Southern Bay of Bengal: A possible hotspot for CO2 emission during the summer monsoon

During the summer monsoon (June-September), the influence of cyclonic curl of local winds causes the formation of a thermocline dome called the Sri Lankan Dome (SLD) in the southern Bay of Bengal (BoB). In addition, the subsurface flow associated with the Summer Monsoon Current (SMC) brings Arabian Sea-High Salinity Water mass to the southern BoB. We show that both these oceanographic features are enriched in dissolved CO2 with the upper boundary shoaling very close to the surface. We observed episodic deep mixing events leading to entrainment of CO2-rich subsurface water with the mixed layer. CO2 disequilibrium within the top 45 m reached as high as + 404 mu atm. Our estimated mixed layer ventilation rates ranged between 2.4 and 4.6 days between sampling stations suggesting equilibration with upwelled waters were still evolving. We also encountered a patch of Arabian Sea-High Salinity Water mass with low aqueous pCO(2) suggesting past ventilation. Our modest estimates suggest a grid area of 2 degrees latitude x 2 degrees longitude can trigger a mean release of 0.78 Gg C day(-1), which is significantly higher than the estimated new production rates due to upwelled nutrients. Our study illustrates that upwelled water associated with the SLD in conjunction with the barrier layer erosion accompanied with the flow of SMC has the potential to occasionally ventilate in southern BoB. We believe that these processes can negate the region's benefits by acting as a CO2 source which underscores the need for detailed investigation.

Automated summary

During the summer monsoon, the Sri Lankan Dome and the Summer Monsoon Current in the southern Bay of Bengal are enriched with dissolved CO2, potentially leading to CO2 release, emphasizing the need for further investigation.