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Climate variabilty in Northeast Brazil lakes since the LGM

Abstract : Home | ePosters | PP41B-2005: Climate variabilty in Northeast Brazil lakes since the LGM Search ePosters Upload Your ePoster PP41B-2005: Climate variabilty in Northeast Brazil lakes since the LGM " Return to search results * New Search Authors: Bruno Turcq1, Ana Luiza Albuquerque2, Renato C Cordeiro2, Renata L Costa2, Abdelfettah Sifeddine1, 2, Renata Zocatelli3, 2 Author Institutions: 1. LOCEAN, IRD, Bondy, France; 2. Departamento de Geoquimica, UFF, Niteroi, Brazil; 3. ISTO, Universite d'Orleans, Orleans, France General InformationDiscussion The Late Glacial and Holocene climate evolution in Northeast Brazil is from different the rest of South America. We present here the results from two Northeast lakes: Caço and Boqueirão, both situated some tens of kilometers from the Atlantic coast. Although there is some indications of wetness during the LGM from stalagmite formation, the Caço lake, which is the only one where late glacial sediments have been sampled, was dry until 17 kyrs when sandy layers were deposited by flash floods. The lake developed during H1 and lake-level peaked from 16 to 12 kyrs. It has been shown that Heinrich events provoked a southward shift of ITCZ which should have enhanced rainfalls in Northeast Brazil. During the Holocene, what dominated the millenary climate trend is the change in insolation, due to the precession of equinoxes, which was increased (decreased) from January to February (June to August) from 12 to 9 kyrs. This forcing difference has been reduced progressively until now with a faster decrease around 5-4 kyrs. The insolation diminution in Austral summer provoked a drop of South American Monsoon, and associated rainfalls, which is marked in Southeast Brazil and Amazonia by savannah development and lake drying. In Northeast Brazil, on the contrary, Early to Middle Holocene climate (12 to 4 kyrs) is markedly wetter. Climate simulations by AOGCM indicate that it is due to a more southern position of ITCZ during austral summers. Analysis with IPSL AOGCM show that this situation lasted until at least 4 kyrs. The two lakes have almost completely dried around 3 kyrs for lake Caço and 1550 AD for Boqueirão. This is in agreement with what we know of Holocene paleoclimate and the diminishing presence of ITCZ in the region. What is surprising is the reappearance of both lakes, very recently, probably during the last 100 yrs. Another striking feature is the great decenal to centennial variability of lake-level observed between 3 and 2 kyrs at lake Boqueirão. Lake Caço was dry at that time but such variability has been also recorded in the north of South America, at Cariaco Basin. Cariaco is an oceanic site that receives continental sediment contributions from Venezuela rivers. The past variations of these inputs are due to variation in the ITCZ position. In this case it concerns the boreal summer position of the ITCZ. The 3-2 kyrs interval therefore appears as a period of large shifts of the ITCZ at a decadal to centennial scale. The Atlantic paleoceanographic records show that this kind of periodicity appears after 5 kyrs. It is interpreted as internal variability of the coupled ocean-atmosphere system and related to variations of the Atlantic Thermohaline Circulation but the onset of El Niño at this same time may have played a role in the high variability of tropical South American climate.
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Submitted on : Thursday, July 11, 2013 - 2:06:05 PM
Last modification on : Wednesday, September 23, 2020 - 4:37:00 AM

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  • HAL Id : insu-00843481, version 1

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Bruno Turcq, Ana Luiza Spadano Albuquerque, Renato Campello Cordeiro, Renata Lima Costa, Abdelfettah Sifeddine, et al.. Climate variabilty in Northeast Brazil lakes since the LGM. AGU, Dec 2012, San Francisco, United States. ⟨insu-00843481⟩

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