Biogeosciences Discuss., 10, 483-528, 2013
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This discussion paper has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG.
Emission of atmospherically significant halocarbons by naturally occurring and farmed tropical macroalgae
E. C. Leedham1, C. Hughes1,2, F. S. L. Keng3,4, S.-M. Phang3,4, G. Malin1, and W. T. Sturges1
1School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
2Now at Environment Department, University of York, Heslington, York YO10 5DD, UK
3Institute of Ocean and Earth Sciences, University of Malaya, Kuala Lumpur, 50603, Malaysia
4Institute of Biological Sciences, University of Malaya, Kuala Lumpur, 50603, Malaysia

Abstract. Current estimates of global halocarbon emissions highlight the tropical coastal environment as an important source of very short-lived (VSL) biogenic halocarbons to the troposphere and stratosphere. This is due to a combination of assumed high primary productivity in tropical coastal waters and the prevalence of deep convective transport potentially capable of rapidly lifting surface emissions to the upper troposphere/lower stratosphere. However, despite this perceived importance direct measurements of tropical coastal biogenic halocarbon emissions, notably from macroalgae (seaweeds), have not been made. In light of this, we provide the first dedicated study of halocarbon production by a range of 15 common tropical macroalgal species and compare these results to those from previous studies of polar and temperate macroalgae. Variation between species was substantial; CHBr3 measured at the end of a 24 h incubation varied from 1.4 to 1129 pmol g FW−1 h−1 (FW = fresh weight of sample). We used our laboratory-determined emission rates to estimate emissions of CHBr3 and CH2Br2 (the two dominant VSL precursors of stratospheric bromine) from the coastlines of Malaysia and South East Asia. We compare these values to previous top-down model estimates of emissions from these regions, and conclude that the contribution of coastal CHBr3 emissions is likely to be lower than previously assumed. The contribution of tropical aquaculture to current emission budgets is also considered. Whilst the current aquaculture contribution to halocarbon emissions in this regional is small, the potential exists for substantial increases in aquaculture to make a significant contribution to regional halocarbon budgets.

Citation: Leedham, E. C., Hughes, C., Keng, F. S. L., Phang, S.-M., Malin, G., and Sturges, W. T.: Emission of atmospherically significant halocarbons by naturally occurring and farmed tropical macroalgae, Biogeosciences Discuss., 10, 483-528, doi:10.5194/bgd-10-483-2013, 2013.
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