Regional Vulnerability of Permafrost Carbon to Climate Change: A Multifactor Experiment and Model Network. DOE, 2015-2018. (Co-PI, PI: Ted Schuur, Northern Arizona University)

The goal of this project is to address the following overarching question: How will regional variation in the response of permafrost ecosystem C balance to warming and thaw affect atmospheric CO2 and CH4 concentrations and future climate? We hypothesize that the transfer of old soil C to the atmosphere will occur as a result of permafrost thaw and the microbial decomposition of organic C. Most importantly, this highly significant change in ecosystem C cycling will be detectable in the radiocarbon values of respiration. Radiocarbon provides a sensitive fingerprint for detecting the loss of old C as permafrost thaws, and can be used to constrain model parameters that control slow cycling C. We also predict that old C loss will be in part offset by increases in plant C uptake with warming but that this dynamic will change through time (years to decades) with plant response being more limited than that of microbes. Finally we expect these biological processes to be influenced by landscape variables of permafrost temperature and drainage. These master variables control the degree to which permafrost is influenced by a given change in climate, as well the response of plants and microbes under both well-drained and saturated conditions common across the Arctic landscape. This project will address the overarching question using: 1) a combination of field and laboratory experiments to measure isotope ratios and C fluxes in a tundra ecosystem that has been exposed to experimental warming and drying. The measurements are designed to develop a mechanistic understanding of the ecosystem sources contributing to C losses following warming and permafrost thaw, and how these dynamics change over time (years to decade); 2) data assimilation techniques that utilize measurement streams from the multifactor experiment to derive parameter values for large scale models, in particular focusing on the utility of radiocarbon measurements for constraining slow C pools, and the effect of ecosystem acclimation on C balance projections; 3) projections of the response of permafrost ecosystem C balance to a range of future climate scenarios using an Earth System Model trained by data assimilation that can simulate the permafrost C-climate feedback at the global scale. The proposed long-term multifactor experiment provides an important experimental framework to address this permafrost C feedback, and provides unique insight alongside existing and planned Arctic networks that are based primarily on observation alone. The data sets and modeling simulations generated by this project will interface with ongoing synthesis that is underway through the Permafrost Carbon Network as a foundation for increasing, distilling, and communicating our understanding of change in this remote region with its important consequences for global climate and society.