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.
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.
The main salt ions that make up 99.9% are the following: By adding the µmol in last column up, multiplied by respective valences, like: -546 468 -56.2 106.6 ....
Note that the figures above differ slightly in differing publications.
Also landlocked seas like the Black Sea and the Baltic Sea, have differing concentrations.
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).
High salinity is found in the ocean 'deserts' in a band coinciding with the continental deserts.