The role of ocean transport in the uptake of anthropogenic CO₂

Abstract. We compare modeled oceanic carbon uptake in response to pulse CO₂ emissions using a suite of global ocean models and Earth system models. In response to a CO₂ pulse emission of 590 Pg C (corresponding to an instantaneous doubling of atmospheric CO₂ from 278 to 556 ppm), the fraction of CO₂ emitted that is absorbed by the ocean is: 37±8%, 56±10%, and 81±4% (model mean ±2σ ) in year 30, 100, and 1000 after the emission pulse, respectively. Modeled oceanic uptake of pulse CO₂ on timescales from decades to about a century is strongly correlated with simulated present-day uptake of chlorofluorocarbons (CFCs) and CO₂ across all models, while the amount of pulse CO₂ absorbed by the ocean from a century to a millennium is strongly correlated with modeled radiocarbon in the deep Southern and Pacific Ocean. However, restricting the analysis to models that are capable of reproducing observations within uncertainty, the correlation is generally much weaker. The rates of surface-to-deep ocean transport are determined for individual models from the instantaneous doubling CO₂ simulations, and they are used to calculate oceanic CO₂ uptake in response to pulse CO₂ emissions of different sizes pulses of 1000 and 5000 Pg C. These results are compared with simulated oceanic uptake of CO₂ by a number of models simulations with the coupling of climate-ocean carbon cycle and without it. This comparison demonstrates that the impact of different ocean transport rates across models on oceanic uptake of anthropogenic CO₂ is of similar magnitude as that of climate-carbon cycle feedbacks in a single model, emphasizing the important role of ocean transport in the uptake of anthropogenic CO₂.