The DOE E3SM Coupled Model v1.1 Biogeochemistry Configuration and Coupled Carbon-Climate Experiments

The presentation will introduce the recently-released biogeochemistry configuration of the Department of Energy's Energy Exascale Earth System Model (E3SM), i.e., model version E3SMv1.1-BGC and related configurations. The model simulates historical carbon cycle dynamics, including the loss in carbon associated with land use and land cover change, and responses of the carbon cycle to changes in climate. In addition, we introduce several innovations in the treatment of soil nutrient limitation mechanisms, including enabling explicit dependence on phosphorus availability. The initial suite of simulations described here includes E3SM contributions to the Coupled Climate-Carbon Cycle Model Intercomparison Project and other projects, as well as simulations to explore the impacts of structural uncertainty in representations of nitrogen and phosphorous limitation. We describe the model spinup and evaluation procedures, provide an overview of results from the simulation campaign, and highlight key features of the simulations. Cumulative warming over the twentieth century is similar to observations, with a mid-century cold bias offset by stronger warming in recent decades. Ocean biomass production and carbon uptake are underpredicted, likely due to biases in ocean transport leading to widespread anoxia and undersupply of nutrients to surface waters. The inclusion of nutrient limitations in the land biogeochemistry results in weaker carbon fertilization and carbon-climate feedbacks than exhibited by other Earth System Models that exclude those limitations. Finally, we compare two alternative representations of terrestrial carbon and nutrient cycling. While both configurations agree well with observational benchmarks, they differ significantly in their distribution of carbon among different pools and in the strength of nutrient limitations.