Chemical release from coral reefs may influence our climate

Coral reefs at Heron Island in the Great Barrier Reef have been shown to emit a gas that helps in the formation of clouds that affect rainfall, a team of Southern Cross University biogeochemists has found.

The study is the first long-term continuous measurement of the naturally occurring gas dimethylsulfide (DMS) over the reef.

The properties of the aerosol DMS allow it to grow to the point where it can help in the seeding of low-level clouds. The researchers say this means DMS may influence the regional climate of the Great Barrier Reef and northeastern Australia.

The results are contained in the paper ‘Coral reef origins of atmospheric dimethysulfide at Heron Island, southern Great Barrier Reef’ published in the latest edition of the leading international journal Biogeosciences.

Working at Heron Island, the researchers used sensitive automated instrumentation to detect pulses of coral-derived DMS above the background DMS naturally derived from the ocean.

The pulses of DMS were usually seen at low tide under low wind speeds, indicating they were derived from the platform reef surrounding the island. At low tide parts of the reef can become exposed to the air, allowing a direct exchange of DMS from coral to the atmosphere.

Mr Hilton Swan, Dr Elisabeth Deschaseaux and Professor Bradley Eyre, from the University’s Centre for Coastal Biogeochemistry Research, and Associate Professor Graham Jones, from the Marine Ecology Research Centre, made up the research team. The work was undertaken as part of Mr Swan’s doctoral thesis.

“The paper published in the journal Biogeosciences illustrates the dynamics of the biosphere showing how the GBR and the atmosphere are linked,” Mr Swan said.

“The study provides compelling environmental evidence that the Great Barrier Reef is a source of atmospheric DMS, a climate active compound. DMS atmospheric oxidation products participate in a climate feedback which can increase low level cloud cover, which can influence solar radiation levels over the Great Barrier Reef.”

Professor Bradley Eyre, director of the Centre for Coastal Biogeochemistry Research, said the study was important.

"The findings from this study are significant because although reefs have previously been thought to be a source of DMS, this is the first long term (two to three weeks) continuous measurements of DMS over the reef.”

Chemical oceanographer Associate Professor Graham Jones has been investigating DMS on the Great Barrier Reef for more than 20 years.

He boarded Australia’s Marine National Facility, RV Investigator in September/October 2016 as part of an internationally-supported research campaign to show that the Great Barrier Reef is a source of climatically-relevant aerosol particles that affects the climate of northern Australia.

“This cloud-coral reef feedback could be linked to frequency and severity of El Nino which strongly influences the climate of northern Australia with major implications for agriculture,” Professor Jones said.

“This research by Hilton Swan means we can now assess the importance of the GBR to the emission of this gas to the atmosphere over the GBR and assess the magnitude of the coral reef feedback.”

This research was funded from grants to Associate Professor Graham Jones of the Marine Ecology Research Centre by ARC Discovery Project grant (ARCDP) DP150101649 with Professor Zoran Ristovski of the Queensland Institute of Technology. Additional funding was provided from ARCDP grant DP150102092 awarded to Professor Bradley Eyre.

Photo: Conceptual diagram showing elevated levels of atmospheric dimethylsulphide (DMS) produced from coral reefs at low tide, which then become oxidised to sulphate (SO2/SO4) aerosols that grow to form cloud condensation nuclei (CCN) which form low level clouds over the Great Barrier Reef. This coral-cloud climate feedback keeps sea surface temperatures (SST) cool in summer, but breaks down when SSTs are too high. (Copyright: Biogeosciences)