An off‐line 3D model of anthropogenic CO2 uptake by the oceans

Abstract

A key unanswered question in global climate research is the extent to which the oceans absorb and redistribute anthropogenic CO2 (ΔDICant). We apply an offline ocean carbon cycle model, one that uses atmospheric CO2 concentrations and simplified ocean ventilation estimates. We estimate ocean ventilation by introducing the full age distributions of water masses obtained from a global ocean circulation model. The two model cases we use are known to respectively underestimate and overestimate observed ventilation rates, thereby providing upper and lower bounds on CO2 uptake. The error in determining ΔDICant is reduced significantly by minimising the number of tunable parameters. The development of the oceanic ΔDICant inventory is resolved from the beginning of industrialisation to the present time. According to the model, 177Gt anthropogenic carbon have been locked up in the oceans by 1999, corresponding to an annual uptake rate of 3.9GtC*a−1 during 1999. Uncertainties in our estimated oceanic CO2 uptake are discussed.