1. Role of Ocean Emissions in the Mercury Budget Sarah Strode, Lyatt Jaeglé Department of Atmospheric Sciences, University of Washington Noelle Eckley Selin, Rokjin Park, Daniel Jacob Noelle Eckley Selin, Rokjin Park, Daniel Jacob Department of Earth and Planetary Sciences, Harvard University

2. The ocean in the global Hg budget From Mason and Sheu, 2002 The ocean represents about a third of the total source to the atmosphere The magnitude, seasonality, and distribution of the flux are still uncertain reemits deposited mercury  role in global transport

3. Ocean-atmosphere cycling of Hg 0 Hg 0 Hg II Surface ocean Evasion (T,wind) deposition transport P(light,biology) reduction Hg 0 Hg II Marine Boundary Layer oxidation Loss Reduction proportional to radiation and net primary productivity (MODIS 2003) Reduction proportional to radiation and net primary productivity (MODIS 2003) d[Hg II ] aq /dt = deposition – Kl*[Hg II ] aq – Kr*[Hg II ] aq d[Hg II ] aq /dt = deposition – Kl*[Hg II ] aq – Kr*[Hg II ] aq d[Hg 0 ] aq /dt = Kr*[Hg II ] aq – Kw([Hg 0 ] aq – H*[Hg 0 ] atmos ) d[Hg 0 ] aq /dt = Kr*[Hg II ] aq – Kw([Hg 0 ] aq – H*[Hg 0 ] atmos ) Evasion based on kw=f(T,u 10 2 ) and H=f(T) Evasion based on kw=f(T,u 10 2 ) and H=f(T) Loss and reduction scaled together to yield total flux=2000 Mg/yr Loss and reduction scaled together to yield total flux=2000 Mg/yr MLD from NRL mixedlayer depth climatology  =7 months  =7 months (4-79 months)

4. Observed & modeled total aqueous Hg June-AugSept-Oct March-MayDec-Feb pM Observations from: Coquery & Cossa 1995, Cossa et al. 2004, Dalziel 1995, Ferrara et al. 2003, Gill & Fitgerald 1987, Kim & Fitgerald 1986, Laurier et al. 2004, Mason & Fitgerald 1993, Mason et al. 1998, Mason et al. 2001, Mason & Sullivan 1999

5. Comparison to Observations DGM (pM)Ocean Flux (ng/m 2 /h) Med. Sea N. Atl. N. Atl. Baltic Pacific JJA SON JJA MAM MAM Med. Sea N. Atl. eq. Pac Baltic eq. Pac N. Atl. JJA JJA JJA MAM DJF SON 12 8 4 0 1.5 1.0 0.5 0 Observation Model Observations from: Baeyens & Leermakers 1998, Coquery & Cossa 1995, Gardfeldt et al. 2003, Kim & Fitzgerald 1986, Laurier et al. 2003, Mason & Fitzgerald 1994, Mason et al. 1998, Wangberg et al. 2001

6. Ocean flux distribution & seasonality 0 100 200 300 kg July ocean flux Jan. ocean flux latitude Jan. July Higher flux in tropics due to high temperature and radiation Higher flux in tropics due to high temperature and radiation High flux in regions of high deposition High flux in regions of high deposition Seasonality due to temperature, npp, radiation, and mixed layer depth Seasonality due to temperature, npp, radiation, and mixed layer depth

7. Effect of Ocean Flux Ocean source: 40-50% of surface Hg0 over the southern ocean 15-35% over northern continents Seasonal variability due to seasonality of ocean source Annual Hg 0 surface concentration Contribution of Ocean Source % Monthly ocean source contribution S. Pacific Europe N. America % ng/m 3 %

8. Summary Model captures some of the spatial and temporal variability in ocean mercury concentrations and fluxes, but misses the extreme values seen in observations Model captures some of the spatial and temporal variability in ocean mercury concentrations and fluxes, but misses the extreme values seen in observations The ocean flux shows a large seasonal cycle and spatial variability due to the variability in mixed layer depth, radiation, npp, temperature, and deposition The ocean flux shows a large seasonal cycle and spatial variability due to the variability in mixed layer depth, radiation, npp, temperature, and deposition Future work: continue comparing model seasonality to observations of atmospheric concentrations at coastal sites Future work: continue comparing model seasonality to observations of atmospheric concentrations at coastal sites

9. Flux Parameters & Observations Ocean Flux (ng/m 2 /h) Med. Sea N. Atl. N. Atl. Baltic Pacific JJA SON JJA MAM MAM 12 8 4 0 Observations from: Baeyens & Leermakers 1998, Gardfeldt et al. 2003, Laurier et al. 2003 N. Atlantic flux with controlling parameters Observation Model

10. Flux and mixed layer depth Jan. ocean fluxJuly ocean flux 0 100 200 300 kg Jan. mixed layer depthJuly mixed layer depth 0 33 66 100 m