Manganese fluxes in the benthic boundary layer1

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Abstract
Diagenetic modeling and mass‐balance calculations were applied to box‐core and sediment‐trap data from three stations at 300–400‐m depth in the Laurentian Trough to estimate downward and upward fluxes of manganese across the sediment‐water interface, fluxes across the redox boundary in the sediment, rates of dissolution and precipitation of manganese, and rates of manganese accumulation. At all stations the cycling of manganese between the oxidizing and the reducing zone of the sediment was quantitatively more important than the cycling between the sediment and the water column. The redox boundary was the site of the largest fluxes. Downward fluxes across this boundary (0.45, 1.23, and 13.9 mmol m−2 d−1) were 3–50 times the rates of sedimentation or accumulation of manganese. The production of dissolved manganese turns over the inventory of particulate manganese in the sediment surface layer in 43–207 days. A small proportion of the dissolved manganese produced (13–29%) escapes the sediment, reprecipitates in the water column and, in part, returns to the sediment. Increased rates of bioturbation increase the rate of internal manganese cycling more than they do the rate of cycling across the sediment surface.