Palaeoenvironmental changes in Southern Patagonia during the last millennium recorded in lake sediments of Laguna Azul (Argentina)

Marked environmental changes in the southern Patagonian steppe during the last 1100 years are detected by a multi-proxy study of radiocarbon-dated sediment cores from the crater lake Laguna Azul (52 degrees 05'S, 69 degrees 35'W). A prominent shift in carbon isotope records occurred between AD 1670 and AD 1890 induced by a change to cooler climate conditions with a concurrent lake level rise. A second perturbation of the lake ecosystem started with a fire event around AD 1830. The fire event triggered increased soil erosion initiating a change of the diatom assemblages. This shift in diatom assemblages may have been enhanced by shrinkage of littoral habitats and higher nutrient supply in the course of permanent European settlement at the end of the 19th century. The introduction of neophytes by European sheep farmers is confirmed by the permanent occurrence of Rumex pollen in the sediment record since the beginning of the 20th century. (c) 2005 Elsevier B.V. All rights reserved