Study Suggests Climate Prediction
By JEFF DONN Associated Press Writer
Thursday December 2, 1999
Researchers have shown links between ocean currents and global temperature changes during the last ice age, a step toward understanding Earth's complicated cycle of warming and cooling.
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. That's the major question that everyone wants to know,'' he said.
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. Some theorize that - as polar ice thins during warmer periods - 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.
The researchers supplied evidence of such a seesaw effect: the temperature of Caribbean surface waters rose from 2 degrees to 2.5 degrees Fahrenheit around the time of two especially cold eras about 15,000 and 12,000 years ago, during a long ice age.
``It's intriguing. It shows there are direct links that actually result in changes in a process that we can understand,'' said climatologist Robert Webb of the National Oceanographic and Atmospheric Administration.
But he cautioned that ice age processes may apply poorly when trying to understand the modern world, where accumulating greenhouse gases from burning fossil fuels appear to be warming the atmosphere.
Climate changes are viewed as a subtle and complex interplay of many factors, including ocean temperature and currents, gases in the atmosphere, ice sheets and fluctuating sunlight from variations in the Earth's orbit.
Ruhlemann said there is hope that measuring ocean circulation could someday give early signs of global climate shifts.
But geochemist Jeff Severinhaus of the University of California's Scripps Institution of Oceanography said if ocean circulation merely fluctuates with world temperatures, instead of driving them, then ``we might not have any warning'' of temperature changes by watching the oceans.