Holocene paleohydrology and glacial history of the central Andes using multiproxy lake sediment studies

Here we document at century to millennial scale the regional changes of precipitation–evaporation from the late Pleistocene to present with multiproxy methods on a north–south transect of lake sites across the eastern cordillera of the central Andes. The transect of study sites covers the area from ∼14°S to 20°S and includes core studies from seven lakes and modern calibration water samples from twenty-three watersheds analyzed to constrain the down-core interpretations of stable isotopes and diatoms. We selected lakes in different hydrologic settings spanning a range of sensitivity to changes in the moisture balance. These include: (1) lakes directly receiving glacial meltwater, (2) overflowing lakes in glaciated watersheds, (3) overflowing lakes in watersheds without active glaciers, and (4) lakes that become closed basins during the dry season. The results of our current work on multiple lakes in the Bolivian Andes show that while the overall pattern of Holocene environmental change is consistent within the region, conditions were not always stable over centennial to over millennial timescales and considerable decadal- to century-scale climate variability is evident [Abbott et al., Quat. Res. 47 (1997) 70–80, Quat. Res. 47 (1997) 169–180, Quat. Sci. Rev. 19 (2000) 1801–1820; Polissar, Master's thesis, University of Massachusetts (1999)]. Comparison of the paleoclimate record from one well-studied site, Lago Taypi Chaka Kkota (LTCK), with others within the region illustrates a consistent overall pattern of aridity from the late glacial through the middle Holocene. Previous work noted a difference between the timing of water-level rise in Lake Titicaca ∼5.0–3.5 ka B.P. [Abbott et al., Quat. Res. 47 (1997) 169–180; Cross et al., Holocene 10 (2000) 21–32; Rowe et al., Clim. Change 52 (2002) 175–199] and the onset of wetter conditions at 2.3 ka B.P. in LTCK, a lake that drains into the southern end of Lake Titicaca [Abbott et al., Quat. Res. 47 (1997) 70–80]. Sedimentary and oxygen isotope evidence from Paco Cocha (13°54′S) located in the northern reaches of the expansive 57 000 km 2 Titicaca watershed, which spans ∼14°S to 17°S, indicates that glaciers returned to the watershed around 4.8 ka B.P. In addition, sedimentary and geochemical data from Llacho Kkota (15°07′S), located between LTCK (16°12′S) and Paco Cocha, indicate wetter conditions around 3.4 ka B.P. This suggests wetter conditions occurred first in the northern reaches of the Titicaca watershed