Highlights
- A coupled atmosphere–ocean-biogeochemistry model is customised for NIO.
- High surface pCO2 in upwelling regions of NIO are controlled by non-thermal processes.
- Surface pCO2 changes in upwelling regions of NIO are more sensitive to changes in DIC.
- Diffusion, CO2 flux and Phytoplankton uptake primarily control DIC variability in NIO.
Abstract
The oceans have absorbed nearly 30% of the anthropogenic CO2 that alters the ocean carbon chemistry. The oceanic processes are highly complex, which mandate approaches that couple its physical, chemical and biological states. Here, we use a coupled atmosphere–ocean-biogeochemistry model, incorporating spatially and temporally varying atmospheric CO2 to simulate the north Indian Ocean (NIO) carbon dynamics for the period 2013–2020. We assess the seasonal variability of Dissolved Inorganic Carbon (DIC), total Alkalinity (ALK), ocean surface pCO2 and buffering capacity. To assess the mechanisms that control carbon dynamics in the region, we segregate the ocean surface pCO2 into temperature-driven (thermal) and bio-physical processes induced (non-thermal) pCO2. We find that the thermally driven pCO2 is dominant in summer (June, July, August and September; JJAS), but the non-thermal component in winter (December, January and February; DJF) in the northern Arabian Sea (AS). The northern AS is characterised by a deep mixed layer and convection-induced vertical mixing during winter. DIC from the subsurface layer is uplifted to the surface, which results in high ocean surface pCO2 in winter. Off the Oman coast, the non-thermal processes control the surface pCO2 in summer. In the northern bay, the thermal component of pCO2 is dominant in summer and non-thermal component is prominent in winter as in northern AS, but their magnitudes are lower due to large riverine flux. The budget analysis reveals strong influence of diffusion, CO2 flux and biological processes in controlling DIC variability in NIO. Low buffering capacity in upwelling regions indicates that pCO2 changes are more sensitive to changes in DIC, primarily due to the upwelled DIC-rich surface waters. Therefore, it results in a reduced ability to absorb CO2. This warrants the need to address recent changes in carbon dynamics in response to the increased levels of atmospheric CO2.
Peter R., Kuttippurath J., Sunanda N. & Chakraborty K., 2025. Effect of thermal and non-thermal processes on the variability of ocean surface pCO2 and buffering capacity in the North Indian Ocean. Progress in Oceanography: 103442. doi: 10.1016/j.pocean.2025.103442. Article (subscription required).
