Cascading effects of climate change on the marine mercury cycle

Under the global implementation of the Minamata Convention on Mercury, anthropogenic mercury (Hg) emissions are being progressively curtailed. However, marine methylmercury (MeHg) risks may not decline synchronously because climate change can trigger cascading changes in the biogeochemical processes linking Hg inputs to biological exposure. This review proposes a process-oriented framework for understanding how climate drivers, including warming, deoxygenation, acidification, cryosphere degradation, hydrological extremes, sea-level rise, and circulation changes, interact across key nodes of the marine Hg cycle: external delivery, Hg(II) activation and bioavailability, MeHg production, removal, burial, and remobilization, and trophic transfer. We synthesize how legacy Hg remobilization, climate-sensitive shifts in Hg speciation, expanding methylation niches, altered plankton communities, bioenergetic responses, and food-web reorganization jointly influence seafood MeHg exposure. Rather than exerting unidirectional effects, these climate drivers can trigger synergistic amplification, antagonistic buffering, and context-dependent bidirectional responses that collectively reshape marine MeHg risk. Based on this synthesis, we identify climate-sensitive marine Hg risk regions, including Arctic margins, estuarine and deltaic input zones, oxygen-deficient upwelling systems, and high-exposure Asian coastal waters. We argue that future effectiveness evaluations under the Minamata Convention should incorporate climate-adjusted baselines to distinguish anthropogenic mitigation effects from climate-driven Hg reactivation and better support marine Hg risk management and global mercury governance.