Influence of sedimentation on enrichment of manganese and growth of ferromanganese micronodules, Bengal Fan, India

Based upon down core variations in OrMn ratio in sediment and in micronodules, Mn content, organic carbon and abundance of micronodules in two box cores from high and low sedimentation regions of the Bay of Bengal, 0–20 and 0–40 cm levels were identified as ‘‘Mn oxidation zone’’ in the western and the eastern regions of the bay. Despite similarity in bottom water O and organic carbon contents of the region, a higher abundance of micronodules down to the deeper levels 2 was observed in the area of low sedimentation. But, in the upper surfaces increased enrichment of Mn was observed in core Ž 1 located in the area of higher sediment accumulation. Rapid recycling of Mn faster burial–transfer to Mn reduction . Ž . zone–Mn dissolution and its upward diffusion–re-precipitation increasing upward flux of Mn II and associated higher consumption of O limits the width of Mn oxidation zone and appears to be responsible for enhanced enrichment of Mn in 2 the area of high sedimentation. The results of the present study also suggest that though the availability of Mn controls the formation of micronodules, their resident time in Mn oxic zone regulates their growth and influences their morphology. q 1999 Elsevier Science B.V. All rights reserved.