I just noticed that the salinity of the Caspian Sea is only 1/3 that of seawater, which surprised me since I naively thought that all endorheic (enclosed basin) salt lakes with no water outlets would eventually reach salt saturation with a salinity much greater than sea water. Looking at the salt lakes on this wikipedia list of bodies of water by salinity, I see that salt lake salinity can vary from 0.59 to over 30 grams salt per 100 grams water. Have low salinity salt lakes just not existed long enough to reach saturation, or are they in a quasi-equilibrium where other processes are removing salt from the water? For example, salt lakes might periodically partially dry out and the evaporated salt on their edges gets blown away, and then the lake gets refilled (to a lower salinity) during wet seasons.
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$\begingroup$ I don't know enough to write an answer, but the main mechanism for concentrating the salt is evaporation. Therefore, one aspect you may want to examine is surface area versus volume. Salt concentration will increase more quickly in lakes with small volume and (relatively) large surface area, and more slowly in lakes with large volume and (relatively) small surface area. I suspect the Caspian Sea falls into the latter group. $\endgroup$– njuffaCommented Aug 10 at 2:33
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Other things to consider are:
- Different types of rocks produce different quantities of salt.
- The age of the aridity process in the region and how much salt has been able to accumulate in salt lakes.
- The type & extent of vegetation in the region. A region with a long history of deep rooted trees which lowers the water table also ensures any salt within the underlying rocks remained buried. When the trees are either clear felled or die off the water table will rise closer to the surface & bring the salt with it. This salt can then runoff into rivers and lakes.
