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

Multiproxy analyses of sediment cores from Lago Taypi Chaka Kkota (LTCK) Cordillera 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 insensitive to changes in P}E because it is largely bu!ered from dry season draw-down 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 watershed. Lake-water d18O values inferred from d18O analysis of sediment cellulose range from !12.9 to !5.3& and average !8.7& between 6.2 and 2.3 ka B.P. Modern lake-water d18O from LTCK averages !14.8& which is compatible with the d18O -8 value of !14.3& for the surface sediment cellulose. Analyses of d18O from modern surface waters in 23 lakes that span the range from glacial-fed to closed basin vary from !16.6 to !2.5&. This approximates the magnitude of the down-core shift in d18O -8 values in LTCK during the middle to late Holocene from !12.9 to !5.3&. Strong paleohydrologic change during the middle Holocene is also evident in diatom assemblages that consist of shallow-water, non-glacial periphytic taxa and bulk organic d13C and d15N that show increases likely resulting from degradation of lacustrine organic matter periodically exposed to subaerial conditions. Neoglaciation began after 2.3 ka B.P. as indicated by changes in the composition of the sediments, lower d18O values, and a return to diatom assemblages characteristic of the glacial sediments that formed during the Late Pleistocene. Collectively, these data indicate that the past 2.3 ka B.P. have been 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 Nevado Sajama, and may be driven by insolation and resultant changes in atmospheric 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 Lake Titicaca (3.5 ka B.P.) provides evidence for variable sub-regional hydrologic response to climate change during the middle to late Holocene. ( 2000 Elsevier Science Ltd. All rights reserved.