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According to Sachs, “The next step is to determine if similar changes occurred in the much larger Pacific Ocean, studies he and Lehman are pursuing. If so, any human-induced changes to the ocean’s plumbing are likely to affect much of the mid-latitudes, where many large population centers are found.”

Columbia’s Broecker said the findings of rapid, wide temperature swings underscore other, recent research.

“In the last five years, it has been shown that these changes have been shown in the Santa Barbara basin, in the Arabian sea off of India, in the Cariaco Trench off of Venezuela, and now, in this beautiful, beautiful record that Julian has gotten on the sediment near Bermuda,” said Broecker. “These things confirm that these changes were not restricted to the north Atlantic — they were global. It beautifully replicates the Greenland record and just adds piece of information to indicate that the global system we live in is a strange one that is capable of doing outrageous things namely jumping form one state of operation to another.”

The mechanism by which temperature change in the warm Atlantic can affect climate globally is via the water vapor feedback. Warm ocean temperatures raise the water vapor content of the atmosphere and thus its heat-trapping or “greenhouse” capacity, with a one-degree rise in water temperature equating to a 6 percent increase in water vapor pressure.

Underscoring the importance of ocean currents, to the surprise of the researchers, the ocean-driven temperature fluctuations they observed were as great as those caused by changes in the tilt of the Earth, and changes in the Earth’s orbit: factors thought to have produced the series of ice ages in geological history.

“The warming at the end of the ice age was supported by the disappearance of enormous ice sheets, a one third increase in atmospheric CO2 levels, and changes in the seasonal distribution of the suns energy, whereas the abrupt changes we document here seem to be almost entirely ocean driven,” said Sachs and Lehman.

Although there had been earlier indications of ocean temperature changes farther south of the Greenland ice cores, those had been based on records of mineral deposits left by plankton-a record that can be unreliable because plankton growth can be influenced by factors besides temperature.

For their study, Sachs and Lehman used a 12-meter section of a 52.7-meter core of sediment drilled 4,462 meters underwater into the sea floor of the Bermuda Rise by French scientists as part of IMAGES (International Marine Global Change Study), an international coring project. The Bermuda Rise is a sediment drift formation where sedimentation rates of 10 to 100 centimeters per 1,000 years far exceed the average for the ocean, giving an unusually detailed picture of temperature over time-providing a method is available to deduce temperature from sediments.

Sachs and Lehman were able to do just that by streamlining and automating a technique developed in the 1980s by researchers at the University of Bristol, England. The technique is based on the observation that the ratio of two molecules produced by certain phytoplankton varies in direct proportion to the water temperature in which they live.

Although the biochemical function of the molecules-called alkenones-is still a mystery, they are thought to play a role in maintaining cell membrane stiffness. Much like butter is stiff while margarine is soft when removed from the refrigerator, plankton may produce more of the unsaturated or margarine-like variety of alkenone when in cold water and more of the saturated or butter-like variety in warm water.

Taking samples every 1 or 2 centimeters throughout the 12-meter section of sediment, each representing 33 to 67 years of deposition on average, the two extracted lipids (fatty substances) from each sample and then used gas chromatography to measure the ratio of alkenones.

Based on the technique, the researchers were able to reconstruct the surface sea temperature, showing that it varied between 15.5 centigrade to 21 centigrade — close to the current water temperature of 22.5 Celsius.

“Our study shows that previously documented disruption of ocean currents during the last ice age produced unexpectedly large and rapid temperature changes in the warm Atlantic Ocean. That implies that Greenhouse warming – which could similarly disrupt ocean currents — could have consequences more global than some current predictions,” said Sachs.