Parameterizing the Impact of Seawater Temperature and Irradiance on Dimethylsulfide (DMS) in the Great Barrier Reef and the Contribution of Coral Reefs to the Global Sulfur Cycle. Issue 3 (8th March 2021) - Jackson, R. L.
Abstract: Biogenic emissions of dimethylsulfide (DMS) are an important source of sulfur to the atmosphere, with implications for aerosol formation and cloud albedo over the ocean. Natural aerosol sources constitute the largest uncertainty in estimates of aerosol radiative forcing and climate and thus, an improved understanding of DMS sources is needed. Coral reefs are strong point sources of DMS; however, this coral source of biogenic sulfur is not explicitly included in climatologies or in model simulations. Consequently, the role of coral reefs in local and regional climate remains uncertain. We aim to improve the representation of tropical coral reefs in DMS databases by calculating a climatology of seawater DMS concentration (DMSw ) and sea‐air flux in the Great Barrier Reef (GBR), Australia. DMSw is calculated from remotely sensed observations of sea surface temperature and photosynthetically active radiation using a multiple linear regression model derived from field observations of DMSw in the GBR. We estimate that coral reefs and lagoon waters in the GBR (∼347, 000 km 2 ) release 0.03–0.05 Tg yr −1 of DMS (0.02 Tg yr −1 of sulfur). Based on this estimate, global tropical coral reefs (∼600, 000 km 2 ) could emit 0.08 Tg yr −1 of DMS (0.04 Tg yr −1 of sulfur), with the potential to influence the local radiative balance. Plain Language Summary: Coral reefs are important sources of biogenic sulfur through stress‐induced emissions of dimethylsulfide (DMS). This volatile sulfur compound has potentially important implications for atmospheric aerosol formation and cloud microphysical properties. However, coral reefs are not accounted for in global DMS climatologies or in model simulations. Consequently, the importance of coral reef‐derived DMS in local climate is uncertain. Here, a proxy for seawater DMS concentration in coral reefs is derived from field measurements taken in the Great Barrier Reef, Australia. This proxy is used to calculate a climatology of DMS flux from coral reefs to estimate the contribution to the global sulfur cycle. Key Points: Seawater dimethylsulfide concentration in coral reefs is parameterized as a function of surface temperature and irradiance Including coral‐air dimethylsulfide release at low tide in sea‐air flux calculations yields a more accurate estimate of coral reef flux Coral reefs emit 0.03–0.04 Tg yr −1 of sulfur as dimethylsulfide, representing up to 0.2% of global sea‐air flux estimates