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210Pb, 137Cs and 14C dated sediments of two late Holocene landslide lakes in the Provincial Park Lagunas de Yala (Laguna Rodeo, Laguna Comedero, 24°06′S, 65°30′W, 2100 m asl, northwestern Argentina) reveal a high-resolution multi-proxy data set of climate change and human impact for the past ca. 2000 years. Comparison of the lake sediment data set for the 20th century (sediment mass accumulation rates MARs, pollen spectra, nutrient and charcoal fluxes) with independent dendroecological data from the catchment (fire scars, tree growth) and long regional precipitation series (from 1934 onwards) show that (1) the lake sediment data set is internally highly consistent and compares well with independent data sets, (2) the chronology of the sediment is reliable, (3) large fires (1940s, 1983/1984-1989) as documented in the local fire scar frequency are recorded in the charcoal flux to the lake sediments and coincide with low wet-season precipitation rates (e.g., 1940s, 1983/1984) and/or high interannual precipitation variability (late 1940s), and (4) the regional increase in precipitation after 1970 is recorded in an increase in the MARs (L. Rodeo from 100 to 390 mg cm-2 yr-1) and in an increase in fern spores reflecting wet vegetation. The most significant change in MARs and nutrient fluxes (Corg and P) of the past 2000 years is observed with the transition from the Inca Empire to the Spanish Conquest around 1600 AD. Compared with the pre-17th century conditions, MARs increased by a factor of ca. 5 to >8 (to 800 +130, -280 mg cm-2 yr-1), PO4 fluxes increased by a factor of 7, and Corg fluxes by a factor of 10.5 for the time between 1640 and 1930 AD. 17th to 19th century MARs and nutrient fluxes also exceed 20th century values. Excess Pb deposition as indicated by a significant increase in Pb/Zr and Pb/Rb ratios in the sediments after the 1950s coincides with a rapid expansion of the regional mining industry. Excess Pb is interpreted as atmospheric deposition and direct human impact due to Pb smelting. © 2006 Elsevier Ltd and INQUA. Fil: Lupo, Liliana Concepcio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Jujuy; Argentina Fil: Bianchi, Maria Martha. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Comahue; Argentina Fil: Aráoz, Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Investigaciones Ecológicas de las Yungas; Argentina Fil: Grau, Hector Ricardo. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Investigaciones Ecológicas de las Yungas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lucas, Christoph. University of Bern; Suiza Fil: Kern, Raoul. University of Bern; Suiza Fil: Camacho, María. Universidad Nacional de Jujuy; Argentina Fil: Tanner, Willi. University of Bern; Suiza Fil: Grosjean, Martin. University of Bern; Suiza

Late Pleistocene palaeolakes on the eastern side of Andes (glacial lakes) and in the Patagonian Steppe (pluvial lakes) along 41°S latitude were studied. Natural dams (glaciers, moraines) that maintained a high water level in glacial palaeolakes were melted or cut by erosion during Late Pleistocene climate amelioration. With the retreat of the glaciers from the Andean valleys during prominent regional deglaciation, outflow from the eastern side of Andes to the Pacific Ocean was formed about 13.2 ka BP. As a result, the water level in glacial palaeolakes fell rapidly in stages. These changes were often preceded by volcanic-tectonic activity, which is suggested to be the “touch of butterfly” releasing mass balance adjustment in the changing landscape. The lacustrine tephra stratigraphic pattern from the Andes, comprising more than 50 horizons since the last glaciation, is presented. The correlation of palaeoenvironmental changes between the Andes and the Patagonian Steppe is suggested on the basis of two dacite marker horizons. The deglaciation event that led to development of the new hydrological system in the Andean palaeolakeland formed several large but short-lived palaeolakes in closed basins in the Patagonian Steppe probably due to melting of local ice and permafrost accumulated during glaciation on the surrounding mountains and elevated plains.