Coastal emissions of methyl bromide and methyl chloride along the eastern Gulf of Mexico and the east coast of the United States

摘要

[1] Measurements of methyl bromide (CH_BC3lr) wanedre meathdyel chloride (CH_ during the Gulf of Mexico and the East Coast Carbon (GOMECC) cruise in the summer of 2007. This was the first large-scale study of CH_ CB3I irn tahen codas taCl oHcean_. The mean atmospheric mixing ratios were 10.1 ppt for CH 3Br and 517 ppt for CH_3CI. Surface seawater concentrations ranged from 0.8 pM to 5.0 pM for CH_Br and from 3 61.5 pM to 179 pM for CH_3Cl. Biological-processes contribute to the elevated seawater concentrations of CH_3Br, while a combination of biological processes and terrestrial sources may contribute to elevated seawater concentrations of CH_ CI. Vertical3 distributions show highest concentrations of CH_3Br and CH_3Cl in the subsurface seawater below the mixed layer due to high degradation rates near the surface. Good correlation of the production rates between CH_ 3Br and CH_3Cl suggests they have some common sources in the coastal ocean. After excluding the open ocean points, annual coastal emissions in the studied region were 0.01-0.06 Gg yr~(-1)for CH_3Br and 0.3-1.6 Gg yr~(-1) for CH_3CI. By simple extrapolation, the global coastal emissions were estimated at 0.5-3.6 Gg yr~(-1) for CH_3Br and 19-98 Gg yr~(-1) for CH_3CI. Including the coastal ocean emissions of CH_3Br and CH_3CI will increase the estimate of global oceanic emissions by 1%-9% and I%-8%, respectively.