Intensified oxygen minimum zone on the western shelf of Bay of Bengal during summer monsoon: influence of river discharge

Effects of Freshwater Stratification on Nutrients, Dissolved Oxygen, and Phytoplankton in the Bay of Bengal

“…OMZ intensity is strongest below the lowsalinity region (<5 µM), where stratification inhibits vertical mixing. Suppression of ventilation by stratification is a fundamental cause of the OMZ in the BoB (Sarma, 2002), and it is intensified in the north due to river discharge (Sarma et al, 2013). However, the low oxygen concentrations observed in this study have not previously been reported in the open ocean, and limited observations from other studies have suggested values in excess of 10 µM during the presouthwest and northeast monsoon periods (Rao et al, 1994).…”

“…Despite such low oxygen levels in the OMZ, denitrification was not observed, and nitrite concentrations were low (<0.1 µM). However, as discussed by Sarma et al (2013), the occurrence of anammox may be possible without accumulation of nitrite in the water column. More work is needed to confirm the possible occurrence of anammox in the BoB.…”

Impact of river discharge on distribution of dimethyl sulfide (DMS) and its fluxes in the coastal Bay of Bengal

“…Relatively cooler surface waters (26.8-28.8°C) associated with high salinity (~34) were observed in the southern transects compared with that of north (28.8-30°C and~31) suggesting occurrence of mild upwelling in the former region. A sharp gradient in salinity and temperature was observed around 18°N resulting from the northward flowing East India Coastal Currents (EICC) and southward flowing discharge water from the Ganges (Sarma et al, 2013;Shetye, 1993). Based on the contrasting differences in the surface water temperature and salinity, the study area is divided into two regions, namely, southern coastal Bay of Bengal (SCB) comprising the transects of KS, KN, GS, and GN, which are influenced by monsoonal estuaries of Godavari and Krishna and northern coastal Bay of Bengal (NCB), including transects of VD, HD, MS and MN, which are more influenced by discharge from the Ganges river.…”

“…The fluvial inputs are major sources of nutrients to the Bay of Bengal (for e.g. Madhupratap and Parulekar, 1993;Sarma et al, 2012Sarma et al, , 2013. The freshwater discharge leads to the formation of salinity fronts (Sarma et al, 2012a) and strong stratification (Shetye, 1993) impacting phytoplankton composition and therefore likely influencing the production of DMS (Sarma et al, 2013).…”

“…Madhupratap and Parulekar, 1993;Sarma et al, 2012Sarma et al, , 2013. The freshwater discharge leads to the formation of salinity fronts (Sarma et al, 2012a) and strong stratification (Shetye, 1993) impacting phytoplankton composition and therefore likely influencing the production of DMS (Sarma et al, 2013). The influence of river discharge on phytoplankton composition was previously studied with reference to DMS production (Chan and Hamilton, 2001;Shenoy and Patil, 2003).…”