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Title: Relationships between CO2, thermodynamic limits on silicate weathering, and the strength of the silicate weathering feedback

Abstract

Recent studies have suggested that thermodynamic limitations on chemical weathering rates exert a first-order control on riverine solute fluxes and by extension, global chemical weathering rates. As such, these limitations may play a prominent role in the regulation of carbon dioxide levels (pCO2) over geologic timescales by constraining the maximum global weathering flux. In this study, we develop a theoretical scaling relationship between equilibrium solute concentrations and pCO2 based on equilibrium constants and reaction stoichiometry relating primary mineral dissolution and secondary mineral precipitation. Here, we test this theoretical scaling relationship against reactive transport simulations of chemical weathering profiles under open-and closed-system conditions, representing partially and fully water-saturated regolith, respectively. Under open-system conditions, equilibrium bicarbonate concentrations vary as a power-law function of pCO2(y =kxn)where nis dependent on reaction stoichiometry and kis dependent on both reaction stoichiometry and the equilibrium constant. Under closed-system conditions, bicarbonate concentrations vary linearly with pCO2 at low values and approach open-system scaling at high pCO2. To describe the potential role of thermodynamic limitations in the global silicate weathering feedback, we develop a new mathematical framework to assess weathering feedback strength in terms of both (1) steady-state atmospheric pCO2 concentrations, and (2) susceptibility to secular changes in degassingmore » rates and transient carbon cycle perturbations, which we term 1st and 2nd order feedback strength, respectively. Finally, we discuss the implications of these results for the effects of vascular land plant evolution on feedback strength, the potential role of vegetation in controlling modern solute fluxes, and the application of these frameworks to a more complete functional description of the silicate weathering feedback. Most notably, the dependence of equilibrium solute concentrations on pCO2 may represent a direct weathering feedback largely independent of climate and modulated by belowground organic carbon respiration.« less

Authors:
ORCiD logo [1];  [1]
  1. Stanford Univ., CA (United States). Dept. of Geological Sciences
Publication Date:
Research Org.:
Stanford Univ., CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)
OSTI Identifier:
1419011
Alternate Identifier(s):
OSTI ID: 1548838
Grant/Contract Number:  
SC0014556; DOE-DESC0014556
Resource Type:
Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 485; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; chemical weathering; negative feedback; thermodynamic limits; carbon cycle; geobiology; paleoclimate

Citation Formats

Winnick, Matthew J., and Maher, Kate. Relationships between CO2, thermodynamic limits on silicate weathering, and the strength of the silicate weathering feedback. United States: N. p., 2018. Web. doi:10.1016/j.epsl.2018.01.005.
Winnick, Matthew J., & Maher, Kate. Relationships between CO2, thermodynamic limits on silicate weathering, and the strength of the silicate weathering feedback. United States. doi:10.1016/j.epsl.2018.01.005.
Winnick, Matthew J., and Maher, Kate. Sat . "Relationships between CO2, thermodynamic limits on silicate weathering, and the strength of the silicate weathering feedback". United States. doi:10.1016/j.epsl.2018.01.005. https://www.osti.gov/servlets/purl/1419011.
@article{osti_1419011,
title = {Relationships between CO2, thermodynamic limits on silicate weathering, and the strength of the silicate weathering feedback},
author = {Winnick, Matthew J. and Maher, Kate},
abstractNote = {Recent studies have suggested that thermodynamic limitations on chemical weathering rates exert a first-order control on riverine solute fluxes and by extension, global chemical weathering rates. As such, these limitations may play a prominent role in the regulation of carbon dioxide levels (pCO2) over geologic timescales by constraining the maximum global weathering flux. In this study, we develop a theoretical scaling relationship between equilibrium solute concentrations and pCO2 based on equilibrium constants and reaction stoichiometry relating primary mineral dissolution and secondary mineral precipitation. Here, we test this theoretical scaling relationship against reactive transport simulations of chemical weathering profiles under open-and closed-system conditions, representing partially and fully water-saturated regolith, respectively. Under open-system conditions, equilibrium bicarbonate concentrations vary as a power-law function of pCO2(y =kxn)where nis dependent on reaction stoichiometry and kis dependent on both reaction stoichiometry and the equilibrium constant. Under closed-system conditions, bicarbonate concentrations vary linearly with pCO2 at low values and approach open-system scaling at high pCO2. To describe the potential role of thermodynamic limitations in the global silicate weathering feedback, we develop a new mathematical framework to assess weathering feedback strength in terms of both (1) steady-state atmospheric pCO2 concentrations, and (2) susceptibility to secular changes in degassing rates and transient carbon cycle perturbations, which we term 1st and 2nd order feedback strength, respectively. Finally, we discuss the implications of these results for the effects of vascular land plant evolution on feedback strength, the potential role of vegetation in controlling modern solute fluxes, and the application of these frameworks to a more complete functional description of the silicate weathering feedback. Most notably, the dependence of equilibrium solute concentrations on pCO2 may represent a direct weathering feedback largely independent of climate and modulated by belowground organic carbon respiration.},
doi = {10.1016/j.epsl.2018.01.005},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 485,
place = {United States},
year = {2018},
month = {1}
}

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Figures / Tables:

Figure 1 Figure 1: Conceptual diagram of 1st and 2nd order silicate weathering feedback strengths for two functional forms of the feedback, Feedbacks a and b. Gray and white shaded areas indicate relative 1st order feedback strength. Colored arrows denote the response of pCO2 to long-term changes in degassing rates from P1more » to P2.« less

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Works referencing / citing this record:

Constraints on Earth System Functioning at the Paleocene‐Eocene Thermal Maximum From the Marine Silicon Cycle
journal, May 2020

  • Fontorbe, Guillaume; Frings, Patrick J.; De La Rocha, Christina L.
  • Paleoceanography and Paleoclimatology, Vol. 35, Issue 5
  • DOI: 10.1029/2020pa003873

    Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.