HR: 14:30h
AN: GC53A-06    [Abstracts]
TI: The Varve Record of Puyehue Lake (Meridional Chile), AD 1412-2002 .
AU: * Boes, X
EM: Xavier.Boes@ulg.ac.be
AF: Clays and Paleoclimate Research Unit, Geology Department, University of Liege, All‚e du 6 Aout, B18, Liege, 4000 Belgium
AU: Arnaud, F
AF: Laboratoire de Geodynamique des Chaines Alpines, Universit‚ de Savoie, Bat. Belledonne, Chamb‚ry, 73376 France
AU: Fagel, N
AF: Clays and Paleoclimate Research Unit, Geology Department, University of Liege, All‚e du 6 Aout, B18, Liege, 4000 Belgium
AB: Puyehue Lake is located in the Southern Volcanic Zone of Chile (Southern Lake District, 40øS). This monomictic lake is under the influence of the oceanic winter polar front (WPF) and constitutes a powerful sedimentary archive for paleoenvironmental reconstruction. The underflow (PUI) and interflow (PUII) coring sites were selected by a high resolution seismic survey (RUG). The sedimentation is driven by the annual blooms of diatoms in association with thermal lake cycles. For each site, one short core (50-60 cm) is analyzed by continuous cover of thin sections for varve counting and chronology for the AD 1412-2002 time window. The varve chronology is constrained by 210Pb,137Cs sedimentation rate estimates, and by the AD 1960 Valdivia'seismite. The sediment laminations are especially emphasized by the continuous grey-scale measurements from thin sections. Detrital clayey material characterizes the dark levels, and biogenic diatom mud defines the light levels. Varve counting is derived from the occurrence of light layers, i.e. formed at the end of winter after nutrient turn-over. In both cores, the grey-scale is influenced by instantaneous tephra layers related to the regional volcanic activity (Puyehue and Cordon Caulle volcanoes). For instance, in PUII, we identify major historical eruptions (AD 1921, 1837, 1790, 1564, and 1544) in accordance with the varve age model. In addition, we measure the total varve thickness. Lower than 500 æm until AD 1780, the varve thickness gradually increases by a factor of four in PUII. The first period suggests a decrease of lake productivity, in agreement with a cooling. The age fits with the end of Little Ice Age in Southern America. Between AD 1780-2002, the thicker varves could be driven by a reinforcement of the WPF since the 19e century. Our local observations require further investigations to be extrapolated over regional or global scale.
UR: http://www.ulg.ac.be/urap/
DE: 9360 South America
DE: 9604 Cenozoic
DE: 3344 Paleoclimatology
DE: 1809 Desertification
SC: Global Climate Change [GC]
MN: 2004 AGU Fall Meeting