Mercury & GCAP
Nicole Smith-Downey, Noelle Eckley Selin, Chris Holmes, Bess Sturges, Daniel JacobHarvard University
Elsie SunderlandUS EPA
Sarah Strode, Lyatt JaegleUniversity of Washington
Why Hg?Phytoplankton Zooplankton Planktivorous fish Piscivorous fish
Bf ~ 104 Bf ~ 105 Bf ~ 106 Bf = 106–107
Reduction in intelligence, reduced reproductive success, brain, liver and kidney damage
Biomagnification of MeHg in the food web impacts global human and animal health
Wet & DryDeposition 2600
ATMOSPHERE5000
(3x pre-industrial)
SURFACE SOILS1,000,000 OCEAN
289,000
Wet & DryDeposition1900
Oceanic Evasion
1500
Net burial200
Land emissions1600
Quantities in Mg/year (106 g, or metric tonnes)Uncertainty ranges in parenthesesAdapted from Mason & Sheu, 2002
AnthropogenicEmissions 2400
Extraction from deep reservoirs2400
Rivers200
(1800-3600) (700-3500)(1680-3120)
(1680-3120)
(1300-2600)(700-3500)
The Mercury Cycle
Hg in GEOS-Chem (current simulation)• Coupled land-atmosphere-ocean (pre-industrial
and present)• OH, O3 oxidation, reduction; sea-salt uptake of
Hg(II)• Wet & dry deposition adjusted to match MDN
observations• 2nd generation ‘under construction’
– Halogens as possible oxidant (Holmes)– New mechanistic terrestrial Hg model linking the lifetime
of Hg in the environment to carbon pools (Smith-Downey)
– New oceanic Hg model including deeper ocean layers (Sunderland)
IPCC Emissions Scenarios for SO2
Emissions Scenarios
Atmospheric chemistry & dynamics
Wet deposition of Hg over US Selin
Possible changes• Patterns in precipitation• Transport• Clouds (Hg(II) -> Hg0)• Wind speed & sea salt• T dependence of Rxns• Feedbacks from other
changes in chemistry
Plan of Action• Changes in dynamics and their
influence on Hg deposition can be analyzed by the current model
• Changes in chemistry (OH, O3) may influence Hg, but uncertainties in those effects are large
Ocean uptake and evasion
Strode 2006
Possible Changes• Hg solubility (T)• Wind speed• Mixed layer depth• NPP
- (Hg(II) -> Hg0)- particulates
• Memory of past emissions
Plan of Action
• Architecture of current model will lead to rapid equilibration with changes in T and deposition– Can be used to examine first order
effects of T, wind speed and deposition
• Deeper ocean model will greatly increase our ability to predict future ocean response to change– Sunderland
Sea Ice - Halogens - and MDE’s
Sea ice extent
Plan of Action• Current standard model does not
include halogens– Holmes
• Possible effects are large, but uncertainties in the interaction between Br, sea-ice and Hg will limit our predictive capabilities
Hg in the terrestrial biosphere
Hg0Hg(II)oxidation
reduction
Binding to organic ligands
litterfallthroughfall(wet)
Hg0
Hg(II)
Hg(II)aq
Biomass Burning
•Changes in fire frequency and intensity expected•Net loss of stored Hg from soils - especially in Arctic•Weidenmeier et al. (in press) estimate domestic BB emissions are nearly equal to primary emissions from coal combustion
Turetsky et al 2006Gillet et al 2004
Soil Respiration• Soil respiration is temperature and moisture
dependent• Decomposition of organic soils will release
stored Hg to the atmosphere– Kirshbaum 1995 suggests 10% C loss in areas
with a MAT = 5C• Because the pool of soil Hg is large, even
small changes in the lifetime will have a significant impact on land emissions
Plan of Action• Architecture of current
model will lead to rapid equilibration with changes in T and deposition
• New land model will allow us to account for new emissions from respiration and biomass burning– Smith-Downey
Spracklen - Harvard
Predicted Biomass Burning
Emissions
Climate
Chemistry
?
Why Hg?Phytoplankton Zooplankton Planktivorous fish Piscivorous fish
Bf ~ 104 Bf ~ 105 Bf ~ 106 Bf = 106–107
MeHg loading of birds and mammals has increased over time
Hg in Polar Bear Hair Hg in Bird Feathers
Dietz 2006 Thompson 1992
Sea Ice - Halogens - and MDE’s
Depends on addition of Halogen chemistry and some link to sea ice/snow
The Mercury Land ModelHg(II) dry Hg0
dry
atm
osph
ere
Veg
etat
ion/
Soi
l sur
face
Soi
ls
Hg(II) wet
Hg(II) dry Hg0 dry
Hg(II) orgHg(II) aq
Hg leaf
(1) (2) (3)
(4)(5) (6)
(8) (9)
(10)(11)
(7)
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