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Natalie Kehrwald
Université de Venise, Italie
Jeudi 12/02/2015, 11:00-13:00
Bât. 701, P. 17C, LSCE Orme des Merisiers

Fires are a major component of the global carbon cycle, by releasing greenhouse gasses, altering primary productivity, and changing surface albedo. Climate is the major driver of fire activity over millennial timescales. However, humans are exceptional agents of starting fires where household and agricultural fires can escape their confines resulting in massive conflagrations. Here, we investigate fire activity in polar and mountain ice cores using the specific molecular markers including levoglucosan (1,6-anhydro-β-Dglucopyranose in comparison with changing climate and human impacts. Low latitude ice cores located in areas with long human histories, yet their fire activity records appear to be more influneced by climate parameters than the polar cores. The Muztag, Tibet ice core (36.35°N; 87.17°E; 5780 masl) contains elevated levoglucosan concentrations occurring throughout the core demonstrating that biomass burning is a major source of Tibetan Plateau aerosols both before and during the industrial era. The Tibetan Plateau contains sparse vegetation and local fires alone are unlikely to create such high levoglucosan concentrations. The Muztagh levoglucosan concentrations are surprisingly substantially greater than in Kilimanjaro, Tanzania (3°04.6’ S; 37°21.2 E, 5893 masl). Kilimanjaro is located in a relatively similar site where both mountains are isolated high-elevation peaks rising out of surrounding plains. Kilimanjaro is encircled by savannas with high levoglucosan emission factors, and so would be expected to have greater levoglucosan concentrations than Muztagh. Kilimanjaro fire activity peaks approximately 1000 years before present, as a result of warm, dry conditions, perhaps in combination with upslope migration of human settlements.


Levoglucosan concentrations peak in the NEEM, Greenland (77°27’N, 51°3’W, 2454 masl) ice core between 2000 and 3000 years BP. Regional charcoal compilations also peak during this time period, yet major boreal climate parameters alone cannot explain this increased fire activity. Models (JSBACH, KK10 and HYDE) demonstrate that deforestation for agriculture in Europe resulted in major biomass burning during this period. Unlike NEEM, EPICA Dome C (75°06’S, 123°21’E, 3233 masl) is one of the locations on Earth located farthest away from possible biomass burning sources. Our analyses of modern aerosols at Dome C demonstrate quantifiable levoglucosan concentrations. Modern emissions studies demonstrate the possibility of New Zealand and Australia as major levoglucosan sources to Dome C. The EPICA Dome C ice core contains a major increase in levoglucosan concentrations beginning 800 to 500 years BP. This increase is also present in New Zealand and southeastern Australia charcoal compilations, yet substantially differs from South American charcoal records. The major biomass burning increase in Dome C during the last 500 years may be due to the arrival and dispersal of the Maori in New Zealand, and further augmented by the arrival of Europeans to Australia. Fire histories in ice cores thus demonstrate quantifiable human impacts on atmospheric chemistry before the industrial era.




Contact : Masa Kageyama
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