Water is the most abundant substance on the earth's surface. About 71% of the surface is covered with water, and the oceans hold around 97% of the earth's water.
Seawater has its salty taste from sodium chloride, on average 35 g/L. Seawater also contains salts of other elements such as potassium, calcium and magnesium. The Red Sea has the highest salt level, 40 g/L, due to high evaporation, low precipitation, no run-off from rivers and a narrow connection to the Indian Ocean. The Baltic Sea has the lowest salt content, ranging from 3 to 9 g/L, due to low evaporation and massive fresh water run-off from the land.
These differences in salinity affect anything that flows, from birds to ships. The more salt, the higher the density and the higher the buoyancy.
The salts in seawater originate from three different sources:
- volcanic eruptions: gases containing sulfur and chlorine react with water and dissolve.
- weathering of soil by precipitation: minerals are washed from the land and transported to the sea by rivers.
- plate tectonics: seawater dissolves salts that are released by moving tectonic plates.
Carbon dioxide is very soluble in water; the concentration in seawater is approx. 60 times higher than in air. A part is absorbed from the atmosphere and the balance comes from animals and bacteria in the sea. As a results, seawater has a pH of 8.1 and is slightly alkaline. Pure water has a pH of 7.0 and is neutral.
Water also determine the weather on out planet. Clouds are formed from ocean water evaporates. Without clouds, temperature differences would be much greater, and fresh water on earth would be scarce.
