Bias and Constraints on Carbon Cycling in Tropical Forest Soils With Measurements and Modeling of Soil Carbon and Radiocarbon

Soil stores three times more carbon than that in the atmosphere, and thus plays a large role in global carbon cycling. Soil carbon has a long residence time, which is very important for future climate stability and climate change mitigation. However, soil carbon dynamics remain one of the biggest uncertainties in Earth System Models (ESMs). Tropical ecosystems are among the most active and diverse ecosystems that could drive significant changes in atmospheric greenhouse gas concentrations and global warming. Therefore, properly quantifying soil C in tropical areas is an important task for studying global climate. In this work we focus on the areas where our group has measured or attained data for soil C and radiocarbon (¹⁴C) values of 44 soil profiles in the Neotropics. We run a global model E3SMv1(DOE Energy Exascale Earth System Model) with vertically resolved C and ¹⁴C, then run the model on site level for all 44 available sites. Comparison between measured soil C stocks and ¹⁴C profiles to data generated from models show that the model consistently underestimates the age of deep soil carbon (deep soil carbon is too young), while over estimating soil age near the surface (too old) and suface carbon stocks. Ongoing work includes expanding observed data to include site characteristics such as forest and tree type, productivity (GPP), root biomass profiles, and depth-resolved mineralogy etc to better capture observed variation in ¹⁴C and C stock profiles within the sites across the Neotropical region, and to evaluate the role of climate and soil properties in explaining the variation in soil carbon age and stocks in tropical forests.