Tuesday 9 December 2008

THE NATURE SEAWATER


Nowhere in nature can absolutely clear water be found. Even rainwater contains dissolved minerals. For example, 30kg of rainwater contains about 1g of solid substances, whereas 1kg of seawater contains about 35g different salts. Salinity is a very important characteristic and it directly influences the viability of the organisms living in the water. The total amount of dissolved salts in the oceans is 48 quadrillion tonnes. Most of it is NaCl (77.8%), to which the saline taste of seawater is due. Magnesium chloride accounts for 10.9% and it gives the water a specific bitterish taste. Then come sulfates (10.8%), carbonates (.5%), etc. The overall amount of salts may vary in different regions of the Ocean but the composition and the percentile content remain the same. The average ocean salinity is 35% and increases starting at the Equator and reaching 15–20ยบ latitude, then it decreases towards the poles. This phenomenon can be explained with the distribution of water vapors and also with the saline waters transported from the tropical zones by warm currents. Salinity in the northern part of the Indian Ocean changes according to the season. Seas have greater salinity than oceans. The Dead Sea has the greatest salinity of all (256%), and the smallest is that of the Baltic Sea (5–7%).
The presence of more than 44 chemical elements has been established so far. Besides the popular oxygen, hydrogen, chlorine, potassium, magnesium, sulfur, calcium, and iodine, seawater also contains Al, Cu, Zn, Tn, Pb, Au, Ag, U, Mn, Hg, etc.
There are many gases dissolved in seawater, the largest amount being contributed by oxygen, nitrogen, and carbon dioxide. Water dissolves oxygen better than nitrogen. That is why the ratio N:O which is 4:1 on dry land, changes to 2:1 under water.

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