Carbon Isotopes in the Ocean Model of the Community Earth System Model (CESM)

Abstract:

Carbon isotopes are frequently used to infer changes in past ocean circulation based on proxy records. Climate models on the other hand simulate the full climate system, but not the isotopic proxy record that corresponds to the climate state, making it difficult to compare model results with isotopic proxy data. In order to bridge this gap, we have implemented carbon isotopes (¹³C and ¹⁴C) in the ocean model of a state-of-the-art earth system model, the Community Earth System Model (CESM1). These improvements will allow us to more directly compare the model results to paleo proxies in future paleo simulations with the widely used CESM. Furthermore, simulating carbon isotopes in the model will allow us to investigate the details of the relationship between physical changes in the ocean circulation and isotopic changes in the self-consistent model system. We will discuss the implementation of abiotic and biotic radiocarbon and biotic ¹³C in the ocean model of the CESM1, to introduce these new features to the community. Then we will show how the model performs compared to present-day data, characterize the sensitivity of the simulated δ¹³C distributions to different biological fractionation parameterizations, and show results from idealized freshwater hosing experiments. In the near future, we plan to use the carbon-isotope enabled CESM to study changes in the ocean circulation during the LGM and the deglaciation.