干旱区生态环境知识资源中心

Lake sediments and pollen, spores and algae from the high-elevation endorheic Laguna Miscanti (22 degrees 45’s, 67 degrees 45’W, 4140 m a.s.l., 13.5 km(2) water surface, 10 m deep) in the Atacama Desert of northern Chile provide information about abrupt and high amplitude changes in effective moisture. Although the lack of terrestrial organic macrofossils and the presence of a significant C-14 reservoir effect make radiocarbon dating of lake sediments very difficult, we propose the following palaeoenvironmental history. An initial shallow freshwater lake (ca. 22,000 C-14 years BP) disappeared during the extremely dry conditions of the Last Glacial Maximum (LGM; 18,000 C-14 years BP). That section is devoid of pollen. The late-glacial lake transgression started around 12,000 C-14 years BP, peaked in two phases between ca. 11,000 and < 9000 C-14 years BP, and terminated around 8000 C-14 years BP. Effective moisture increased more than three times compared to modern conditions ( 200 mm precipitation), and a relatively dense terrestrial vegetation was established. Very shallow hypersaline lacustrine conditions prevailed during the mid-Holocene until ca. 3600 C-14 years BP, However, numerous drying and wetting cycles suggest frequent changes in moisture, maybe even individual storms during the mid-Holocene. After several humid spells, modern conditions were reached at ca. 3000 C-14 years BP, Comparison between limnogeological data and pollen of terrestrial plants suggest century-scale response lags. Relatively constant concentrations of long-disance transported pollen from lowlands east of the Andes suggest similar atmospheric circulation patterns (mainly tropical summer rainfall) throughout the entire period of time. These findings compare favorably with other regional paleoenvironmental data. (C) 2001 Elsevier Science B.V. All rights reserved.