The contrasting biogeochemistry of iron and manganese in the Pacific Ocean

Details The contrasting biogeochemistry of iron and manganese in the Pacific Ocean The contrasting biogeochemistry of iron and manganese in the Pacific Ocean

Jan 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51...29l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 51, Issue 1, pp.29-43

Physics

42

Scientific paper

Vertical and horizontal distributions of dissolved and suspended particulate Fe and Mn, and vertical fluxes of these metals (obtained with sediment traps) were determined throughout the Pacific Ocean. In general, dissolved Fe is low in surface and deep waters (0.1 to 0.7 nmol/kg), with maxima associated with the intermediate depth oxygen minimum zone (2.0 to 6.6 nmol/kg). Vertical distributions of dissolved Mn are similar to previous reports, exhibiting a surface maximum, a subsurface minimum, a Mn maximum layer coincident with the oxygen minimum zone, and lowest values in deep waters. Near-shore removal processes are more intense for dissolved Fe than for dissolved Mn. Dissolved Mn in the surface mixed layer remains elevated much farther offshore than dissolved Fe. Elevated near-surface dissolved Mn concentrations occur in the North Pacific Equatorial Current, suggesting transport from the eastern boundary. Near-surface mixed-layer dissolved Mn concentrations are higher in the North Pacific gyre reflecting enhanced northern hemisphere aeolian sources. Residence time estimates for the settling of refractory paniculate Fe and Mn from the upper water column are 62-220 days (Fe), and 105-235 days (Mn). In contrast, residence times for the scavenging of dissolved Fe and Mn are 2-13 years (Fe) and 3-74 years (Mn). Scavenging residence times for dissolved Mn based on horizontal mixing in the surface mixed layer of the northeast Pacific are 0.4 years (nearshore) to 19 years (1000 km offshore). There is no evidence for in situ Fe redox dissolution within sub-oxic waters in the eastern tropical North Pacific. Dissolved Fe appeared to be controlled by dissolution from sub-oxic sediments, with oxidative scavenging in the water column or upper sediment layers. However, in situ Mn dissolution within the oxygen minimum zone was evident.

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