HR: 1340h
AN: U13B-1154    [Abstracts]
TI: Climate Variability of Southern South America During the Late Holocene: The Multi-proxy Sedimentary Record of Chilean Fjord Sediments (46°S)
AU: * Bertrand, S
EM: sbertrand@whoi.edu
AF: Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Road, MS#25, Woods Hole, MA 02543, United States
AU: Hughen, K
EM: khughen@whoi.edu
AF: Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Road, MS#25, Woods Hole, MA 02543, United States
AU: Sepulveda, J
EM: sepulved@uni-bremen.de
AF: Research Center Ocean Margins (RCOM), University of Bremen, Leobener Strasse, Bremen, 28359, Germany
AU: Pantoja, S
EM: spantoja@udec.cl
AF: Center for Oceanographic Research in the eastern South Pacific (COPAS) and Department of Oceanography, University of Concepcion, PO Box 160-C, Concepcion, 3349001, Chile
AU: Lange, C
EM: clange@udec.cl
AF: Center for Oceanographic Research in the eastern South Pacific (COPAS) and Department of Oceanography, University of Concepcion, PO Box 160-C, Concepcion, 3349001, Chile
AB: High-resolution paleoclimate records from the Southern Hemisphere are essential to improve the understanding of the interhemispheric pattern of paleoclimate changes. Due to their intermediate location between the terrestrial and marine realms of southern South America, the sediments deposited in the fjords of Southern Chile contain a high resolution record of paleoclimate changes that occurred in the area since the last deglaciation. In this project, a 2m long gravity core from the Quitralco fjord (PC29A, 46°S) has been studied by a multi-proxy sedimentological and geochemical approach. To better understand the spatial variability of the sediment composition and to characterize the marine and terrestrial end-members, we also analyzed soil, river and surface sediment samples from the same area (44-47°S). The multi-proxy analysis includes high resolution XRF core scanning (ITRAX core scanner) with calibration by ICP-AES, biogenic silica, TIC, bulk and clay mineralogy, elemental and isotopic composition of the bulk organic matter (C/N, d13C, d15N), grain-size, magnetic susceptibility and loss-on-ignition. The analysis of surface, river and soil samples demonstrates that the terrestrial end-member of the sediment is rich in iron, titanium and olivine, and is characterized by low d13C and high C/N values. When applied to sediment core PC29A, these proxies allow us to estimate variations in the input of terrestrially-derived particles during the last 1400 years and therefore to reconstruct the intensity of the terrestrial runoff, which is directly linked to the intensity of precipitation in the Andes. Between 750 and 1400 AD, the sediments of site PC29A show low Ti concentrations, high Rb/Sr ratios and a high content in biogenic silica, which indicate dry climate conditions and high biogenic productivity during the Medieval Warm Period (MWP). The high TOC values and low C/N ratios between 1100 AD and 1400 AD also suggest high marine productivity at the beginning of the second millennium AD. Around 1500 AD, the Fe and Ti concentrations increase significantly and the TOC values decrease, indicating higher terrestrial supply and therefore wetter climate conditions until the beginning of the 20th century. This wet period is believed to represent the local signature of the Little Ice Age (LIA), which seems to be characterized in southern Chile by an intensification of the Westerlies along a wide latitudinal range. Our data demonstrate that the MWP and LIA are global climate events, not only restricted to the Northern Hemisphere.
DE: 1051 Sedimentary geochemistry
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 3022 Marine sediments: processes and transport
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 9360 South America
SC: Union [U]
MN: 2007 Fall Meeting