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Interaction of the South American Monsoon System and the Southern Westerly Wind Belt during the last 14 kyr

Texto completo
Razik, Sebastian [1] ; Chiessi, Cristiano M. [2] ; Romero, Oscar E. [1] ; von Dobeneck, Tilo [1, 2]
Número total de Autores: 4
Afiliação do(s) autor(es):
[1] Univ Bremen, Dept Geosci, D-28359 Bremen - Germany
[2] Univ Bremen, MARUM Ctr Marine Environm Sci, D-28359 Bremen - Germany
Número total de Afiliações: 2
Tipo de documento: Artigo Científico
Citações Web of Science: 17

Surface currents and sediment distribution of the SE South American upper continental margin are under the influence of the South American Monsoon System (SAMS) and the Southern Westerly Wind Belt (SWWB). Both climatic systems determine the meridional position of the Subtropical Shelf Front (STSF) and probably also of the Brazil-Malvinas Confluence (BMC). We reconstruct the changing impact of the SAMS and the SWWB on sediment composition at the upper Rio Grande Cone off southern Brazil during the last 14 cal kyr BP combining sedimentological, geochemical, micropaleontological and rock magnetic proxies of marine sediment core GeoB 6211-2. Sharp reciprocal changes in ferri- and paramagnetic mineral content and prominent grain-size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments. Our interpretations support the assumption that the SAMS over SE South America was weaker than today during most of the Late Glacial and entire Early Holocene, while the SWWB was contracted to more southern latitudes, resembling modern austral summer-like conditions. In consequence, the STSF and the BMC were driven to more southern positions than today's, favoring the deposition of Fe-rich but weakly magnetic La Plata River silts at the Rio Grande Cone. During the Mid Holocene, the northern boundary of the SWWB migrated northward, while the STSF reached its northernmost position of the last 14 cal kyr BP and the BMC most likely arrived at its modern position. This shift enabled the transport of Antarctic diatoms and more strongly magnetic Argentinean shelf sands to the Rio Grande Cone, while sediment contributions from the La Plata River became less important. During the Late Holocene, the modern El Nino Southern Oscillation set in and the SAMS and the austral tradewinds intensified, causing a southward shift of the STSF to its modern position. This reinforced a significant deposition of La Plata River silts at the Rio Grande Cone. These higher magnetic silts with intermediate Fe contents mirror the modern more humid terrestrial climatic conditions over SE South America. (C) 2012 Elsevier B.V. All rights reserved. (AU)

Processo FAPESP: 10/09983-9 - Mudanças na temperatura da superfície do mar no Oeste do Atlântico Sul e variabilidade na precipitação no Sudeste da América do Sul desde o Último Máximo Glacial
Beneficiário:Cristiano Mazur Chiessi
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 11/50394-0 - Variabilidade do sistema de monção da América do Sul dos últimos três milênios integrando registros lacustres, espeleotemas e marinhos
Beneficiário:Francisco William da Cruz Junior
Linha de fomento: Auxílio à Pesquisa - Programa de Pesquisa sobre Mudanças Climáticas Globais - Regular