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Stalagmites are an important archive of terrestrial climate information. However, there remains questions about the ability of stalagmites to form in oxygen isotopic equilibrium and thus record, in a simple manner, the oxygen isotopic composition and temperature of formational fluids. Recent studies have suggested that the combined application of 48 and 47 carbonate clumped isotope measurements can quantify the extent of kinetic isotope fractionation in stalagmites and thus used to correct for these kinetic isotope effects and solve for the original formation temperatures. Here we measure the 47 and 48 values from 16 different samples of the same stalagmite from central California that spans the deglaciation (11 to 20 kya). Each sample is replicated three to five times. We find that based on these measurements the extent of kinetic fractionation present in the carbonate from this stalagmite is minimal. The temperature calculated from 47 in this stalagmite ranges from 11.6 to 19.9 °C, in agreement with regional reconstructions of temperatures from 47 values of lake carbonates. In contrast, previously published the 18O and 2H values of inclusion fluids (Wortham et al., 2022) from this stalagmite suggest periods of increasing kinetic fractionation of the water isotopes at 13 and 15 ka. These periods have been previously interpreted to be times of a reduction in effective moisture regionally. We suggest by this comparison that the use of both water isotopes and the dual clumped isotope system in stalagmites can aide the interpretation of where kinetic fractionation occurs in the hydrologic and carbonate precipitation system in caves. We will discuss the work’s implications for paleoclimate records from stalagmites and other terrestrial systems in seasonally dry and Mediterranean regions.
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Quantum kinetic energy and isotope fractionation in aqueous ionic solutions
At room temperature, the quantum contribution to the kinetic energy of a water molecule exceeds the classical contribution by an order of magnitude. The quantum kinetic energy (QKE) of a water molecule is modulated by its local chemical environment and leads to uneven partitioning of isotopes between different phases in thermal equilibrium, which would not occur if the nuclei behaved classically. In this work, we use ab initio path integral simulations to show that QKEs of the water molecules and the equilibrium isotope fractionation ratios of the oxygen and hydrogen isotopes are sensitive probes of the hydrogen bonding structures in aqueous ionic solutions. In particular, we demonstrate how the QKE of water molecules in path integral simulations can be decomposed into translational, rotational and vibrational degrees of freedom, and use them to determine the impact of solvation on different molecular motions. By analyzing the QKEs and isotope fractionation ratios, we show how the addition of the Na + , Cl − and HPO 4 2− ions perturbs the competition between quantum effects in liquid water and impacts their local solvation structures.
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- PAR ID:
- 10147976
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- ISSN:
- 1463-9076
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9CP06483D
