HR: 15:00h
AN: GC53A-09    [Abstracts]
TI: Paleoenvironmental and Paleoclimate Changes Since 21,000 Cal Years BP in the Northeastern part of Brazil Inferred From Sediment Records in Lagoa do Caco (Maranhao State, Brazil)
AU: * Sifeddine, A
EM: sifeddin@bondy.ird.fr
AF: Paleotropique, Institut de Recherche pour le Developpement, 32, avenue Henri Varagnat, Bondy, 93143 France
AU: Meyers, P A
EM: pameyers@umich.edu
AF: Department of Geological Sciences, The University of Michigan, 425 East University Avenue, Ann Arbor, MI 48109-1063 United States
AU: Gustavo, A
AF: Departamento de Geoquimica, Universidade Federal Fluminense, Outeiro de Sao Joao Batista, s/n Centro, Niteroi, RJ 24.020-007 Brazil
AU: Spadano Albuquerque, A L
AF: Departamento de Geoquimica, Universidade Federal Fluminense, Outeiro de Sao Joao Batista, s/n Centro, Niteroi, RJ 24.020-007 Brazil
AU: Turcq, B
AF: Paleotropique, Institut de Recherche pour le Developpement, 32, avenue Henri Varagnat, Bondy, 93143 France
AU: Campbello Cordeiro, R
AF: Departamento de Geoquimica, Universidade Federal Fluminense, Outeiro de Sao Joao Batista, s/n Centro, Niteroi, RJ 24.020-007 Brazil
AU: Abrao, J J
AF: Departamento de Geoquimica, Universidade Federal Fluminense, Outeiro de Sao Joao Batista, s/n Centro, Niteroi, RJ 24.020-007 Brazil
AB: Two cores from Caco Lake, Maranhao State (North Brazil) record different histories of sediment accumulation on the margin and center of the lake that reflect changes in lake level. Seismic profiles, mineralogy and organic geochemical studies, backed by radiocarbon dating, reveal variable climatic and environmental conditions over the last 21 Cal Kyr BP. During the Last Glacial Maximum, regional climate was predominantly dry but was interrupted by short humid phases as reflected by a succession of very thin layers of sand and organic matter. The late glacial climate was relatively wet and included two rapid lake-level increases accompanied by forest expansion. The two wet phases were separated by a phase where the lake level remained stable and the forest changes were marked by the development of cool "Podocarpus" forest. These humid climate periods differed significantly from present warm tropical conditions.. The Holocene period is characterized by progressive increase of lake level, which reaches his maximum at around 7,000 Cal years BP. The period between 4,000 Cal years BP and the present shows high variability in lake level. Comparing with other South American and African records, we conclude that Late Glacial humid conditions were controlled by intensification of the ITCZ or shifts of its position, resulting in southeasterly trade wind variations and in interconnection between northern South America and the Atlantic tropical ocean-atmosphere system. The climatic variability during the Holocene is probably the result of sub-Milankovitch solar cycles and regional responses to these global forcings that are related to Atlantic and Pacific variability and their interconnections.
DE: 3344 Paleoclimatology
DE: 1833 Hydroclimatology
DE: 1845 Limnology
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
SC: Global Climate Change [GC]
MN: 2004 AGU Fall Meeting