Biogeochemistry of carbon, nitrogen and oxygen in the Bay of Bengal: New insights through re-analysis of data

Abstract

Primary production is reported to be a fraction of heterotrophic carbon demand in the Bay of Bengal (BoB), and it is attributed to the unavailability of inorganic nutrients and faster sinking of organic matter in association with mineral particles.The contribution of nutrients through external sources to total primary production is low (<5%), suggesting internal cycling of nutrients is important in the BoB.Organic nutrients support primary production in the absence of inorganic nutrients in the BoB.It was noticed that about 45% of particulate organic carbon (POC) production is exudated as dissolved organic carbon (DOC).Therefore, the total organic carbon production is revised to twice that of the earlier estimate and it is sufficient to support heterotrophic carbon demand.Balance among the ventilation of oxygen by anticyclonic eddies, strengthening due to cyclonic eddies and salinity stratification controls the oxygen levels in the OMZ than hitherto hypothesized as ballasting of organic matter.The stable isotopic composition of nitrogen in nitrate and particulate organic nitrogen (PON) does not evidence a significant contribution of anthropogenic nitrogen in the BoB.This negates the hypothesis that anthropogenic inputs modify the biogeochemistry of BoB.The deposition of anthropogenic aerosols decreases the pH of surface waters in the western BoB, whereas a decrease in salinity due to an increase in freshwater flux due to warming of the Himalayan glacier may increase pH and decrease pCO2 levels.As a result, BoB is turning into more sink for atmospheric CO2, which is contrasting to that of elsewhere in the global ocean