The surface water N2O saturation ranged from 70.6 to 253% with
Cyt387 average of 106 ± 31% (anomaly (N2Oana) of + 6%). The N2O saturation was high in the SW region (126 ± 27%; N2Oana = + 26%) compared to NW region (81 ± 6%; N2Oana = − 19%) during SW monsoon. The highest super saturation of 253% (N2Oana = + 153%) was observed off Godavari estuary (Table 1). The super saturation of N2O in the SW region was driven by coastal upwelling. Naqvi et al. (1994) observed the overall super saturation of 125% (N2Oana = + 25%) in the coastal Bay of Bengal during dry
period (March–April, 1991) and varied from under-saturation (89%; N2Oana = − 11%) to super saturation (214%; N2Oana = + 114%) when monsoonal rivers were almost dried up and minimal discharge from the Ganges River. Under saturation of N2O was attributed to strong stratification resulted by immense river runoff (Naqvi et al., 1994) as it was evidenced from low vertical exchange coefficient (0.16 cm2 s− 1) at the top of the thermocline in the Bay of Bengal compared to that of the Arabian Sea (0.55 cm2 s− 1).
