Geochemical cycling of silver in marine sediments along an offshore transect
Date
2008-02-08Author
Morford, Jennifer L.
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Kalnejais, Linda H.
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Helman, Peter
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Yen, Gloria
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Reinard, Melissa
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https://hdl.handle.net/1912/2350Keyword
Silver; Rhenium; Diagenesis; Continental margins; Trace metalsAbstract
Although there have been many surface water and water column silver (Ag)
analyses in the ocean, the absence of high resolution pore water and solid phase Ag
profiles has hampered our understanding of its oceanic geochemical cycling. This
manuscript presents pore water and solid phase profiles of Ag along an offshore transect
in the northeast Pacific off the coasts of Washington/Oregon states, U.S.A.. Pore water
Ag concentrations are uniformly low (< 0.3 nmol kg-1) in profiles from sediments that
have low bottom water oxygen concentrations, have shallow oxygen penetration depths
(O2,pen < 1 cm) and underlie short water columns (< 500 m water depth). The solid phase
Ag concentrations at these sites are also low (< 1 μmol kg-1). This is in contrast to
sediments from intermediate water depths (~2000 m) that have similar oxygen
penetration depths (O2,pen < 1 cm), but have elevated pore water Ag concentrations (0.7
nmol kg-1) at the sediment–water interface and higher solid phase Ag concentrations (4–
8 μmol kg-1). At sites from ~3000–4000 m water depth, where O2,pen > 1 cm, pore water
Ag concentrations reach extremely high concentrations in the top 5 cm (8–24 nmol kg-1).
High concentrations in pore waters provide evidence for a flux of Ag from ocean
sediments, but the more oxidizing nature of these sediments precludes appreciable solid
phase Ag accumulation in the top 30 cm (< 2 μmol kg-1). The accumulation of Ag in
sediments is not simply dependent on redox conditions; more oxidizing sediments do not
accumulate solid phase Ag, and neither do more reducing sediments from shallow water
depths. Only a sufficiently long water column will result in additional delivery of Ag to sediments by scavenging onto settling particles, and result in Ag accumulation in
sediments where O2,pen < 1 cm.
Although upward Ag fluxes from sediments underlying shorter water columns are
small (0.02–0.07 nmol cm-2 y-1), calculated fluxes increase for sediments underlying
longer water columns and are largest for the more oxidizing sediments (2–5 nmol cm-2 y-
1). Calculated fluxes of pore water Ag to the solid phase at these more oxidizing stations
are inconsistent with measured solid phase Ag concentrations and suggest that the pore
water profiles represent non–steady state conditions. Clearly, the early diagenesis of Ag
is a highly dynamic process and more research is required to fully understand Ag cycling
in sediments in continental margin locations.
Description
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 110 (2008): 77-88, doi:10.1016/j.marchem.2008.02.008.
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Suggested Citation
Preprint: Morford, Jennifer L., Kalnejais, Linda H., Helman, Peter, Yen, Gloria, Reinard, Melissa, "Geochemical cycling of silver in marine sediments along an offshore transect", 2008-02-08, https://hdl.handle.net/1912/2350Related items
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