What's in the Ocean?

Abstract

THE WORLD'S OCEAN basins are filled with approximately 330 million cubic miles of seawater. This great volume contains almost unimaginable amounts of dissolved materials, some very precious. For example, over 8 billion tons of gold reside in the sea; and if all the water were magically removed, about 50 quadrillion tons of salt, enough to cover the exposed land of the Earth to a depth of 500 feet, would remain. It is a little easier to imagine a single cubic mile of seawater, but it is still impressive to list its dissolved contents: 150 million tons of salts including 120 million tons of sodium chloride (table salt), 8 million tons of magnesium sulfate (Epsom salt), 250 thousand tons of bromine, 60 thousand tons of strontium, 45 tons of silver, 25 tons of gold, about an ounce of radium, and smaller amounts of nickel, copper, uranium, lead, zinc, and manganese. A more formal look at seawater shows that some are present in abundance, others in lesser amounts. The chemicals are thus divided into major and minor groups, the former being constant in their relation to one another, the latter varying more widely from time to time and place to place. In table 1, the numbers are given in more useful units, milligrams per kilogram, or parts per million. Manganese, copper, zinc, lead, selenium, cesium, and uranium range from 0.001 to 0.01 parts per million. Molybdenum, thorium, celurium, silver, vanadium, lanthanum, yttrium, and nickel all range from 0.0005 to 0.0001 ppm. Scientium, mercury, gold, radium, cadmium, cobalt, tin, and about 40 other are included as trace elements in seawater. Most of the combine with others to form countless numbers of compounds dissolved in the sea or precipitated in its sediments. Many can be detected only as they are concentrated by certain organisms. Although all natural are present in seawater, some obviously are in very low concentration. Nevertheless, each year about 2 million tons of uranium go past Key West, Florida in the Florida Current which, while flowing at just two and a half knots, represents 30 million cubic meters of water going by every second. The overall salinity of the open ocean ranges from 33 to 37 parts per thousand near the surface where evaporation and rain exert their greatest influence. Salinity may drop even lower near land due to run-off and the entry of rivers. But in general, the salinity of the ocean is fairly constant at 35 parts per thousand. This means that there are 35 grams of dissolved solids of all kinds present in each liter of seawater. Of the salts present, 89% are chlorides, 10% are sulfates, and 0.02% are carbonates. The least saline part of the sea is the Gulf of Bothnia between Sweden and Finland where there is so much fresh melt-water and river water entering, that the salinity at times is near zero. On the other hand, the saltiest part of the sea is the Red Sea where so much water is evaporated by the sun and dry air that the remainder has a salinity of 41 parts per thousand. Although it is not presently part of the world ocean, it is interesting for comparison to note that Great Salt Lake, Utah has a salinity up to 280 parts per thousand. But even with all this, perhaps the most important component of seawater is the water itself. The world ocean contains 97% of the Earth's total water supply. Another 1% is in the atmosphere, and the remaining 2% is found in ground water and frozen in the ice caps. Presently, about 6 million cubic miles of water are locked in the Greenland and Antarctic ice caps, but during ice ages much more water was in such cold storage and sea levels were much lower than they are today. Now, as the ice caps continue to melt in our warming atmosphere, the sea level is gradually rising. In past interglacial periods, it has been much higher than it is today.