Coupled C13 isotope transfer in the Community Earth System Model – CESM 2.1

Anthropogenic emissions of carbon dioxide and other biogeochemical compounds perturb climate with far-reaching implications for natural and socio-economic systems. Earth System Models (ESMs) help us to investigate the complex cycling of carbon and other significant elements through land, ocean, and atmosphere. However, the uncertainties in anthropogenic emissions and modeled Earth system processes pose a big challenge for future scenario estimations. The analysis of the carbon isotopes offers a useful approach to narrow uncertainties in the coupled Earth system as the flow of carbon and other elements through the atmosphere-ocean-land system is traced with respect to distinct sources and processes by isotopic signatures.

Despite the potential advantages, carbon isotopes have only been implemented recently in state-of-the-art ESMs and fully coupled carbon isotope-enabled simulations with such models are missing. Here we use the CESM 2.1 model with the already developed land and ocean C13 components. We implemented atmospheric transport for C13 to perform fully coupled isotope simulations.

We will present results from transient simulations over the historical period and the 21^st century and analyse the changes in C13 stocks within and fluxes among different Earth system components. To investigate the role of atmospheric transport, we compare results from fully coupled atmosphere – land – ocean simulations with the control cases without the atmospheric C13 isotope transport.

The implementation of carbon isotope tracers in the atmosphere, land, and ocean components provides an avenue to exploit the large suite of available carbon isotope measurements in the context of the comprehensive CESM2. The new carbon isotope-enabled model version will be the basis to investigate past climate-carbon cycle changes as well as strengthening our knowledge on modern day terrestrial and ocean carbon sinks.