Author: Himanshu  Saxena, M.S. Senior Research Fellow (Physical Research Laboratory)

Designation: 

Description:
The Bay of Bengal, north-eastern part of the Indian Ocean is a meagrely explored oceanic region, be it in the context of primary production or biological dinitrogen (N₂) fixation. It is highly dynamic due to seasonal reversal of winds and also possesses the fourth intense oxygen minimum zone (OMZ) of the world ocean which may provide a suitable niche for diazotrophs owing to low oxygen concentration. With this supposition, we estimated N₂ fixation rates using the bubble ¹⁵N tracer incubation technique in the euphotic zone and the OMZ of the coastal and the central Bay of Bengal during spring inter-monsoon. In addition, primary production was also estimated along with their environmental controls. The euphotic zone N₂ fixation rates were low, ranged from below detectable limit to 0.38 nmol N L^-1 d^-1 and contributed up to 0.8% to the primary production. The N₂ fixation rates in the OMZ were also low which ranged from below detectable limit to 0.35 nmol N L^-1 d^-1. Notably, the OMZ depth-integrated N₂ fixation rates contributed up to 90% of water column activity confirming the vitality of the OMZ N₂ fixation. Thus, active N₂ fixation in the OMZ, even at low rates, would increase the overall marine nitrogen budget estimates and expand our understanding of the overlooked non-cyanobacterial (primarily heterotrophic) diazotrophs.

Category: Scientific Program Abstract > Special Sessions > SS39 The present and future of nitrogen fixation in aquatic systems