Sources and sinks of CO₂ in the west coast of Bay of Bengal

Abstract

A B S T R A C TObservations at high spatial resolution (100 )50 km 2 ) in the western continental shelf of Bay of Bengal during southwest monsoon, when peak discharge occurs into the Bay through major rivers of the Indian subcontinent, revealed that freshwater discharge exerts dominant control on the inorganic carbon components in surface waters. Lower than present atmospheric pCO 2 levels were found in the northwestern (NW) than southwestern (SW) coastal Bay of Bengal. The pCO 2 levels in the peninsular rivers were an order of magnitude higher (5000Á 17000 matm) than that of atmospheric levels and glacial river Ganges ( Â500 matm). The discharge from the peninsular rivers has a stronger influence in the SW region, whereas the Ganges river discharge has a stronger influences in the NW region. Source or sink of CO 2 in the shelf region depends on the discharged river characteristics and the East India Coastal Current that distributes discharged water along the coast. Although during northeast monsoon, the situation is briefly reversed and the region acts as a sink, and on annual scale, the western Bay of Bengal acts as a source for atmospheric CO 2 than hitherto hypothesised.

Impact of river discharge on the coastal water pH and pCO2 levels during the Indian Ocean Dipole (IOD) years in the western Bay of Bengal

“…Recently, Sarma et al (2015) reported coastal water acidification due to increased anthropogenic aerosol loading in the northern BoB in winter and spring during recent decades, and the pH of the coastal waters decreased at the rate of 0.007 units yr À 1 , which was 2-3 times higher than that of elsewhere in the world. Sarma et al (2012b) reported that the direction of CO 2 flux (source or sink) from the coastal western BoB was dependant on the characteristics of the discharged water from the rivers. They further noted that the coastal regions influenced by the peninsular rivers were the strong net source while glacial river, the Ganges, was a net sink for atmospheric CO 2 .…”

“…They further noted that the coastal regions influenced by the peninsular rivers were the strong net source while glacial river, the Ganges, was a net sink for atmospheric CO 2 . It was hypothesized that decreased river discharge, either due to weak intensity of the monsoon or dam regulation of freshwater release, would decrease pCO 2 levels and acidification in the coastal BoB and therefore decreases the CO 2 flux to atmosphere (Sarma et al, 2012b). On the contrary, weakening of stratification would promote upwelling and in turn would increase the pCO 2 levels and acidification in the coastal BoB.…”

Sea–air CO<sub>2</sub> fluxes in the Indian Ocean between 1990 and 2009

“…This is recognized as a challenging area to capture the physical and biogeochemical responses related to both the role of the monsoon and the significant amount of discharge from the major rivers such as Ganges, Brahmaputra, Godavari, etc., with variable characteristics of an inorganic carbon system. Recently Sarma et al (2012) observed that whether coastal Bay of Bengal acts as a source or sink may depend on the characteristics of the discharge water received by the coastal zone; in many cases, the current OBGMs either do not incorporate freshwater river inputs at all or treat the lateral river boundary condition as the addition of freshwater only without incorporating explicit water chemistry (dissolved inorganic carbon, alkalinity). The OBGMs underestimated the discharge by as much as 50 % (Dia and Trenberth, 2002).…”

“…The northeastern region (Bay of Bengal) receives a significant amount of freshwater and is strongly stratified compared to the northwestern Indian Ocean, leading to contrasting behavior in physical processes and biogeochemical cycling (George et al, 1994). Consequently, the northeastern Indian Ocean acts as a mild net sink of atmospheric CO 2 , whereas the northwestern Indian Ocean acts as a net source Sarma, 2003;Takahashi et al, 2009;Valsala and Maksyutov, 2010a;Sarma et al, 2012). The pCO 2 in this region shows large seasonal variations associated with the monsoonal circulation, with maxima during summer and winter and minima in the transition periods (Sarma et al, 1998(Sarma et al, , 2000(Sarma et al, , 2012Goyet et al, 1998;Sarma et al, 2003.…”

Variation in Carbonate System and Air-Water CO2 Flux During Summer in the Mahanadi Estuary, India

“…Previous reports suggest that the coastal Bay of Bengal acts as a source for atmospheric CO 2 throughout the year except for some monsoon months [8], [9]. However, the source/sink nature and its magnitude is mainly regulated by the riverine influx and east Indian coastal current [10]. The work reported here was aimed to quantify the summer CO 2 flux in the riverine and near shore waters of Mahandi estuary and to evaluate the environmental control on CO 2 flux.…”