Coral Reef Emissions of Atmospheric Dimethylsulfide and the Influence on Marine Aerosols in the Southern Great Barrier Reef, Australia

Abstract

Variability in atmospheric dimethylsulfide (DMSa) and the potential influence on atmospheric aerosols was investigated at Heron Island in the southern Great Barrier Reef (GBR), Australia. This work compiles previously published DMSa data (reported in Swan, Jones, Deschaseaux, & Eyre, 2017, https://doi.org/10.1007/s00216-017-0385-8), with additional surveys of DMSa, atmospheric particle number concentration, and other oceanic and atmospheric data sets. DMSa was higher in summer (mean 3.2 nmol m−3/78 ppt) than winter (mean 1.3 nmol m−3/32 ppt), reflective of seasonal shifts in phytoplankton biomass and emissions from corals in the southern GBR. Seasonally extreme spikes in DMSa were detected during low tide and low wind speed, supporting findings that the coral reef can be an important source of DMSa above background oceanic emissions. A significant link was present between DMSa and aerosol concentration (ranging from 0.5 to 2.5 μm) during calm, daylight hours, when conditions were optimal for the local oxidation of DMSa to sulfate aerosol precursors. This link may reflect condensational growth of existing fine particles (< 0.5 μm), which is the dominant pathway by which biogenic trace gases influence aerosols in the marine boundary layer. Aerosol concentration significantly correlated with reduced surface solar irradiance and sea surface temperature, which is potential evidence of a local negative feedback mitigating coral physiological stress. These findings provide a step toward a better understanding of the processes influencing DMSa and aerosol concentrations and of the consequences for the local radiative balance over coral reefs; an increasingly important topic with ongoing ocean warming and coral bleaching.