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Title: The influence of temperature, pH, and growth rate on the δ 18 O composition of inorganically precipitated calcite

We report the oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables. For carbonates that precipitate slowly, under conditions that approach thermodynamic equilibrium, the temperature-dependence of 18O uptake is the dominant signal and the measured 18O content can be used as a paleotemperature proxy. In the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution, their oxygen isotope compositions are a convolution of multiple environmental variables. Here we present results from calcite growth experiments demonstrating the occurrence of large (> 2‰) non-equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems. We show that these non-equilibrium effects vary systematically with pH and crystal growth rate. An isotopic ion-by-ion crystal growth model quantifies the competing roles of temperature, pH, and growth rate, and provides a general description of calcite–water oxygen isotope fractionation under non-equilibrium conditions. The crystal growth model results show that (1) there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates, (2) calcite does not directly inherit the oxygen isotope composition of DIC even at fast growth rates, (3) theremore » is a kinetically controlled variation of about 1‰ per pH unit between pH=7.7 and 9.3 at constant growth rate for inorganic calcite as well as biogenic calcite, and (4) extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among DIC species in aqueous solution. The model can be extended to 13C uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes. Lastly, the experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non-equilibrium effects.« less
Authors:
 [1] ;  [2] ; ORCiD logo [2] ;  [3]
  1. Univ. of Oregon, Eugene, OR (United States). Dept. of Geological Sciences
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science
Publication Date:
Report Number(s):
LLNL-JRNL-695464
Journal ID: ISSN 0012-821X; 825229
Grant/Contract Number:
AC52-07NA27344; AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 404; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; calcite; oxygen isotopes; carbonic anhydrase; paleothermometry; kinetic effects
OSTI Identifier:
1466154

Watkins, James M., Hunt, Jonathan D., Ryerson, Frederick J., and DePaolo, Donald J.. The influence of temperature, pH, and growth rate on the δ18 O composition of inorganically precipitated calcite. United States: N. p., Web. doi:10.1016/j.epsl.2014.07.036.
Watkins, James M., Hunt, Jonathan D., Ryerson, Frederick J., & DePaolo, Donald J.. The influence of temperature, pH, and growth rate on the δ18 O composition of inorganically precipitated calcite. United States. doi:10.1016/j.epsl.2014.07.036.
Watkins, James M., Hunt, Jonathan D., Ryerson, Frederick J., and DePaolo, Donald J.. 2014. "The influence of temperature, pH, and growth rate on the δ18 O composition of inorganically precipitated calcite". United States. doi:10.1016/j.epsl.2014.07.036. https://www.osti.gov/servlets/purl/1466154.
@article{osti_1466154,
title = {The influence of temperature, pH, and growth rate on the δ18 O composition of inorganically precipitated calcite},
author = {Watkins, James M. and Hunt, Jonathan D. and Ryerson, Frederick J. and DePaolo, Donald J.},
abstractNote = {We report the oxygen isotope composition of carbonate minerals varies with temperature as well as other environmental variables. For carbonates that precipitate slowly, under conditions that approach thermodynamic equilibrium, the temperature-dependence of 18O uptake is the dominant signal and the measured 18O content can be used as a paleotemperature proxy. In the more common case where carbonate minerals grow in a regime where they are not in isotopic equilibrium with their host solution, their oxygen isotope compositions are a convolution of multiple environmental variables. Here we present results from calcite growth experiments demonstrating the occurrence of large (> 2‰) non-equilibrium oxygen isotope effects under conditions relevant to biogenic calcite growth and many natural inorganic systems. We show that these non-equilibrium effects vary systematically with pH and crystal growth rate. An isotopic ion-by-ion crystal growth model quantifies the competing roles of temperature, pH, and growth rate, and provides a general description of calcite–water oxygen isotope fractionation under non-equilibrium conditions. The crystal growth model results show that (1) there are both equilibrium and kinetic contributions to calcite oxygen isotopes at biogenic growth rates, (2) calcite does not directly inherit the oxygen isotope composition of DIC even at fast growth rates, (3) there is a kinetically controlled variation of about 1‰ per pH unit between pH=7.7 and 9.3 at constant growth rate for inorganic calcite as well as biogenic calcite, and (4) extreme light isotope enrichments in calcite in alkaline environments are likely due to disequilibrium among DIC species in aqueous solution. The model can be extended to 13C uptake into carbonates as well as clumped isotopes but additional data are needed to constrain the kinetic fractionation factors for carbon isotopes. Lastly, the experimental and model results constitute an important step in separating the relative influence of inorganic and biologic processes on isotopic fractionation and may aid the development of new paleoproxies based on non-equilibrium effects.},
doi = {10.1016/j.epsl.2014.07.036},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 404,
place = {United States},
year = {2014},
month = {8}
}