Summary of Abstract Submission

Abstract Submission No. IO50-03-0062PresentationPoster

BIOGEOCHEMICAL CYCLING OF METHANE DURING THE SEASONAL ANOXIA OVER THE EASTERN ARABIAN SEA

Gayatri Shirodkar*1, S.W.A. Naqvi1, Hema Naik 1, Anil Pratihary 1

1 C.S.I.R.-National Institute of Oceanography, Dona Paula, Goa, India

ABSTRACT :

The western continental shelf of India seasonally harbors the world┐s largest naturally formed coastal Oxygen Deficient Zone (ODZ). The suboxia/anoxia during the late south west monsoon stimulates the high production of N2O and CH4. The shelf in fact displays well- defined spatial redox zonations, with sulfide bearing waters hugging the coast. The H2S recorded over the shelf is found to be associated with methane build up (~40-100nM) in these waters. However, CH4 accumulation display a large inter-annual variability which is correlated with the water column H2S (r2= 0.62). The eastern Arabian Sea is the only eastern boundary upwelling system (EBUs) in the Indian Ocean. The CH4 concentrations associated with this EBUs is moderate as compared to other EBUs in Atlantic and Pacific Ocean. The methane build-up over the shelf is very well correlated with the intensification of anoxic events in recent times. The highest CH4 concentrations recorded off Goa during a monthly time-series observations in 2009 ranged between 40 and 57 nM which is about twice (~24nM) of that observed in 1997. In spite of intensification of reducing conditions, the methane build up seems to be moderate and the possible reason could be the combination of water column low productivity as well as low organic carbon content of sediment.