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

This study presents a new estimate of the oceanic anthropogenic CO2 (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 CO2 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.