Distribution of dissolved organic carbon in the Bay of Bengal: Influence of sediment discharge, fresh water flux, and productivity

Dissolved organic carbon (DOC) plays an important role in the oceanic carbon cycle, with its distribution and variation primarily controlled by in situ productivity. The vertical and spatial distribution of DOC measured during two cruises has been investigated to decipher the processes controlling DOC in the Bay of Bengal (BoB). The terrestrial DOC flux to the BoB constitutes a significant fraction of the total DOC and has implications for the carbon budget of the northern Indian Ocean. High concentrations of DOC were observed in the northern BoB, which is primarily due to high flux of terrestrially derived fresh water from various rivers draining to the BoB. Compared to surface DOC concentration of the world oceans, BoB surface water generally has a higher DOC concentration (75-100 μM), which can be attributed to the high DOC content of the riverine flux. Stratification of surface water helps to maintain DOC content due to inhibited vertical mixing in the BoB as a result of the fresh water lens. High subsurface DOC concentration is due to the remineralisation of biogenic sinking particles brought along with the sediments. Subsurface DOC concentrations in the BoB exhibit a conspicuous decreasing trend southwards due to reduced influence of riverine biogenic flux. This study demonstrates that the average contribution of apparent oxygen utilization (AOU) to the DOC remineralisation in the BoB was ~18%.