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The dimerization of (p-hydroxyphenyl)acetlc acid by hydrogen peroxide In the presence of peroxidase has been adapted to the determination of hydrogen peroxide In seawater. The fluorometrlc method presented requires only one mixed reagent for sample analysis and produces a stable product that does not require Immediate measurement. Changes In reaction stoichiometry resulting from naturally occurring organic material have been addressed. The detection limit, defined as 3 times the standard deviation of the blank, Is 4 and 5 nM for open ocean and coastal seawater, respectively.

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.

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A series of leaching experiments designed to determine the soluble fraction of atmospheric iron in seawater was conducted. Aerosol samples collected in 1986 at four island stations (Midway, Oahu, Enewetak, and Fanning) of SEAREX (Sea-Air Exchange) and in May 1988 at station 4 (33.3øN, 139.1øW) of VERTEX (Vertical Transport and Exchange) were leached by surface seawater collected from the North Pacific and Sargasso Sea and at a pH range of 3-8. The results from these experiments indicated that for all marine aerosol samples examined, the dissolution of atmospheric iron was limited by a similar saturated concentration range. Using the operationally defined concept of a dissolved fraction that could pass through a 0.4-pro filter, the "saturated concentration" of dissolved atmospheric iron in seawater was found to be -10-17 nmol/kg. If 0.05-pro Millipore filter was used to separate the soluble fraction from the particulate fraction, the "saturated concentration" of dissolved atmospheric iron in seawater was found to be -5-8 nmol/kg. The dissolution of atmospheric iron in seawater takes place within a few minutes. If the total iron concentration was less than 2 nmol/kg (the open Pacific Ocean is in this category), -50% of the atmospheric iron dissolved in seawater. A comparison of the atmospheric dissolved iron flux into the North Pacific with the dissolved iron profile in this area suggests that more than 99% of the dissolved iron is provided by atmospheric input. Iron, like nitrogen and phosphorus, is a critical nutrient for particularly in open ocean regions. While there have been several primary productivity in the ocean. Iron is essential for organisms studies of the solubilization of metals present on aerosol particles in since it is a important element of respiratory pigments, proteins, distilled water or acidic solutions, there have been relatively few and many enzymes. There are a number of papers related to iron studies of the solubility of these metals in seawater. Crecelius chemistry in the ocean [Landing and Bruland, 1987' Hong and [1980] investigated the solubility in seawater of coal fly ash and Kester, 1986; Symes and Kester, 1985; Waite et al., 1984; Gordon aerosols collected from the Washington coastline. He found that et al. 1982; Anderson and Morel, 1982; Danielsson, 1980; Kester et less than 1% of the iron in fly ash was soluble and that 7-8% of the al., 1975], but only a few investigate atmospheric iron in the iron incoastalmarine aerosols dissolved within 1 hour. Hardy and marine environment. Crecelius [1981] investigated the seawater solubility of iron on Arimoto et al. [1985] showed that the rate at which atmospheric urban aerosols collected in Seattle, Washington, and St. Louis, iron is deposited in the ocean is similar to its rate of removal to the Missouri, as well as at a rural site, Quillayute, 5 km from the sediments in the tropical North Pacific. Murphy et al. [1984] Washington coastline. They found iron solubility in seawater suggested that iron limitation may be quite important in the...