Sarma, V.V.S.S.

National Institute of Oceanography, Dona Paula –403 004, Goa, India, Present address: HyARC, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan, Tel: +81 52 789 3443, Fax: +81 52 789 3436, E-mail: sarma@ihas.nagoya-u.ac.jp

Existence of perennial oxygen minimum zone (OMZ) in the northern Indian Ocean

I evaluated the physical and biological processes controlling oxygen minimum zone (OMZ; 100-1000 m) in the northern Indian Ocean (Arabian Sea and Bay of Bengal) using recent JGOFS, WOCE and other available data sets and Modular Ocean Model. These results suggest that, unlike earlier studies, vertical mixing at the upper boundary of the OMZ significantly influences OMZ by supplying oxygen compared to horizontal advection in the Arabian Sea whereas it is completely opposite in case of Bay of Bengal due to strong stratification driven by fresh water discharge by rivers. The oxygen consumption rates are found to be higher in the Arabian Sea (~400 Tg/y) compared to Bay of Bengal (~100 Tg/y) which is due to faster scavanging of organic matter in the latter region by mineral particles injected by rivers. The oxygen consumption rates are found to be higher during monsoon seasons when higher sinking carbon rates are observed, in both the regions, however, formation of anoxic conditions was controlled by supply of higher amount of oxygen by physical pump during this season. This suggests that tuning of physical and biological pumps of oxygen in the northern Indian Ocean leads to maintenance of perennial OMZ in the northern Indian Ocean.