Magazine article Science News

Getting the Drift of Ocean Circulation

Magazine article Science News

Getting the Drift of Ocean Circulation

Article excerpt

Sopping up greenhouse gases and heat from the atmosphere, the world's oceans function as a climatic brake, slowing down the pace of global warming. Just how well this brake works depends on how quickly the oceans stir themselves, a process that carries away materials dissolved at the surface and stores them in deeper water. Results of an experiment in the North Atlantic give oceanographers their first direct measurement of how quickly ocean water mixes in the vertical direction.

To gauge the rate of stirring, an international team pumped 139 kilograms of an inert "tracer" called sulfur hexafluoride into the ocean last May and then tracked its dispersal. The oceanographers released the liquid at a depth of 310 meters, 1,200 kilometers west of the Canary Islands.

The experiment's results confirm suspicions that vertical mixing occurs exceptionally slowly, report James R. Ledwell of the Woods Hole (Mass.) Oceanographic Institution and Andrew J. Watson and Clifford S. Law of the Plymouth (England) Marine Laboratory. They discuss their work in the Aug. 19 NATURE.

Immediately after a first ship injected the tracer, a second ship measured the tracer's concentration in the water and found that the compound formed horizontal streaks with a vertical width of 7 meters. When they returned to the region six months later, the oceanographers located some of the plumes, which had spread very little vertically, measuring only about 18 meters from top to bottom. …

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