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Factors and processes governing the C-14 content of carbonate in desert soilsA model is presented describing the factors and processes which determine the measured C-14 ages of soil calcium carbonate. Pedogenic carbonate forms in isotopic equilium with soil CO2. Carbon dioxide in soils is a mixture of CO2 derived from two biological sources: respiration by living plant roots and respiration of microorganisms decomposing soil humus. The relative proportion of these two CO2 sources can greatly affect the initial C-14 content of pedogenic carbonate: the greater the contribution of humus-derived CO2, the greater the initial C-14 age of the carbonate mineral. For any given mixture of CO2 sources, the steady-state (14)CO2 distribution vs. soil depth can be described by a production/diffusion model. As a soil ages, the C-14 age of soil humus increases, as does the steady-state C-14 age of soil CO2 and the initial C-14 age of any pedogenic carbonate which forms. The mean C-14 age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate. This discrepancy increases the older a soil becomes. Partial removal of outer (and younger) carbonate coatings greatly improves the relationship between measured C-14 age and true age. Although the production/diffusion model qualitatively explains the C-14 age of pedogenic carbonate vs. soil depth in many soils, other factors, such as climate change, may contribute to the observed trends, particularily in soils older than the Holocene.
Document ID
19950033828
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Amundson, Ronald
(University of California, Berkeley, CA United States)
Wang, Yang
(University of California, Berkeley, CA United States)
Chadwick, Oliver
(Jet Propulsion Laboratory, Pasadena, CA United States)
Trumbore, Susan
(University of California, Irvine, CA United States)
Mcfadden, Leslie
(University of New Mexico, Albuquerque, NM United States)
Mcdonald, Eric
(University of New Mexico, Albuquerque, NM United States)
Wells, Steven
(University of California, Riverside, CA United States)
Deniro, Michael
(University of California, Santa Barbara, CA United States)
Date Acquired
August 16, 2013
Publication Date
July 1, 1994
Publication Information
Publication: Earth and Planetary Science Letters
Volume: 125
Issue: 4-Jan
ISSN: 0012-821X
Subject Category
Geophysics
Accession Number
95A65427
Funding Number(s)
CONTRACT_GRANT: NSF DMB-84-05003
CONTRACT_GRANT: NSF BSR-88-15637
CONTRACT_GRANT: NSF EAR-91-18335
CONTRACT_GRANT: NSF BNS-84-18280
Distribution Limits
Public
Copyright
Other

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