Summary of Abstract Submission

Abstract Submission No. IO50-02-0017PresentationPoster

CONTRASTING N2O CYCLING IN THE UPWELLING ZONES OF THE EASTERN AND WESTERN ARABIAN SEA DURING THE SOUTHWEST MONSOON

Hema Naik*1, S.W. A. Naqvi1, Gayatree Narvenkar 1, Anil Pratihary 1

1 CSIR-National Institute of Oceanography, Dona Paula, Goa 403 004, India

ABSTRACT :

The Arabian Sea contains the only major western-boundary upwelling system in the world. The nutrient-rich subsurface water upwelling off the Somali, Yemeni and Omani coasts during the Southwest Monsoon (SWM) advects over 1000 km offshore, supporting high biological productivity that is in part responsible for the formation of a thick and intense mesopelagic oxygen minimum zone. Weak upwelling also occurs during the SWM in the eastern Arabian Sea along the Indian west coast. Although the water upwelling along both the eastern and western boundaries of the Arabian Sea is oxygen-depleted, difference in residence time of water over the shelf leads to very different redox regimes. To investigate the effect of this difference on nitrous oxide (N2O) cycling, N2O concentrations were measured along the coasts of India and Oman during the SWM of 2004. Surface concentrations along the Indian and Omani coasts were 58-295 nM and 10-25 nM, respectively. Maximal value recorded over the Indian shelf (~550 nM) was much higher than that measured over the Omani shelf (~36 nM). It is suggested that N2O is mostly formed through heterotrophic and/or autotrophic denitrification over the Indian shelf and through nitrification over the Omani shelf.