COSMOGENIC DATING OF LATE QUATERNARY GLACIAL EVENTS IN THE MIDDLE AND HIGH LATITUDES OF SOUTH AMERICA

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 ¹⁴C 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.