Mn Maximum Research Articles

Relative Efficacies of Cationic and Anionic Surfactants and their Mixtures in the Suppression of Polarographic Negative Maximum of Mn(II) vis-a-vis their Influence on the Kinetics of the Electrode Reaction

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Relative Efficacies of Cationic and Anionic Surfactants and their Mixtures in the Suppression of Polarographic Negative Maximum of Mn(II) vis-a-vis their Influence on the Kinetics of the Electrode Reaction

Relative Efficacies of Cationic and Anionic Surfactants and their Mixtures in the Suppression of Polarographic Negative Maximum of Mn(II) vis-a-vis their Influence on the Kinetics of the Electrode Reaction

Pathways of manganese in an open estuarine system

The distribution of Mn was examined in the bottom sediments and water column (suspended paniculate matter) of the Laurentian Trough. Gulf of St. Lawrence. A characteristic profile of Mn with depth in the sediment consisted of a Mn-enriched surface oxidized zone, less than 20 mm thick, and a Mn-depleted subsurface reducing zone. A subsurface Mn maximum occurred within the oxidized zone. Below this maximum the concentration dropped sharply to nearly constant residual levels in the reducing zone. The accumulating estuarine sediments are deficient in Mn compared to the river input of suspended matter and are definitely not the ultimate sink for manganese. Manganese escapes from the sediment by diffusion and resuspension, forming Mn-enriched, fine-grained particles which are flushed out in the estuarine circulation. 5.0 × 10 9 g yr −1 of Mn, or 50% more than the river input of dissolved Mn. are exported to the open ocean. In spite of the efficient mobilization and export of Mn, the quantity exported is a small fraction (0.2%) of the total flux to the deep-sea sediments. This is related to the low levels of paniculate matter transported by the St. Lawrence River. The export phénomenon, however, is probably true of many coastal regions of muddy sediments and thus has interesting implications for the oceanic budget of Mn.

Manganese in the North Pacific

A quantitative and precise method for determination of dissolved Mn at the nanomole(nmol)/kg level in seawater has been developed and used to study the distribution of Mn in the northeast Pacific. Mn concentrations in the surface mixed layer decrease from 1.0 to 0.6 nmol/kg between the central gyre and the western boundary of the California Current, then increase to values from 2 to 6 nmol/kg near the coastal boundary (in contrast to the distribution of 210Pb). Particulate Mn in the surface waters accounts for only about 1% of the total. Vertical distributions of Mn are characterized by surface maxima, minima near 300 m, maxima at mid-depth coinciding with the oxygen minimum and the labile nutrient maxima, and concentrations in Pacific bottom waters of approximately 0.2 nmol/kg. The oceanic distribution of Mn appears to be dominated by external inputs superimposed upon overall scavenging which can lead to Mn maxima in (1) the surface waters due to riverine and atmospheric sources; (2) the deep ocean as a result of hydrothermal injection and/or sediment resuspension; and (3) the oxygen minimum region resulting from in-situ breakdown of organic matter, in-situ MnO 2 reduction, and/or advective-diffusive transport of dissolved Mn from anoxic slope sediments.