The ocean, then, is not fresh like river water because of the huge accumulation of salts by evaporation and the contribution of raw salts from the land. In fact, since the first rainfall, the seas have become saltier. This is partly due to the lack of precise methods and procedures for measuring the constituents in sea water. Some of the problems confronting scientists stem from the enormous size of the oceans, which cover about 70 percent of the Earth's surface, and the complex chemical system inherent in a marine environment in which constituents of sea water have intermingled over vast periods of time.
At least 72 chemical elements have been identified in sea water, most in extremely small amounts. Probably all the Earth's naturally occurring elements exist in the sea.
Elements may combine in various ways and form insoluble products or precipitates that sink to the ocean floor. But even these precipitates are subject to chemical alteration because of the overlying sea water which continues to exert its environmental influence. The salinity of ocean water varies. It is affected by such factors as melting of ice, inflow of river water, evaporation, rain, snowfall, wind, wave motion, and ocean currents that cause horizontal and vertical mixing of the saltwater.
Of the major oceans, the North Atlantic is the saltiest; its salinity averages about Within the North Atlantic, the saltiest part is the Sargasso Sea, an area of about 2 million square miles, located about 2, miles west of the Canary Islands. The Sargasso Sea is set apart from the open ocean by floating brown seaweed "sargassum" from which the sea gets its name.
Low salinities occur in polar seas where the salt water is diluted by melting ice and continued precipitation. Partly landlocked seas or coastal inlets that receive substantial runoff from precipitation falling on the land also may have low salinities.
Water of the Puget Sound in the Tacoma, Wash. This area is drained by a number of fresh-water streams which discharge an average of about 4. Salinity of sea water along the coastal areas of the conterminous United States varies with the month of the year as well as with geographic location. For example, the salinity of the ocean water off Miami Beach, Fla. The water off the coast of Miami Beach has a high salt content because it is undiluted sea water. Off the coast of Astoria, however, the sea water is less saline because it is mixed with the fresh water of the mighty Columbia.
Sometimes river water travels far from shore before it mixes with sea water. This is shown by data gathered from a study of the Columbia River, which, in an average year, carries to the ocean enough water to cover an area of 1 million acres to a depth of feet. Using a radio- active tracer, scientists at Oregon State University have followed the river's water from its mouth near Astoria to a point southwest of Coos Bay, miles away.
This average salinity was obtained by William Dittmar in from chemical analyses of 77 sea water samples collected from many parts of the world during the scientific expedition of the British corvette, H. The Challenger expedition, organized by the British Government at the suggestion of the Royal Society, set out to study the biology of the sea, examine the chemical and physical properties of the water, sample deposits on the ocean floor, and measure water temperatures.
The voyage began in and ended almost 4 years later after covering 68, nautical miles. This expedition remains today the longest continuous scientific investigation of the ocean basins.
Dittmar's 77 samples are still the only worldwide set of samples of sea water for which complete data each principal constituent on chemical composition are available.
More recent data, reflecting improvements in analytical and sampling techniques, show slight deviations from Dittmar's results, but these changes do not affect the overall usefulness of his work. The average composition of the 77 samples is as shown on the following table. But in the latitudes bordering the Equator the opposite condition prevails -- evaporation exceeds rainfall because high temperatures plus increased winds accelerate evaporation losses.
But this is not so. Comparisons of Dittmar's data on ocean water with the average salt concentrations in river waters of the world is as shown on the preceding table above. Sea water and river water obviously are very different from each other: 1 Sodium and chloride the components of common table salt constitute a little more than 85 percent of the dissolved solids in ocean water and give to the water its characteristic salty taste, but they represent less than 16 percent of the salt content of river water.
These variations seem contrary to what one would expect. Part of the explanation is the role played by marine life -- animals and plants -- in ocean water's composition. Sea water is not simply a solution of salts and dissolved gases unaffected by living organisms in the sea. Shallow water often appears clear as there are fewer water molecules to absorb the light, so other colours are able to reach the sea floor and reflect. The deeper you go, the more other colours are absorbed and the deeper blue the light becomes, until you reach the point where no visible light can reach, where it is completely dark.
The colour of the water also depends on other factors, such as what particles are floating in it. Coastal areas can sometimes look murky and brown as they contain sand from the seabed that has been churned up by waves. Living things influence the colour, too. Phytoplankton are tiny organisms that act a bit like plants, using chlorophyll to absorb sunlight and grow. They absorb red and blue light, reflecting green light and giving the sea a greener look.
Generally speaking, the more phytoplankton there are in the water, the greener it is. Have you ever wondered why the sea is blue, or whether dolphins sleep? The two ions that are present most often in seawater are chloride and sodium. By the way, the concentration of salt in seawater salinity is about 35 parts per thousand. In other words, about 35 of 1, 3.
And, just so you don't think seawater is worthless, a cubic mile of it also can contain up to 25 pounds of gold at a concentration of 0. Before you go out and try alchemy on seawater, though, just think about how big a cubic mile is 1 cubic mile contains 1,,,, gallons! In , scientists exploring the NW Eifuku volcano near the Mariana Islands reported seeing small white chimneys emitting a cloudy white fluid near the volcano's summit, as well as masses of bubbles rising from the sediment around the chimneys.
In this picture you can see masses of minerals and carbon dioxide escaping from the earth's crust into the ocean. These vents contribute dissolved minerals to the oceans, which is one reason the oceans are salty. Credit: NOAA. Rivers and surface runoff are not the only source of dissolved salts. Hydrothermal vents are recently-discovered features on the crest of oceanic ridges that contribute dissolved minerals to the oceans.
These vents are the exit point on the ocean floor from which sea water that has seeped into the rocks of the oceanic crust has become hotter, has dissolved some of the minerals from the crust, and then flows back into the ocean. With the hot water comes large amounts of dissolved minerals. Estimates of the amount of hydrothermal fluids now flowing from these vents indicate that the entire volume of the oceans could seep through the oceanic crust in about 10 million years.
Thus, this process has a very important effect on salinity. The reactions between seawater and oceanic basalt, the rock of ocean crust, are not one-way, however; some of the dissolved salts react with the rock and are removed from seawater. A final process that provides salts to the oceans is submarine volcanism, the eruption of volcanoes under water.
This is similar to the previous process in that seawater is reacting with hot rock and dissolving some of the mineral constituents. Humans cannot drink saline water, but, saline water can be made into freshwater, for which there are many uses. The process is called "desalination", and it is being used more and more around the world to provide people with needed freshwater. In your everyday life you are not involved much with saline water. You are concerned with freshwater to serve your life's every need.
But, most of Earth's water, and almost all of the water that people can access, is saline, or salty water. Do you wear contact lenses?
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