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Les résidus carbonés de feux dans les sédiments: Implications méthodologiques, climatiques et anthropiques

Abstract : Biomass burning in the tropics release about 25% of annual anthropogenic CO2 emissions, and large amounts of aerosol particles that play an important role in atmospheric chemistry and climate. The sedimentary carbonaceous particles emitted by plant organic matter combustion represent proxies of past fire activity. The analysis of refractory carbonaceous species behavior with different analytical methods has allowed to characterize with an increasing oxidation level : charcoal, refractory carbon and Black Carbon (BC). Despite that the analysis of the graphite concentration introduced in synthetic powders presents ca. 20% mass loss, the BC extractive methods indicate a satisfactory reproducibility and reliability to reconstruct sedimentary changes in biomass burning. Elemental analysis of carbon resistant to thermal and/or chemical extraction, combined with automatic-image analysis of charcoal, was applied to a marine record from the Western Pacific Warm Pool (WPWP) spanning the last 360 kyr and to a Tanzanian lacustrine record spanning the last 4 kyr. In the oceanic record, carbonaceous aerosols (charcoal and BC) display orbital precession plus its harmonics related frequencies, suggesting that fire activity closely responded to the variations in seasonal radiation forcing at the equator, but also that changes in high-latitudes forcing (Dansgaard-Oeschger periodicities) on the winter monsoon contribute to ENSO-like conditions. In addition, carbonaceous aerosol clearly registered human-induced fire-regime alteration in the Indo/Pacific area, with great increases in fire-activity between 53-43 and 12-10 kyr. Charcoal abundance and distribution in lake Masoko reveal that runoff and erosion on woodland soils are the dominant processes for charred particle transportation. However, the carbonaceous aerosol fraction (charcoal<1µm and BC) clearly illustrate fire activity. Its abrupt increase between 1,8 and 1,6 cal. kyr B.P. in lake Masoko testifies regional emissions from forest fires prior the local fire extend. This latter event is contemporaneous with an abrupt deforestation and coincides with the extend of Late Iron Age and agricultural activities in the East African Rift. These results demonstrate that carbonaceous residues analysis in sediments provides informations on past-climatic changes, human impact on the environment, and global carbon budget.
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https://tel.archives-ouvertes.fr/tel-00008908
Contributor : Florian Thevenon <>
Submitted on : Wednesday, March 30, 2005 - 4:38:44 PM
Last modification on : Wednesday, October 14, 2020 - 3:50:43 AM
Long-term archiving on: : Friday, November 25, 2016 - 9:05:27 AM

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  • HAL Id : tel-00008908, version 1

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Florian Thevenon. Les résidus carbonés de feux dans les sédiments: Implications méthodologiques, climatiques et anthropiques. Minéralogie. Université de droit, d'économie et des sciences - Aix-Marseille III, 2003. Français. ⟨tel-00008908⟩

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