HR: 14:10h
AN: GC53A-04    [Abstracts]
TI: High-resolution Stable Isotope Record From Lago Cardiel ($49\deg$S), Argentina - Implications for Past Hydroclimatic Conditions in Patagonia Since the Late Pleistocene
AU: * Gilli, A
EM: agilli@geology.ufl.edu
AF: Dept. of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 11210, Gainesville, FL 32611 United States
AU: Ariztegui, D
EM: daniel.ariztegui@terre.unige.ch
AF: Institute F.A. Forel & Dept. of Geology and Paleontology, University of Geneva, Geneva, 1205 Switzerland
AU: Anselmetti, F S
EM: flavio@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zuerich, 8092 Switzerland
AU: McKenzie, J A
EM: sediment@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zuerich, 8092 Switzerland
AU: Markgraf, V
EM: markgraf@spot.colorado.edu
AF: INSTAAR, University of Colorado, Boulder, CO 80309-0450 United States
AB: Lacustrine authigenic carbonates are excellent archives of the prevailing water conditions at the time of precipitation. Their stable carbon and oxygen isotope compositions provide powerful proxies to reconstruct past environmental conditions in a high-resolution mode. Our study site, Lago Cardiel, is a large closed basin located at the southern tip of Patagonia (Argentina) on the eastern edge of the modern rain shadow caused by the combination of persistent westerly winds and the topographic barrier of the Andes. This geographical setting combined with the fact that the lake catchment area was not glaciated during the Last Glaciation makes it very sensitive to past atmospheric changes in the hydrological conditions. Previous studies on shorelines and seismic sequence stratigraphy calibrated with sedimentary core data revealed former large lake level fluctuations, which can now be assessed and constrained using stable isotope data from authigenic precipitated carbonates. During the last ca. 16,000 years Lago Cardiel underwent substantial changes in volume. The oxygen isotope record is to a large extend controlled by the precipitation/evaporation ratio leading to more negative oxygen isotopic values in times of wetter hydroclimatic conditions and vice versa. A clear stepwise structure characterized the Late Glacial-Holocene transition (LG-H) with the lowest lake level between 13,160 and 12,900 cal yr BP revealing relative positive oxygen isotope values. Conversely, a rapid lake level rise between 12,600 and 10,300 cal yr BP is characterized by a decrease in the oxygen isotope value of more than 3 \permil. The oxygen isotope record reveals a mid-Holocene lake level highstand and indicates highly variable environmental conditions in the late Holocene as a result of an intensification of the El Ni\~{n}o/Southern Oscillation (ENSO). The observed changes in the hydroclimatic condition of Patagonia are of more than just regional significance since they have substantial intra-hemispheric linkages controlling partly the dust content of Antarctic ice cores. The comparison of these results with those from other Patagonian sites shows a significant latitudinal gradient at critical time windows such as the LG-H transition. The latter point towards the complexity of the climate system and the need for more refined climate models.
DE: 1655 Water cycles (1836)
DE: 1845 Limnology
DE: 1040 Isotopic composition/chemistry
SC: Global Climate Change [GC]
MN: 2004 AGU Fall Meeting