Mathematical Reconstruction of Radiocarbon From 12C: Application in the E3SM Land Model
Radiocarbon (14C) is a powerful tracer of the global carbon cycle that is commonly used to assess carbon cycling rates in various Earth system reservoirs and as a benchmark to assess model performance. Therefore, it has been recommended that Earth System Models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) report predicted radiocarbon values for relevant carbon pools. However, a detailed representation of radiocarbon dynamics may be an impractical burden on model developers. Here, we present an alternative approach to compute radiocarbon values from the numerical output of an ESM that does not explicitly represent these dynamics. We evaluated our approach using the E3SM land model (ELMv1).
Results from our proposed method are highly accurate (relative error <0.01%) compared with the ELMv1 12C and 14C predictions, demonstrating the potential to use this approach in CMIP6 and other models that do not explicitly represent 14C. Since comparisons against observations indicate that ESM land models inaccurately predict soil C turnover, our approach provides a framework to improve process representations affecting these biases.
Models representing ecosystem carbon dynamics are generally complex and difficult to analyze. Comparing different models with different structures is even more challenging due to the variety of processes represented in the models. However, it is possible to use the numerical output of models to reconstruct the original structure using a common mathematical framework. In this manuscript, we demonstrate this approach and apply it to compute the radiocarbon dynamics of the E3SM land model. The proposed approach reconstructed the carbon and radiocarbon dynamics of the original model very accurately and can be used to study the system-level dynamics of complex contrasting models. We are working to apply the approach to analyze other ESM simulations.