Tuesday, 8 January 2013: 4:15 PM
Ballroom F (Austin Convention Center)
Bromoform (CHBr3), dibromomethane (CH2Br2) and other very short-lived substances (VSLS) were measured during 5 cruises in the Atlantic Ocean from 1998 to 2010. These cruises were conducted over large meridional (62° N - 60° S) and zonal (11° W 86° W) ranges in the Atlantic Ocean. Elevated atmospheric mixing ratios and seawater concentrations of CHBr3 were observed coincident with regions of elevated chlorophyll a, such as the equatorial region, upwelling zones and coastally influenced shelf waters, suggesting that processes related to ocean primary production may have contributed to CHBr3 production. While CH2Br2 seawater concentrations exhibit similar trends with CHBr3, it is more well-mixed in the atmosphere, due to its longer atmospheric lifetime. The sea-to-air flux maxima for CHBr3 and CH2Br2 were observed in coastally influenced shelf waters. Assuming the fluxes measured in the Atlantic open ocean are globally representative, the extrapolated CHBr3 global open ocean annual net sea-to air flux is 0.13 - 3.6 Gmol Br yr-1. Biological parameters including pigment biomarkers and flow cytometeric picoplankton counts were measured during one of the cruises conducted in 2010 (HalocAST A). None of the pigment biomarkers yield significant correlations with CHBr3 and CH2Br2. While zeaxanthin does not distinguish between Synechococcus and Prochlorococcus, flow cytometeric cell counts do allow for their separation and determination of their individual abundances, as well as providing cell abundance information for other picoeukaryotes and heterotrophic bacteria. Seawater concentrations of CHBr3 were significantly correlated with Synechococcus near the Northwestern African upwelling zone but not anywhere else during the HalocAST A cruise. These findings suggest that more specific parameters are needed for assessing biogenic sources of the VSLS during large oceanographic transects due to changing biomes during the course of the cruise. A new solubility relationship to temperature and salinity determined from recent laboratory studies will be presented along with an updated VSLS net sea-to-air net flux.
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