Tall tower observations of isotopic CO2 exchange within an agricultural landscape

The isotopic composition of atmospheric CO2 represents an important signal of global change and has the potential to provide important constraints on local, regional, and global carbon cycling. Understanding carbon cycle processes requires a multi-scale approach – capable of addressing short-term and longer-term temporal dynamics of processes ranging from the leaf to regional scales. Combining meteorological and stable isotope techniques provide a meaningful way of linking these spatial scales while providing greater process information. However, quantifying isotopic CO2 exchange between the biosphere and atmosphere presents a very significant measurement challenge. Here we present high temporal resolution isotopic CO2 mixing ratios and the first direct eddy isoflux measurements at the ecosystem and regional scale to better understand the influence of agricultural ecosystems (land surface heterogeneity) and boundary layer dynamics on carbon exchange processes and atmospheric isotopic forcing. Flux partitioning, based on isotopic mass balance, is used to estimate the relative importance of C3 and C4 species to the local and regional-scale carbon and water budgets within a heavily managed landscape in the Upper Midwest, United States.