Warming Climate Can Support Glacial Ice

Sea Technology, Feb 2008

New research challenges the generally accepted belief that substantial ice sheets could not have existed on Earth during past super-warm climate events. The study by researchers at Scripps Institution of Oceanography at the University of California, San Diego, provides strong evidence that a glacial ice cap about half the size of the modern day glacial ice sheet existed 91 million years ago during a period of intense global wanning. This study offers valuable insight into current climate conditions and the environmental mechanisms for global sea level rise.

The new study examines geochemical and sea-level data retrieved from marine microfossils deposited on the ocean floor during the Cretaceous Thermal Maximum. This extreme warming event in Earth's history raised tropical ocean temperatures to 35-37° C, about 10° C warmer than today, thus creating an intense greenhouse climate.

Using two independent isotopic techniques, researchers at Scripps Oceanography studied the microfossils to gather geochemical data on the growth and eventual melting of large Cretaceous ice sheets.

The researchers compared stable isotopes of oxygen molecules in bottom-dwelling and near-surface marine microfossils, known as foraminifera, to show that changes in ocean chemistry were consistent with the growth of an ice sheet.

A second method in which an ocean surface temperature record was subtracted from the stable isotope record of surface ocean microfossils yielded the same conclusion.

These independent methods provided Andre Bornemann, lead author of the study, with strong evidence to conclude that an ice sheet about 50 to 60 percent the size of the modern Antarctic ice cap existed for about 200,000 years. Bornemann conducted this study as a postdoctoral researcher at Scripps Oceanography and continues this research at Universitat Leipzig in Germany.

"Until now, it was generally accepted that there were no large glaciers on the poles prior to the development of the Antarctic ice sheet about 33 million years ago," said Richard Noms, professor of paleobiology at Scripps Oceanography and coauthor of the study. "This study demonstrates that even the super-warm climates of the Cretaceous Thermal Maximum were not warm enough to prevent ice growth."