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Importance of Biospheric Co2 in a Subcanopy Atmosphere Deduced From 14C AMS Measurements

Published online by Cambridge University Press:  18 July 2016

P M Grootes ,
G W Farwell ,
F H Schmidt ,
D D Leach  and
Minze Stuiver
P M Grootes
Affiliation:
Nuclear Physics Laboratory and Department of Physics Quaternary Isotope Laboratory, Department of Geological Sciences
G W Farwell
Affiliation:
Nuclear Physics Laboratory and Department of Physics
F H Schmidt
Affiliation:
Nuclear Physics Laboratory and Department of Physics
D D Leach
Affiliation:
Nuclear Physics Laboratory and Department of Physics
Minze Stuiver
Affiliation:
Quaternary Isotope Laboratory, Department of Geological Sciences
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Abstract

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14C concentrations in the stem cellulose of a Sitka spruce from the Pacific coast of Washington respond to changes in atmospheric 14CO2 concentration within 5–6 weeks. δ14C values for cellulose were consistently lower than those of the corresponding clean troposphere during rapid increase in atmospheric 14C caused by nuclear weapons tests (1962–64). Possible reasons for this include: 1) a delay of days or weeks in incorporation of recent photosynthate, 2) the use of stored photosynthate, and 3) photo-assimilation of biospheric decay CO2. We estimate that the influence of process 1 is small or negligible. The respective contributions to the total carbon deposited as radial stem growth in our Sitka spruce then are 2) < 15% (possibly 0), and 3) 10%–23% (13%–28% if the possible effect of root respiration is included in the biosphere decay component). We plan to test this concept by looking for a vertical 14C gradient in the 1963 growth ring of a tree located in a dense forest canopy; we do not expect to find such a gradient in a similar tree from a strongly wind-washed location.

Type
II. Carbon Cycle in the Environment
Information
Radiocarbon , Volume 31 , Issue 3: June 20-25, 1988 Dubrovnik, Yugoslavia , 1989 , pp. 475 - 480
Copyright
Copyright © The American Journal of Science 

References

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