Sea water

Sea water is water as of a sea or ocean. On normal, sea water in the world's oceans has a salinity of ~3.5%. This means that for every 1 liter of sea water there are 35 grams of salts dissolved in it. This can be expressed as 0.6M NaCl. Water with this level of osmolality is, of course, not potable.

Sea water is not consistently saline throughout the world. The planet's freshest sea water is in the Gulf of Finland, part of the Baltic Sea. The most saline open sea is the Red Sea, where high temperatures and controlled circulation result in high rates of surface evaporation and there is little fresh inflow from rivers. The salinity in isolated seas can be considerably greater.

The thickness of sea water is between 1020 and 1030 kg/m3. Due to chemical buffering, seawater pH is limited to the range 7.5 to 8.4.

Ocean salinity

Scientific theories behind the beginning of sea salt started with Sir Edmond Halley in 1715, who proposed that salt and other minerals were carried into the sea by rivers, having been leached out of the ground by rainfall runoff. Upon reaching the ocean, these salts would be retained and determined as the process of vanishing removed the water. Halley noted that of the small number of lakes in the world without ocean outlets, most have high salt content. Halley termed this process "continental weathering".

Halley's theory is partially correct. In addition, sodium was leached out of the ocean floor when the oceans first formed. The presence of the other leading element of salt, chloride, results from "out gassing" of chloride with other gases from Earth's interior via volcano’s and hydrothermal vents. The sodium and chloride consequently became the most abundant constituents of sea salt.

Ocean salinity has been stable for millions of years, most likely as an importance of a chemical/tectonic system which recycles the salt. Since the ocean's creation, sodium is no longer leached out of the ocean floor, but instead is captured in sedimentary layers covering the bed of the ocean. One theory is that plate tectonics result in salt being forced under the continental land masses, where it is again gradually leached to the surface.