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Ancient coral reveals CO2 levels from Earth's past climate

Until now, researchers haven't had a reliable way to measure the behavior of the ancient ocean over brief timescales.

By Brooks Hays
Ancient coral reveals CO2 levels from Earth's past climate
Researchers are studying ancient coral fossils to learn more about the Earth's past climate. Photo by Norm Diver/Shutterstock

BRISTOL, England, Sept. 24 (UPI) -- Modeling Earth's past climate can help scientists better understand today's climate and what rising CO2 levels might mean for the future of the planet.

But clues to the makeup of Earth's early atmosphere aren't easy to find. Recently, researchers at the University of Bristol went to the bottom of the ocean for a climatic glimpse back in time. Deep sea corals, in turns out, are the ideal time machine for paleoclimate scientists.

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Ice cores show that between 18,000 and 11,000 years ago Earth experienced its last deglaciation period. The broader rise in CO2 levels, melting ice caps and rising seas was marked by three sharp bursts in CO2 levels.

Researchers believe a pattern of deepwater upwelling called the Atlantic Meridional Overturning Circulation may be closely associated with the rising temperatures and CO2 spikes that precipitated the last glaciation.

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But until now, researchers haven't had a reliable way to measure the behavior of the ancient ocean over brief timescales. Deep-sea coral fossils are helping scientists solve this problem.

By radiocarbon dating ancient corals retrieved from the Atlantic and Southern oceans, researchers are able plot the changing levels of radiocarbon in the ancient ocean. Radiocarbon is introduced at the surface of the ocean and slowly makes its way deeper. Fluctuations in radiocarbon reveal patterns of ocean circulations and upwelling events.

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Analysis of the coral fossils showed that the middle depths of the equatorial Atlantic and the Drake Passage experienced two significant transient events, during which water layers were neutralized and large levels of radiocarbon were introduced. These events correspond with the last two CO2 bursts revealed by ice core samples.

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The new research -- carried out by scientists from Bristol, as well as the University of St. Andrews and University of California, Irvine -- was published in the journal Science.

"Our radiocarbon data are consistent with two transient and enhanced deep Atlantic overturning events which flushed out respired carbon in the deep water, causing a rapid rise of atmosphere CO2 concentration and abrupt warming of the high latitude North Atlantic," lead author Tianyu Chen, Bristol earth scientist and author of the new study, said in a news release.

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