Redox state of iron in the offshore waters of Peru1

Abstract

The 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 preconcentration 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.

von Liebig's law of the minimum and plankton ecology (1899–1991)

“…Ferric citrate added to seawater was observed to decompose under light and produce soluble ferrous Fe(II) ions. This light effect is similar to that reported by PELTZ and LYNN (1938) and more recently has been observed to occur in natural seawater (WAITE and MOREL, 1984a,b;HONG and KESTER, 1986; KUMA, NAKABAYASHI, SUZUKI, KUDO and MATSUNAGA, 1992). The experiments yielded Fe uptake by Asterionellajaponica in the ratio Fe:P = 3.6:1 in keeping with results of COOPER (1935b), i.e.…”

“…In the intense oxygen-minima of the East Equatorial Pacific and the NorthWest Indian Oceans very similar dissolved Fe maxima were observed (LANDING and BRULAND, 1987;SAAGER, DE BAAR and BURKILL, 1989). In surface waters, dissolved Fe was found to be very low at ~0.05 to 5nM in surface waters of the Atlantic, Indian and Pacific Oceans (see also SYMES and KESTER, 1985;HONG and KESTER, 1986). FITZWATER, KNAUER and MARTIN (1982) demonstrated that 14C uptake determination of the rate of primary production has to be done with similar ultraclean techniques if artefacts caused by contamination with either toxic or stimulating metals, are to be avoided.…”

Effects of solar ultraviolet radiation on biogeochemical dynamics in aquatic environments : report of a workshop, Marine Biological Laboratory, Woods Hole, Massachusetts, October 23-26, 1989

“…Sunda et al(1983) have shown that light enhances the dissolution of an amorphous manganese oxide in seawater and have suggested that this process accounts for the surface maxma in dissolved manganese observed in the oceans. Hong and Kester (1986) have found some evidence of a similar light induced generation of reduced iron in waters off Peru.…”

1,10-Phenanthroline Modulated Redox Potentials Explored for Benign Iron Speciation Analysis

“…The chemical speciation 1,2 and simultaneous determination 3 of the two iron oxidation states is increasingly needed in areas such as bio/clinical chemistry, environmental chemistry and other scientific and industrial fields. [4][5][6][7] This stimulates progress in developing analytical methods and instrumentation applied to the determination and speciation of iron. 8 Although good analytical methods of metal ion estimation like atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES) and X ray fluorescent spectrometry (XRF) detect metal ions at mg L −1 (ppm) and even lower concentrations, they cannot distinguish any difference in the metal oxidation states and as such are inappropriate for iron speciation.…”