Holocene hydrological reconstructions from stable isotopes and paleolimnology, Cordillera Real, Bolivia

Multiproxy analyses of sediment cores from Lago Taypi Chaka Kkota (LTCK) Co rdillera Real, Bolivia, provide a record of drier conditions following late Pleistocene deglaciation culminating in pronounced aridity between 6.2 and 2.3 ka B.P. Today LTCK is a glacial-fed lake that is relatively insensitiv e to changes in P-E because it is largely buffered from dry season draw-dow n through the year-round supply of glacial meltwater. This was not the case during the middle to late Holocene when glaciers were absent from the wate rshed. Lake-water delta O-18 values inferred from delta O-18 analysis of se diment cellulose range from - 12.9 to - 5.3 parts per thousand and average - 8.7 parts per thousand between 6.2 and 2.3 ka B.P. Modern lake-water delt a O-18 from LTCK averages - 14.8 parts per thousand which is compatible wit h the delta O-18(lw) value of - 14.3 parts per thousand for the surface sed iment cellulose. Analyses of delta O-18 from modern surface waters in 23 la kes that span the range from glacial-fed to closed basin vary from - 16.6 t o - 2.5 parts per thousand. This approximates the magnitude of the down-cor e shift in delta O-18(lw) values in LTCK during the middle to late Holocene from - 12.9 to - 5.3 parts per thousand. Strong paleohydrologic change dur ing the middle Holocene is also evident in diatom assemblages that consist of shallow-water, non-glacial periphytic taxa and bulk organic delta C-13 a nd delta N-15 that show increases likely resulting from degradation of lacu strine organic matter periodically exposed to subaerial conditions. Neoglac iation began after 2.3 ka B.P. as indicated by changes in the composition o f the sediments, lower delta O-18 values, and a return to diatom assemblage s characteristic of the glacial sediments that formed during the Late Pleis tocene. Collectively, these data indicate that the past 2.3 ka B.P. have be en the wettest interval during the Holocene. Millennial-scale shifts in the paleohydrologic record of LTCK during the early to middle Holocene conform to other regional paleoclimatic time-series, including Lake Titicaca and N evado Sajama, and may be driven by insolation and resultant changes in atmo spheric circulation and moisture supply. In contrast, an apparent 1200-year lag in the onset of wetter conditions at LTCK (2.3 ka B.P.) compared to La ke Titicaca (3.5 ka B.P.) provides evidence for variable sub-regional hydro logic response to climate change during the middle to late Holocene. (C) 20 00 Elsevier Science Ltd. All rights reserved.