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GDRI-Sud : Impact of Black Carbon in South East Asia

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Le projet de Groupement De Recherche International SOOT-SEA (Impact of Black Carbon in South East Asia) porté par Xavier Mari, chercheur MIO , a été sélectionnée par l’IRD et débutera en 2018 pour une période de 4 ans. Il regroupe 29 laboratoires/institutions de différents pays (Allemagne, Autriche, Belgique, Cambodge, Danemark, France, Italie, Laos, Myanmar, Principauté de Monaco, Royaume Uni, Thaïlande, Vietnam).

Black Carbon (BC ; or soot) is the product of incomplete combustion of fossil fuels, biofuels and biomass, and is co-emitted with other aerosols. BC and co-emitted aerosols make up the majority of fine particle air pollution, and is the leading environmental cause of poor health and premature death. BC also impacts climate by : (i) exerting a direct net positive radiative forcing at the top-of-the atmosphere equivalent to 40% of the current radiative forcing due to the CO2 greenhouse effect, (ii) influencing cloud formation/properties and rainfall patterns, and (iii) reducing the albedo of the cryosphere when deposited on ice and snow, hence increasing melting rate. Owing to its impacts on health and climate, BC is receiving growing attention. Another impact of BC, much less known than its direct impacts on health and climate, is related to its introduction in the ocean. The atmospheric lifetime of BC ranges from a few days to one month, and BC eventually deposits on the surface of lands and oceans. In addition to the direct deposition on the surface of the ocean, large amounts of BC deposited on land are washed out by rainfall and transported by rivers, hence ultimately ending up in the ocean. The estimated total flux of BC to the ocean via atmospheric deposition and fluvial transport is equivalent to the estimated emission rate. Considering that most BC ends up in the ocean, it is important to understand how this material impacts marine systems. Because BC particles are highly porous and surface-active, with a high density, they can sorb dissolved compounds, increase aggregation processes and ballast sinking particulate organic matter. Because they bring nutrients and contaminants to the surface ocean, and modify the structuring of the environment at the microscale, BC may alter phyto- and bacterio-plankton composition and activity. As a result, BC may alter the efficiency of the biological carbon pump, and lead to either a positive or a negative feedback on the atmospheric concentration of CO2. In addition, BC can sorb contaminants in seawater and either introduce them into the food chain, hence alter food security, or export them to the seafloor, hence cleanse the water column. In order to determine the actual impacts of BC, it is necessary to obtain accurate emission and deposition rates. At present, there are still large uncertainties related to the magnitude of the impact of atmospheric BC due to difficulties in obtaining accurate emission inventories, and in particular in South East Asia (SEA). For example, current climate models systematically underrate aerosol absorption by 3-fold when compared to observations, which is attributed to the underestimation of BC emissions. Since estimates of the atmospheric flux of BC to the ocean are derived from emission estimates, they may be underestimated as well. In order to determine the effects of BC on marine resources and biogeochemistry, it is also necessary to understand how BC interacts with biological/chemical/physical marine processes. Owing to its short residence time in the atmosphere, atmospheric BC is currently considered a short-lived climate/health forcer. In contrast, because BC in the ocean will last for millennia, and its impacts on carbon cycling in the ocean can have long-lasting feedbacks on climate and marine biogeochemistry, marine BC may act as a long-lived climate/ecosystem forcer. SOOT-SEA seeks to stimulate research, innovation, observation and capacity-building activities related to the impacts of BC on climate, health and ecosystem, taking into account for the first time its marine dimension, by increasing interactions between scientists from the South and the North.