Chloroform emissions from the Alaskan Arctic tundra

Chloroform (trichloromethane, CHCl3) is the second largest carrier of natural chlorine in the troposphere after methyl chloride, contributing to the reactive chlorine burden in the troposphere and to ozone destruction in the stratosphere. Here we report CHCl3 flux measurements from coastal and interior tundra sites in northern Alaska, showing that the Arctic tundra can contribute substantial amounts of CHCl3 to the atmosphere. Emissions were measured during the 2005 and 2006 growing seasons over a range of vegetation types and hydrologic conditions, from wet sedge coastal to upland tussock tundra. Overall emissions averaged 45 nmol m(-2) d(-1), but fluxes were highly variable, ranging from < 1 up to 260 nmol m(-2) d(-1), with the highest emissions from moist tundra. Laboratory soil core incubations show that flooded conditions sharply reduce emission rates. A rough extrapolation suggests that the tundra globally could account for 1-2% of the total estimated source of atmospheric CHCl3.