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Title:
10-Be Constraints on the Timing of the Last Glacial Maximum and Deglaciation in the Northern Peruvian Andes
Authors:
Shakun, J. D.; Clark, P. U.; Marcott, S. A.; Brook, E. J.; Caffee, M. W.
Affiliation:
AA(Oregon State University, Department of Geosciences, Corvallis, OR 97333, United States ; ), AB(Oregon State University, Department of Geosciences, Corvallis, OR 97333, United States ; ), AC(Oregon State University, Department of Geosciences, Corvallis, OR 97333, United States ; ), AD(Oregon State University, Department of Geosciences, Corvallis, OR 97333, United States ; ), AE(Purdue University, Department of Physics, West Lafayette, IN 47904, United States ; )
Publication:
American Geophysical Union, Fall Meeting 2007, abstract #PP33B-1280
Publication Date:
12/2007
Origin:
AGU
AGU Keywords:
0720 Glaciers, 1105 Quaternary geochronology, 1150 Cosmogenic-nuclide exposure dating (4918), 1650 Solar variability (7537), 9360 South America
Abstract Copyright:
(c) 2007: American Geophysical Union
Bibliographic Code:
2007AGUFMPP33B1280S

Abstract

Eighteen 10Be ages were determined on quartzite boulders from two latest Pleistocene moraines in the northern Peruvian Andes at 7°S. Pleistocene moraines in this area are only a few hundred meters below the highest summits and represent small glaciers sensitive to climate change. A moraine corresponding to the local Last Glacial Maximum (LGM) yields a mean age of 19.2 +/- 1.1 10Be ka using the scaling of Lal (1991) and the production rate of Stone (2000). This age agrees fairly well with the onset of deglaciation inferred from other records in the tropical Andes including 10Be dating of moraines in the Cordillera Blanca, glaciogenic sediment input into Lakes Junin and Titicaca, and Huascaran d18O, as well as the initiation of warming seen in many marine records throughout the tropics at ~19 ka. These data do not seem to support an early local LGM in the tropical Andes, although ongoing cosmogenic work at our field site seeks to better clarify this issue. A deglacial moraine in an adjacent valley has a mean age of 15.8 +/- 1.4 10Be ka and best represents the timing of ice withdrawal from this region. Numerous other moraines throughout Peru and northern Bolivia have also been dated to ~15 10Be ka (Farber et al, 2005; Smith et al, 2005). Other records from the southern tropics indicate drying at this time, perhaps in response to a northward shift of the intertropical convergence zone associated with a resumption of thermohaline circulation, which may explain this deglacial event. While Schaefer et al. (2006) found a near-synchronous termination of the LGM in the mid-latitudes of both the Northern and Southern Hemispheres at ~17 10Be ka, the ~15 10Be ka age of moraines from the tropical Andes may indicate an asynchronous onset of the last deglaciation between the low and mid-latitudes.
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