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Hydrological changes related to the variability of tropical South American climate from the Cabo Frio lagoonal system (Brazil) during the last 5000 years

Universite d'Angers, Departement de Geologie, Laboratoire d'etude des bioindicateurs actuels et fossiles EA2644, 2 boulevard Lavoisier, 49045 Angers cedex 01, France; CEREGE Equipe Bio-Indicateurs, CNRS-UMR6635, Europole mediterraneen de l'Arbois BP 80, 13545 Aix-en-Provence cedex 04, France sylvestre{at}cerege.fr

Abdelfettah Sifeddine

Institut de Recherche pour le Developpement (IRD), UR055 PALEOTROPIQUE, 32 avenue Henri Varagnat, 93143 Bondy cedex, France

Bruno Turcq

Institut de Recherche pour le Developpement (IRD), UR055 PALEOTROPIQUE, 32 avenue Henri Varagnat, 93143 Bondy cedex, France; Universite Federal Fluminense, De'partement de Geochimie, Outeiro Sdo Joao Batista s/no, 5 andar-centro, Niteroi, 20.020-007, Brazil

Isabelle Martins Gil

Universite d'Angers, Departement de Geologie, Laboratoire d'etude des bioindicateurs actuels et fossiles EA2644, 2 boulevard Lavoisier, 49045 Angers cedex 01, France

Ana Luiza S. Albuquerque

Universite Federal Fluminense, De'partement de Geochimie, Outeiro Sdo Joao Batista s/no, 5 andar-centro, Niteroi, 20.020-007, Brazil

Elisabeth Lallier-Verges

Institut des Sciences de la Terre d'Orleans-UMR 6113 CNRSIUO, 1A rue de la FHrollerie, 45072 Orleans cedex, France

Jorge Abrao

Institut de Recherche pour le Developpement (IRD), UR055 PALEOTROPIQUE, 32 avenue Henri Varagnat, 93143 Bondy cedex, France

From west to east, the Fluminense coastline, composed of two series of lagoons, presents an aridity gradient induced by a local upwelling that is controlled by trade winds coming from the south Atlantic. The physico-chemical conditions of the lagoons are controlled by the duration of the dry season. They are characterized by hypersaline conditions with organic-carbonate sedimentation in the upwelling-influenced area, and by hyposaline conditions with organic-detrital sedimentation out of the upwelling-influenced area. On a core collected in the Brejo do Espinho hypersaline lagoon, diatom analysis supported by sedimentological data revealed a varying high water level from 4500 to 2200 ¹⁴C yr BP induced by successive freshwater inputs in to the lagoon. Two major dry events occurred during this period, probably related to relative sea-level fluctuations. At 2200 ¹⁴C yr BP, a drastic change occurred, as indicated by a carbonate nodule, carbonate-dominated sediments and polyto hypersaline diatoms, all suggesting arid conditions. The Brejo do Espinho record suggests that before 2200 ¹⁴C yr BP, the central part of the Brazilian coast was mostly subjected to south to southeasterly winds and weaker trade winds, whereas after 2200 ¹⁴C yr BP, trade winds dominated, implying drier conditions at the easternmost part of the Fluminense coastline. These results would also suggest a late Holocene increase in El Ninlo activity (after 2200 ¹⁴C yr BP), consistent with several El Nifio records from western South America.

Key Words: Lagoons • diatoms • palaeoclimate • El Nino • palaeohydrology • hyposalinity • arid regions • Brazil • Holocene

The Holocene, Vol. 15, No. 4, 625-630 (2005)
DOI: 10.1191/0959683605hl823rr


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