SUPPORTING INFORMATION
A New Global Simulation of Mercury Air-Sea Exchange for
Evaluating Impacts on Marine Boundary Layer
Concentrations
Anne L.
Soerensen*,†
†
, Elsie M. Sunderland‡‡, Christopher D.
‡, Daniel J.
Holmes
Jacob
†§, Sarah A. Strode|| , and Robert P.
‡†, Henrik Skov
Mason
, Robert
Yantosca, J. Christensen
National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399,
DK-4000 Roskilde, Denmark
‡Harvard University, School of Engineering and Applied Sciences and Department
of Earth and Planetary Sciences, Cambridge MA, 02138, USA
§Department of Atmospheric Sciences, University of Washington, Seattle, WA,
98195 USA
||University of Connecticut, Department of Marine Sciences, 1080 Shennecossett
Road, Groton, CT, 0634, USA Contents
Page(s)
0 Data sources for observations shown in Figures 2 and 4. 1 Section I Supplemental
Results 3-5 Section II Model Updates and Formulation 6-11 References 12-13
Figure S1 Modeled seasonal surface water Hg saturation values for 2008. 3 Figure
S2 Seasonal variability in modeled oceanic evasion for 2008. 4 Figure S3
Comparison of monthly modeled and observed seawater total inorganic Hg. 5
0Figure S4 Comparison of modeled and observed seawater Hg0. 5 Figure S5 Modeled
contribution of oceanic Hg0 emissions to marine boundary Hg concentrations. 6
Figure S6 Conceptual diagram of model resolution, subsurface ocean
7
compartments and specified intermediate seawater Hg concentrations.
Table S1 Model differential equations 8 Table S2 Particle associated mercury reservoirs
and fluxes. 8 Table S3 Redox reactions. 11 Table S4 Gas-exchange parameterization. 12
1
Data sources for observations shown in Figures 2 and 4 in the main text:
for Figure 2 “Modeling results for 2008 atmospheric deposition to the global
Data sources
oceans, surface ocean fluxes, and aqueous Hg concentrations” are as follows: Atlantic (1-4);
0Pacific
(5-8); Arctic (9, 10); Mediterranean (11). We omitted outliers in Hg observations
from two cruises in the Atlantic Ocean in the 1990s due to an apparent contamination
problem (2, 3).
0Data
sources for Figure 4 “Modeled seasonal mean marine boundary layer Hg
concentrations and relative contributions of oceanic emissions” are as follows for cruise
observations: (12-18).
2
Section I: Supplemental Results
0Figure
S1. Modeled seasonal surface water Hg0 saturation values for 2008. The degree of
saturation indicates the direction of the flux across the air-sea interface. Less than 100%
indicates net deposition and greater than 100% indicates net evasion of Hg.
3
0Figure
4
S2. Seasonal variability in modeled oceanic Hg evasion for 2008.
Figure S3. Comparison of monthly modeled (2008) and observed (various years) total
inorganic Hg concentrations. Data sources are as follows: Pacific (5-7, 19-21); Atlantic
Ocean (1-3, 21); Arctic Ocean (9).
Figure S4. Comparison of monthly modeled (2008) and observed (various years) seawater
Hgconcentrations. Pacific Ocean: (5, 8, 19, 22); Atlantic Ocean (2, 11); Arctic Ocean: (9).
5
0
0
emissions to marine boundary Hg
Figure S5. Modeled contribution of
oceanic Hg
concentrations.
6
0
Section II: Model Updates and Formulation
Figure S6. Conceptual diagram of model resolution, subsurface ocean compartments and
specified intermediate seawater Hg concentrations.
7
Mup Hg0± Ment Hg±0 Moa kox M Hg0 + kr
/dt Change in HgHg(II)II mass over
time (dt)
F
red
M
HgII
M Hg
II
0
-1
dep
ent
Mup
(kg) Mass of Hgoa0
M (kg) Flux of HgsinkII
(kg) Reservoir of HgHg(0)0
o
(kg) Reservoir of HgHg(II)II
x
(s-1) Hg0 oxidation rate kox1 + kox2
r (s-1)
IIReduction rate of reducible pool of Hg kred1 + kbio
fraction in the dissolved phase 1/(1 + KD
(unitless) Hg
(unitless) Reducible fraction of the filtered Hg
w
(kg)Hg(p)
HgII mass in the particulate phase
( OC Hg ( II )
II
-1 (L kg
) Concentration of suspended particles 10
A
(m2
a
-2)
Standing stock of organic carbon in mixed layer
t
o
t
dMMdep+ Mup HgII± Ment HgIIMsin k+ koxMHgkrF
) Model time step M(kg) Deposition of Hg to the ocean surface M (kg) Mass of
/
mercury species introduced or removed due to deep
convection or shoaling of the
dt Change in HgTable S1. Model
mixed-layer
differential equations dMHg(0)0 mass over
time (dt)
(kg) Wind-driven mass transfer of mercury species due to Ekman
pumping
dt
(s
ev
ad
ed
fr
o
m
th
e
oc
ea
n
to
th
e
at
m
os
ph
er
e
M
lo
st
fr
o
m
m
ix
ed
la
ye
r
wi
th
si
nk
in
g
pa
rti
cl
es
M
in
th
e
su
rf
ac
e
m
ix
ed
la
ye
r
M
in
th
e
su
rf
ac
e
m
ix
ed
la
ye
r
k
k
FII
S
P
M
)
red
II
po
ol
0.
40
(3
,
23
,
24
)
C:
C
hl
a
(u
ni
tle
ss
)
C
ar
bo
n
to
ch
lo
rp
hy
ll
a
ra
ti
o
80
:1
(2
6)
w
et
wt
(u
ni
tle
ss
)
C
on
ve
rsi
on
fo
r
w
et
w
ei
gh
ts
of
pl
an
kt
on
ic
bi
o
m
as
s
10
m
g
w
et
w
ei
gh
t:
m
g
ca
rb
on
N
P
P
(
m
g
C
m2
d1)
N
et
pr
i
m
ar
y
pr
od
uc
ti
vi
ty
20
03
M
O
D
IS
sa
tel
lit
e
da
ta
(2
7)
n
(u
ni
tle
ss
)
E
xp
on
en
t
de
sc
ri
bi
ng
re
lat
io
ns
hi
p
-0
.7
4
(2
8)
P
8
to organic carbon ratio in the mixed layer (1 F
M
) Hg ( II ) • A )
M 6OCtot
tot
(1
D
• wetwt •
A
3
-1
Chl
w
(mg m
Table S2. Particle associated mercury reservoirs and fluxes. K) Seawater partition coefficient for Hg 5.5±0.5 (3, 5) SPM (k
M
layer depth WOCE data assimilation (25)
tot
) Water surface area OC
•C:
Chl
Chltot (mg m-2) Integrated water column pigment
See text for derivation
content
2
1
Jorg
C
1.7
7
(mg C
m
n
) Organic carbon flux out of the mixed
d layer
0.1NPP
MLD
Hg:C (unitless) HgHg ( P )/(10
between declines in organic carbon flux
due to mineralization in the water column
with depth
MHg(P) (kg) Mass of Hg(II) sorbed to particles
JorgC • Hg : C •
A
P
Msin (kg) Mass of Hg lost from the mixed layer due to
k
particle sinking
( dt )
w
Method used for estimating suspended particulate matter concentrations No global data
sets on SPM concentrations in the ocean mixed layer are available. We therefore estimate SPM
concentrations in the surface mixed layer based on the standing biomass in the water column
derived from MODIS satellite chlorophyll a (Chl a, mg m-3) concentrations
(http://oceancolor.gsfc.nasa.gov/ftp.html) for the year 2003. We calculate the water column
integrated pigment content within the euphotic layer (Chl, mg mtot-2 1.0 mg m) based on the
statistical fits for subsurface algal productivity in the ocean developed by Morel and Berthon
(29) and updated by Uitz et al. (30).
These equations are as follows: 1. STRATIFIED
WATERS For stratified waters in low and mid latitude stations, where Chlsat-3
= 36.1 Chltota 0.357
1.0 mg msat
(1) Chl
(2) Chl
(3) Chl
= 37.7 Chltota
0.615
= 42.1 Chltotsat 0.538
eu
and z are calculated iteratively in the model to determine whether waters are
stratified or well mixed and the appropriate equations for Chl is derived as a
function of Chl. zby Morel and Maritorena (31):
tot -0.839
tot -0.547
eu
Chl
<102 m and Chleu
> 13.65 mg m-2
-2 < 13.65 mg m
For stratified waters in low and mid latitude stations, where Chl
eu
-3
z/MLD >1 then the waters are consider
2. WELL-MIXED WATERS For
well-mixed waters at high latitudes:
Waters are defined as well-mixed if z/MLD <1 Conversely, if
is the euphotic depth and is defined as the depth where the PAR et al. (25) from the National Oceanograp
irradiance is 1% of its value at the surface.
Experiment (WOCE) database, and the A
MLD (m) is the mixed layer depth derived from de Boyer Montegut http://www.loceanipsl.upmc.fr/~cdblod/m
tot
eu
tot
tot
eu
(4) zeu = 912 Chl
when 10 m < z
(5) zeu = 426.3 Chl
whe
n
102
m<
z
9
tot
<180 m and
Chltot
-2
We calculate the standing stock of organic carbon (OCtot, mg m) from the integrated water column pigment c
C:Chl a ratio of 80:1 based on Wetzel et al. (26). Thi
processes in the ocean where the C:Chla ratios are kno
limitation, depth, and phytoplankton growth rates amo
= Chltot • C : Chla
(6) OCtot
w
(7) SPM = 103(OCtot
We approximate the concentration of suspended particles in each
model grid cell from wet weights of planktonic biomass that are
derived by assuming that organic carbon is 50% of the dry weight
and the dry weight is 20% of the weight for phytoplankton, resulting
in an overall conversion factor of 10 mg wet weight: mg carbon (33).
This results in an overall conversion factor of 10 mg wet weight: mg
carbon.
• wetwt • A)/ MLD
Although the majority of particles in open ocean environments are
living and dead planktonic biomass, we allow for up to an additional
10% increase in SPM to account for allochtonous abiotic particles
such as mineral dust (34).
10
•RADµ
Table S3. Redox reactions. ) Photo-oxidation rate constant 6.6 10
(24) When RAD>
k(sox1 -1
-6min: 5.6x10 s-1-4-1 s (35) max: 9.7x10 (24) kox2-1 (s-7) Dark oxidation rate
constant 1.0x10 (35, 36) k(sred1 -16) Photolytic reduction rate constant 1.7
10•RADµ (24) When RAD>0
-7min: <1.0x10 s-4-1 (24, 35) max: 8.7x10 s (s (24) kbio-16) Biotic reduction rate constant 4.5 10-7-1 s•
1
NPP (24) min: 3.5x10-5-1 max: 8.3x10 s (37)
MLD
RADµ (W -2 ) Average shortwave radiation
RAD
m
intensity in the mixed layer
0
RA (W -2 ) Total local shortwave radiation
• RAD[ex1 ex 2]
MLD
1
x
2x1
D m
penetration in the mixed layer
6
0
-2RAD
(W m) Total shortwave radiation intensity GEOS-5 meteorology x(m)1
Surface depth 0 m x2 -1) Extinction coefficient for radiation (m) Bottom depth
MLD (mwater+ ChlCChl+ DOCC water-1 (m) Extinction coefficient for water 450 nm
(vis) = 0.0145 Chla-1 (m) Extinction coefficient for pigments 450 nm (vis) = 31
CChla (mg L-1) Average concentration of Chl a in mixed layer (Chltot• Aw)/ MLD
DOC
(mg L-1) Extinction coefficient for dissolved organic
carbon (DOC)
CDOC (mg L-1) Concentration of DOC in water column
DOC
av
g
450 nm (vis) = 0.654
1.5 • (
NPPi
/
)
NPPglobalavg (38)
-1
d
PPi (gC m-2
) NPP
N in model grid cell 2003 MODIS satellite data (27) NPP Global average NPP global
NPP/ocean surface area
11
12
Table S4. Gas exchange parameterization. M (kg) Air-sea
F • Aw ) dt /
v
exchange of Hgoa0-1 for each model time step (dt, s) (1 0
3600
0
) Hg
air-sea exchange flux Fv
= ( Ca
Fv
0
Kw Cw
(ng
m
w-3
(ng
0
ma-2(ng m-3
hr-1
/ H ( T)) C) Concentration of Hg in seawater See differential equations C)
Concentration of Hg in air GEOS-Chem atmospheric simulation
H'(T) Temperature dependent dimensionless Henry’s
ln H = ( 2403.3T + 6.92)
law constant
(39)
0.5
1
Kw (m ) Water-side mass transfer coefficient for
A u10 2( Sc /
)
(40)
hr
steady winds
ScCO2
A (unitless) Constant based on the Weibull distribution of
0.25 (41)
wind speeds over oceans
u1 -1 (m s) Wind speed normalized to 10 m above sea
GEOS-5 data
0 surface
2
ScCO Schmidt number for CO
2 0.11 T 6.16 T + 644.7 (42) T (ºC)Water temperature GEOS-5
number for Hg(0) / D
- ) Kinematic viscosity N/ = 0.017e( 0.025 T )
2 (cm
1
s
(42) (cP) Viscosity of water See text
(w Mw 1 /
2)
(g molw-1
(cmB3 mol-1) Molal volume of mercury at its normal
boiling temperature
w Solvent association factor introduced to define the
effective molecular weight of the solvent with respect to
the diffusion process
(8) log() =
1301 (998.333 + 8.1855( T 20) + 0.00585( T 20)2)
3.30233
T VB 0.6 M12.74 ) Molecular weight of
GEOS-5 data V
-3 (mg cm2-1 s) Diffusivity (Wilke-Chang (43)
method) ) Seawater density D (cm7.4 108
Aqueous Viscosity Loux (45) prov
viscosity as a function of aqueous tem
For water temperatures 20-100° C:
Where 20
/ 20) = 1.3272(20 T ) 0.001053( T 20) T
+1052
9) log(T
(
=
aqueous
viscosity
at 20ºC.
12
References Cited: (1) Mason, R.; Sullivan, K. A., The distribution and speciaiton of mercury
in the South
and equatorial Atlantic. Deep-Sea Research II 1999, 46, 937-956. (2) Mason, R.;
Lawson, N.; Sheu, G.-R., Mercury in the Atlantic Ocean: factors
controlling air-sea exchange of mercury and its distribution in upper waters. Deep-Sea
Research II 2001, 48, 2829-2853.
(3) Mason, R.; Rolfhus, K.; Fitzgerald, W., Mercury in the North Atlantic. Marine
Chemistry 1998, 61, 37-53.
(4) Lamborg, C. H.; Hammerschmidt, C. R.; Saito, M.; Goepfert, T.; Lam, P. J., Mercury
methylation in the Gyre and Benguela Upwelling Regions of the tropical south Atlantic Ocean. In
9th International Conference on Mercury as a Global Pollutant, Guiyang, China, June 7-12,
2009.
(5) Mason, R. P.; Fitzgerald, W., The distribution and cycling of mercury in the equatorial
Pacific Ocean. Deep-Sea Research Part 1: Oceanographic Research Papers 1993, 40, (9),
1897-1924.
(6) Sunderland, E. M.; Krabbenhoft, D. P.; Moreau, J. W.; Strode, S. A.; Landing, W. M., Mercury
sources, distribution, and bioavailability in the North Pacific Ocean: Insights from data and
models. Global Biogeochemical Cycles 2009, 23, 14.
(7) Laurier, F.; Mason, R.; Gill, G.; Whalin, L., Mercury distribution in the North Pacific Ocean 20 years of observations. Marine Chemistry 2004, 90, (1-4), 3-19.
(8) Kim, J.; Fitzgerald, W., Sea-Air partitioning of mercury in the equatorial Pacific Ocean.
Science 1986, 231, (4742), 1131-1133.
(9) Kirk, J. L.; St. Louis, V.; Hintelmann, H.; Lehnherr, I.; Else, B.; Poissant, L., Methylated
mercury species in marine waters of the Canadian High and Sub Arctic. Environmental Science
and Technology 2008, 42, (22), 8367-8373.
(10) Andersson, M. E.; Sommar, J.; Gardfeldt, K.; Lindqvist, O., Enhanced concentrations of
dissolved gaseous mercury in the surface waters of the Arctic Ocean. Marine Chemistry 2008,
110, (3-4), 190-194.
(11) Gardfeldt, K.; Sommar, J.; Ferrara, R.; Ceccarini, C.; Lanzillotta, E.; Munthe, J.;
Wangberg, I.; Lindqvist, O.; Pirrone, N.; Sprovieri, F.; Pesenti, E.; Stromberg, D., Evasion of
mercury from coastal and open waters of the Atlantic Ocean and the Mediterranean Sea.
Atmospheric Environment 2003, Supplement No. 1, S73-S84.
(12) Soerensen, A. L.; Skov, H.; Jacob, D. J.; Soerrensen, B. T.; Johnson, M. S., Global
concentrations of gaseous elemental mercury and reactive gaseous mercury in the marine
boundatry layer. Environmental Science & Technology 2010, submitted.
(13) Temme, C.; Slemr, F.; Ebinghaus, R.; Einax, J., Distribution of mercury over the Atlantic
Ocean in 1996 and 1999-2001. Atmospheric Environment 2003, 37, 18891897.
(14) Laurier, F.; Mason, R., Mercury concentration and speciation in the coastal and open ocean
boundary layer. Journal of Geophysical Research 2007, 112, D06302.
(15) Laurier, F.; Mason, R.; Whalin, L.; Kato, S., Reactive gaseous mercury formation in the
North Pacific Ocean's marine boundary layer: a potential role of halogen chemistry. Journal of
Geophysical Research 2003, 108, (D17), 4529.
(16) Lamborg, C. H.; Rolfhus, K. R.; Fitzgerald, W. F.; Kim, G., The atmospheric cycling and
air-sea exchange of mercury species in the South and equatorial Atlantic Ocean. Deep-Sea
Reasearch II 1999, 46, 957-977.
(17) Fitzgerald, W. F., Cycling of mercury between the atmosphere and oceans. In The Role of
Air-Sea Exchange in Geochemical Cycling, NATO Advanced Science Institute Series,
Buat-Manard, P., Ed. Reidel: Netherlands, 1986; pp 363-408.
13
(18) Fitzgerald, W. F.; Gill, G. A.; Kim, J. P., An Equatorial Pacific source of atmospheric
mercury. Science 1984, 224, (4649), 597-599.
(19) Mason, R. P.; Fitzgerald, W., Alkylmercury species in the equatorial Pacific. Nature 1990,
347, 457-459.
(20) Gill, G.; Bruland, K., Mercury in the northeast Pacific Ocean. EOS Trans. Amer.
Geophys. Union 1987, 68, 1763.
(21) Gill, G.; Fitzgerald, W. F., Vertical mercury distributions in the oceans. Geochimica
Cosmochimica Acta 1988, 52, 1719-1728.
(22) Kim, J.; Fitzgerald, W., Gaseous mercury profiles in the tropical Pacific Ocean.
Geophysical Research Letters 1988, 15, 40-43.
(23) Guentzel, J. L.; Powell, R. T.; Landing, W. M.; Mason, R. P., Mercury associated with
colloidal material in an estuarine and open-ocean environment. Marine Chemistry 1996, 55,
177-188.
(24) Whalin, L.; Kim, E.; Mason, R., Factors influencing the oxidation, reduction,
methylation and demethylation of mercury species in coastal waters. Marine Chemistry
2007, 107, 278-294.
(25) Montegut, C. D.; Madec, G.; Fischer, A. S.; Lazar, A.; Iudicone, D., Mixed layer depth
over the global ocean: An examination of profile data and a profile-based climatology.
Journal of Geophysical Research-Oceans 2004, 109, (C12), 20.
(26) Wetzel, P.; Maier-Reimer, E.; Botzet, M.; Jungclaus, J.; Keenlyside, N.; Latif, M., Effects
of ocean biology on the penetrative radiation in a coupled climate model. Journal of Climate
2006, 19, (16), 3973-3987.
(27) Behrenfeld, M. J.; Falkowski, P. G., Photosynthetic rates derived from satellite-based
chlorophyll concentration. Limnology and Oceanography 1997, 42, (1), 1-20.
(28) Antia, A.; Koeve, W.; Fischer, G.; Blanz, T.; Schulz-Bull, D.; Scholten, J.; Neuer, S.;
Kremling, K.; Kuss, J.; Peinert, R.; Hebbeln, D.; Bathmann, U.; Conte, M.; Fehner, U.;
Zeitzschel, B., Basin-wide particulate organic carbon flux in the Atlantic Ocean: Regional export
patterns and potential for CO2 sequestration. Global Biogeochemical Cycles 2001, 15, (4),
845-862.
(29) Morel, A.; Berthon, J. F., Surface pigments, algal biomass profiles, and potential
production of the euphotic layer - relationships reinvestigated in view of remotesensing
applications. Limnology and Oceanography 1989, 34, (8), 1545-1562.
(30) Uitz, J.; Claustre, H.; Morel, A.; Hooker, S. B., Vertical distribution of phytoplankton
communities in open ocean: An assessment based on surface chlorophyll. Journal of Geophysical
Research-Oceans 2006, 111, (C8), 23.
(31) Morel, A.; Maritorena, S., Bio-optical properties of oceanic waters: A reappraisal.
Journal of Geophysical Research-Oceans 2001, 106, (C4), 7163-7180.
(32) Westberry, T.; Behrenfeld, M.; Siegel, D.; Boss, E., Carbon-based primary
productivity modeling with vertically resolved photoacclimation. Global
Biogeochemical Cycles 2008, 22, GB2024.
(33) O'Reilly, J.; Evans-Zetlin, C.; Busch, D., Primary Production. In Georges Bank, Backus, R.
H.; Bourne, D. W., Eds. MIT Press: Cambridge, MA, 1987; pp 220-233.
(34) Millero, F. J., Chemical Oceanography, 3rd ed. CRC Press: Boca Raton, FL USA, 2006;
p 496.
(35) Lalonde, J. D.; Amyot, M.; Orvoine, J.; Morel, F. M. M.; Auclair, J. C.; Ariya, P. A.,
Photoinduced oxidation of Hg-0 (aq) in the waters from the St. Lawrence estuary. Environmental
Science & Technology 2004, 38, (2), 508-514.
(36) Lalonde, J.; Amyot, M.; Kraepiel, A.; Morel, F., Photooxidation of Hg(0) in artificial and
natural waters. Environmental Science and Technology 2001, 35, 1367-1372.
14
(37) Amyot, M.; Gill, G. A.; Morel, F. M. M., Production and loss of dissolved gaseous
mercury in coastal seawater. Environmental Science & Technology 1997, 31, (12),
3606-3611.
(38) Chester, R., Marine Geochemistry, 2nd Ed. Blackwell Science Ltd.: Berlin, Germany, 2003;
p 506.
(39) Andersson, M. E.; Gardfeldt, K.; Wangberg, I.; Stromberg, D., Determination of Henry's
law constant for elemental mercury. Chemosphere 2008, 73, (4), 587-592.
(40) Wanninkhof, R., Relationship between wind-speed and gas-exchange over the ocean.
Journal of Geophysical Research-Oceans 1992, 97, (C5), 7373-7382.
(41) Nightingale, P.; Malin, G.; Law, C.; AJ, W.; Liss, P.; Liddicoat, M.; Boutin, J.;
Upstill-Goddard, R., In situ evaluation of air-sea gas exchange parameterizations using novel
conservative and volatile tracers. Global Biogeochemical Cycles 2000, 14, (1), 373-387.
(42) Poissant, L.; Amyot, M.; Pilote, M.; Lean, D., Mercury water-air exchange over the upper
St. Lawrence River and Lake Ontario. Environmental Science and Technology 2000, 2000,
(34), 3069-3078.
(43) Wilke, C. R.; Chang, P., Correlation of diffusion coefficients in dilute solutions. Aiche
Journal 1955, 1, (2), 264-270.
(44) Hayduk, W.; Laudie, H., Prediction of diffusion-coefficients for nonelectrolytes in dilute
aqueous solutions. Aiche Journal 1974, 20, (3), 611-615.
(45) Loux, N. T. In Monitoring cyclical air/water elemental mercury exchange, 2001; Royal
Soc Chemistry: 2001; pp 43-48.
15