Carbon cycle as reflected in atmospheric CO₂ in the western US

Description

The carbon isotope ratios of atmospheric CO₂ reflect a balance between source (respiration, anthropogenic activities, fires) and sink (photosynthesis) processes. As turbulence dominates the mixing of CO₂ in the atmosphere, the distribution of [CO₂] values within and above the convective boundary have been used for scaling carbon cycle activities. Here stable isotopes play a role constraining interpretations on the role of fluxes at large scales. Typically, Keeling-plots are used to characterize terrestrial fluxes. The utility of carbon isotopes in CO₂ is to constrain interpretations of what is driving changes in biosphere-atmosphere CO₂ estimates (net ecosystem exchange, NEE). Increasingly, atmospheric models (e.g., WRFF, STILT) can be combined with concentrations and carbon isotopes in CO₂ to make predictions of fluxes and to dissect out the sources contributing to these fluxes.

The project will support a postdoc to compile and synthesize the data from published Keeling plot studies and local to global-scale monitoring networks to elaborate the role of isotopic data in describing CO₂ flux attribution and ecosystem-level gas exchange over multiple spatial scales. Data anlaysis will involve significant quantitative work with a number of ecosystem, atmospheric, and chemical transport models.

Several initial projects are anticipated:

• First, what are the relative contributions of C₃ and C₄ photosynthesis to gross primary productivity in grasslands, forests, and other dominant ecosystems across North America?
• Second, what is the role of the anthropogenic signal in modifying atmospheric concentrations and carbon isotopes in CO₂?
  
• Third, how can concentrations and carbon isotopes in CO₂ be used to study urban metabolism in cities across North America?
  
• Fourth, what are the relative roles and variation of different human and non-human emissions sources on the CO₂ emission budgets for urban ecosystems?

Affiliated faculty

Bowling, Ehleringer, Gurney, Pataki, Randerson, Wofsy

Image courtesy of the Institute of Arctic and Alpine Research, University of Colorado, and NOAA Global Monitoring Division