The sea water is denser than fresh water due to
Evaporation
Mixing of sand
Mixing of salts
Stagnation
Mixing of salts causes the density of sea water to rise.
Why is sea water denser than normal water?
Weight of 1m3 of sea water is lesser than the weight of fresh water of the same volume.
Density of sea water = 1.3g/cm3
Density of fresh water = 1g/cm3