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Sea water

Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of ~3.5%. This means that for every 1 liter (1000mL) of seawater there are 35 grams of dissolved salts (mostly, but not entirely, sodium chloride). Water with this level of osmolarity is not potable.

Sea water is not uniformly saline throughout the world. The planet's freshest sea water is in the Gulf of Finland in the Baltic Sea. The most saline sea is the Red Sea, where heat increases the rate of surface evaporation and there is little fresh inflow from rivers.

Composition of Earth's ocean water by element
Element Percent Element Percent
Oxygen 85.7 Sulfur 0.0885
Hydrogen 10.8 Calcium 0.04
Chlorine 1.9 Potassium 0.0380
Sodium 1.05 Bromine 0.0065
Magnesium 0.1350 Carbon 0.0026

Table of contents
1 Ocean Salinity
2 Cultural Aspects
3 Related Links

Ocean Salinity

Scientific theories behind the origins 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 concentrated as the process of evaporation (see Hydrologic cycle) removed the water. Halley noted that of the small number of lakes in the world without ocean outlets (such as the Dead Sea and the Caspian Sea), most have high salt content. Halley termed this process "continental weathering".

Halley's theory is partly correct. In addition, sodium was leached out of the ocean floor when the oceans first formed. The presence of the other dominant element of salt, chlorine, results from "outgassing" of chlorine (as hydrochloric acid) with other gases from Earth's interior via volcanos and hydrothermal vents. The sodium and chlorine subsequently combined to become the most abundant constituent of sea salt.

Ocean salinity has been stable for millions of years, most likely as a consequence 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 slowly leached to the surface.

Cultural Aspects

Even on a ship or island in the middle of the ocean, there can be a "shortage of water" meaning, of course, a shortage of fresh water. This is described most famously by a line from Samuel Taylor Coleridge's The Rime of the Ancient Mariner:

"Water, water, every where,
Nor any drop to drink.".

Seawater can be turned into drinkable water by the process of desalination.

Related Links