Skip to Main content Skip to Navigation
Journal articles

Late Holocene paleoenvironmental changes in Northeast Brazil recorded by organic matter in lacustrine sediments of Lake Boqueirão

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 kyrs. 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.
Complete list of metadatas

Cited literature [38 references]  Display  Hide  Download

https://hal-insu.archives-ouvertes.fr/insu-00730933
Contributor : Nathalie Pothier <>
Submitted on : Tuesday, September 11, 2012 - 2:44:40 PM
Last modification on : Monday, October 19, 2020 - 2:34:02 PM
Long-term archiving on: : Friday, December 16, 2016 - 11:39:17 AM

File

zocatelli.pdf
Files produced by the author(s)

Identifiers

Citation

Renata Zocatelli, Bruno Turcq, Mohammed Boussafir, Renato Campello Cordeiro, Jean-Robert Disnar, et al.. Late Holocene paleoenvironmental changes in Northeast Brazil recorded by organic matter in lacustrine sediments of Lake Boqueirão. Palaeogeography, Palaeoclimatology, Palaeoecology, Elsevier, 2012, 363-364, pp.127-134. ⟨10.1016/j.palaeo.2012.08.021⟩. ⟨insu-00730933⟩

Share

Metrics

Record views

1065

Files downloads

721