Constraining internal variability of oceanic carbon uptake in MPI-ESM super ensemble simulations

The ocean, as a major sink for anthropogenic CO₂ emissions, is playing an essential role in modulating global carbon cycle and climate change. Model intercomparison exercises, such as Coupled Model Intercomparison Project Phase 5 (CMIP5) indicate that evolution of the global mean oceanic carbon uptake is quite robustly projected in the models. Yet, there are large regional discrepancies between different models and their origin is not well understood. Likewise, the contribution of internal model variability to the uncertainty in the oceanic carbon uptake remains unclear. By using a large ensemble of 100 simulations based on the Max Planck Institute Earth System Model (MPI-ESM), we investigate the internal variability of oceanic carbon uptake. We focus on the historical period and also on the temporal evolution of the internal variability in a high CO₂ world, such as in the idealized scenario of 1% per year CO₂ increase. Further insights are gained based on the multi-model variability of oceanic carbon uptake across the CMIP5 ensemble and the data base estimates. We find that the internal variability of the ensemble accounts for 68% of the multi-model spread of the globally integrated oceanic carbon uptake. Moreover, the spread among data based estimates on the oceanic carbon uptake is also larger than the internal variability produced in the MPI-ESM model ensemble. We will discuss spatial distribution and temporal evolution of internal variability in oceanic carbon uptake and to what extent we can constrain model uncertainty in ESM projections of the future oceanic carbon sink.