Tracing source–sink processes and productivity from trace metals (Ba, Zn, Pb, Cd) of the surface sediments off Mahanadi to Pennar, western Bay of Bengal

Abstract

In this paper, an attempt is made to understand the provenance of sediments and the role of dissolved oxygen in the preservation of metals and the productivity variations. Sixty-one surface sediment samples collected along eight transects from western Bay of Bengal off Mahanadi, Vamsadhara, Godavari, Krishna and Pennar Rivers were analyzed for spatial variations in selected metals (Ba, Zn, Pb, Cd). A change in source of sediment from north to south was very well reflected from the distribution of metals. Ba and Pb were dominant in the northern transects off Mahanadi and Vamsadhara indicating a felsic source for the sediments as Ba and Pb are more associated with rocks rich in feldspar. Conversely, lower Ba and Pb off Godavari, Krishna and Pennar indicated mafic source for the sediments as these metals are less associated with Deccan basalts. Furthermore, the preservation and distribution pattern of the redox-sensitive metals Zn and Ba was largely controlled by the oxygen minimum zone prevalent in the region at intermediate water depths. Negative biogenic Ba values and a poor correlation of Cd with Chl-a and P indicated low Ba and Cd input from plankton productivity, further enhancing the existing knowledge regarding low productivity in western Bay of Bengal.