Multidecadal- to century-scale arid episodes on the northern Altiplano during the middle Holocene

We present reconstructions of multidecadal- to centennial-scale shifts in the hydrologic balance of the northern Altiplano during the middle Holocene using stable isotopic, geochemical, and sedimentologic evidence from Lake Titicaca sediments. Large downcore changes in the δ13Corg of bulk organic matter, previously shown to be a site-specific lake-level proxy, indicate that extended periods of lake-level regression occurred in response to sustained reductions in mean annual precipitation and/or increases in air temperature. Supporting evidence from a floating interval of finely-laminated sediments indicates that salinity and stratification were enhanced at Lake Titicaca during the middle Holocene. The age model used in this study is based on 7 AMS 14C age dates estimated from bulk decalcified sediment from a 60 cm sequence spanning 7200–5600 14C cal yr BP. Simulations from a hydrological-energy balance model of the Titicaca Basin indicate that the ∼ 38 m drop in lake level that preceded the maximum lowstand at ∼ 6200 yr BP would require a significant decrease in mean annual precipitation of up to 50% and/or a significant increase in mean annual temperature of up to 8 °C. Today, the Altiplano is often affected by drought during periods of enhanced summertime westerly wind flow, which reduces the delivery of moisture from the east. This investigation supports the idea of sustained periods of enhanced westerly air flow during the mid-Holocene and provides additional submillennial-scale information about the timing and magnitude of regional drought. Results of our frequency-domain analysis of the floating lamination interval indicate significant power at a decadal periodicity (10–12 yr) associated with the Schwabe cycle of solar activity. Frequency domain analysis also reveals power in a 75 year time series of modern lake level. We suspect that solar influence on large-scale atmospheric circulation features results in changes to the moisture balance in the Titicaca basin over decadal and possibly century-scale time periods.