Ocean Acidification

Highlights

• Fe(III) inputs increased CH₃I emission by photochemical and biogenic processes.
• Nutrient inputs enhanced volatile halocarbons by boosting biogenic processes.
• Ocean acidification enhanced CH₂Br₂/CHBr₃ emissions by BrPO-mediated halogenation.

Abstract

Short-lived volatile halocarbons (SLVHCs) are important trace greenhouse gases and ozone-depleting substances influencing global climate. Anthropogenic activities have accelerated ocean acidification (OA) and enhanced atmospheric deposition, yet how these perturbations regulate SLVHCs production in open ocean remains unclear. Herein, we investigated the effects of OA and atmospheric deposition derived Fe(III) and nutrient input on SLVHCs production through ship-based incubation experiments at two stations in the tropical eastern Indian Ocean (10°N-10°S) from March to May 2022. Our findings revealed that nutrient addition promoted phytoplankton growth with the maximum Chlorophyll a (Chl a) increasing to 6.17 μg L⁻¹, enhanced bromoperoxidase (BrPO) activity (by 108.3 % compared to the control group), and stimulated release of dissolved organic carbon (DOC), ultimately driving the production of CH₃I, CH₂Br₂, and CHBr₃ (by 152.0 %, 200.2 %, and 141.8 % increases, respectively). OA and Fe(III) additions promoted phytoplankton growth (Chl a up to 1.85 μg L⁻¹), thereby enhancing SLVHCs production through biological and photochemical processes, whereas they exhibited no significant effects on SLVHCs production in relatively oligotrophic regions. Mechanistically, CH₃I release was regulated by phytoplankton-mediated biogenic processes and photochemical processes. In contrast, CH₂Br₂ and CHBr₃ production was predominantly associated with phytoplankton-mediated biogenic processes (BrPO-mediated halogenation). These results demonstrating that OA, Fe(III), and nutrient inputs regulate marine SLVHC production by altering phytoplankton-mediated biogenic processes and photochemical reactivity. Our study offers a novel perspective and direct evidence for quantifying the production of SLVHCs under climate change scenarios, thereby underscoring the need to reassess oceanic climate feedbacks in the context of anthropogenic forcing.

Yu W.-R., Ni J., Liu S.-S., Lang X.-P., He Z. & Yang G.-P., 2026. Response of volatile halocarbons release to atmospheric deposition and ocean acidification in the tropical eastern Indian Ocean. Progress in Oceanography 249: 103831. doi: 10.1016/j.pocean.2026.103831. Article (subscription required).