Why does evaporation make gulfs in arid regions saltier?

In arid regions, gulfs become significantly saltier because they experience intensive evaporation while receiving very little river runoff to dilute the water.1

This process is further accentuated by the geography of the gulf itself. When a gulf is isolated from the open ocean—such as by a narrow mouth or a submarine sill—the exchange of water is restricted, preventing the saltier, evaporated water from mixing with the broader ocean. As fresh water is removed through evaporation, the concentration of dissolved salts increases, sometimes reaching extreme levels. For example, salinity in the Persian Gulf can reach 60 parts per thousand, while in the Kara-Bogaz-Gol, it can rise as high as 350 parts per thousand. In these high-salinity environments, the water may eventually reach a point where specific salts begin to precipitate out of the solution.123