Legacy impacts of all‐time anthropogenic emissions on the global mercury cycle

Abstract

Elevated mercury (Hg) in marine and terrestrial ecosystems is a global health concern because of the formation of toxic methylmercury. Humans have emitted Hg to the atmosphere for millennia, and this Hg has deposited and accumulated into ecosystems globally. Here we present a global biogeochemical model with fully coupled atmospheric, terrestrial, and oceanic Hg reservoirs to better understand human influence on Hg cycling and timescales for responses. We drive the model with a historical inventory of anthropogenic emissions from 2000 BC to present. Results show that anthropogenic perturbations introduced to surface reservoirs (atmosphere, ocean, or terrestrial) accumulate and persist in the subsurface ocean for decades to centuries. The simulated present‐day atmosphere is enriched by a factor of 2.6 relative to 1840 levels, consistent with sediment archives, and by a factor of 7.5 relative to natural levels (2000 BC). Legacy anthropogenic Hg re‐emitted from surface reservoirs accounts for 60% of present‐day atmospheric deposition, compared to 27% from primary anthropogenic emissions, and 13% from natural sources. We find that only 17% of the present‐day Hg in the surface ocean is natural and that half of its anthropogenic enrichment originates from pre‐1950 emissions. Although Asia is presently the dominant contributor to primary anthropogenic emissions, only 17% of the surface ocean reservoir is of Asian anthropogenic origin, as compared to 30% of North American and European origin. The accumulated burden of legacy anthropogenic Hg means that future deposition will increase even if primary anthropogenic emissions are held constant. Aggressive global Hg emission reductions will be necessary just to maintain oceanic Hg concentrations at present levels.

Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species

“…15a). On average the models have a total atmospheric mercury burden of 4800 Mg (ECHMERIT 4650 Mg, GEOS-Chem 5100 Mg, GLEMOS 4200 Mg, GEM-MACH-Hg 5300 Mg), which is comparable to the 5300 Mg estimated by Amos et al (2013). The average vertical distribution in the model ensemble is 1500 Mg in the PBL, 2800 Mg in the FT, and 500 Mg in the stratosphere.…”

Benefits of mercury controls for the United States

“…Our GEOS-Chem simulations take into account the effect of anthropogenic emissions changes on concentrations of mercury in surface reservoirs only, and consequently underestimate the total deposition benefits attributable to policy. To roughly estimate the extent of this underestimation, we use a seven-box, biogeochemical model developed by Amos et al (28,29), which captures the deep ocean and soil reservoirs, but not the spatial distribution of impacts (SI Appendix, Chemical transport modeling). We find that globally, deposition reductions under policy are ∼30% larger when taking into account enrichment of these subsurface pools.…”

Atmospheric wet and litterfall mercury deposition at urban and rural sites in China

“…Hg in the atmosphere could be from anthropogenic and natural emission sources. At a global scale, direct and legacy anthropogenic emissions represent the predominant (∼ 2/3) sources of Hg in the atmosphere (Seigneur et al, 2004;Selin et al, 2007;Pirrone et al, 2010), and account for most of the deposition of Hg to the earth's surface Amos et al, 2013). Hg is removed from the atmosphere through wet deposition and dry deposition pathways.…”