EMBARGOED—NOT FOR PUBLIC RELEASE BEFORE:
Monday, May 11, 2015
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Tuesday, May 12, 2015
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Complete list of articles expected to publish in PNAS the week of May 11:
<http://www.eurekalert.org/jrnls/pnas/subject.htm>
IMPORTANT NOTE: The articles listed below will publish on Monday, May 11, 2015.
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
Atmospheric record in Antarctic blue ice
Air bubbles, trapped in some of the oldest known ice on Earth, suggest that Antarctic
temperatures 1 million years ago were linked to greenhouse gas concentrations, according
to a study. Decades ago, researchers extracted samples of past atmospheres from ice cores
and found that greenhouse gas concentrations track a 100,000-year glacial cycle dating
back 800,000 years. Deep-sea sediment cores, however, show that this cycle developed
only 900,000 years ago, and that previous glacial cycles occurred every 40,000 years. To
better understand the shift from 40,000-year- to 100,000-year glacial cycles, John A. Higgins
and colleagues used a shallow ice core from the Allan Hills blue ice area in Antarctica to
reconstruct atmospheric CO2 and methane concentrations around 1 million years ago. Blue
ice forms where mountains force glacial ice to flow upward and strong winds persistently
scour material from the surface, allowing the oldest ice at the bottom to rise to the top.
According to the authors, shallow blue ice cores are difficult to interpret, but the findings
suggest that CO2 and Antarctic temperatures were linked in the warm world of the MidPleistocene, according to the authors.
Article #14-20232: “Atmospheric composition 1 million years ago from blue ice in the Allan
Hills, Antarctica,” by John A. Higgins et al.
MEDIA CONTACT: John A. Higgins, Department of Geosciences, Princeton University, NJ;
tel: 609-258-7024; e-mail: <jahiggin@princeton.edu>
http://www.eurekalert.org/jrnls/pnas/14-20232.htm