Between 50% and 20%, gypsum precipitates out (Ca SO4.2H2O), which also tastes like chalk.Between 20% and 1% sea salt precipitates (Na Cl) but going further, the bitter potassium and magnesium chlorides and sulfates precipitate, which is to be avoided, unless for health reasons.
Interestingly, their proportions are always the same, which can be understood if salinity differences are caused by either evaporating fresh water or adding fresh water from rivers. Salinity affects marine organisms because the process of osmosis transports water towards a higher concentration through cell walls.A fish with a cellular salinity of 1.8% will swell in fresh water and dehydrate in salt water.Marine plants (seaweeds) and many lower organisms have no mechanism to control osmosis, which makes them very sensitive to the salinity of the water in which they live.The main nutrients for plant growth are nitrogen (N as in nitrate NO3) and potassium (K) followed by Sulfur (S), Magnesium (Mg) and Calcium (Ca).Dissolved gases in seawater The gases dissolved in sea water are in constant equilibrium with the atmosphere but their relative concentrations depend on each gas' solubility, which depends also on salinity and temperature.
As salinity increases, the amount of gas dissolved decreases because more water molecules are immobilised by the salt ion.So, saltwater fish drink water copiously while excreting excess salts through their gills.Freshwater fish do the opposite by not drinking but excreting copious amounts of urine while losing little of their body salts.The density of 35ppt saline seawater at 15ºC is about 1.0255, or s (sigma)= 25.5. The relationship between temperature, salinity and density is shown by the blue isopycnal (of same density) curves in this diagram.In red, green and blue the waters of the major oceans of the planet is shown for depths below -200 metre.This world map shows how the salinity of the oceans changes slightly from around 32ppt (3.2%) to 40ppt (4.0%).