The average salinity of the oceans is about 35 parts per thousand (ppt), which means that there are about 35 kilograms of dissolved solids in each 1,000 kilograms of seawater. The salinity of seawater varies from about 30 ppt in the Baltic Sea to over 40 ppt in the Red Sea.
The major components of seawater are:
* Sodium (Na+): 30.61 g/L
* Chloride (Cl-): 19.35 g/L
* Sulfate (SO42-): 2.65 g/L
* Magnesium (Mg2+): 1.28 g/L
* Calcium (Ca2+): 0.42 g/L
* Potassium (K+): 0.39 g/L
In addition to these major components, seawater contains trace amounts of many other elements, including copper, zinc, iron, manganese, and iodine.
The composition of seawater is influenced by a number of factors, including:
* Evaporation: When water evaporates from the ocean, it leaves behind the dissolved salts. This is why the salinity of the ocean is higher in areas with high evaporation rates, such as the tropics.
* Precipitation: Precipitation can add freshwater to the ocean, which can lower the salinity of seawater. This is why the salinity of the ocean is lower in areas with high precipitation rates, such as the polar regions.
* River discharge: Rivers discharge freshwater into the ocean, which can lower the salinity of seawater. This is why the salinity of the ocean is lower near the mouths of large rivers.
* Sea ice formation: When seawater freezes, it forms sea ice. Sea ice is made up of pure water, so the salinity of the seawater that remains behind increases. This is why the salinity of the ocean is higher in areas where sea ice forms, such as the Arctic and Antarctic Oceans.
The composition of seawater is also important for the survival of marine life. Many marine organisms, such as fish and corals, are adapted to live in a specific range of salinities. If the salinity of the ocean changes too much, it can disrupt the life cycle of these organisms and even cause them to die.
