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Fig. 4 Plot of silver (pmol/kg) vs. dissolved copper (nmol/kg) in oceanic waters. Data from Martin
et al. ( 1983 ), Flegal et al. ( 1995 ), Sañudo-Wilhelmy et al. ( 2002 ), and Ranville and Flegal ( 2005 )
Other factors have been advanced to explain the spatial variation of silver vertical
concentration profi les in the North Pacifi c and the observed departures from the
linear correlation between silver and silica. Ranville and Flegal ( 2005 ) proposed
that the discrepancies observed between measurements in waters collected in
2001 in the western North Pacifi c and those previously measured in the eastern
North Pacifi c could be explained by the incorporation into intermediate waters in
the Sea of Okhotsk of surface waters enriched by atmospheric inputs of contaminant
silver aerosols. Silver concentrations in surface waters collected near the Asian
mainland during the same cruise had values as high as 12 pmol/kg, higher than any
previously reported value for the open ocean (Fig. 5 ). Concentrations then steadily
decreased eastward to levels of 1-2 pmol/kg near the central part of the North
Pacifi c Gyre (Fig. 6 ). Since this eastward decrease corresponds with the prevailing
westerly wind fl ow from the Asian mainland, it was suggested that atmospheric
transport of mineral and industrial aerosols over the North Pacifi c is responsible for
elevated silver concentrations in these surface waters.
The enrichment of silver over aluminum and the lack of correlation between the
two elements in surface waters suggested a dominance of atmospheric fl uxes of indus-
trial emissions rather than natural processes—with the qualifi cation that the biogeo-
chemical processes governing the residence times of silver and aluminum in oceanic
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