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Mediterranean fossils offer new climate clues

Findings shed new light in links between temperatures, CO2 and glaciation

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How will Antarctic ice sheets and glaciers respond to global warming? bberwyn photo.

Staff Report

FRISCO — The relationship between global temperatures and the massive glaciation of historic ice ages may be a bit more complex than previously believed.

By studying the chemical composition of Mediterranean Sea fossils as old as 5.3 million years, scientists found a new way to assess sea-level changes and deep-sea temperature variability over the past 5.3 million years. The findings will result in a better understanding of ice age climate, and could offer new insight into the relationship between carbon dioxide levels, global temperatures and sea levels.

The researchers focused on the flow of water through Strait of Gibraltar, which was particularly sensitive to sea-level changes.

“As continental ice sheets grew during the ice ages, flow through the Strait of Gibraltar was reduced, causing measurable changes in oxygen isotope ratios in Mediterranean waters, which became preserved in the shells of the ancient plankton,” said lead researcher Eelco Rohling, with the ANU Research School of Earth Sciences.

University of Southhampton researcher  Gavin Foster said the research for the first time found long-term trends in cooling and continental ice-volume build-up cycles over the past 5.3 Million years were not the same.

“In fact, for temperature the major step toward the ice ages of the past two million years was a cooling event at 2.7 million years ago,” Foster said. “But for ice-volume, the crucial step was the development of the first intense ice age at around 2.15 million years ago. Before our results, these were thought to have occurred together at about 2.5 million years ago.”

Rohling said the findings will help scientists better understand the nature of ice ages and development of coastal sediment.

“The observed decoupling of temperature and ice-volume changes provides crucial new information for our understanding of how the ice ages came about,” he said.

“However, there are wider implications. For example, a more refined sea-level record over millions of years is commercially interesting because it allows a better understanding of coastal sediment sequences that are relevant to the petroleum industry,” he said.

“Our record is also of interest to climate policy developments, because it opens the door to detailed comparisons between past atmospheric carbon dioxide concentrations, global temperatures, and sea levels, which has enormous value to long-term future climate projections,” Rohling concluded.

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