The ocean takes up about a quarter of our annual CO2 emissions from burning of fossil fuels and land-use change. The ocean is thus one of the two “natural sinks” for atmospheric CO2, the other one being the biosphere on land (plants and soils). The ocean thus plays a crucial role in the global carbon cycle and human societies rely on the ocean’s continued CO2 uptake for mitigating climate change.
However, there are fundamental open questions with how the ocean carbon sink functions currently and how it will operate in the future. The fundamental questions addressed in this project are explained in the following.
1) Ventilation is the transport of carbon from the surface ocean to the deep ocean and is thought to be the bottle-neck of ocean uptake of anthropogenic carbon. Yet, it is poorly evaluated in the ocean carbon cycle models that are used to quantify the ocean uptake of anthropogenic carbon for the present day and the future. Novel data sets now allow to evaluate ventilation and its role for carbon uptake and distribution much better. Here we ask: what is the role of ventilation for ocean carbon uptake? How large are ventilation biases in the ocean carbon cycle model(s) and what is their impact on ocean carbon sink estimates??
2) The coastal ocean carbon sink and its future evolution is conceptually included in the carbon budgets, but in reality, it is poorly represented in current ocean carbon cycle models. A reliable baseline for coastal ocean carbon fluxes is urgently needed for carbon budgets and their management. We ask: how large is the coastal ocean carbon sink and how will it change in the future?
3) The future ocean carbon sink is often analyzed in worst case high-emission scenarios. Yet, we argue, that the dynamics of the ocean carbon sink will be different on low emission or overshoot scenarios. Here we ask in particular: how will the ocean carbon sink behave after peak emissions (open and coastal ocean)?
By addressing these questions, projections of the ocean carbon sink will become more robust and society and policy makers can be better informed on the carbon and climate response to certain socioeconomic pathways.
