Sources, Fluxes, and Biogeochemical Cycling of Silver in the Oceans - Reviews of Environmental Contamination and Toxicology - page 33

Fig. 2 Vertical profi les of silver concentrations (pmol/kg) in the oceans. Data from Murozumi
( 1981 ), Martin et al. ( 1983 ), Flegal et al. ( 1995 ), Rivera-Duarte et al. ( 1999 ), Ndung'u et al. ( 2001 ),
Sañudo-Wilhelmy et al. ( 2002 ), Zhang et al. ( 2001 , 2004 ), Ranville and Flegal ( 2005 ), and Kramer
et al. ( 2011 ). Also included are previously unpublished data from our laboratory

a more effi cient transfer of silver out of surface waters in sinking particle aggregates,
and/or a relatively greater input (e.g., hydrothermal vents) of silver in deep oce-
anic waters.
In addition to silica, silver concentrations in seawater profi les also correlate with
those of copper (Fig. 4 ). The position of silver immediately under copper in the
Periodic Table attests to its role as a biogeochemical analog of copper, an essential
trace element. This similarity also accounts for some of silver's toxicity to many
marine invertebrates, whose respiratory pigment is the copper-based hemocyanin
(Burmester 2002 ). However, as with silica, silver concentrations deviate from a true
linear correlation with those of copper, especially at higher concentrations—again
attesting to dissimilarities in the biogeochemical cycles of the two elements.
Those differences are illustrated in Table 3 , which lists concentrations of silver,
silicate and copper that are present in hydrothermal plumes. Based on the sea water
concentrations of silver (0.023 nmol/kg) and copper (0.0033

mol/kg), as given in
the original compilation by Douville et al. ( 2002 ), the atomic ratio of silver to cop-
per in the plumes (3.4-8.9 × 10 −4 ) is one order of magnitude lower than it is in sea
water. Consequently, the relative excess of silver compared to copper in deep ocean
water is not due to a simple enrichment from hydrothermal inputs. But differences

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