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Science 17 September 2004:
Vol. 305. no. 5691, pp. 1766 - 1770
DOI: 10.1126/science.1100061
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Reports

Middle Miocene Southern Ocean Cooling and Antarctic Cryosphere Expansion

Amelia E. Shevenell,* James P. Kennett, David W. Lea

Magnesium/calcium data from Southern Ocean planktonic foraminifera demonstrate that high-latitude (~55°S) southwest Pacific sea surface temperatures (SSTs) cooled 6° to 7°C during the middle Miocene climate transition (14.2 to 13.8 million years ago). Stepwise surface cooling is paced by eccentricity forcing and precedes Antarctic cryosphere expansion by ~60 thousand years, suggesting the involvement of additional feedbacks during this interval of inferred low-atmospheric partial pressure of CO2 (pCO2). Comparing SSTs and global carbon cycling proxies challenges the notion that episodic pCO2 drawdown drove this major Cenozoic climate transition. SST, salinity, and ice-volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat/vapor transport, triggering ice growth and global cooling.

Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, CA 93106–9630, USA

* To whom correspondence should be addressed. E-mail: ashevenell{at}umail.ucsb.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)