Emission of atmospherically significant halocarbons by naturally occurring and farmed tropical macroalgae

[摘要] Current estimates of global halocarbon emissions highlight the tropicalcoastal environment as an important source of very short-lived (VSL) biogenichalocarbons to the troposphere and stratosphere, due to a combination ofassumed high primary productivity in tropical coastal waters and theprevalence of deep convective transport, potentially capable of rapidlylifting surface emissions to the upper troposphere/lower stratosphere.However, despite this perceived importance, direct measurements of tropicalcoastal biogenic halocarbon emissions, notably from macroalgae (seaweeds),have not been made. In light of this, we provide the first dedicated study ofhalocarbon production by a range of 15 common tropical macroalgal species andcompare these results to those from previous studies of polar and temperatemacroalgae. Variation between species was substantial; CHBr₃ productionrates, measured at the end of a 24 h incubation, varied from 1.4 to1129 pmol g FW⁻¹ h⁻¹ (FW = fresh weight of sample). We usedour laboratory-determined emission rates to estimate emissions of CHBr₃and CH₂Br₂ (the two dominant VSL precursors of stratosphericbromine) from the coastlines of Malaysia and elsewhere in South East Asia(SEA). We compare these values to previous top-down model estimates ofemissions from these regions and, by using several emission scenarios, wecalculate an annual CHBr₃ emission of 40 (6–224 Mmol Br⁻¹ yr),a value that is lower than previous estimates. The contribution of tropicalaquaculture to current emission budgets is also considered. Whilst thecurrent aquaculture contribution to halocarbon emissions in this regional issmall, the potential exists for substantial increases in aquaculture to makea significant contribution to regional halocarbon budgets.

[学科分类] 地球化学与岩石