The seasonal pattern of the carbon isotope content (delta C-13) of atmospheric CO2 depends on local and nonlocal land-atmosphere exchange and atmospheric transport. Previous studies suggested that the delta C-13 of the net land-atmosphere CO2 flux (delta(source)) varies seasonally as stomatal conductance of plants responds to vapor pressure deficit of air (VPD). We studied the variation of (source) at seven sites across the United States representing forests, grasslands, and an urban center. Using a two-part mixing model, we calculated the seasonal delta(source) for each site after removing background influence and, when possible, removing delta C-13 variation of nonlocal sources. Compared to previous analyses, we found a reduced seasonal (March-September) variation in delta(source) at the forest sites (0.5 parts per thousand variation). We did not find a consistent seasonal relationship between VPD and delta(source) across forest (or other) sites, providing evidence that stomatal response to VPD was not the cause of the global, coherent seasonal pattern in (source). In contrast to the forest sites, grassland and urban sites had a larger seasonal variation in (source) (5) dominated by seasonal transitions in C-3/C-4 grass productivity and in fossil fuel emissions, respectively. Our findings were sensitive to the location used to account for atmospheric background variation within the mixing model method that determined (source). Special consideration should be given to background location depending on whether the intent is to understand site level dynamics or regional scale impacts of land-atmosphere exchange. The seasonal amplitude in delta C-13 of land-atmosphere CO2 exchange (delta(source)) varied across land cover types and was not driven by seasonal changes in vapor pressure deficit. The largest seasonal amplitudes of delta(source) were at grassland and urban sites, driven by changes in C-3/C-4 grass productivity and fossil fuel emissions, respectively. Mixing model approaches may incorrectly calculate delta(source) when background atmospheric observations are remote and/or prone to anthropogenic influence.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/625792 |
| Date | 08 1900 |
| Creators | Raczka, B., Biraud, S. C., Ehleringer, J. R., Lai, C.-T., Miller, J. B., Pataki, D. E., Saleska, S. R., Torn, M. S., Vaughn, B. H., Wehr, R., Bowling, D. R. |
| Contributors | Univ Arizona, Dept Ecol & Evolutionary Biol, Department of Biology; University of Utah; Salt Lake City Utah USA, Earth and Environmental Sciences Area; Lawrence Berkeley National Laboratory; Berkeley California USA, Department of Biology; University of Utah; Salt Lake City Utah USA, Department of Biology; San Diego State University; San Diego California USA, Earth System Research Laboratory; NOAA; Boulder Colorado USA, Department of Biology; University of Utah; Salt Lake City Utah USA, Department of Ecology and Evolutionary Biology; University of Arizona; Tucson Arizona USA, Earth and Environmental Sciences Area; Lawrence Berkeley National Laboratory; Berkeley California USA, Institute for Arctic and Alpine Research; University of Colorado Boulder; Boulder Colorado USA, Department of Ecology and Evolutionary Biology; University of Arizona; Tucson Arizona USA, Department of Biology; University of Utah; Salt Lake City Utah USA |
| Publisher | AMER GEOPHYSICAL UNION |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | ©2017. American Geophysical Union. All Rights Reserved. |
| Relation | http://doi.wiley.com/10.1002/2017JG003795 |
Page generated in 0.0031 seconds