The two million year old ice provides a snapshot of the Earth's greenhouse gas history

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CORVALLIS, Oregon – Two years ago the Antarctic ice, recently discovered by a team of researchers, provides a clearer picture of the connections between greenhouse gases and climate in ancient times and will help scientists understand future climate change .

In a article published today in nature, a group of scientists used air trapped in bubbles in the ice of just 2 million years to measure the levels of carbon dioxide and methane in greenhouse gases. The group was led by John Higgins and Yuzhen Yan of Princeton University and Andrei Kurbatov of the University of Maine and included Ed Brook at Oregon State University and Jeff Severinghaus at the University of California, San Diego.

This is the first time that scientists have been able to study such an old ice core. Previously, the oldest complete ice core provided data at 800,000 years ago. Previous studies that have used that core and others have shown that the levels of carbon dioxide in the atmosphere are directly related to the Antarctic and global temperature over the past 800,000 years. Before that, the connection between climate and carbon dioxide levels was not well understood.

The article published today in Nature begins to change it.

In the last one million years the cycle of ice ages followed by hot periods has occurred every 100,000 years. But between 2.8 million years ago and 1.2 million years ago, those cycles were shorter, around 40,000 years and the ice ages were less extreme.

The team that included Brook wanted to find out how carbon dioxide levels changed during that older period, which until now was only indirectly known from sediment chemistry in the ocean and on the earth.

They found that the highest levels of carbon dioxide corresponded to levels in the warmer periods of more recent times. The lower levels, however, did not reach the very low concentrations found in the ice ages of the last 800,000 years.

"One of the important findings of this study is to show that carbon dioxide is temperature-related in this previous time period," Brook said.

This conclusion is based on studies of ice chemistry, which provide an indication of the temperature change in Antarctica simultaneously with changes in carbon dioxide.

"This is an important basis for understanding climate science and calibrating models that predict future changes," Brook said.

The ice core with ice of 2 million years ago comes from an area known as the Allan Hills, which is located about 130 miles from the Antarctic research station of the United States known as McMurdo Station. Ancient meteorites had been found on the surface in this area, leading scientists to believe that there may have been ancient ice in the ice sheet.

The 2 million-year-old ice core was drilled to a depth of 200 meters during the 2015-16 cross-country season. It takes one to two weeks to drill and retrieve such a nucleus, and several nuclei have been collected in the region.

The research team is returning to Allan Hills in the coming days for two months of additional work. They will collect large amounts of 2 million years old ice and look for even older samples.

"We don't know the age limit in this area," Brook said, "it could be a lot older in some places. That's why we're going to go back. Going beyond two million years would be pretty amazing."

Other co-authors of the Nature paper come from the Shanghai Jiao Tong University in China, Boston University and the California Institute of Technology. The research was funded by the National Science Foundation.

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