Manganese mobilization from the Western
Continental margin of India

D. N. Yadav

Physical Research Laboratory, Ahmedabad 380 009, India

The Western Continental margin of India (WCMI) exhibits distinct features with respect to vertical distribution of manganese in sediments. There is no signiricant manganese downcore variation in upper slope sediments whereas high concentration (by an order of magnitude relative to bottom sections) has been observed in top sediment cores for the lower slope region. Also, in the upper slope sediments, average manganese concentration is low by a factor of three compared to that (~ 1000 ppm) transported by the Narbada/Tapti river suspended particles. The low manganese concentration is attributed to its reductive mobilization. Typical value of manganese flux being .mobilized into overlying seawater from reducing upper slope sediments coverin an area of 5^oLat x 3^oLong is calculated to be 3 x 10¹⁰g/y, which is nearly 10% of dissolved manganese supply to the ocean by world rivers. Although calculated flux of manganese mobilized from upper slope sediments is not the highest among the values from other margin regions, yet this shows a potential source for dissolved manganese in seawater. Interestingly, the calculated carbon oxidation flux (based on manganese reduction rate) in the upper slope sediments is found to be less than 1% of primary productivity and, thus it provides a limiting value of organic matter combustion. Contrary to upper slope sediments, there is no signiricant supply of soluble manganese to overlying seawater, which is expected due to prevailing oxidizing conditions at the sedimentwater interface in the lower slope region.