HR: 17:00h
AN: A14C-04    [Abstracts]
TI: Carbon 13 Enrichment in Atmospheric Methane at Mace Head, Ireland: are Boreal Forest Fires the Source?
AU: * Lowry, D
EM: d.lowry@gl.rhul.ac.uk
AF: Royal Holloway, University of London, Egham Hill, Egham, TW20 0EX, United Kingdom
AU: O'Brien, P
EM: p.obrien@epa.ie
AF: Martin Ryan Marine Science Institute, University of Galway, Galway, GA, Ireland
AU: Nisbet, E
EM: e.nisbet@gl.rhul.ac.uk
AF: Royal Holloway, University of London, Egham Hill, Egham, TW20 0EX, United Kingdom
AU: Fisher, R
EM: r.fisher@gl.rhul.ac.uk
AF: Royal Holloway, University of London, Egham Hill, Egham, TW20 0EX, United Kingdom
AU: Sriskantharajah, S
AF: Royal Holloway, University of London, Egham Hill, Egham, TW20 0EX, United Kingdom
AB: A bi-weekly record of δ¹³C of CH₄ was maintained for ambient air collected at the Mace Head Atlantic background site over the period 1995-2004. These data have been used in conjunction with AGAGE and NOAA CH₄ and CO mixing ratio records for the site and records of forest fires in Canada to assess the influence of biomass burning on the North Atlantic CH₄ record. Enrichments in ¹³C of CH₄ and anomalies in CH₄ and CO mixing ratios in the Mace Head record during the latter parts of 1998 and 2002 can be correlated with extensive summer boreal forest burning in the Northern Hemisphere. Prior to October in these years there is a significant ¹³C-depleted wetland CH₄ emission, in addition to relatively ¹³C-enriched CH₄ from biomass burning, suppressing the isotopic anomaly. The enrichments were identified using δ¹³C of CH₄ both crudely using monthly excess ¹³C for air from the Atlantic sector over a 10-year period and by comparing results for individual trajectories from Canada with expected background conditions for that period. Both techniques suggest a source with δ¹³C in the range -30 to -25‰. Recent analysis of samples collected downwind of controlled burns in Canada confirms that the excess CH₄ emitted by burning has δ¹³C around - 28 to -27‰. Continued enrichment of the δ¹³C signal at Mace Head throughout 2003 and early 2004 is consistent with the circulation at these latitudes of CH₄ from the very large boreal fires that persisted in Siberia for much of 2003. The data also suggest that the burning of boreal forests contributed significantly to the high CH₄ growth rate in mid- to high- northern latitudes during 1998.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting