Decadal Predictions of the Oceanic Carbon Uptake

The strength of the oceanic carbon sink controls the airborne fraction of CO₂ and thereby affects climate change. While the long-term trends in the oceanic carbon uptake are determined by emissions of fossil fuel CO₂, there are substantial multiyear variations and their nature is not yet fully understood. The state-of-the-art decadal prediction systems reveal robust prediction skill of the physical state of the ocean, such as the Atlantic meridional overturning circulation (AMOC) and sea surface temperature (SST) achieved by initialization of Earth system models (ESMs). To date, only few attempts have been made to predict the oceanic carbon uptake and the corresponding biogeochemical processes. Based on the Max Planck Institute Earth System Model (MPI-ESM), we investigate the predictability of variations in CO₂ uptake by initialization of the MPI-ESM decadal prediction system. Our results suggest significant multiyear and decadal variability of oceanic carbon sink. In a first step, focusing on the North Atlantic CO₂ uptake, we demonstrate that the potential predictability of CO₂ uptake in the western subpolar gyre (SPG) region is up to 4 years. Further comparison with observational data confirms predictability of the CO₂ uptake. The predictive skill of CO₂ uptake in the North Atlantic SPG is closely related to that of the SST and both are assured by initialization of the AMOC. Through our first steps towards Earth system prediction, we find that beside the trend due to CO₂ emissions increase, predictions of the oceanic uptake and storage of carbon are largely affected by decadal variations of the background oceanic circulation and thermal state. We will discuss multiyear predictability of the oceanic carbon uptake and associated underlying mechanisms including a combination of physical, biological and chemical processes.