Global Terrestrial Mercury Model

Overview

The global terrestrial mercury model (GTMM) is a global 1° × 1° biogeochemical model of mercury accumula- tion and emissions that we apply to the continuous evolution of soil mercury from preindustrial to present day with a monthly time step. Figure 1 presents an overview of the model. Mercury is deposited to the land surface as either wet deposition of Hg(II) or dry deposition of Hg(II) and Hg0. Monthly deposition of Hg(II) and Hg0 are taken from the mercury simulation in the GEOS‐Chem chemical transport model [Selin et al., 2008]. GEOS‐Chem also includes a small deposition flux of Hg(p) emitted by combustion; this Hg(p) is not considered available for terrestrial cycling. In the model, dry deposition of Hg0 and Hg(II) can be fixed into the interior of leaves or remain on leaf and soil surfaces. Hg(II) on leaf and soil surfaces is subject to photoreduction, and Hg0 is subject to revolatilization. Wet deposition of Hg(II) and Hg(II) washed off of leaf and soil surfaces enters soils and can bind to reduced sulfur groups in organic material. At this point, the cycling of mercury in organic soils is controlled by the cycling of carbon and is modeled within the carbon cycling framework of the CASA biogeochemical model [Potter et al., 1993; van der Werf et al., 2003, 2006].We use the GEOS‐Chem mercury simulation as described by Selin et al. [2008] to supply monthly, spatially resolved, and speciated dry and wet mercury deposition fluxes to the GTMM.

-- Smith‐Downey, N. V, E. M. Sunderland, and D. J. Jacob (2010), Anthropogenic impacts on global storage and emissions of mercury from terrestrial soils: Insights from a new global model, J. Geophys. Res., 115, G03008, doi:10.1029/2009JG001124.

Authors and collaborators:

• Nicole Smith-Downey (U. Austin) -- Principal Investigator
• Chris Holmes (Harvard)
• Bess Corbitt (Harvard)
• Helen Amos (Harvard)

Implementation notes

GTMM has been implemented into GEOS-Chem v8-03-02 by Claire Carouge.

Validation

Text to be added

Documentation

Please see the GTMM user's manual for information about how to compile and run GEOS-Chem with GTMM.

More information in the GEOS-Chem user guide Appendix 8: http://acmg.seas.harvard.edu/geos/doc/man/

Notes

See Smith-Downey et al. 2010 for description of the simulation.

The input files provided with the code are those described by the Smith-Downey paper. The mercury deposition comes from the Selin et al. 2008 version of the atmospheric mercury simulation. Meteorology inputs are from GEOS-4. If a user wishes to run the model with the v8-03-02 version of the code (Holmes et al. 2010, Soerensen et al. 2010), then a new spin-up from the preindustrial with new input files is recommended. Contact corbitt [at] seas [dot] harvard [dot] edu for more information. (I've done a preliminary spin-up and coupled run using v8-03-02 mercury deposition inputs, but have not redone the meteorology inputs with GEOS-5 yet - eds)

At this point, running the GTMM coupled online to GEOS-Chem will result in higher TGM values than are observed due to the higher soil emissions than in the previous simulation with 2D soil (Selin et al. 2008a). This is an area of ongoing development (eds, nvd).