Papers Accepted
Abstract:
Strontium concentrations and strontium isotopic ratios were measured in natural waters and carbonate sediments from throughout the Bolivian and Peruvian Altiplano in order to improve hydrologic and paleohydrologic mass balances with the ultimate goal of better understanding the paleoclimatic history of the central Andes. Rivers flowing into Lake Titicaca have a wide range of strontium isotopic ratios that exhibit spatial patterns consistent with the lithologies of the different drainage basins. Because of the limited exchange of water between the two main sub-basins of Lake Titicaca, Lago Grande and Lago Huiñaimarca, and between the sub-basins of Lago Huiñaimarca, there are significant differences in strontium isotopic ratios between the sub-basins. Calculated elemental balances of strontium in Lake Titicaca are in reasonable agreement with previously published budgets of water and major elements. However, the strontium isotopic budget indicates that the lake is not in isotopic steady state. This also implies that the major-element budgets are unlikely to be in steady state. Lake Titicaca had a higher-than-modern strontium isotopic ratio during the early and middle Holocene. Elevated values persisted in Lago Grande until at least 2000 cal yr BP, consistent with other evidence that modern hydrologic conditions (namely overflow) were not established until that time. An isotopic budget calculated for late-Pleistocene paleolake Tauca in the central Altiplano suggests that between 70% and 83% of its riverine inputs were derived from Lake Titicaca overflow. This calculated flow represents about a 30-fold increase over the average discharge of the modern Río Desaguadero at Desaguadero or a seven-fold increase over its average discharge into Lago Poopó. The strontium isotopic budget (if complete) precludes the possibility that decreased evaporation alone could have accounted for the existence of paleolake Tauca. © 2003 Elsevier Science B.V. All rights reserved.