HR: 11:50h
AN: PP32A-07    [Abstracts]
TI: The late glacial paleoclimate of the central Altiplano constrained by cosmogenic ³He dating and 'clumped-isotope' paleothermometry
AU: * Blard, P
EM: blard@gps.caltech.edu
AF: Division of Geological and Planetary Sciences California Institute of Technology, Pasadena, USA, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Lave, J
AF: CRPG, Rue Notre Dame des Pauvres, Vandoeuvre les Nancy, 54501, France
AU: Farley, K A
AF: Division of Geological and Planetary Sciences California Institute of Technology, Pasadena, USA, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Tripati, A
AF: Division of Geological and Planetary Sciences California Institute of Technology, Pasadena, USA, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Tripati, A
AF: Department of Earth Sciences University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Eiler, J
AF: Division of Geological and Planetary Sciences California Institute of Technology, Pasadena, USA, 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Sylvestre, F
AF: CEREGE, Europole de l Arbois, Aix en Provence, 13845, France
AB: One of the ongoing debates in paleoclimatology is whether climate change in the tropics is simply a response to global climate change, or actually forces it. The Altiplano is a highland area (>3600 m) located in the tropical Andes that is particularly well-suited to address this question since both paleo-glacier footprints and paleolake shorelines are very well preserved in this region. Because glacier extents and lake levels have differential sensitivity to change in temperature and in precipitation, they can be used to place tight constraints on the amplitude of past changes in these atmospheric variables. However, because the timing of the deglaciation in this region is still uncertain and poorly documented, this task requires new chronological constraints on paleoglacier fluctuations. New cosmogenic ³He dates from several glacial moraines and striated rocks of the Cerro Tunupa (Bolivia, 20 ° S) show that, in the central part of the Altiplano, glaciers persisted at their maximum extent between 18 and 15 ka, synchronously with the highest level of paleolake Tauca at 17-15 ka (Placzek et al., 2006) (Clayton and Clapperton, 1997). Abrupt glacial retreat occurred approximately 15 ka and was followed by a small amplitude readvance during the Younger Dryas. This result is different from previous moraine dating (Smith et al., 2005) that indicates an earlier (~34 ka) local glacial maximum in the northern part of the Altiplano. This discrepancy most probably reflects spatial variations in past precipitation. Consequently, climatic conditions inferred from the past extent of mountain glaciers must take into account local atmospheric variations before being interpreted in a global context. To this end, we have coupled a numerical modeling approach with an independent estimate of past air temperature based on "clumped isotope" thermometry, a technique based on the temperature dependence of the abundances of ¹³C-¹⁸O bonds in carbonate minerals (Ghosh et al., 2006). This technique was applied to shallow-water biogenic carbonates from the Tauca paleolake. To reproduce the synchronous paleoglacier and paleolake maxima, climate modeling shows that air temperatures dropped between 5 and 7 ° C, and that local precipitation increased four-fold between 17 and 15 ka in the central Altiplano. This temperature change is consistent with the drop in diurnal temperature of about 5 ° C estimated from clumped isotopes measurements of algal bioherms. This quantitative reconstruction suggests that the Tauca paleolake episode (from 17 to 15 ka) is the result of wet and cold (rather than wet and warm) conditions. References Clayton J.D. and Clapperton C.M. (1997) J. of Quat. Science 12, 169-182. Ghosh P. et al (2006) GCA 70, 1439-1456. Placzek C. et al., 2006. Geol. Soc. of Am. Bull.118, 515-532. Smith J. A., et al (2005) Science 308, 678-681.
DE: 0720 Glaciers
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1105 Quaternary geochronology
DE: 1130 Geomorphological geochronology
DE: 1847 Modeling
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting