Science: Ocean Frontier

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Deep & Narrow. Before the war, even such well-known currents had not been thoroughly mapped in detail. For Woods Hole oceanographers, the first order of business was a new study of the great Gulf Stream, which exports tropical water to northern Europe. With the aid of loran, the new Atlantis surveys proved that it is not a wide, steady stream, but a jet that whips from side to side over hundreds of miles and sometimes curls into eddies. It may run fast or slow or backward, and only the general sum of its motion carries warm water to Europe.

But the major discovery of postwar oceanographers was that huge currents flow far below the surface; often these currents move faster than their surface counterparts. One such discovery came in 1951, when the U.S. Fish and Wildlife Service sent a ship west of the Galapagos Islands to experiment with a Japanese technique of fishing for deep-swimming tuna. The scientists were surprised to see the fish lines drifting eastward while their ship was carried westward on the well-known equatorial surface current. The next year the Service's Townsend Cromwell established the reason: a hitherto unsuspected current, deep below the surface current and moving in the opposite direction. Later investigation revealed that the Cromwell Current is a tremendous thing. It is 250 miles wide, at least 3,500 miles long. Three hundred feet below the surface, its high-speed core flows eastward at up to 3 knots, carrying 1,000 times as much water as the Mississippi.

Years of patient measurements of water temperature, salinity and density have begun to pay off by providing oceanography with a substructure of theory. Doubting the conventional view that ocean currents are simply streams of water pushed around by prevailing winds, Henry Stommel of Woods Hole analyzed thousands of such observations, predicted that a current would be found flowing under the Gulf Stream in the opposite direction. In 1957 the Atlantis and the British oceanographic ship Discovery II went looking for this current. Their tool was an ingenious buoy invented by British Oceanographer John C. Swallow, which sinks slowly until it reaches a level where the sea water, compressed by the weight of water above it, has the same density as the buoy. There, the Swallow buoy hangs and drifts with the deep-down water, broadcasting strong pings of ultrasound that can be heard by listening ships on the surface. Dumped into the Gulf Stream, the Swallow buoys proved that Stommel's theory was exactly right. About 8,000 feet under the famed stream is a Counter Gulf Stream carrying cold water southward at ⅓ of a knot.

No Quiet Place. This discovery gave a wholly new look to theories about the circulation of the Atlantic. The long-established notion of nearly stagnant ocean depths is now doubtful. Photographs taken of the bottom show ripple marks much like those caused by tidal currents on bathing beaches. Ocean basins with ripple marks on their bottoms must have been stirred by currents at some time in their past, and they may be stirred still.