Analytical effects on clumped isotope thermometry: Comparison of a common sample set analyzed using multiple instruments, types of standards, and standardization windows

Abstract

Rationale Carbonate clumped isotope geothermometry is being increasingly used in multiple disciplines in the geosciences. However, potential interlaboratory issues are arising from different standardization procedures that may contribute to the multiple Δ47‐temperature calibrations reported in the literature. We investigate this issue by comparing a common temperature calibration sample set across three different mass spectrometers, using multiple standardization methods. Methods The same temperature calibration sample set was analyzed on three different mass spectrometers. Several standardization methods were utilized, including the use of carbonate versus gas standards, and different types of background correction were applied to the raw data. Results All standardization types applied resulted in statistically indistinguishable Δ47‐temperature slopes, with the exception of standardization calculations that did not correct for background effects. Some instruments and standardizations showed different intercepts relative to each other. The use of carbonate standards improved comparability between different instruments relative to gas standards. Conclusions Our results show that background effects are the largest factor potentially affecting Δ47 results, and there may be an improvement in interlaboratory precision using carbonate standards. Critically, all techniques used for standardizing Δ47 results converge on a common slope as long as background effects are properly corrected. The use of carbonate standards is recommended as a component of standardization procedures.

Carbonate clumped isotope analysis (Δ47) of 21 carbonate standards determined via gas source isotope ratio mass spectrometry on four instrumental configurations using carbonate-based standardization and multi-year datasets

“…The main contribution of this study is presenting standard values for 21 internal and international carbonate standards run on multiple mass spectrometer systems. We demonstrate the stability of different types of instruments, showing that considerable drift can occur on timescales of more than a month, consistent with a recent report by Defliese and Tripati (2020). We also find that carefully chosen measurement windows associated with frequent analysis of standards are necessary to yield results that are comparable across multiple instruments.…”

“…In carbonate minerals and dissolved inorganic carbon (DIC) species, heavy isotopes 13 C and 18 O are rare relative to light isotopes, 12 C and 16 O. Combinations of these isotopes form isotopologues of carbonate ions with masses varying from 60 to 67 amu.…”

“…Initially, clumped isotope measurements utilized 1000 o C equilibrated gases of different bulk compositions that had stochastic distributions as working standards to implement a linearity correction (1,26) . Subsequent standardization approaches included multiple sets of heated and water equilibrated gases (16,18,19) , use of carbonate standards (16,17,18) , or a mixed gas and carbonate standards approach (18,20) , to implement both a linearity correction and a scale compression/stretching correction.…”

“…Equilibrium fractionations of multiply-substituted molecular species are governed by temperature-dependent homogeneous isotope exchange reactions (3,5,6,7) . The most widely studied system in clumped isotope geochemistry is based on the proportion of 13 C and 18 O isotopes bound to each other within carbonate ion ( 13 C 18 O 16 O 2 2-) groups in carbonate-containing minerals, relative to a stochastic distribution of isotopes (1,2,3,6,7) . Carbonate clumped isotope thermometry has been used to probe the temperature history of surface (8) and subsurface environments (9) , paleo-physiology (10) , biomineralization processes (11) , the alteration history of meteorites (12,13,14) , as well as the origin of possible kinetic effects (3,15) .…”

“…However, a range of instrumentation and techniques have been employed by different labs. Several studies comparing a breadth of instrumentation have identified factors that contribute to inter-lab offsets and proposed advances to address inter-comparability (16,17,18,19) . In addition, community-wide changes in standardization methods have occurred (16) , in addition to laboratory-specific practices (17) .…”