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Atmospheric composition 1 million years ago from blue ice in the Allan Hills, Antarctica

Higgins, John A., Kurbatov, Andrei V., Spaulding, Nicole E., Brook, Ed, Introne, Douglas S., Chimiak, Laura M., Yan, Yuzhen, Mayewski, Paul A., Bender, Michael L.
Proceedings of the National Academy of Sciences of the United States of America 2015 v.112 no.22 pp. 6887-6891
air, atmospheric chemistry, bubbles, climate, greenhouse gases, ice, temperature, Antarctic region, Antarctica
Here, we present direct measurements of atmospheric composition and Antarctic climate from the mid-Pleistocene (∼1 Ma) from ice cores drilled in the Allan Hills blue ice area, Antarctica. The 1-Ma ice is dated from the deficit in ⁴⁰Ar relative to the modern atmosphere and is present as a stratigraphically disturbed 12-m section at the base of a 126-m ice core. The 1-Ma ice appears to represent most of the amplitude of contemporaneous climate cycles and CO ₂ and CH ₄ concentrations in the ice range from 221 to 277 ppm and 411 to 569 parts per billion (ppb), respectively. These concentrations, together with measured δD of the ice, are at the warm end of the field for glacial–interglacial cycles of the last 800 ky and span only about one-half of the range. The highest CO ₂ values in the 1-Ma ice fall within the range of interglacial values of the last 400 ka but are up to 7 ppm higher than any interglacial values between 450 and 800 ka. The lowest CO ₂ values are 30 ppm higher than during any glacial period between 450 and 800 ka. This study shows that the coupling of Antarctic temperature and atmospheric CO ₂ extended into the mid-Pleistocene and demonstrates the feasibility of discontinuously extending the current ice core record beyond 800 ka by shallow coring in Antarctic blue ice areas.