Coastal Inorganic Mercury Time Series Reveals Interannual and Seasonal Variability Driven by Regional Climate Factors

Inorganic mercury (iHg) is an anthropogenic pollutant that forms monomethylmercury, a neurotoxicant affecting human health through seafood consumption. Despite iHg emission reduction policies, the impact on oceanic concentrations remains unclear due to limited long-term data. Here, we present a four-year weekly time series of iHg concentrations at Scripps Pier in La Jolla, California, capturing seasonal and interannual variability. Interannual variability is driven by wet season precipitation, with wet conditions exhibiting sevenfold higher iHg variance than dry conditions, potentially linking to climate modes, such as El Niño-Southern Oscillation. Seasonally, precipitation and wave dynamics influence iHg inputs, with wet seasons driven by precipitation and runoff and dry seasons by upwelling. Using a model informed by these parameters, we reconstructed a 20-year record of iHg, suggesting a long-term decline of 0.005 pM yr ^− 1 . Our findings highlight the challenges in detecting long-term trends and emphasize the need for sustained monitoring of oceanic iHg concentrations.