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dc.contributor.authorHong, H. S.zh_CN
dc.contributor.authorKester, D. R.zh_CN
dc.identifier.citationLimnology and Oceanography,31(3):512-524zh_CN
dc.description.abstractThe total concentration and redox state of iron were examined along a transect across the continental shelf off the Peruvian coast during. January 1984. Total and dissolved iron (0.4~pm filter) were measured by the Co-APDC coprecipitation method. Fe(II) was measured by a precon- centration step with S-hydroxyquinoline bonded to silica as the stationary phase, followed by elution and the ferrozine method. Up to 40 nmol kg-l of Fe(II) was detected in the bottom water at 5-10 km offshore and decreased markedly upward in the water column and with distance offshore. A good correlation between the distribution of Fe(II) and nitrite in the bottom water indicated a common source from the shelf sediments. Elevated Fe(II) concentrations near the sea surface and a diel change were probably due to photochemical reactions involving iron. Total iron levels were >300-500 nmol kg-' in the surface and the bottom water at 5-6 km offshore. About 80-90% of the iron was in the particulate form, indicating a substantial input of iron from continental dust and from the sediments on the shelf. The total iron level decreased considerably within 35 km of the coastline and the iron seemed to be trapped on the shelf. Iron is found in natural waters in both Fe(II) and Fe(III) oxidation states. The dis- tribution of these two forms of iron is gov- erned by several factors, including redox po- tential, pH, and the presence of organic material. From thermodynamic consider- ations, the concentration of reduced forms of iron in oxic natural waters will be much lower than that of the oxidized forms of iron due to the rapid oxidation of Fe(II) by Oz. Nevertheless, it has been suggested that nonequilibrium processes may enable Fe(II) species to persist at appreciable concentra- tions in natural waters even in the presence of oxygen. McMahon (1969) suggested that annual and diurnal variations of acid-sol- uble ferrous iron in lake water were a result of photochemical reactions or of metabolic activity of microorganisms. Recently, the photochemistry of iron in natural waters has been emphasized by several studies as re- viewed by Zafiriou ( 1983). Miles and Bre- zonik (198 1) showed that the oxygen con- sumption in humic-colored freshwaters involved a photochemical ferrous-ferric catalytic cycle. Waite and Morel (1984)zh_CN

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