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)