Can corals form aerosol particles through volatile sulphur compound emissions?

Acropora dominated coral reefs are a substantial source of atmospheric dimethylsulphide (DMSa), one of the most abundant reduced sulphur gases present in the marine boundary layer. DMS is believed to act as a climate regulator of solar radiation and sea surface temperatures through the formation of non-sea-salt sulphate aerosols and cloud condensation nuclei (CCN), although this regulation has not yet been demonstrated. A bubbling chamber experiment was conducted on coral reef seawater containing a branch of Acropora pulchra, to investigate whether the coral-generated DMSa could be oxidised to non-seasalt sulphate aerosols under treatment with UV light and O3. Results indicated that A. pulchra produced significant amounts of dimethylsulphoniopropionate (DMSP) and dissolved DMS although emissions of DMSa in the chamber headspace were reduced by the presence of the coral, probably as a result of antioxidant activity in the coral tissue. Significant amounts of carbon disulphide (CS2) and ethanethiol (ESH), other sulphur gases that could be involved in CCN formation, were also indicated in the bubbling chamber, most likely from coral production. A decrease in DMSa and CS2 in the presence of UV light and O3 followed by an occurrence of freshly nucleated nanoparticles (<10nm) suggested that these two sulphur compounds were oxidised and potentially participated in aerosol particle formation and thus could be involved in CCN formation and possibly climate regulation. The study provided insights into the production of sulphur compounds by Acropora dominated coral reefs with potential impact on local climate

Air exposure of coral is a significant source of dimethylsulfide (DMS) to the atmosphere

Corals are prolific producers of dimethylsulfoniopropionate (DMSP). High atmospheric concentrations of the DMSP breakdown product dimethylsulfide (DMS) have been linked to coral reefs during low tides. DMS is a potentially key sulfur source to the tropical atmosphere, but DMS emission from corals during tidal exposure is not well quantified. Here we show that gas phase DMS concentrations (DMSgas) increased by an order of magnitude when three Indo-Pacific corals were exposed to air in laboratory experiments. Upon re-submersion, an additional rapid rise in DMSgas was observed, reflecting increased production by the coral and/or dissolution of DMS-rich mucus formed by the coral during air exposure. Depletion in DMS following re-submersion was likely due to biologically-driven conversion of DMS to dimethylsulfoxide (DMSO). Fast Repetition Rate fluorometry showed downregulated photosynthesis during air exposure but rapid recovery upon re-submersion, suggesting that DMS enhances coral tolerance to oxidative stress during a process that can induce photoinhibition. We estimate that DMS emission from exposed coral reefs may be comparable in magnitude to emissions from other marine DMS hotspots. Coral DMS emission likely comprises a regular and significant source of sulfur to the tropical marine atmosphere, which is currently unrecognised in global DMS emission estimates and Earth System Models