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CO2 Concentrations in Vertisols: Seasonal Variability and Shrink–Swell

By
Daniel O. Breecker
Daniel O. Breecker
Department of Geological Sciences, The University of Texas at Austin, 1 University Station C1100, Austin, Texas 78712, USA breecker@jsg.utexas.edu
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Junyeon Yoon
Junyeon Yoon
Department of Geological Sciences, The University of Texas at Austin, 1 University Station C1100, Austin, Texas 78712, USA breecker@jsg.utexas.edu
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Lauren A. Michel
Lauren A. Michel
Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA
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Takele M. Dinka
Takele M. Dinka
Soil and Crop Sciences Department, Texas A&M University, 2474 TAMU, College Station, Texas 77843, USA
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Steven G. Driese
Steven G. Driese
Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA
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Jason S. Mintz
Jason S. Mintz
Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA
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Lee C. Nordt
Lee C. Nordt
Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798, USA
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Katherine D. Romanak
Katherine D. Romanak
Bureau of Economic Geology, The University of Texas at Austin, Austin, Texas 78712, USA
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Cristine L.S. Morgan
Cristine L.S. Morgan
Soil and Crop Sciences Department, Texas A&M University, 2474 TAMU, College Station, Texas 77843, USA
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Published:
January 01, 2013

Abstract

The paleosol–carbonate CO2 barometer is widely accepted to be the most reliable method for reconstructing Earth’s atmospheric CO2 concentrations in deep time. Currently, the largest source of error in atmospheric CO2 calculated using the paleosol barometer originates from uncertainty in soil CO2 concentrations during soil carbonate formation. Many of the paleosols used for CO2 reconstruction were formed in clay-rich alluvium and have vertic properties, which may influence soil CO2.We hypothesized that the cracking during drying of shrink–swell clays results in rapid CO2 escape and low soil CO2 concentrations. We tested our hypothesis by monitoring soil cracking and the concentration of CO2 in the pore spaces of surface Vertisols (the Houston Black and Heiden series fine, smectitic, thermic Udic Haplusterts). Crack porosity of soils was estimated by measuring soil subsidence, and CO2 was measured in syringe samples collected from soil gas wells. During the period of study, pore-space CO2 concentrations at ~1-m soil depth varied by two orders of magnitude, from 10% during water-saturated conditions to <0.1% during hot, dry episodes. These large seasonal variations likely result in significant calcite dissolution and reprecipitation during pedogenesis. Soil CO2 concentrations decreased as soil-crack porosity increased. Moreover a compilation of published records of soil CO2 variability indicates that the variability of CO2 concentrations in Vertisols is significantly larger than the variability in other soil orders, regardless of climate or vegetation. These results suggest that soil cracking is a primary control on soil CO2 in Vertisols and that a soil-order-specific calibration of the paleosol barometer should be developed for application to clay-rich paleosols with soil cracks and/or pedogenic slickensides.

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SEPM Special Publication

New Frontiers in Paleopedology and Terrestrial Paleoclimatology: Paleosols and Soil Surface Analog Systems

Steven G. Driese
Steven G. Driese
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Lee C. Nordt
Lee C. Nordt
Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798-7354, USA
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SEPM Society for Sedimentary Geology
Volume
104
ISBN electronic:
9781565763036
Publication date:
January 01, 2013

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