Antarctic ice core record extended to 2.7 million years ago

Detailed information about the Earth’s surface temperature and the composition of the atmosphere over the past 800,000 years has been obtained from Antarctic ice cores, primarily from the Vostok and Dome C sites.  These ice cores were obtained by vertical drilling to ice depths of over two kilometers.  In Paris a team has just reported the initial analysis of ice cores captured by horizontal drilling in the Allan Hills in Antarctica where because of the geology very old ice has been folded upwards. Dating was accomplished by measuring the isotopic composition of Argon (Ar40, Ar38, AR36) in the trapped air which is estimated to be precise to within 100,000 years. The ice cores of what is described as clean, ancient, bubbly ice has been dated to as old as 2.7±0.3 million years ago roughly when the cycle of glacials/interglacials began, initially with a 41,000 year cycle.  The researchers were able atmosphereic composition from the bubbles.  They were also able to measure Xe/Kr ratios in the ice core gas, allowing the reconstruction of past mean ocean temperature.   Initial analysis has revealed that atmospheric carbon dioxide (CO2) levels at that time did not exceed 300 parts per million.  During the past 800,000 years the Dome C ice core record has revealed that CO2 concentrations at this level are only found during ice ages.

2.7-million-year-old ice from Allan Hills Blue Ice Areas, East Antarctica reveals climate snapshots since early Pleistocene, YUZHEN YAN, JESSICA NG, JOHN HIGGINS, ANDREI KURBATOV, HEATHER CLIFFORD, NICOLE SPAULDING, JEFFREY SEVERINGHAUS, ED BROOK, PAUL MAYEWSKI, AND MICHAEL BENDER, Goldschmidt Paris 2017 August 13-18.