The global ocean carbon cycle after peak emissions: Dynamics and process attribution in a seamless model framework from coastal shelves to the open ocean

Atmospheric CO2 levels are 49% above preindustrial levels due to anthropogenic CO2 emissions. The ocean takes up ~25% of these emissions and thereby mitigates climate change. The Global Carbon Budget annually quantifies the atmospheric CO2 sources (emissions) and sinks (e.g. ocean uptake), and I coordinate its ocean CO2 sink estimate. The uncertainty of the ocean sink estimate is huge: The range of estimates is 2.5 times larger than the CO2 emissions of the EU27. It is unknown whether the ocean sink has grown or stagnated since 2016. And yet, we face an even larger challenge with the imminent transition to a new regime: In the past, the ocean sink was controlled by fast-growing atmospheric CO2. After peak emissions, atmospheric CO2 will grow slower, stagnate or even decrease. I hypothesize that the dynamics of the ocean carbon sink will then be fundamentally different and poorly quantified ocean ventilation processes will be even more important. Ventilation transports carbon to the deep ocean and is the ‘bottleneck’ of the ocean sink.OceanPeak will establish a game-changing forecasting capacity of the truly global ocean CO2 uptake in societally-relevant low-emission scenarios. OceanPeak will go beyond the ‘surface and open ocean’ estimate with a seamless transition to coastal shelves and from surface to depth. With a unique multi-resolution ocean carbon cycle model, I will:1) develop a seamless coastal shelf to open ocean carbon cycle model and ground-truth ventilation processes based on newly-emerging observations to robustly quantify the ocean carbon sink to date2) characterize the dynamics of the ocean carbon sink under regimes after peak emissions3) attribute the evolution of the global ocean carbon sink to processes and quantify the time-scale of carbon sequestration.Quantification and understanding of the ocean sink from coastal to global scales will be paramount for an independent monitoring system of greenhouse gases as foreseen in the Paris Agreement.