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National Geographic : 1981 Dec
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(Continuedfrom page 810) crevices and hollow rock pillars along the rifts [page 804]. They made me think of Pittsburgh's smoke stacks a generation ago. "We drove Alvin up to one of the black smokers. Our claw thrust a plastic heat probe into the vent. The temperature re corder in the sub went off scale. Then we saw the plastic rod itself begin to melt, to droop like taffy. It didn't take long to realize Alvin's portholes might not stand such tem perature [later calculated to be above 350°C--650°F]. We backed off in a hurry!" More cautiously, time after time, Alvin's pilots and scientists nosed as close as they dared to other such geysers, made film and television images, and brought up samples of bright-colored minerals-sulfides and ox ides of copper, iron, and zinc. The fact of hydrothermal mineral forma tion in the oceans, which earlier was simply theory, is one more milestone discovery. It opens the way for more confident prospect ing on land, and someday for mining the seabed itself. For the oceans, it is now clear, will inevitably be man's next mother lode for many of the natural resources he must have. Today the United States draws 12 percent of its domestic crude oil from offshore wells-in the Gulf of Mexico, off California and Alaska. Soon it may tap its Atlantic shelf as well. Worldwide, a fifth of all oil and gas now comes from under the oceans. Finding it, extracting it, and bringing it ashore safely have spawned extraordinary new industrial tools and techniques: Drill platforms taller than the Washington Monument stand amid the smashing waves of the North Sea; floating rigs ride on hulls submerged far under the surface; storage tanks, ship-loading terminals, and pipelines rest on the seafloor itself, from Persian Gulf to South China Sea to Gulf of Mexico. All this too has happened largely in the past 30 years. The offshore oil industry de pends on the ability to "see" rock layers deep within the sea bottom, using seismic echoes, computers, neutron emitters, heat probes, and gas sniffers. The oil wells offshore, and the tankers that endlessly plow the oceans, bring great dangers as well. The chances of polluting the seas, possibly causing irreversible damage to their life forms and the shores 816 they wash, grow with every offshore discov ery, every supertanker leaving port. Capt. Jacques-Yves Cousteau, roaming the world's seas for the past 31 years in his Calypso, now finds tar balls and other oil traces wherever he goes. "The oceans are sick and in trouble," he says grimly. OCEANOGRAPHERS in these 30 years have learned almost as much about the waters of the seas, and how they move, as they have about the vast mountain ranges of the seafloor. When World War II ended, the charts of surface currents, wind patterns, tides, and wave patterns were the legacy of centuries of shipmasters' lore, of Matthew Maury's "Sailing Directions," of sealed bottles cast adrift during pioneering cruises of research ships, but primarily of data gathered by competing-and often warring-navies. Today the charts have been largely re drawn by instruments developed for peace ful research. With buoys that broadcast from mid-ocean for years and floats that drift great distances at constant depths be neath the surface, with hydrophones that pick up sonic signals from afar, with long distance aircraft and cloud-piercing satel lites that record sea ice and warm currents from space, physical oceanographers have refined their concepts of ocean circulation. It was known that cold water from the polar regions creeps slowly at great depth toward the Equator, to replace warm sur face currents, such as the Gulf Stream, that carry the sun's heat to high latitudes. In these few decades, however, it has been learned just how far north Antarctic bottom water reaches-to the northern limits of the Atlantic, Pacific, and Indian Oceans. Massive currents and countercurrents be neath them flow in opposite directions along the Equator and the edges of continents. They help the oceans turn over and mix in as little time as a thousand years-an impor tant control over climate. In studying the North Atlantic, Bruce Heezen and Maurice Ewing recognized the tracks of tremendous undersea mud ava lanches, called turbidity currents. The slides explained many things: why there are giant undersea ravines and valleys, such as the Hudson Canyon off New York; why NationalGeographic,December 1981
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