g m−2 yr−1). 210Pbanalyses indicate a strong impact of particles on rain Hg concentrations. Particle-phaseHg (range 5-25 fmol m−3; mean 12 ± 1 fmol m−3;66% "reactive") was comparable to values over the Equatorial Pacific. The drydepositional flux is ca. 0.4 nmol m−2 yr−1,or 0.4-1.0% of the wet flux. Particle-phase Hg concentrations did not changesignificantly when African dust was present during sampling. However, the Hg/Alratios were consistent with crustal values during the dust periods. The residencetime of TGM was calculated to be 1.3-3.4 yr in this region, based on standingstock estimates. Incubation of rainwater added to surface seawater gave reductionrates [i.e., production of elemental Hg (Hg°); 1.6-4.3% d of total Hg added]comparable to additions of inorganic ionic standards, indicating that Hg+2 fromprecipitation is reduced in a similar manner in surface waters. Thus, precipitation-phaseHg is generally available for evasion to the atmosphere following depositionto the surface ocean, effectively enhancing the mobility and residence time ofHg at the Earth's surface. " />
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THE ATMOSPHERIC CYCLING AND AIR-SEA EXCHANGE OF MERCURY SPECIES IN THE SOUTH AND EQUATORIAL ATLANTIC OCEAN. (R829796)
Citation:
Lamborg, C. H., K. R. Rolfhus, W. F. Fitzgerald, AND G. Kim. THE ATMOSPHERIC CYCLING AND AIR-SEA EXCHANGE OF MERCURY SPECIES IN THE SOUTH AND EQUATORIAL ATLANTIC OCEAN. (R829796). 46(5):957-977
, (1999).Description:
Measurements of gas-, particle- and precipitation-phases of atmospheric mercury
(Hg) were made in the South and equatorial Atlantic Ocean as part of the 1996
IOC Trace Metal Baseline Study (Montevideo, Uruguay to Barbados). Total gaseous
mercury (TGM) ranged from 1.17 to 1.99 ng m−3, with a weighted
mean of 1.61 ± 0.09 ng m−3. These values compare well
with Pacific Ocean data and earlier results from the Atlantic. The open-ocean
samples recorded a distinctive inter-hemispheric gradient, which is consistent
with a long-lived trace gas emitted to a greater extent from the Northern than
from the Southern Hemisphere. Correlations with surface 222Rn measurements
indicate an influence of regional terrestrial sources on open-ocean TGM concentrations.
Total Hg in precipitation ranged from 10 to 99 pM (volume-weighted average: 17.8 ± 2.9
pM). On average, about 72% of the total Hg was "reactive" (i.e., reducible by
SnCl2). The data showed an apparent rapid nonlinear decrease in concentration
with event size ("washout curve"). The wet depositional flux was estimated at
18-36 nmol m−2 yr−1 (4−7 alt="small mu, Greek"
src="http://es.epa.gov/ncer/images/greek/mu.jpg" border=0>g m−2 yr−1),
which is slightly lower than that found in mid-continental locations of North
American (6−12 src="http://es.epa.gov/ncer/images/greek/mu.jpg" border=0>g m−2 yr−1). 210Pb
analyses indicate a strong impact of particles on rain Hg concentrations. Particle-phase
Hg (range 5-25 fmol m−3; mean 12 ± 1 fmol m−3;
66% "reactive") was comparable to values over the Equatorial Pacific. The dry
depositional flux is ca. 0.4 nmol m−2 yr−1,
or 0.4-1.0% of the wet flux. Particle-phase Hg concentrations did not change
significantly when African dust was present during sampling. However, the Hg/Al
ratios were consistent with crustal values during the dust periods. The residence
time of TGM was calculated to be 1.3-3.4 yr in this region, based on standing
stock estimates. Incubation of rainwater added to surface seawater gave reduction
rates [i.e., production of elemental Hg (Hg°); 1.6-4.3% d of total Hg added]
comparable to additions of inorganic ionic standards, indicating that Hg+2 from
precipitation is reduced in a similar manner in surface waters. Thus, precipitation-phase
Hg is generally available for evasion to the atmosphere following deposition
to the surface ocean, effectively enhancing the mobility and residence time of
Hg at the Earth's surface.