Contemporary Southern Ocean CO2 Sink as a Constrain for Reducing Uncertainty of Future Ocean Carbon Sink

The ocean sequesters roughly 25% of the emitted anthropogenic carbon annually and is the largest net anthropogenic carbon sink since the preindustrial period. We analyzed a suite of fully interactive Earth system model simulations from the CMIP5 project. Under the high-CO₂ emissions RCP8.5 scenario, the projected ocean uptakes range between 4 and 6 Pg C/year by 2100. This inter-model spread represents bias in projected atmospheric CO₂ concentration of up to 70 ppmv. We found significant inter-model linear relationship between contemporary carbon sink in the Southern Ocean and the projected future global ocean sink. Inter-model spread in the SOC carbon sink arises from variations in the surface pCO₂ seasonality, which is attributed by the uncertainty in the simulated timing and amplitude of the seasonal cycle of biological production and SST. Our finding highlights the need for more accurate representation of Southern Ocean carbon sources and sinks in models. Improved spatial and temporal coverage of in-situ measurements in the Southern Ocean would be necessary to independently evaluate the current model performance and consequently increase the fidelity in future climate projections.