Counter Gulf Stream

Large-scale charts show ocean currents circling neatly back on the surface to the places from which they come. Oceanographer Henry Stommel of the Woods Hole Oceanographic Institution became convinced by theory that much water also returns along the ocean bottom. The north-flowing Gulf Stream, he suspected, should have directly under it a south-flowing countercurrent. Nature tells how a joint expedition of the Woods Hole Oceanographic Institution and Britain's National Institute of Oceanography found the counter Gulf Stream exactly where Stommel figured it should be.

Measuring deep ocean currents was almost impossible until Britain's Dr. John Crossley Swallow developed a "float" (it sinks). Made of strong aluminum tubing closed at the ends, it is carefully weighted so that it barely sinks in sea water. As the depth increases, pressure makes the water heavier. The aluminum tubes resist the pressure better than the water does, so eventually the float stops sinking. It will hang at any desired level while a battery-powered transmitter sends ultrasonic beeps that carry for miles.

Two research ships, Britain's Discovery II and the Atlantis from Woods Hole, selected stations off the South Carolina coast where the Gulf Stream runs rapidly northward. The scientists on the Atlantis began sampling water from the surface to the bottom. This gave the differences of temperature, salinity, oxygen content, etc., that theoreticians think are associated with deep-down currents.

Dr. Swallow released successive floats from the Discovery II. Each sank to a predetermined depth and sent back ultrasonic beeps that allowed them to be followed by submarine-detecting apparatus. When set to sink only a few thousand feet, the floats drifted north with the Gulf Stream, but between 4,500 and 6,000 ft. their motion practically stopped. Deeper down they drifted southward, at as much as one-third mile per hour. With the counter Gulf Stream proved to be real, the oceanographers can apply their theories with stepped-up confidence to other parts of the ocean depths.

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