AsianScientist (Dec. 2, 2011) – Atmospheric carbon dioxide levels plunged by 40 percent before and during the formation of the Antarctic ice sheet 34 million years ago, according to a new study.
Published today in the journal Science, the international study by researchers from the U.S., Hong Kong, Sweden, and Australia, is the first multidisciplinary research of its kind to show that C02 could dramatically alter global climate.
It confirms that significant falls in the greenhouse gas result in global cooling, just as rises result in global warming, reinforcing carbon dioxide’s place as a primary driver for global temperatures.
Previous studies had suggested that atmospheric carbon dioxide over the Southern Ocean was climbing during the Eocene to Oligocene climate transition, when ice first formed over Antarctica. This presented a conundrum, suggesting the climate was warming at the same time as Antarctica was freezing.
But when the vastly different ancient Southern Ocean currents and temperatures of that period were factored in, it quickly became apparent that Antarctica’s big freeze followed a plunge in carbon dioxide levels.
“Our research recognized that the flows of deep ocean currents at the end of the Eocene were dramatically different from those of today because of the altered position and shape of continental masses,” said co-author Dr. William Sijp of the UNSW Climate Change Research Center.
“Previous research relied on different temperature estimates and had also not taken these different currents into account. This led to significant upward biases in calculated C02 which made it appear that carbon dioxide was actually increasing around the Southern Ocean as the Antarctic ice sheet formed. We can now see the reverse was true,” he said.
The nature of ocean currents is vital in calculating atmospheric carbon dioxide, because the estimates of atmospheric carbon dioxide are derived from measurements of molecules from algae deposited on the ocean floor at six ocean sites millions of years ago.
The fundamentally different circulation of the Southern Ocean during the Eocene directly affected the algae by changing the temperatures of these ocean currents and significantly lowering the nutrient load.
Led by Mark Pagani of Yale University, the team found a 40 percent carbon dioxide decrease over a three million year period which was critical for global cooling and the emergence of the Antarctic ice sheet. This study refutes previous accounts that there was a rise in carbon dioxide levels during Antarctic glaciation.
The article can be found at: Pagani M et al. (2011) The Role of Carbon Dioxide During the Onset of Antarctic Glaciation.
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Source: UNSW.
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