Halomethane gas exchange in northern Alaskan coastal ecosystems

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Coastal ecosystems are believed to be globally important sources of methyl halides (CH3Br, CH3Cl, and CH3I) to the atmosphere, but fluxes from the arctic coastal zone have not yet been measured. CH3Br and CH3Cl are the dominant carriers of bromine and natural chlorine to the stratosphere, where they catalyze the destruction of ozone. CH3Br is also a widely used agricultural fumigant whose use is regulated by international agreement. CH3I is involved in tropospheric ozone chemistry and aerosol production and is a potential replacement fumigant for CH3Br. Our understanding of the tropospheric budgets of these compounds remains out of balance, with major uncertainties about the magnitude of biosphere-atmosphere fluxes. The biogeochemical cycles of these halomethanes must be understood in order to assess how halogen loading in the atmosphere will respond to changes in public policy, land use, and climate. The proposed project will a) determine whether arctic coastal terrestrial ecosystems are significant sources or sinks of atmospheric methyl halides and chloroform; b) examine the environmental and biological controls on their fluxes; and c) help understand and possibly predict the potential effect that climatic change in the Arctic will have on the overall fluxes of these compounds, based on their biogeochemical controls. Flux chambers will be deployed in coastal tundra ecosystems near Barrow, Alaska, in 2005 and 2006. Air samples will be analyzed by gas chromatography-mass spectrometry for the halomethanes and the inert tracers SF6 and F-113, and the sampling strategy will address the expected spatial and temporal variability of the fluxes. CO2 fluxes will also be measured. This work will complement the prior research of the principal investigator (P.I.) on halomethane fluxes in temperate coastal ecosystems. This project will provide scientific training and thesis research opportunities for a doctoral graduate student and 3-6 undergraduate students. The students and P.I. will present results at regional and international geoscience meetings, and results will be published in peer- reviewed journals. Ilisagvik College students from Barrow, Alaska, will be invited to participate in the field research, and two students will be invited to UC-Berkeley to learn the associated laboratory analytical techniques. In concert with the Barrow Arctic Science Consortium, the P.I. and students will participate in science outreach classes at northern Alaskan schools and community centers.