Coral Casts Doubts On Glaciation Theory

New study finds orbital changes alone cannot account for changes in glacial buildup or recession.

Published: 18-Jan-2002

AUSTIN, Texas, Jan. 14 (AScribe Newswire) -- Scientists studying climate change by researching fossil corals have found an inconsistency in a widely accepted theory linking cycles of glaciation to changes in Earth's orbit. A research team from The University of Texas at Austin and the University of Minnesota has found that the Milankovitch Theory - also known as orbital forcing - cannot account for an early thawing of glaciers that occurred prior to 136,000 years ago.

Research by Dr. Frederick W. Taylor, a senior research scientist at The University of Texas at Austin's Institute for Geophysics (UTIG), was published in the Jan. 11 issue of the journal Science. Lead author of the paper is Dr. Christina Gallup, an assistant professor of geology at the University of Minnesota-Duluth. Co-authors include University of Minnesota-Twin Cities geology Professor Dr. Lawrence Edwards and postdoctoral fellow Hai Cheng. The work was supported by the National Science Foundation.

The research was based on extensive examinations of fossil corals in the Barbados that track sea level changes and volumes of glacial ice. Sea level falls when glaciers build up and rises when glaciers melt, so that the elevation at which corals grow depends largely on global ice volume. According to the theory of Serbian scientist Milutin Milankovitch, cycles in the Earth's orbit provide changes in solar insolation that are the impetus for ice buildup and melting. Solar insolation is the amount of the sun's radiation that reaches Earth.

This study found that the Milankovitch theory alone could not account for a rise in sea level that enabled Barbados coral reefs to grow to a height near modern-day sea level during a period 136,000 years ago believed to have been glaciated. The evidence points to a thaw, raising sea level about 80 percent higher than its lowest level. The researchers said that their findings cast some doubt on the simple correlation in the phasing of ice sheet response to changes in Earth's orbit. This points to the existence of factors driving cycles of glaciation in addition to orbital change.

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