If freshwater is added to a region, what happens to seawater density and salinity?

The density and salinity goes down.

Explanation:

Salt water is denser than pure water.  As fresh water is added to salt water the concentration of salt goes down.  Since salinity is the amount of salt in the water that would go down with the concentration.  This would also mean that the density goes down since there is less salt per unit of volume which makes it so that there is less mass per unit of volume.  The formula for density is d=m/v so as the mass goes down per unit of volume so does the density.

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