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Title: Does vapor pressure deficit drive the seasonality of δ 13C of the net land-atmosphere CO 2 exchange across the United States?

ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1];  [3]; ORCiD logo [4];  [1];  [5]; ORCiD logo [2]; ORCiD logo [6]; ORCiD logo [5]; ORCiD logo [1]
  1. Department of Biology, University of Utah, Salt Lake City Utah USA
  2. Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley California USA
  3. Department of Biology, San Diego State University, San Diego California USA
  4. Earth System Research Laboratory, NOAA, Boulder Colorado USA, Cooperative Institute for Research in Environment Sciences, University of Colorado Boulder, Boulder Colorado USA
  5. Department of Ecology and Evolutionary Biology, University of Arizona, Tucson Arizona USA
  6. Institute for Arctic and Alpine Research, University of Colorado Boulder, Boulder Colorado USA
Publication Date:
Sponsoring Org.:
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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Biogeosciences
Additional Journal Information:
Related Information: CHORUS Timestamp: 2017-10-23 17:19:29; Journal ID: ISSN 2169-8953
American Geophysical Union
Country of Publication:
United States

Citation Formats

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., and Bowling, D. R. Does vapor pressure deficit drive the seasonality of δ13C of the net land-atmosphere CO2 exchange across the United States?. United States: N. p., 2017. Web. doi:10.1002/2017JG003795.
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. Does vapor pressure deficit drive the seasonality of δ13C of the net land-atmosphere CO2 exchange across the United States?. United States. doi:10.1002/2017JG003795.
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., and Bowling, D. R. 2017. "Does vapor pressure deficit drive the seasonality of δ13C of the net land-atmosphere CO2 exchange across the United States?". United States. doi:10.1002/2017JG003795.
title = {Does vapor pressure deficit drive the seasonality of δ13C of the net land-atmosphere CO2 exchange across the United States?},
author = {Raczka, B. and Biraud, S. C. and Ehleringer, J. R. and Lai, C. -T. and Miller, J. B. and Pataki, D. E. and Saleska, S. R. and Torn, M. S. and Vaughn, B. H. and Wehr, R. and Bowling, D. R.},
abstractNote = {},
doi = {10.1002/2017JG003795},
journal = {Journal of Geophysical Research. Biogeosciences},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 8

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on August 10, 2018
Publisher's Accepted Manuscript

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Cited by: 1work
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  • The seasonal pattern of the carbon isotope content (δ 13C) of atmospheric CO 2 depends on local and nonlocal land-atmosphere exchange and atmospheric transport. Previous studies suggested that the δ13C of the net land-atmosphere CO 2 flux (δsource) varies seasonally as stomatal conductance of plants responds to vapor pressure deficit of air (VPD). We studied the variation of δ 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 δsource for each site after removing background influence and, when possible, removing δ 13C variation of nonlocalmore » sources. Compared to previous analyses, we found a reduced seasonal (March–September) variation in δ source at the forest sites (0.5‰variation). We did not find a consistent seasonal relationship between VPD and δ source across forest (or other) sites, providing evidence that stomatal response to VPD was not the cause of the global, coherent seasonal pattern in δsource. In contrast to the forest sites, grassland and urban sites had a larger seasonal variation in δ 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 δsource. 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 δ 13C of land-atmosphere CO 2 exchange (δ source) varied across land cover types and was not driven by seasonal changes in vapor pressure deficit. The largest seasonal amplitudes of δsource 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 δs ource when background atmospheric observations are remote and/or prone to anthropogenic influence.« less
    Cited by 1
  • A warming climate is altering land-atmosphere exchanges of carbon, with a potential for increased vegetation productivity as well as the mobilization of permafrost soil carbon stores. Here we investigate land-atmosphere carbon dioxide (CO 2) cycling through analysis of net ecosystem productivity (NEP) and its component fluxes of gross primary productivity (GPP) and ecosystem respiration (ER) and soil carbon residence time, simulated by a set of land surface models (LSMs) over a region spanning the drainage basin of Northern Eurasia. The retrospective simulations cover the period 1960–2009 at 0.5° resolution, which is a scale common among many global carbon and climatemore » model simulations. Model performance benchmarks were drawn from comparisons against both observed CO 2 fluxes derived from site-based eddy covariance measurements as well as regional-scale GPP estimates based on satellite remote-sensing data. The site-based comparisons depict a tendency for overestimates in GPP and ER for several of the models, particularly at the two sites to the south. For several models the spatial pattern in GPP explains less than half the variance in the MODIS MOD17 GPP product. Across the models NEP increases by as little as 0.01 to as much as 0.79 g C m⁻² yr⁻², equivalent to 3 to 340 % of the respective model means, over the analysis period. For the multimodel average the increase is 135 % of the mean from the first to last 10 years of record (1960–1969 vs. 2000–2009), with a weakening CO 2 sink over the latter decades. Vegetation net primary productivity increased by 8 to 30 % from the first to last 10 years, contributing to soil carbon storage gains. The range in regional mean NEP among the group is twice the multimodel mean, indicative of the uncertainty in CO 2 sink strength. The models simulate that inputs to the soil carbon pool exceeded losses, resulting in a net soil carbon gain amid a decrease in residence time. Our analysis points to improvements in model elements controlling vegetation productivity and soil respiration as being needed for reducing uncertainty in land-atmosphere CO 2 exchange. These advances will require collection of new field data on vegetation and soil dynamics, the development of benchmarking data sets from measurements and remote-sensing observations, and investments in future model development and intercomparison studies.« less
  • The Weather Research and Forecasting (WRF) model has been used to study the role of land-atmosphere coupling in influencing interannual summer climate variability over the contiguous U.S. Two long-term climate simulations are performed: A control experiment (CTL) allows soil moisture to interact freely with the atmosphere, and an additional experiment uncouples the land surface from the atmosphere by replacing soil moisture at each time step with the climatology of CTL. The CTL simulation reproduces well the observed temperature and precipitation variability, despite some discrepancies in daily mean and maximum temperature variability in the Midwest/Ohio Valley region and the adjacent areas,more » and precipitation variability in the Great Plains and some other areas. Strong coupling of soil moisture with daily mean temperature appears mainly over the transitional zone between cold and warm climates from the Southwest to the northern Great Plains to the Southeast, contributing up to about 30%-60% of the total interannual variance of temperature. There is a significantly different influence on daily maximum and minimum temperatures. Whereas soil moisture plays a leading role in explaining the variability of maximum temperature over the transitional zone, minimum temperature variability is highly constrained by external factors including atmospheric circulation and sea surface temperature almost everywhere over land. Soil moisture, mainly through its effects on convection, makes a dominant contribution to precipitation variability over about half of the northern U.S. The model’s behavior agrees generally well with land-atmosphere relationships diagnosed using available observations and soil moisture data from the Global Land Data Assimilation System.« less
  • Understanding of the underlying causes of spatial variation in exchange of carbon and water vapor fluxes between grasslands and the atmosphere is crucial for accurate estimates of regional and global carbon and water budgets, and for predicting the impact of climate change on biosphere–atmosphere feedbacks of grasslands. We used ground-based eddy flux and meteorological data, and the Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) from 12 grasslands across the United States to examine the spatial variability in carbon and water vapor fluxes and to evaluate the biophysical controls on the spatial patterns of fluxes. Precipitation was strongly associatedmore » with spatial and temporal variability in carbon and water vapor fluxes and vegetation productivity. Grasslands with annual average precipitation <600 mm generally had neutral annual carbon balance or emitted small amount of carbon to the atmosphere. Despite strong coupling between gross primary production (GPP)and evapotranspiration (ET) across study sites, GPP showed larger spatial variation than ET, and EVI had a greater effect on GPP than on ET. Consequently, large spatial variation in ecosystem water use efficiency (EWUE = annual GPP/ET; varying from 0.67 ± 0.55 to 2.52 ± 0.52 g C mm⁻¹ET) was observed. Greater reduction in GPP than ET at high air temperature and vapor pressure deficit caused a reduction in EWUE in dry years, indicating a response which is opposite than what has been reported for forests. Our results show that spatial and temporal variations in ecosystem carbon uptake, ET, and water use efficiency of grasslands were strongly associated with canopy greenness and coverage, as indicated by EVI.« less