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

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, 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 production rates, measured at the end of a 24 h incubation, varied from 1.4 to 1129 pmol g FW-1 h-1 (FW Combining double low line 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 elsewhere in South East Asia (SEA). We compare these values to previous top-down model estimates of emissions from these regions and, by using several emission scenarios, we calculate an annual CHBr3 emission of 40 (6-224 Mmol Br-1 yr), a value that is lower than previous estimates. 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. © 2013 Author(s)

Isotopic composition of polyhalomethanes from marine macrophytes – systematic effects of the halogen substituents on isotopic composition

“…It may be related to changes in the activity of bromoperoxidases, a decreasing production of PHM precursors, reduced oxidative stress, or the build-up of substrates that can be halogenated but compete with PHM formation. However, our results corroborate those of Leedham et al, [25] who reported 3-to 10-fold higher production rates from 4-h incubations as compared with 24-h incubations.…”

“…Other factors that may account for the different production rates are the pH of the seawater (IFBM, 8.1; IOW, ,7), the sampling location and the sampling season. However, in summary, the production rates and their variability found here (Tables S1, S4, S5) fit in the range of previous studies, [25] with the IOW production rates being at the lower end and the IFBM production rates being in the middle to upper range.…”

“…This is consistent with differences in halocarbon production previously reported for several Fucus and Laminaria species. [22,25] As for L. digitata, CHBr 3 and CH 2 I 2 were the most abundant compounds in the Fucus incubations, with average production rates of 7.2 and 5.9 pmol g À1 FW h À1 respectively. Other PHMs produced in sufficient amounts for carbon isotope determination were CH 2 Br 2 and CH 2 Cl 2 .…”

“…Marine macroalgae have long been recognised as potent sources of diverse halocarbons and their production has been studied in numerous laboratory and field experiments. [16][17][18][19][20][21][22][23][24][25] More recently, seagrass meadows have also been recognised as halocarbon sources. [26,27] Brown algae -particularly from the order Laminariales -produce a wide range of polyhalomethanes (PHMs).…”

Bromocarbons in the tropical coastal and open ocean atmosphere during the 2009 Prime Expedition Scientific Cruise (PESC-09)

“…Biogenic emissions from the oceans have been identified as one of the main natural sources where organisms such as macroalgae (seaweeds) and microalgae (phytoplankton) can release large quantities of halocarbon gases into the atmosphere (Sturges et al, 1993;Moore et al, 1996;Laturnus and Adams, 1998). Previous ship and coastal measurements have collected bromocarbon data for many different global regions, summarised in Montzka et al (2011).…”