Photoreduction of manganese oxides in seawater and its geochemical and biological implications

Effect of light on birnessite catalysis of the Maillard reaction and its implication in humification

“…Samples were studied at two different light intensities, 0 and 168 µE s -1 m -2 , in an environment chamber at 25.5 ± 0.5°C. For comparison purposes, the intensity of the midday sun is approximately 2000 µE s -1 m -2 and the lower limit of the light intensity on a typical cloudy day is approximately 500 µE s -1 m -2 (Sunda et al 1983). The results after 30 d are shown in Table 2 and Fig.…”

Diagnosing oceanic nutrient deficiency

“…Dissolved Mn is frequently elevated in the surface waters of the low latitudes as a result of atmospheric inputs alongside increased solubility due to photoreduction [114][115][116]. However, concentrations in the surface SO can be very low and are associated with marked near surface depletion [69,100,116] alongside some evidence suggesting the potential for (co-)limitation by this element alongside Fe [110,112,113].…”

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

“…Collenne (1983) and McKnight et al(1988a, 1988b) present convincing evidence for a sunlight-driven diurnal cycling in Fe(II) concentration in acidic streams and lakes which involves a concomitant dissolution of solid iron oxide/hydroxide. 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.…”

“…Indeed, Anderson and Morel (1983), Finden et al(1984), Sunda et al(1983) and Sunda (1988) note that iron or manganese may limit algal productivity in some situations and speculate that in such cases, enhancement of limiting nutrient supply through reduction processes may significantly alter algal growth rate, primary productivity, and species distribution. Field evidence that iron or manganese are limiting nutrients in some situations has been provided by Brand et al(1983), Entsch et aL.…”

“…If changes in stratospheric ozone result in increased levels of UV light in the surface waters of the ocean, the rates and the quasi-steady state concentrations of iron redox cycling could change. (Waite and Morel, 1984;Zika, 1987, 1988;Sunda et aL, 1983) in surface waters leading to an increase in their availability to organisms. The reactions involved in these processes are poorly understood so it is important to consider primary productivity from a biological oceanographic perspective to determine what constraints can be placed on the importance of these processes.…”