COSMOGENIC DATING OF LATE QUATERNARY GLACIAL EVENTS IN THE MIDDLE AND

HIGH LATITUDES OF SOUTH AMERICA

KAPLAN, Michael R.1, DOUGLASS, Daniel C.2, SINGER, Bradley S.2, ACKERT,

Robert P.3, HULTON, Nicholas R.J.1, SUGDEN, David E.1, CAFFEE, Marc W.4,

and KUBIK, Peter W.5, (1) School of GeoSciences, Univ. of Edinburgh,

Drummond Street, Edinburgh, EH8 9XP, mkaplan@geo.ed.ac.uk, (2) Geology

and Geophysics, Univ of Wisconsin-Madison, 1215 W. Dayton St, Madison,

WI 53706, (3) Earth and Planetary Sciences, Harvard Univ, 20 Oxford

Street, Cambridge, MA 02138, (4) Physics, Purdue Univ, W. Lafayette, IN

47906, (5) Paul Scherrer Institute c/o Teilchenphysik, ETH Hönggerberg,

Zurich, CH-8093

In southern South America, the glacial geologic record is one of the few

available paleoclimate proxies at orbital and suborbital time scales,

and contributes information that helps identify the underlying driving

mechanism(s) of global climatic variability. Cosmogenic nuclide dating

of the Patagonian moraines provides a precise chronology of the former

Andean glacial fluctuations. At Lago Buenos Aires, 46°S, 5 advances

occurred between ca. 23 and 16 ka. In the Strait of Magellan, 53°S, at

least 4 advances occurred between ca. 25 and 17 ka. In both areas, the

maximum expansion of ice occurred before ca. 20 ka, there was another

advance ca. 15-13 ka, and the data are in good agreement with available

14-C ages. The chronologies are indistinguishable between the two areas

given present uncertainties. The Patagonian record suggests that

equatorward movement of the Southern Hemisphere westerlies and polar

front, which causes snowline depression, was in step with major Northern

Hemisphere ice volume change, despite a local high in summer insolation.

A global glacial maximum, associated with low Northern Hemisphere

insolation, included millennial-scale advances of middle to high

latitude Southern Hemisphere mountain glaciers.