NOAA 2002-R305
Contact: Pat Viets
NOAA News Releases 2002
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Scientists comparing the chemistry of today's oceans with that of ice age oceans 20,000 years ago have concluded that pH levels were about the same, proving that the ocean's composition remains relatively stable over long periods of time.

Writing in the March 7, 2002 issue of Nature magazine, David M. Anderson, of the Commerce Department's National Oceanic and Atmospheric Administration's Paleoclimatology Program, and David Archer of the University of Chicago, developed a new method to determine the carbonate ion concentration of seawater, using shells on the ocean floor deposited over thousands of years. By studying the concentration of carbonate ion, the scientists are able to understand the amount of alkaline vs. acidity, or pH, of the ocean over time.

"Our results indicate that the calcium carbonate that lines the ocean floor can act as a buffer against chemical change, much the same as an antacid works in the stomach," Anderson said. "We know from ice cores that atmospheric carbon dioxide was 30 percent lower during the last ice age 20,000 years ago, and while we speculate the ocean must have played a role in the atmospheric CO2 lowering, changes in the ocean appear to be buffered by the presence of calcium carbonate, so that any change in carbon dioxide is not apparent."

"Our results are important in understanding the ocean's role in the global carbon cycle," Anderson said. "Prior to this study, large changes in ocean carbonate chemistry had been proposed to explain the changes in atmospheric carbon dioxide. Over thousands of years, calcium carbonate compensation appears to be the dominant variable controlling the ocean carbonate (and carbon dioxide) inventory. When carbon dioxide from the atmosphere is added to the oceans, the calcium carbonate on the seafloor dissolves to minimize the carbon dioxide change in the ocean."

By reconstructing past climates, scientists are better able to understand today's climate. "The climate system changes slowly over thousands of years," Anderson said. "By understanding past and present climates, we will be able to predict future climates."

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The Nature magazine article, "Glacial-Interglacial Stability of the Ocean pH Inferred from Foraminifer Dissolution Rates," will be available online to journalists at:

For more information on NOAA's Paleoclimatology Program, please visit: