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Lake highstands on the Altiplano during Heinrich 1 and Younger Dryas

Blard, P.H. ; Sylvestre, F. ; Tripati, A.K. ; Claude, C. ; Causse, C. ; Coudrain, A. ; Condom, T. ; Seidel, J.L. ; Vimeux, F. ; Moreau, C. ; Dumoulin, J.P. ; Lavé, J.

Lake highstands on the Altiplano (Tropical Andes) contemporaneous with Heinrich 1 and the Younger Dryas : new insights from 14C, U-Th dating and δ18O of carbonates

P.-H. Blard, F. Sylvestre, A.K. Tripati, C. Claude, C. Causse, A. Coudrain, T. Condom, J.-L. Seidel, F. Vimeux, C. Moreau, J.-P. Dumoulin, J. Lavé

Quaternary Science Reviews 30 (2011) 3973-3989

Abstract : This study provides new geochronological and stable isotope constraints on Late Pleistocene fluctuations in lake level that occurred in the closed-watershed of the Central Altiplano between w25 and w12 ka. U-series isochrons and 14C ages from carbonates are used to confirm and refine the previous chronology published (Placzek et al., 2006b). Our new data support three successive lake highstands during the Late Pleistocene : (i) the Lake Sajsi cycle, from w25 to 19 ka, that culminated at 3670 m at about 22 ka, almost synchronously with the global last glacial maximum, (ii) the Lake Tauca cycle, that lasted from 18 to 14.5 ka and was characterized by the highest water level, reached at least 3770 m from 16.5 to 15 ka, (iii) the Lake Coipasa cycle, from 12.5 to 11.9 ka, that reached an elevation of w3700 m, 42 m above the elevation of the Salar de Uyuni (3658 m). These high amplitude lake level fluctuations are in phase with the coldewarm oscillations that occurred in the North Atlantic and Greenland during the Late Pleistocene (Heinrich 1, BøllingeAllerød, Younger Dryas). Such temporal coincidence supports the hypothesis that wet events recorded in the Central Altiplano are controlled by the northesouth displacement of the Inter Tropical Convergence Zone resulting from changes in the meridional temperature gradient. Finally, the oxygen isotope ratios measured in these lacustrine carbonates allows for calculation of the d18O value of paleolake waters. Estimates of water d18O (V-SMOW) are 2.8 0.7& for Lake Tauca and 1.6 0.9& for Lake Coipasa. These data are used to constrain changes in lake hydrology and can be interpreted to indicate that the proportion of precipitation arising from local water recycling was less than 50%.

Fig. 8. A) Lake chronology of the Altiplano paleolakes during the last 30 ka. The blue curve has been drawn fitting all the geochronological data of the shoreline deposits. The green curve indicates an alternative transgression scenario based on the diatoms assemblages determined by Sylvestre et al. (1999). B) North Atlantic SST Uk’37 record from ODP core ODP977A (Martrat et al., 2004 ; Martrat et al., 2007). C) Greenland temperatures from NGRIP δ18O record (Andersen et al., 2004) rescaled according to the GICC05 time scale (Rasmussen et al., 2006 ; Svensson et al., 2006 ; Vinther et al., 2006). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Voir en ligne : http://dx.doi.org/doi:10.1016/j.qua...




publié lundi 16 janvier 2012