GLOBAL CYCLING OF MERCURY Daniel J. Jacob with Team Hg: Helen M. Amos, Claire Carouge, Bess D. Corbitt, Christopher D. Holmes, Noelle E. Selin (now at MIT), Nicole Smith-Downey (now at U. Texas), Anne L. Soerensen (now at U. Aarhus), Elsie M. Sunderland, Feiyue Wang (visiting from U. Manitoba) Atmospheric Chemistry Modeling Group (May 2009) on my Harvard interview (May 1984) fast forward

RISING MERCURY IN THE ENVIRONMENT Merucry in polar bear fur Wyoming ice core Dietz et al., 2006 US fish consumption advisories (EPA) Schuster et al., 2002 EPA, 2007 2 2 2

THE MERCURY CYCLE: MAJOR PROCESSES ANTHROPOGENIC PERTURBATION: fuel combustion waste incineration mining oxidation (~1 y) Hg(0) Hg(II) reduction highly water-soluble volcanoes erosion ATMOSPHERE volatilization deposition SOIL/OCEAN oxidation Hg(II) particulate Hg Hg(0) biological uptake reduction uplift burial SEDIMENTS

GEOS-Chem simulation of environmental mercury (2000) Global 3-D atmospheric simulation driven by GEOS assimilated meteorological data and coupled to 2-D surface ocean and land reservoirs Holmes et al. [2010]

GLOBAL MERCURY CYCLE (NATURAL) Hg uptake by soil and ocean driven by formation of Hg-organic complexes Inventories in Mg Rates in Mg a-1 Selin et al. [2008]

GLOBAL MERCURY CYCLE (PRESENT-DAY) x3 Hg uptake by soil and ocean driven by formation of Hg-organic complexes x7 x1.2 x3 Inventories in Mg Rates in Mg a-1 Selin et al. [2008]

SOIL DYNAMICS OF MERCURY Based on CASA model by analogy to soil organic carbon Mercury has a mean lifetime in soil of 630 years, but deposited anthropogenic mercury has a lifetime of only 80 years Coupling to soil organic carbon means that increased respiration rates could lead to large soil mercury release 50 y 8,000 y Smith-Downey et al. [2010]

ATMOSPHERIC REDOX CHEMISTRY OF MERCURY oxidation (~ 1y) OH, O3, Br Hg(0) Hg(II) ? reduction hν, aq Observed BrO columns from space (N. polar view, April) 0.5-2 ppt BrO in troposphere Model Br from bromocarbons, sea salt [Holmes et al., 2010] Thule GMI TOMCAT

GEOS-Chem MODEL COMPARISON TO OBSERVATIONS Total gaseous mercury TGM ≡ Hg(0) +Hg(II)(g) Arctic aircraft profiles (ARCTAS) summer spring Altitude, km obs model Background = GEOS-Chem model Surface air High mercury from ship cruises in N Atlantic and Pacific: accumulated legacy of anthropogenic mercury in the deep ocean? Depletion of mercury above tropopause in Arctic spring – oxidation by Cl? Holmes et al. [2010]

MERCURY WET DEPOSITION FLUXES, 2004-2005 Circles: observations Background: GEOS-Chem model Model contribution from N. American anthropogenic sources Model contribution from external sources Selin and Jacob [2008]

SOURCE ATTRIBUTION FOR U.S. MERCURY DEPOSITION % contribution of N. American sources to annual total mercury deposition Legacy anthropogenic re-emitted from soil on centurial time scale (16%) Natural (32%) North American anthropogenic (20%) Rest of world anthropogenic (31%) – half cycled through ocean on annual time scale Selin and Jacob [2008]

WHAT DOES THE FUTURE HOLD? Global anthropogenic emissions [Streets et al., 2009] Anthropogenic emissions projected to either rise or stabilize Increased soil respiration: mobilization of Hg, transfer to oceans? Disappearing sea ice: impact on Br chemistry? Stay tuned for MBM’s 110th birthday!