Researchers are exploring whether these ubiquitous fluorinated molecules might worsen infections or hamper vaccine effectiveness.
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Edited by James P. Kennett, University of California, Santa Barbara, CA, and approved June 3, 2008 (received for review March 12, 2008)
Abstract
A major obstacle in understanding the evolution of Cenozoic climate has been the lack of well dated terrestrial evidence from high-latitude, glaciated regions. Here, we report the discovery of exceptionally well preserved fossils of lacustrine and terrestrial organisms from the McMurdo Dry Valleys sector of the Transantarctic Mountains for which we have established a precise radiometric chronology. The fossils, which include diatoms, palynomorphs, mosses, ostracodes, and insects, represent the last vestige of a tundra community that inhabited the mountains before stepped cooling that first brought a full polar climate to Antarctica. Paleoecological analyses, 40Ar/39Ar analyses of associated ash fall, and climate inferences from glaciological modeling together suggest that mean summer temperatures in the region cooled by at least 8°C between 14.07 ± 0.05 Ma and 13.85 ± 0.03 Ma. These results provide novel constraints for the timing and amplitude of middle-Miocene cooling in Antarctica and reveal the ecological legacy of this global climate transition.
Footnotes
- dTo whom correspondence should be sent at the present address: Department of Geosciences, North Dakota State University, Fargo, ND 58105. E-mail: adam.r.lewis.1{at}ndsu.edu
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Author contributions: A.R.L., D.R.M., A.C.A., L.H., S.R.H., J.V.J., M.J.L., M.L.M., A.E.N., J.I.R., J.K.W., M.W., and A.P.W. performed research; A.R.L. and A.C.A. analyzed data; and A.R.L., D.R.M., A.C.A., and A.P.W. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0802501105/DCSupplemental.
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↵ n British Antarctic Survey Plant Database, www.antarctica.ac.uk/bas_research/data/access/plantdatabase/index.php. Last updated 2007; last accessed January 8, 2008.
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↵ o Antarctic Climate Data: Results from the SCAR Reader Project. www.antarctica.ac.uk/met/gjma/temps.html. Last updated June 3, 2007; last accessed January 8, 2008.
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↵ p Antarctic CRC and Australian Antarctic Division Climate Data Sets. www.antarctica.ac.uk/met/READER/temperature.html. Last updated February 29, 2000; last accessed January 8, 2008.
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Freely available online through the PNAS open access option.
- © 2008 by The National Academy of Sciences of the USA
Mid-Miocene cooling and the extinction of tundra in continental Antarctica
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