Distributions of volatile halocarbons and impacts of ocean acidification on their production in coastal waters of China

Abstract The volatile halocarbons (VHCs) CH3I, C2HCl3, C2Cl4, and CH2Br2 were measured in the Changjiang Estuary and adjacent waters during autumn 2018. Results revealed that their concentrations in coastal waters were influenced by anthropogenic activities, biological release, and complex hydrographic features. The vertical distributions of VHCs were determined mostly by the mixing of water masses. By investigating the impacts of temperature, salinity, chlorophyll a, nutrients, and pH on the distributions of these trace gases we revealed that C2HCl3 and C2Cl4 were positively correlated with salinity and nutrient availability. The sea-to-air fluxes of CH3I, C2HCl3, C2Cl4, and CH2Br2 were estimated to be 27.62, 280.3, 221.73, and 142.41 nmol m−2 day−1, respectively, suggesting that the study area was a net source of these trace gases. The impact of elevated fCO2 on the production of the four volatile halocarbons was studied using mesocosms in Wu Yuan Bay, Xiamen. The results showed that elevated fCO2 had little impact on the VHCs. Positive relationships were observed between CH2Br2 and phytoplankton biomass when fCO2 was low, and between CH3I and phytoplankton biomass when fCO2 was high, suggesting that algal release was a significant source of both compounds.