A German scientist argues that sea circulation likely exerts some control over the millennial cycle of warming and cooling. But Carsten Ruhlemann, the marine geologist who supervised the study, acknowledged that ocean currents could be an effect rather than cause of temperature shifts.
Nobody knows what causes the process.
The study, which was published today in the journal Nature , is based on samples of organic sediment taken from the ocean floor in 4,300 feet of water off the Caribbean island of Grenada. The team led by the University of Bremen analyzed the types of animals and chemicals in the sediment to calculate the water's surface temperature thousands of years ago when the material sank. The study focuses on sea currents that push cold Arctic water southward along the ocean bottom and forces warm tropical water northward. Arctic waters become less dense, sink to the bottom more slowly and reduce the deep-sea southern flow. More hot water then stays in the tropics, cooling the Arctic region back down in a seesaw fashion.