Summary of Abstract Submission

Abstract Submission No. IO50-10-0017PresentationPoster


Anil Pratihary*1, S.W.A. Naqvi1, Amit Sarkar1, Gayatree Narvenkar1, Siby Kurian1, Damodar Shenoy1, Hema Naik1, Gaute Lavik2, Marcel Kuypers2

1 National Institute of Oceanography, India
2 Max Planck Institute for Marine Microbiology, Germany


The western Indian shelf is a known oceanic biogeochemical hotspot because of monsoon induced upwelling and seasonal oxygen deficiency including frequent prevalence of sulphidic conditions in near bottom water. Effect of anoxia on pathways and rates of nitrogen loss was studied along the west coast of India during September-October 2011-2013 through 15N labeled incubation experiments. Results showed high rate of 30N2 production with transient build up of 45N2O and 46N2O indicating N loss through denitrification pathway. Incubations with sulphide yielded low rates (2-98 nmol N L-1 d-1) of dissimilatory nitrate reduction to ammonium (DNRA). Very high rates of N2 production (0.39 to 5.24 μmol N L-1d-1, mean = 2.8, which was 7 times higher than the average heterotrophic denitrification rate) showed that most of the N loss was through sulphide-driven autotrophic denitrification. Occurrence of this process was also indicated by high abundance of Thiobacilus denitrificans that is known to couple denitrification with sulphide oxidation. Incubations with sulphide also showed an initial build-up of N2O and its subsequent consumption. These results suggest that sulphide-driven denitrification could be a thermodynamically and energetically favorable pathway of N loss (0.7-2.12 Tg N) over the inner shelf off western India. The stoichiometry based chemoautotrophic carbon fixation rate is computed to be 0.11-1.49 Ámol C L-1 d-1 corresponding to total production of 0.85-2.59 Tg organic carbon during September-October over the inner shelf. With the expansion of OMZs and increasing frequency of sulphidic events induced by global climate change, sulphide-driven denitrification is likely to play a more significant role in oceanic N cycle.