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)

on my Harvard interview (May 1984)Atmospheric Chemistry

Modeling Group (May 2009)

fastforward

Merucry in polar bear fur

US fish consumption advisories (EPA)

Wyoming ice core

EPA, 2007

RISING MERCURY IN THE ENVIRONMENT

Schuster et al., 2002

Dietz et al., 2006

THE MERCURY CYCLE: MAJOR PROCESSES

Hg(0) Hg(II)

particulate

Hg

burial

SEDIMENTS

uplift

volcanoeserosion

oxidation (~1 y)

reduction

volatilization

Hg(0) Hg(II)oxidation

reduction

deposition

biologicaluptake

ANTHROPOGENIC PERTURBATION:fuel combustion

waste incinerationmining

highly water-soluble

ATMOSPHERE

SOIL/OCEAN

GEOS-Chem simulation of environmental mercury

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]

(2000)

GLOBAL MERCURY CYCLE (NATURAL)

Inventories in MgRates in Mg a-1

Selin et al. [2008]

Hg uptake by soil and ocean driven

by formation of Hg-organic complexes

GLOBAL MERCURY CYCLE (PRESENT-DAY)

Inventories in MgRates in Mg a-1

Selin et al. [2008]

Hg uptake by soil and ocean driven

by formation of Hg-organic complexes

x7x1.2

x3

x3

SOIL DYNAMICS OF MERCURY

• 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

Based on CASA model by analogy to soil organic carbon

50 y 8,000 y Smith-Downey et al. [2010]

ATMOSPHERIC REDOX CHEMISTRY OF MERCURY

Hg(0) Hg(II)OH, O3, Br

oxidation (~ 1y)

reductionhν, aq

Model Br from bromocarbons, sea salt[Holmes et al., 2010]

Thule

Observed BrO columns from space(N. polar view, April)

0.5-2 ppt BrO in troposphere

?

TOMCAT

GMI

GEOS-Chem MODEL COMPARISON TO OBSERVATIONS

Total gaseous mercury TGM ≡ Hg(0) +Hg(II)(g)

Surface air

Alt

itu

de,

km

Background = GEOS-Chem model

Arctic aircraft profiles (ARCTAS)

obsmodel

• 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?

summer spring

Holmes et al. [2010]

MERCURY WET DEPOSITION FLUXES,

2004-2005

Circles: observationsBackground: GEOS-Chem model

Model contribution from N. Americananthropogenic 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

Natural (32%)

North Americananthropogenic (20%)

Rest of world anthropogenic (31%) – half cycled through oceanon annual time scale

Legacy anthropogenicre-emitted from soil oncenturial time scale(16%)

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!