Holocene Paleohydrology of the tropical andes from lake records

摘要

Two century-scale time series in northern Bolivia constrain the ages of abrupt changes in the physical, geochemical, and biological characteristics of sediments obtained from lakes that formed during deglaciation from the late Pleistocene glacial maximum. The watersheds of Laguna Viscachani (16(degrees) 12'S, 68(degrees)07'W, 3780m) and Lago Taypi Chaka Kkota (16(degrees)13'S, 68(degrees)21'W, 4300m), located on the eastern and western slopes of the Cordillera Real, respectively, contain small cirque glaciers. A high-resolution chronology of the lake sediments is provided by 23 AMS (sup 14)C dates of discrete macro-fossils. Late Pleistocene glaciers retreated rapidly, exposing the lake basins between 10,700 and 9700 (sup 14)C yr B.P. The sedimentary facies suggest that after 8900 (sup 14)C B.P. glaciers were absent from the watersheds and remained so during the middle Holocene. An increase in the precipitation-evaporation balance is indicated above unconformities dated to about 2300 (sup 14)C yr B.P. in both Lago Taypi Chaka Kkota and Laguna Viscachani. An abrupt increase in sediment accumulation rated after 1400 (sup 14)C yr B.P. signals the onset of Neoglaciation. A possible link exists between the observed millennial-scale shifts in the regional precipitation- evaporation balance and seasonal shifts in tropical insolation.