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An integrated model for soil organic carbon and CO 2 : Implications for paleosol carbonate p CO 2 paleobarometry
Author(s) -
Bowen Gabriel J.,
Beerling David J.
Publication year - 2004
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2003gb002117
Subject(s) - paleosol , organic matter , soil water , soil organic matter , soil science , carbonate , soil carbon , total organic carbon , environmental chemistry , soil horizon , geology , carbon cycle , environmental science , mineralogy , chemistry , loess , paleontology , ecosystem , ecology , organic chemistry , biology
The geologic history of atmospheric CO 2 concentration ( C Atm ) is relevant to studies of paleoclimate, paleobiology, and elemental cycling at the Earth's surface. Here we present a model that represents processes controlling the concentration, stable carbon isotope composition, and vertical distribution of organic matter and CO 2 within soils. In the model we include a volumetric scaling term necessary to calculate the soil pore CO 2 concentration and δ 13 CO 2 from soil respiration rate per unit area, which has been omitted in previous work. Our model provides several new insights into the commonly used method for estimating paleo‐ C Atm based on the δ 13 C of paleosol carbonates. We show that because refractory, microbially processed organic matter is increasingly abundant toward the base of the soil, isotope effects associated with organic matter decay can potentially lead to significant offset between the δ 13 C of soil‐respired CO 2 (δ φ ) and that of soil organic matter at depth. The magnitude of this effect depends on the production and decay characteristics of the individual soil, and can lead to substantial underestimation of paleo‐ C Atm if organic matter preserved in subsurface paleosol horizons is used to approximate δ φ . Paleo‐ C Atm reconstruction will be more accurate if surface‐layer fossil organic matter is used as a proxy for δ φ . In this case, however, there is a small (200–300 ppm), consistent, positive bias in C Atm estimates resulting from the decay of 13 C‐enriched organic matter deep within the soil. Re‐examination of earlier studies using the soil carbonate approach to estimate C Atm identifies examples where each bias may be present.