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(Cant) 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 Cant 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 Cant storage is 160-166 PgC in 2012, and the oceanic Cant 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 Cant entering the ocean, taking up about 1.1 PgC yr-1 in 2012, which represents about 40% of the contemporary oceanic Cant uptake. It is suggested that the most significant source of remaining uncertainty in the oceanic Cant sink is due to potential variability in the ocean circulation over the industrial era. Key Points The oceanic anthropogenic C sink is estimated in a data assimilation model Combining tracer and dynamical constraints reduces uncertainty of estimates The global ocean storage of anthropogenic carbon in 2012 is 160-166 Pg C ©2014. American Geophysical Union. All Rights Reserved.