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Reconstitution of Holocene El Niño Cycles in Southern America from High-Resolution Lake Sediments.

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  • Physical
  • Chemical
  • Mathematical & Earth Sciences :: Earth Sciences & Physical Geography [G02]
  • Physique
  • Chimie
  • Mathématiques & Sciences De La Terre :: Sciences De La Terre & Géographie Physique [G02]
  • Communication


RECONSTITUTION OF HOLOCENE EL NIÑO CYCLES IN SOUTHERN AMERICA FROM HIGH-RESOLUTION LAKE SEDIMENTS �PAGE � �PAGE �1� BELLA workshop Productivity of large lakes Reconstitution of Holocene El Niño Cycles in Southern America from High-Resolution Lake Sediments. X. Boës1, M.F. Loutre2, M. De Batist3, N. Fagel4 1Royal Observatory, Ringlaan 3, 1180 Brussels, Belgium 2Institut d'astronomie et de géophysique G. Lemaître, Université catholique de Louvain, Louvain-la-Neuve, Belgique 3Ghent University, Department of Geology, Renard Centre for Marine Geology Krijgslaan 281-S8, 9000 Gent. 4University of Liège, Geology Department, 1000 Liege,Belgium. The aim of this communication is to show how laminated lake sediments driven by winds can be utilized for age modeling and for tracking El Niño Cycles. In South America, the lake systems located between 40° to 55° S are particularly sensitive to atmospheric air-humidity changes driven by the Southern Westerlies, El Niño, and the polar front. For example, Lago Puyehue (40°S) is stratified in summer and mixed by the stronger austral winter winds (i.e., monomictic temperate lake). The autumn/winter atmospheric conditions involve water circulation and nutrients (phosphorus and nitrogen) increase in the lake (Campos, 1989). The seasonal thermal lake cycle and nutrients increase lead to annual blooms of phytoplankton (diatoms). A varved micro-structure (varve couplets) is formed every year at the floor of the lake. The recurrence of the distinct light layers produced by the mass flocculation of diatoms blooms after winter nutrient turn-over therefore provides an annual temporal resolution (by varve counting). We present chronologies obtain over the “Little Ice Age” (LIA) and the Last Deglaciation. The comparison between radionuclide (210Pb,137Cs) and 14C sedimentation rates estimate validate the annual character of the laminations over thousand years, making this lake one of the few resolved varved record in southern hem

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