1. 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

2. 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

3. 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

4. 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]

5. 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]

6. 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]

7. 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]

8. 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

9. 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]

10. 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]

11. 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]

12. 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!