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Science 18 July 2008:
Vol. 321. no. 5887, pp. 392 - 395
DOI: 10.1126/science.1157215
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Reports

Patagonian Glacier Response During the Late Glacial–Holocene Transition

Robert P. Ackert, Jr.,1* Richard A. Becker,2 Brad S. Singer,2 Mark D. Kurz,3 Marc W. Caffee,4 David M. Mickelson2

Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (50°S), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 ± 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49°S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation—reflecting changes in the Southern Westerly circulation—rather than regional cooling.

1 Department of Earth and Planetary Science, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA.
2 Department of Geology and Geophysics, University of Wisconsin–Madison, 1215 West Dayton Street, Madison, WI 53706, USA.
3 Woods Hole Oceanographic Institution, Clark 419, MS #25, Woods Hole, MA 02543, USA.
4 Purdue Rare Isotope Measurement Laboratory, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907–2036, USA.

* To whom correspondence should be addressed. E-mail: rackert{at}fas.harvard.edu

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