Halomethane Gas Exchange in Northern Alaskan Coastal Ecosystems

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.

This project will 1) determine whether arctic coastal terrestrial ecosystems are significant sources or sinks of atmospheric methyl halides and chloroform; 2) examine the environmental and biological controls on their fluxes; and 3) 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 to measure halomethanes and CO2 fluxes.