HOLOCENE ENVIRONMENTAL CHANGE ACROSS THE CENTRAL ANDES

Results from down-core analyses on sediment cores collected from 7 lakes ranging from 16°S to 20°S were used to document changing climatic conditions during the Holocene. Modern calibration samples from twenty-three watersheds along the same transect were analyzed to constrain the down-core interpretations of stable isotopes and diatoms. Lakes were selected from different hydrologic settings spanning a range of sensitivity to changes in the moisture balance including lakes directly receiving glacial meltwater, overflowing lakes in glaciated watersheds, overflowing lakes in watersheds without active glaciers, and lakes that drop below the overflow level during the dry season.

The results of analyses on multiple sites indicate that while the overall pattern of Holocene aridity is consistent across the region, conditions were not always stable over century to millennial timescales. Comparison of the paleoclimate record from Lago Taypi Chaka Kkota with other paleoclimate records within the region including Lake Titicaca and Nevado Sajama illustrates a consistent overall pattern of aridity from the late glacial through the middle Holocene. There is a notable discrepancy between the timing of water-level rise in Lake Titicaca, around 3.5 ka B.P., and the onset of wetter conditions in the Taypi Chaka watershed at 2.3 ka B.P. This suggests wetter conditions occurred in the northern reaches of the Titicaca watershed first resulting in rising water levels in Lake Titicaca while the Taypi Chaka watershed remained unglaciated. This is supported by sedimentological and stable isotope studies at Paco Cocha and Llacho Kkota located further to the north. The effect of changing insolation patterns on precipitation can explain this north-south asynchronous change in effective moisture, however it does not explain the century-scale variability that demonstrably exists. Overall the last 2.3 ka has been the wettest period during the Holocene, however there are notable century-scale lowstands in lakes that are not glacial-fed including Titicaca, Potosi, Cupextani, and Juntutuyo during this relatively wet period.