Holocene paleohydrology of the tropical Andes from lake records

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, 3780 m) and Lago Taypi Chaka Kkota (16 degrees 13'S, 68 degrees 21'W, 4300 m), 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 C-14 dates of discrete macrofossils. Late Pleistocene glaciers retreated rapidly, exposing the lake basins between 10,700 and 9700 C-14 yr B.P. The sedimentary facies suggest that after 8900 C-14 Yr 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 similar to 2300 C-14 yr B.P. in both Lago Taypi Chaka Kkota and Laguna Viscachani. An abrupt increase in sediment accumulation rates after 1400 C-14 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. (C) 1997 University of Washington.