Title
Late Holocene paleoenvironmental changes in Northeast Brazil recorded by organic matter in lacustrine sediments of Lake Boqueirão
Date Issued
20 November 2012
Access level
open access
Resource Type
journal article
Author(s)
Zocatelli R.
Boussafir M.
Cordeiro R.C.
Disnar J.R.
Costa R.L.
Albuquerque A.L.S.
Bernardes M.C.
Jacob J.
Universidad Federal Fluminense
Research Institute Development
Abstract
Northeast Brazil represents a key area in terms of Holocene environmental changes in South America due to its distinct semi-arid climate at near equatorial latitudes as well as to a wetter Early and Middle Holocene paleoclimate in comparison with other South America regions, which also experienced a reduced monsoon at that time. We studied the lacustrine sediments of Lake Boqueirão, which is located at 5°S latitude on the Brazilian Atlantic coast; it is directly influenced by displacement of the Intertropical Convergence Zone (ITCZ). A short (1. m) core "Boqc0701" was collected at a 7.5. m water depth during a seismic survey. Organic matter (OM) geochemical [Rock-Eval Total Organic Carbon (TOC), Hydrogen Index (HI), Oxygen Index (OI)] and petrographical studies allowed us to distinguish five sedimentary intervals during the last 3. kyr. Phase E (3000 to 2050. cal. yr BP) presents the largest TOC, HI and OI fluctuations in the entire core. The most probable cause of these variations is a great instability in the lake level during this period. Phase D (2050 to 1830. cal. yr BP) is marked by an increase in sedimentation rate and a higher contribution from a well-preserved OM with an algal origin; this was interpreted as a higher and more stable lake level. During phase C (1830 to 1550. cal. yrs BP), low HI and high OI indicate the input of more oxidized, degraded and detrital OM, reflecting a lower lake level. In phase B (1550 to 1470. cal. yr BP), the OM quality and quantity (HI and TOC) indicate an algal contribution. During phase A (1470 to 570. cal. yr BP), the high stability of the proxies may be due to a deep environment where OM fluctuations are strongly buffered. These changes in lake level can be compared with other tropical South America high resolution records. A correspondence seems to exist between phases of low ENSO, cool North Atlantic Ocean and Boqueirão wet phases. We did not encounter this same pattern during the last 1050. years, during which the 1050-570. cal. yrs BP interval was generally wet (although probable fluctuations are buffered in our proxies) while the North Atlantic was warm (Mann et al., 2009). A prolonged dryness occurred in Lake Boqueirão from 570. cal. yrs BP until recent decades. This phase corresponds to the Little Ice Age characterized by a cooler North Atlantic Ocean (Mann et al., 2009). These data indicate that the teleconnection pattern between the tropical Atlantic, ENSO and Northeast Brazil rainfalls has changed in the past. © 2012 Elsevier B.V.
Start page
127
End page
134
Volume
363-364
Language
English
OCDE Knowledge area
Geoquímica, Geofísica
Geociencias, Multidisciplinar
Subjects
Scopus EID
2-s2.0-84867634889
Source
Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN of the container
00310182
Sponsor(s)
This work was supported by the Universidade Federal Fluminense (Brazil), LOCEAN (UMR UPMC/IRD/CNRS/MNHN) and ISTO (UMR Université d'Orléans/CNRS). This project was developed within the PALEOTROPICA Project (IRD,France/CNPq Brazil) and Paleotrace LMI (IRD) by two frameworks of cooperation between the Environmental Geochemistry Program-UFF and IRD-France. This paper contributes to the ESCARSEL project funded by the French National Agency of Research (program VMC, project ANR-06-VULN-010 ) and ANR ELPASO ( 2008 blanc 60801 ). Carbon-14 data were obtained at the “Laboratoire de mesures du 14 C” UMS 2572 LMC14 (CEA/CNRS/IRD/IRNS/MCC) for 14 C data. The authors acknowledge CNPq project 482837/2009-8 “Interconexões entre mudanças paleoclimáticas, o sistema de monção sul americana e distúrbios relacionados ao fogo em sistemas florestais”. The authors also wish to thank the reviewers for their constructive remarks on a previous version of the manuscript.
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