A late Holocene record of arid events from the Cuzco region, Peru

The small recently infilled lake basin of Marcacocha (1313 S, 7212 W, 3355 m) in the Cuzco region of Peru has a morphology and location that renders it extremely sensitive to environmental change. A record of vegetation, human impact and climatic change during the last 4200 years has been obtained from a highly organic core taken from the centre of the basin. Sustained arid episodes that affected the Peruvian Andes may be detectable using the proxy indicator of sedge (Cyperaceae) pollen abundances. As the lake level was lowered during sustained drier conditions, the local catchment was colonized by Cyperaceae, while during lake floods, they retreated or were submerged and pollen production was correspondingly reduced. Drier episodes during prehistoric times occurred around 900 B.C., 500 B.C., A.D. 100 and A.D. 550, with a longer dry episode occurring from A.D. 900-1800. Evidence from the independently derived Quelccaya ice core record and the archaeological chronology for the Cuzco region appears to support the climatic story derived from the sedge data. Many of these aridity episodes appear to correspond with important cultural changes in the Cuzco region and elsewhere in the Central Andes.