Constraints on marine gas-phase sulfur emissions during an induced phytoplankton bloom and their impact on sulfate formation in a coastal marine environment

Abstract:

The ocean accounts for the largest source of natural sulfur into the atmosphere, primarily as dimethyl sulfide (DMS). DMS has well-established links to sulfate secondary aerosol formation, cloud condensation nuclei, and climate. Less measurements exist of other marine sulfate aerosol precursor gases. These gases are often emitted in smaller quantities than DMS, and understanding of their oxidative pathway to form sulfate aerosol is limited.

Here we present measurements of gas-phase volatile organosulfur molecules emitted from coastal seawater during a mesocosm bloom experiment in a low-oxidant environment at the Scripps Institute of Oceanography Hydraulics Laboratory wave channel in 2019. We show that the majority of the sulfur budget can be constrained by DMS, methanethiol (MeSH), and a new marine emission, benzothiazole. The relative contribution of each molecule varies through the stages of the bloom. We do not find evidence for the emission of methane sulfonamide, which was recently observed as a major marine sulfur species during bloom conditions in the Arabian Sea. Additional waterside measurements of DMSP, chlorophyll-A, and heterotrophic bacteria provide insight into controls on the molecules’ production and loss processes in the seawater. Flux measurements conducted shortly after the wave channel experiment and at the same location as where the wave channel water was collected show that the ambient DMS to MeSH flux ratio is consistent with the ratio of DMS to MeSH at the beginning of the experiment, before the ratio increases significantly during the bloom. The evolving ratio of DMS to MeSH and potential new precursor gas, benzothiazole, have important implications for secondary sulfate formation pathways in a coastal marine environment.