This answer to Salinity of Martian water 3.5 Billion years ago in Astronomy says that most estimates of Mars' ocean's salinity are pretty high;
The article "Water Activity and the Challenge for Life on Early Mars" finds that the early martian ocean would have been acidic and almost as salty as the dead sea.
The estimates for salinity of the europan ocean vary widely, but most place the salinity above 50g/kg, more than that of sea water (about 45 g/kg).
I've commented there the possibility that:
- those estimates may change as more is learned about Mars
- there could be regional variations in surface water salinity since there is believed to have been rain, and tidal mixing may have been much less than on Earth
I support my amateur hypothesis in item 2 with the following
- Mars has no massive moon like the Earth's
- Mars's orbit is about 1.67 times further from the Sun than Earth on average, and tidal accelerations vary as $1/r^3$ putting the tidal acceleration at 22% of what Earth experiences at 1 AU.
However we should remember that Mars' surface gravity is only 38% of that on Earth, so the effect is not reduced as much as one might first think.
Question: How large were Mars' ocean tides and to what extent could they keep the oceans mixing and tend to keep salinity uniform? Can this at least be estimated, and has this been modeled?