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| Abstract Submission No. | ABS-2022-07-0056 |
| Title of Abstract | Massive Methane Loss During Seasonal Hypoxia/Anoxia in the Nearshore Waters of Southeastern Arabian Sea |
| Authors | Sudheesh V*, G.V.M. Gupta, S.W.A. Naqvi |
| Organisation | Central University of Kerala |
| Address | Central University of Kerala, Kasararagod Kochi, Kerala, India Pincode: 671320 Mobile: 9747621911 E-mail: sudhikeloth13@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Repeated observations over the Kochi and Mangalore shelves of the south-eastern Arabian Sea (SEAS) from April to December 2012 revealed substantial accumulation of methane (CH4) in the nearshore waters (48.6 ± 34.4 nM) compared to the outer shelf (2.9 ± 0.7 nM). Sediment methanogenesis and estuarine discharge appear to be the major sources of CH4 in the nearshore regions during the non-upwelling period. But under oxygen-deficient upwelling conditions, substantial reduction of CH4 concentration in the nearshore anoxic region of Mangalore (14±2 nM) than the similar region of hypoxic Kochi shelf (35.5±15.4 nM) has been observed. We propose that this is mainly due to its greater loss through anaerobic oxidation and in part by the reduced sedimentary inputs by weak bioturbation over Mangalore relative to Kochi. On an annual basis, SEAS is found to be a net source of CH4 to the atmosphere; its effluxes ranged from 0.03 to 170 µmol m-2 d-1 (21.9±36.7 µmol m-2 d-1). Following a new zonal extrapolation approach, the estimated CH4 efflux from the SEAS (7-14oN; 3.2Gg Tg y-1) accounts for ~16% of its total CH4 emission from the Arabian Sea. |