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.

In this research, how can we know that the fish was anadromous by its $\delta {}^{18} \text{O}$ value?

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    $\begingroup$ It depends on what latitudes the fresh vs saline water samples are drawn from. $\endgroup$ Jan 14, 2022 at 17:58
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    $\begingroup$ Did you have a visit at NASA' Goddard Institute and the open access Global Seawater Oxygen-18 Database? $\endgroup$
    – Buttonwood
    Jan 14, 2022 at 21:31
  • $\begingroup$ 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. $\endgroup$
    – Kernel
    Jan 18, 2022 at 7:59


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