Analyzing the oldest ice core ever retrieved in Antarctica, U.S. scientists have shown a correlation between atmospheric carbon dioxide levels and temperature as far back as 2 million years. The core, drilled in an area 130 miles from the U.S.’s McMurdo research station, also showed a significant shift in the frequency of ice ages over the past 2 million years.
Until this latest research, published in Nature, the oldest complete ice core data — also from Antarctica — dated back 800,000 years. Analyzing gases trapped in air bubbles in that ice, scientists demonstrated that atmospheric CO2 levels have been directly linked with Antarctic and global temperatures for nearly 1 million years.
The 2 million-year-old ice core also demonstrates that correlation. “One of the important results of this study is to show that carbon dioxide is linked to temperature in this earlier time period,” said Ed Brook of Oregon State University. The research group was led by scientists at Princeton University and the University of Maine.
The ancient ice core also shed light on changes in the frequency of ice ages. During the past 1 million years, cycles of ice ages followed by warm periods occurred every 100,000 years. But from 1.2 million years ago to more than 2 million years ago, ice age cycles were shorter — occurring every 40,000 years — and were less extreme.
The ice core was drilled to a depth of 200 meters during the 2015-2016 field season in an area known as Allen Hills. Deeper ice cores have been drilled in Antarctica, but the age of this core was especially old because of its location. Allen Hills has experienced intensive compaction of snow and ice, meaning that older sections of ice were closer to the surface than in some other regions of Antarctica.