dc.description.abstract | The Arabian Sea, off SW India, is becoming more anoxic in recent years. Poor ventilation
affects microbial degradation of organic matter in oxygen minimum zone (≤2.85 ml l -1 O 2 , ≤0.02µM
NO 2 ) and anoxic marine zone (≤0.09 ml l -1 O 2 , ≥0.5µM NO 2 ). We posit that one of the reasons at the
microbial level could be due to a more prominent increase in sulfate-reducing activity (SRA), than
sulfur-oxidizing activity (SOA). Hence, the objective was to measure the extent to which SOA can
counter the effect of SRA. We, therefore examined these activities along with relevant environmental
variables from 2009 to 2011 off Kochi (9.55˚N–75.33˚E) and Trivandrum (8.26˚N–76.50˚E),
covering the three phases of upwelling. SRA was measured radiometrically using 35 S, and SOA by
iodometry. Off Kochi, the SOA of the water column increased 6x (194–1151 µM d -1 ) and SRA 4x
(13–54 nM d -1 ) from phase I to III. Off Trivandrum, the increase in SOA was 1.7x (339–560 µM d -1 )
and SRA 7x (24 nM d -1 -–165 nM d -1 ) contributing to the build-up of reducing/oxidizing conditions.
This increase in SOA moderates the effect of increase in SRA. Besides, the average concentrations
of dissolved oxygen and nitrite off TVM were 1.80±1.66, 1.48±1.55, 1.93±1.86 ml l -1 and 0.14±0.14,
1.69±0.67, 0.34±0.42 µM during the three phases respectively. Hence, it is suggested that, the coastal
waters examined in this study could probably be between oxygen minimum zone (OMZ) and anoxic
minimum zone (AMZ) in patches temporarily. The present paper highlights the interactions between
sulfate-reducing and sulfur-oxidizing activities, during upwelling for the first time in these waters.
These observations give an important and timely insight into the implications | |