Observational and Modeling Constraints on Global Anthropogenic Enrichment of Mercury

Centuries of anthropogenic releases have releases in a global legacy of mercury (Hg) contamination. Here we use a global model to quantify the impact of uncertainty in Hg atmospheric emissions and cycling -On anthropogenic enrichment and discuss implications for future Hg levels. The plausibility of sensitivity simulations is evaluated against multiple independent lines of Observation, including natural archives and direct measurements of present-day environmental Hg concentrations. It has been previously reported that pre-industriaVenrichment recorded in sediment and peat disagree by more than a factor of 10. We find this difference is largely erroneous and caused by comparing peat and sediment against different reference time periods. After correcting this inconsistenr-yi, median enrichment in Hg accumulation since pre-industrial 1760 to 1880 is a factor of 4.3 for peat and 3.0 for sediment. Pre-industrial accumulation in peat and sediment is a factor of greater than the precolonial era (3000-BC to 1550 AD). Model scenarios that omit atmospheric emissions of Hg,froin early mining are inconsistent with observational constraints on the present-day atmospheric, oceanic, and soil Hg reservoirs, as well as the magnitude of enrichment in archives. Future reductions in anthropogenic emissions will initiate a decline in atmospheric concentrations within 1 year, but stabilization of subsurface and deep oaearr Hg levels requires aggressive controls. These findings are robust to the ranges of uncertainty in past emissions arid Hg cycling.