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 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 Atmosphere-Ocean Modeling Linkages
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 w V 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 Atlantic 35 S-55 N Pacific & Indian 40 S-30 N North Pacific >30 N Med. Sea N
Recap: GEOS-Chem Surface Ocean Model Source: Strode et al., 2007 avg mixed depth = 53 m /yr 14.1/yr sorption reduction All units Mmol 0.06 pM 0.5 pM surface mixed layer thermocline atmosphere particle sinking entrainment 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 (10 12 L/yr) N. Atlantic >55 N Atlantic 65 S-35 S Pacific & Indian 40 S-30 N N. Pacific >30 N Med N Antarctic >65 S Source: Dai & Trenberth, 2002; Sunderland & Mason, Riverine Discharges of Hg *compare: anthropogenic emissions ~ 12 Mmol/yr
4. Methylmercury (MeHg) Speciation North Pacific Ocean N Source: D. Krabbenhoft, USGS, unpublished data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