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Strong regional atmospheric 14 C signature of respired CO 2 observed from a tall tower over the midwestern United States
Author(s) -
LaFranchi B. W.,
McFarlane K. J.,
Miller J. B.,
Lehman S. J.,
Phillips C. L.,
Andrews A. E.,
Tans P. P.,
Chen H.,
Liu Z.,
Turnbull J. C.,
Xu X.,
Guilderson T. P.
Publication year - 2016
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2015jg003271
Subject(s) - biosphere , atmosphere (unit) , ecoregion , terrestrial ecosystem , environmental science , boreal , disequilibrium , atmospheric sciences , ecosystem , earth science , geology , geography , ecology , meteorology , paleontology , biology , medicine , ophthalmology
Radiocarbon in CO 2 ( 14 CO 2 ) measurements can aid in discriminating between fast (<1 year) and slower (>5–10 years) cycling of C between the atmosphere and the terrestrial biosphere due to the 14 C disequilibrium between atmospheric and terrestrial C. However, 14 CO 2 in the atmosphere is typically much more strongly impacted by fossil fuel emissions of CO 2 , and, thus, observations often provide little additional constraints on respiratory flux estimates at regional scales. Here we describe a data set of 14 CO 2 observations from a tall tower in northern Wisconsin (USA) where fossil fuel influence is far enough removed that during the summer months, the biospheric component of the 14 CO 2 budget dominates. We find that the terrestrial biosphere is responsible for a significant contribution to 14 CO 2 that is 2–3 times higher than predicted by the Carnegie‐Ames‐Stanford approach terrestrial ecosystem model for observations made in 2010. This likely includes a substantial contribution from the North American boreal ecoregion, but transported biospheric emissions from outside the model domain cannot be ruled out. The 14 CO 2 enhancement also appears somewhat decreased in observations made over subsequent years, suggesting that 2010 may be anomalous. With these caveats acknowledged, we discuss the implications of the observation/model comparison in terms of possible systematic biases in the model versus short‐term anomalies in the observations. Going forward, this isotopic signal could be exploited as an important indicator to better constrain both the long‐term carbon balance of terrestrial ecosystems and the short‐term impact of disturbance‐based loss of carbon to the atmosphere.