HR: 17:45h
AN: A24A-07    [Abstracts]
TI: Global Simulation of Air-Sea Exchange of Mercury
AU: * Strode, S A
EM: sstrode@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, University of Washington Box 351640, Seattle, WA 98195 United States
AU: Jaegle, L
EM: jaegle@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, University of Washington Box 351640, Seattle, WA 98195 United States
AU: Eckley Selin, N
EM: eck@io.harvard.edu
AF: Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Pierce Hall, 29 Oxford St. Harvard University, Cambridge, MA 02138 United States
AU: Jacob, D J
EM: djj@io.harvard.edu
AF: Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Pierce Hall, 29 Oxford St. Harvard University, Cambridge, MA 02138 United States
AU: Park, R
EM: rjp@io.harvard.edu
AF: Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Pierce Hall, 29 Oxford St. Harvard University, Cambridge, MA 02138 United States
AU: Yantosca, R M
EM: bmy@io.harvard.edu
AF: Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Pierce Hall, 29 Oxford St. Harvard University, Cambridge, MA 02138 United States
AB: We present results from a new global atmospheric mercury model coupled with a slab mixed layer ocean. The slab ocean model describes conversion of mercury between elemental Hg⁰_aq, divalent Hg^II_aq, and non-reactive Hg^nr_aq forms. In particular, we assume that aqueous reduction of Hg^II_aq to Hg^O_aq is a photochemical/biological process proportional to local net primary productivity and radiation. The model includes sources from atmospheric deposition (for Hg^II_aq), upwelling (all species), and diffusion from the thermocline (all species), and sinks through gas exchange with the atmosphere (Hg^O_aq) and loss to the deep ocean through changes in mixed layer depth (all species) and particle sinking (Hg^nr_aq). Similar to observations, model aqueous species of mercury show larger concentrations in regions of high deposition: the western North Atlantic and western North Pacific, located downwind of anthropogenic sources in North America and Asia, as well as in the Tropics because of large precipitation fields. Aqueous concentrations are also high in regions of upwelling. The distribution of Hg^O_aq shows seasonal variability, with larger concentrations in the summer hemisphere following the pattern of biological productivity. If we assume a global ocean flux of 10 Mmol/year (compared to 11 Mmol/year for direct anthropogenic sources and 10 Mmol/year for land sources) in the mid-range of published estimates, we obtain global mean modeled aqueous concentrations of 0.05 pM Hg^O_aq, 0.63 pM reactive mercury (Hg^O_aq + Hg^II_aq), and 1.02 pM total mercury (Hg^O_aq + Hg^II_aq+ Hg^nr_aq). The model underestimates observed Hg^O_aq concentrations by 60% on average and displays a smaller variability than the observations for all species. The model also underestimates observed total atmospheric concentrations over the ocean by 10%. We therefore test the sensitivity of the model to different assumptions about the magnitude of the ocean source. Increasing the ocean source by 50%, to 15 Mmol/year improves the agreement with atmospheric observations over the Atlantic but leads to overestimates of the atmospheric concentration in coastal areas, where the influence of the ocean source is strongest. Increasing the flux reduces the overall bias in the modeled Hg^O_aq but does not improve the variability. The ocean flux displays spatial and seasonal variations, with the strongest flux occurring during periods of warm temperature and strong biological productivity and deposition. Oceanic emissions are found to contribute approximately 45% (50%) of atmospheric mercury in the Southern hemisphere, and 25% (35%) in the Northern hemisphere, for the 10 Mmol/year (15 Mmol/year) case.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0368 Troposphere: constituent transport and chemistry
DE: 0461 Metals
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005