Air‐Sea Fluxes of CO<sub>2</sub> in the Indian Ocean Between 1985 and 2018: A Synthesis Based on Observation‐Based Surface CO<sub>2</sub>, Hindcast and Atmospheric Inversion Models
V. V. S. S. Sarma, B. Sridevi, Nicolas Metzl, Prabir K. Patra, Zouhair Lachkar, Kunal Chakraborty, C. Goyet, Marina Lévy, M. Mehari, Naveen Chandra
Abstract
Abstract The Indian Ocean significantly influences the global carbon cycle but it is one of the undersampled regions with reference to surface ocean p CO 2 . As a part of the Regional Carbon Cycle Assessment and Processes‐2 (RECCAP2) project, several approaches, such as interpolated observational climatology, hindcast model, observation‐based surface CO 2 (empirical models), and atmospheric inversion models have been employed for estimating net sea‐to‐air CO 2 fluxes between 1985 and 2018. The seasonal, spatial and long‐term variability in sea‐to‐air fluxes of CO 2 were compared with observational climatology. The mean value of CO 2 in the Indian Ocean (north of 37.5°S) for the period of 1985–2018 using all models is estimated to be −0.19 ± 0.1 PgC yr −1 and it is consistent with the observational climatology (−0.07 ± 0.14 PgC yr −1 ). The Indian Ocean north of 18°S is found to be the mean annual source (0.04 ± 0.05 PgC yr −1 ) whereas a net sink (−0.23 ± 0.11 PgC yr −1 ) in the south of 18°S. All models captured observed spatial patterns but underestimated the net source of CO 2 in the Oman/Somalia upwelling, the Equatorial Indian Ocean and the Bay of Bengal whereas CO 2 sink is overestimated in the South Indian Ocean. Overall, all models captured the seasonality in p CO 2 levels and CO 2 fluxes but overestimated the amplitude of their variability. All models suggested the strengthening of the sink over the period between 1985 and 2018 by 0.02 PgC yr −1 decade −1 . A significant increase in the collection of surface ocean p CO 2 and atmospheric CO 2 measurements improves the model simulations in the Indian Ocean.