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

Based upon down core variations in O/Mn ratio in sediment and in micronodul es, Mn content, organic carbon and abundance of micronodules in two box cor es 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-2 and org anic carbon contents of the region, a higher abundance of micronodules down to the deeper levels was observed in the area of low sedimentation. But, i n the upper surfaces increased enrichment of Mn was observed in core 1 loca ted in the area of higher sediment accumulation. Rapid recycling of Mn (fas ter burial-transfer to Mn reduction zone-Mn dissolution and its upward diff usion-re-precipitation) increasing upward flux of Mn(II) and associated hig her consumption of O-2 limits the width of Mn oxidation zone and appears to be responsible for enhanced enrichment of Mn in the area of high sedimenta tion. The results of the present study also suggest that though the availab ility of Mn controls the formation of micronodules, their resident time in Mn oxic zone regulates their growth and influences their morphology. (C) 19 99 Elsevier Science B.V. All rights reserved.