Might be interesting to see what CO2 levels were like 2.7 million years ago.


Described at the Goldschmidt Conference in Paris by Yuzhen Yan, a graduate student at Princeton University, the ice revealed atmospheric carbon dioxide (CO2) levels that did not exceed 300 parts per million, well below today’s levels. Some models of ancient climate predict that such relatively low levels would be needed to tip Earth into a series of ice ages. But some proxies gleaned from the fossils of animals that lived in shallow oceans had indicated higher CO2 levels. If the new result holds up, says Yige Zhang, a paleoclimatologist at Texas A&M University in College Station, the proxies will need to be recalibrated. “We have some work to do.”


2.7-Million-Year-Old Ice from Allan Hills Blue Ice Areas, East Antarctica Reveals Climate Snapshots Since Early Pleistocene

Yan Y, Ng J, Higgins J, Kurbatov A, Clifford H, Spaulding N, Severinghaus J, Brook E, Mayewski P & Bender M

2.7-million-year-old ice from Allan
Hills Blue Ice Areas, East Antarctica
reveals climate snapshots since early

Department of Geosciences, Princeton University, Princeton,
NJ (*correspondence: yuzheny@princeton.edu) 2
Scripps Institution of Oceanography, University of
California, San Diego, CA 3
University of Maine, Climate Change Institute, Orono, ME 4
College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR

A tight coupling between atmospheric CO2 and global
climate over the last 800 thousand years (kyr) has been established by analyzing ancient air trapped in Antarctic ice cores. 1-million-year-old (Ma) ice has been found in Allan Hills Blue Ice Areas (AH BIAs), East Antarctica [1], a region where old ice flows along the rising bedrock and approaches the surface. Although the blue ice core is stratigraphically disturbed, it provides the first direct observations of pCO2 before 800 kyr as “climate snapshots”.
Here we report the discovery of clean, ancient, bubbly ice as old as 2.7±0.3 Ma at shallow depth from AH BIAs. The ice is dated by precisely measuring the isotopic composition of argon in the trapped air. Radiogenically produced by 40K in the solid Earth, 40Ar accumulates over time in the atmosphere.
By contrast 38Ar and 36Ar are primordial and have constant atmospheric burdens. A further benefit of our analytical procedures is the ability to measure Xe/Kr ratios in the same aliquot of extracted ice core gas, allowing the reconstruction of past mean ocean temperature.
The old ice can be binned into three age groups: 1 Ma, 1.5 Ma, and 2+ Ma, disturbed by layers of ≤800 ka ice. This age depth relationship indicates large-scale disturbance in the ice stratigraphy, reinforcing the concept of climate snapshots instead of time-series. Three climate proxies (Xe/Kr, δDice, and pCH4) fall within the range of variations in the in the recent
100-kyr glacial cycles, but with reduced variability.

Note to denialists, this does not disprove the current scientific consensus and does not bode well for those predicting a new ice age or even a reversal of the diminishing Arctic sea ice volume trend.

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