The oceanic anthropogenic CO2 sink: Storage, air‐sea fluxes, and transports over the industrial era

Abstract This study presents a new estimate of the oceanic anthropogenic CO 2 (C ant ) sink over the industrial era (1780 to present), from assimilation of potential temperature, salinity, radiocarbon, and CFC‐11 observations in a global steady state ocean circulation inverse model (OCIM). This study differs from previous data‐based estimates of the oceanic C ant sink in that dynamical constraints on ocean circulation are accounted for, and the ocean circulation is explicitly modeled, allowing the calculation of oceanic C ant storage, air‐sea fluxes, and transports in a consistent manner. The resulting uncertainty of the OCIM‐estimated C ant uptake, transport, and storage is significantly smaller than the comparable uncertainty from purely data‐based or model‐based estimates. The OCIM‐estimated oceanic C ant storage is 160–166 PgC in 2012, and the oceanic C ant uptake rate averaged over the period 2000–2010 is 2.6 PgC yr −1 or about 30% of current anthropogenic CO 2 emissions. This result implies a residual (primarily terrestrial) C ant sink of about 1.6 PgC yr −1 for the same period. The Southern Ocean is the primary conduit for C ant entering the ocean, taking up about 1.1 PgC yr −1 in 2012, which represents about 40% of the contemporary oceanic C ant uptake. It is suggested that the most significant source of remaining uncertainty in the oceanic C ant sink is due to potential variability in the ocean circulation over the industrial era.