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

Project Information

OceanPeak

Grant agreement ID: 101077209

DOI

10.3030/101077209

EC signature date 25 January 2023

Start date 1 May 2023

End date 30 April 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 499 953,75

EU contribution

€ 1 499 953,75

Coordinated by

ALFRED-WEGENER-INSTITUT HELMHOLTZ-ZENTRUM FUR POLAR- UND MEERESFORSCHUNG
Germany

Periodic Reporting for period 1 - OceanPeak (The global ocean carbon cycle after peak emissions: Dynamics and process attribution in a seamless model framework from coastal shelves to the open ocean)

Reporting period: 2023-05-01 to 2025-10-31

Summary of the context and overall objectives of the project

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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The ocean model used (FESOM-REcoM) was successfully updated to and evaluated in its latest version. A new mesh with higher resolution in coastal regions was set up and is being tested and tuned.

The large bgcArgo data set (robots in the ocean measuring the physical and biogeochemical state of the ocean from surface to 2000 m) was processed. New metrics for model evaluation were developed and used to evaluate ventilation of physical and biogeochemical tracers in the ocean carbon cycle model FESOM-REcoM. These comparisons provide important insights into ventilation biases that are now prepared for publication. They will form the basis for model tests on how the representation of ventilation processes can be improved.

Future low emission and overshoot scenarios were analyzed for carbon dynamics after peak emissions. Initial results point to a large role of carbon-concentration and carbon-climate feedbacks in these scenarios. A publication is in preparation.

A large number of synthesis papers on the ocean carbon sink were published in the Regional Carbon Cycle Assessment and Processes (RECCAP phase 2) community effort with strong contribution and leadership by the OceanPeak PI.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The bgcArgo data set has, to the best of our knowledge, not been used to evaluate ventilation in ocean carbon cycle models and proves to be a highly valuable tool to do so.

Ocean carbon cycle dynamics after peak emissions are poorly understood and our on-going analysis will provide highly relevant insights going beyond the start of the art.