ORCID Profile
0000-0002-0709-9192
Current Organisation
University of Michigan
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Publisher: Elsevier BV
Date: 03-2015
Publisher: Elsevier BV
Date: 2016
Publisher: Wiley
Date: 26-03-2015
DOI: 10.1002/RCM.7175
Abstract: Mass-47 CO(2) clumped isotope thermometry requires relatively large (~20 mg) s les of carbonate minerals due to detection limits and shot noise in gas source isotope ratio mass spectrometry (IRMS). However, it is unreasonable to assume that natural geologic materials are homogenous on the scale required for s ling. We show that s le heterogeneities can cause offsets from equilibrium Δ(47) values that are controlled solely by end member mixing and are independent of equilibrium temperatures. A numerical model was built to simulate and quantify the effects of end member mixing on Δ(47). The model was run in multiple possible configurations to produce a dataset of mixing effects. We verified that the model accurately simulated real phenomena by comparing two artificial laboratory mixtures measured using IRMS to model output. Mixing effects were found to be dependent on end member isotopic composition in δ(13)C and δ(18)O values, and independent of end member Δ(47) values. Both positive and negative offsets from equilibrium Δ(47) can occur, and the sign is dependent on the interaction between end member isotopic compositions. The overall magnitude of mixing offsets is controlled by the amount of variability within a s le the larger the disparity between end member compositions, the larger the mixing offset. S les varying by less than 2 ‰ in both δ(13)C and δ(18)O values have mixing offsets below current IRMS detection limits. We recommend the use of isotopic subs ling for δ(13)C and δ(18)O values to determine s le heterogeneity, and to evaluate any potential mixing effects in s les suspected of being heterogonous.
Publisher: American Geophysical Union (AGU)
Date: 05-2002
DOI: 10.1029/2000PA000593
Publisher: Society for Sedimentary Geology
Date: 07-11-2007
Publisher: American Geophysical Union (AGU)
Date: 07-2019
DOI: 10.1029/2018GC008127
Abstract: The clumped isotopic composition of carbonate‐derived CO 2 (denoted Δ 47 ) is a function of carbonate formation temperature and in natural s les can act as a recorder of paleoclimate, burial, or diagenetic conditions. The absolute abundance of heavy isotopes in the universal standards VPDB and VSMOW (defined by four parameters: R 13 VPDB , R 17 VSMOW , R 18 VSMOW , and λ ) impact calculated Δ 47 values. Here, we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured T‐Δ 47 relationship. Using the updated parameters, we reprocess 14 published calibration data sets measured in 11 different laboratories, representing many mineralogies, bulk compositions, s le types, reaction temperatures, and s le preparation and analysis methods. Exploiting this large composite data set ( n = 1,253 s le replicates), we investigate the possibility for a “universal” clumped isotope calibration. We find that applying updated parameters improves the T‐Δ 47 relationship (reduces residuals) within most labs and improves overall agreement but does not eliminate all interlaboratory differences. We reaffirm earlier findings that different mineralogies do not require different calibration equations and that cleaning procedures, method of pressure baseline correction, and mass spectrometer type do not affect interlaboratory agreement. We also present new estimates of the temperature dependence of the acid digestion fractionation for Δ 47 (Δ* 25‐X ), based on combining reprocessed data from four studies, and new theoretical equilibrium values to be used in calculation of the empirical transfer function. Overall, we have ruled out a number of possible causes of interlaboratory disagreement in the T‐Δ 47 relationship, but many more remain to be investigated.
Publisher: American Geophysical Union (AGU)
Date: 28-07-2005
DOI: 10.1029/2004PA001098
Publisher: Wiley
Date: 30-12-2005
DOI: 10.1002/HYP.5876
Publisher: American Geophysical Union (AGU)
Date: 02-2017
DOI: 10.1002/2016PA003014
No related grants have been discovered for Kyger Lohmann.