Biogenic influence on the growth of ferromanganese micronodules in the Central Indian Ocean

Abstract

In a 20 cm core collected from the Central Indian Basin, with increasing depth, the abundance of ferromanganese micronodules decreases as their size increases, and the surface texture changes from rough to smooth. Biological debris, including radiolarian fragments, diatom tests and bacterial cells were found associated with the micronodules. Dissolution of biological debris with increasing core depth was evident. Ferromanganese oxides are present as fine imprints and coarse lumpy growths on the biological debris. They are also present in different crystal forms in vugs and cavities in the micronodules. Electron microprobe spot analyses indicate that the micronodules are particularly high in manganese and iron in the upper and lower levels of the sediment column respectively. Diagenetic effects may account for the metal enrichment. It appears that biological debris play an important role in the growth of the micronodules.