1. Trends in atmospheric mercury and implications for past and future mercury accumulation in surface reservoirs Daniel J. Jacob with Anne Sørensen, Hannah Horowitz, Helen Amos, Elsie Sunderland, David Streets (ANL)

2. Biogeochemical cycle of mercury Hg(0) Hg(II) particulate Hg burial SEDIMENTS uplift volcanoes erosion oxidation Hg(0)Hg(II) reduction biological uptake ANTHROPOGENIC PERTURBATION: fuel combustion mining ATMOSPHERE OCEAN/SOIL VOLATILE WATER-SOLUBLE (months)

3. History of global anthropogenic Hg emissions Large past (legacy) contribution from N. American and European emissions; Asian dominance is a recent phenomenon Streets et al., 2011

4. 1977-2010 surface air trend of Hg(0) over the Atlantic Ocean 1990-2010 data from ship cruises show a 50% decrease over North Atlantic, no significant trend over South Atlantic Surface ocean Hg in North Atlantic also show a 50% decrease for 1990-2010, while subsurface Hg shows a 80% decrease [Mason et al., 2012] Sørensen et al., submitted Cruises Mace Head Cruises Cape Point ocean mixed layer 50-100 m thermocline (~1000 m) surface ocean subsurface ocean

5. GEOS-Chem simulation of Hg(0) 1990-2010 trends in surface air Forced by Streets emission trends ng m -3 a -1 Simulation forced by 80% decrease in subsurface North Atlantic yields 50% decrease in surface air Hg(0) over 1990-2010, consistent with observations Subsurface decrease must reflect a large decline in Hg inputs to the North Atlantic over 1970-2010. Sørensen et al., submitted Global 3-D atmospheric model coupled to 2-D surface ocean and land models, with subsurface ocean as boundary condition Forced by observed subsurface Atlantic trends

6. Decreasing Hg input to subsurface North Atlantic, 1970-2010 1. Atmospheric deposition explanation Hg(0) Hg(II) Br Hg(0) Hg(II) Br marine boundary layer ocean mixed layer subsurface ocean (down to thermocline) 1970 2000 Hg deposition is thought to be driven by MBL oxidation of Hg(0) by Br atoms MBL ozone ~doubled during 1970-2000; Br concentrations would have correspondingly decreased (Br/BrO photochemical equilibrium) Sørensen et al., submitted fast slow Br BrO O3O3 h

7. Decreasing Hg input to subsurface North Atlantic, 1970-2000 2. Disposal of Hg-containing commercial products Hg Disposed Hg- containing commercial products wastewater, leaching incineration Secondary wastewater treatment and phase-out of Hg from commercial products would have greatly decreased Hg input to the subsurface N Atlantic Hg(II) Hg 1970 2000 Sørensen et al., submitted N AMERICA, EUROPE

8. Disposal of Hg in commercial products: a missing component of the Hg biogeochemical cycle? Global production of commercial Hg peaked in 1970 Streets et al. [2011] and Hannah Horowitz (Harvard)

9. Global biogeochemical model for mercury Primary emissions 7-box model with 7 coupled ODEs dm/dt = s(t) – km where s is primary emission Transfer rate constants k are specified from best knowledge Model is initialized at natural steady state, and then forced with anthropogenic emissions for 2000 BC – present; % present-day enrichments are indicated Amos et al., submitted

10. Time scale for dissipation of an atmospheric emission pulse Reservoir fraction Pulse gets transferred to subsurface ocean within a few years and stays there ~100 years, maintaining a legacy in the surface ocean Amos et al., submitted

11. Global source contributions to Hg in present-day surface ocean Human activity has increased 7x the Hg content of the surface ocean Half of this human influence is from pre-1950 emissions N America, Europe and Asia share similar responsibilities for anthropogenic Hg in present-day surface ocean Amos et al., submitted Europe Asia N America S America former USSR ROW pre-1850 natural emissions

12. Looking toward the future: UNEP global treaty for Hg Negotiations to be completed by 2013 Effect of zeroing global anthropogenic emissions by 2015 Zeroing anthropogenic emissions would decrease ocean Hg by 30% by 2100, while keeping emissions constant would increase it by 40% Elevated Hg in surface ocean will take centuries to fix; the only thing we can do in short term is prevent it from getting worse. Amos et al., submitted