Atmosphere-Ocean �Modeling Linkages

3^rd GEOS-Chem Users’ Meeting

April 12, 2007

​

Elsie Sunderland

U.S. Environmental Protection Agency

Office of Research & Development

National Center for Environmental Research

sunderland.elsie@epa.gov

Primary

Anthropogenic

Emissions

LAND

ATMOSPHERE

OCEAN

recycling &

terr. emission

Hg(II)

Hg(0)

Hg(p)

MeHg

Net reduction

Net Evasion

methylation

demethylation

EVASION

ATMOSPHERIC

DEPOSITION

RIVERS

LATERAL

OCEAN

FLOW

RESERVOIR M_w = C_wV_w

MARINE BOUNDARY LAYER

DEEP WATER �FORMATION

PARTICLE

SETTLING

Conceptual Model for Each Basin

UPWELLING

Temporal Trends in Ocean Hg with GEOS-Chem Forecasted Deposition

Source: Sunderland & Mason, 2007

Temporal Lag in Ocean Hg Enrichment

Source: Sunderland & Mason, 2007

Estimated Fraction of Annual Hg Inputs

Source: Sunderland & Mason, 2007

Atlantic

35°S-55°N

Pacific & Indian

40°S-30°N

North Pacific

>30°N

Med. Sea

30-35°N

Recap: GEOS-Chem Surface Ocean Model

Source: Strode et al., 2007

avg mixed

depth = 53 m

1.9

15.5

16.6

22.8/yr

14.1/yr

sorption

reduction

All units Mmol

0.06 pM

0.5 pM

0.5 pM

surface mixed layer

thermocline

atmosphere

particle sinking

entrainment

diffusion

diffusion

upwelling

entrainment

upwelling

diffusion

entrainment

upwelling

HgT = 1.53 pM

HgT = 1.06 pM

Model Improvements

1. Lateral Ocean Flow

Source: Anderson, 2003

2. Temporal Lag between Ocean Hg & Atmospheric Hg

Source: IPCC/WMO/UNEP

Atlantic

35°S-55°N

River Hg Discharge (Mmol/yr)

Q (10¹² L/yr)

N. Atlantic

>55°N

Atlantic

65°S-35°S

Pacific & Indian

40°S-30°N

N. Pacific

>30°N

Med.

30-35°N

Antarctic

>65°S

Source: Dai & Trenberth, 2002; Sunderland & Mason, 2007

3. Riverine Discharges of Hg

*compare: anthropogenic emissions ~ 12 Mmol/yr

4. Methylmercury (MeHg) Speciation

North Pacific Ocean 23-55°N

Source: D. Krabbenhoft, USGS, unpublished data

Next Steps

​

• Historical anthropogenic emissions on a continental scale to estimate temporal responses of oceans
• Coupled pre-industrial deep ocean & GEOS-Chem models
• Expand surface “slab” model of ocean to include deep ocean waters
• Account for methylmercury speciation?
• Explore effects of climate change?

Now

Later