Responses of biogenic trace gases to atmospheric deposition and acid-processed atmospheric deposition in the oligotrophic western Pacific Ocean

Abstract

Dimethylsulfide (DMS) and very short-lived bromocarbons (VSL^Br) are important biogenic trace gases emitted from oceans that can affect the global climate. Atmospheric deposition (AD) can provide nutrients and trace metals to the ocean, which can enhance primary productivity, but the complex effects of AD on DMS and VSL^Br are still largely unexplored. A deck incubation experiment with aerosol additions was conducted to simulate the effects of acid-processed AD on the production of trace gases, including DMS and four VSL^Br such as bromoform (CHBr₃), dibromomethane (CH₂Br₂), dibromochloromethane (CHBr₂Cl), and bromodichloromethane (CHBrCl₂), in the oligotrophic western Pacific Ocean (WPO). During the incubation, the average concentrations of inorganic nitrates, DMS and VSL^Br were significantly higher in the two aerosol treatments, indicating significant increases due to AD. Furthermore, the introduction of aerosols led to increases in the abundances of high DMS producers, specifically dinoflagellates, which contributed to the production of DMS. The acidified aerosol additions had a more pronounced influence on chlorophyll a and DMS, than non-acidified aerosol additions. However, the responses of VSL^Br to the acidified aerosol treatment were more complex. The average CHBr₃ and CH₂Br₂ values showed no significant differences between these two aerosol treatments, while the values of CHBr₂Cl and CHBrCl₂ were significantly lower in the acidified aerosol treatment. These results illustrated that aerosol additions promoted the production of DMS and the four VSL^Br. Nevertheless, the concentrations of CHBr₂Cl and CHBrCl₂ were suppressed in the acidified aerosol treatment relative to the non-acidified aerosol addition.