fish was anadromous or catadromous by examining $$\delta {}^{18} \text{O}$$ value of the fish fossil.

• It depends on what latitudes the fresh vs saline water samples are drawn from. Jan 14 at 17:58
• Did you have a visit at NASA' Goddard Institute and the open access Global Seawater Oxygen-18 Database? Jan 14 at 21:31
• I found out that δ18O differs by salinity because of precipitation and evaporation. But I'm not sure if it can also be applied to δ18O difference between seawater and freshwater. Jan 18 at 7:59