Carbonate clumped isotope paleothermometry: a review of recent advances in CO2 gas evolution, purification, measurement and standardization techniques

Rationale: Acid digestion of carbonates to release CO 2 is a crucial and sensitive step in sample preparation for clumped isotope analysis. In addition to data reduction and instrumental artefacts, many other uncertainties in the clumped isotope analysis of carbonates arise from the method used for the preparation of CO 2 .We describe here an in-house-designed reaction vessel that circumvents degassing and contamination problems commonly associated with the McCrea-type digestion protocols. Methods:We designed a leak-free break seal reaction vessel (made of Pyrex™) suitable for prolonged acid digestion at 25°C. Using this new vessel, several carbonate reference materials widely used in the clumped isotope community and other inhouse laboratory standards were acid-digested and analysed for their δ 13 C, δ 18 O and Δ 47 values with a dual inlet MAT 253 isotope ratio mass spectrometer following standard gas chromatography purification and data evaluation protocols.Results: Long-term reproducibility in Δ 47 determination was established using international references and in-house working standards as follows (mean and SE):Carrara-1 (0.395 ± 0.002‰, n = 43), Carrara-2 (0.441 ± 0.003‰, n = 22), OMC (0.587 ± 0.004‰, n = 16), NBS 19 (0.393 ± 0.005‰, n = 10), NBS 18 (0.473 ± 0.003‰, n = 5), ETH 1 (0.271 ± 0.005‰, n = 7), ETH 3 (0.698 ± 0.005‰, n = 3), MZ (0.715 ± 0.002‰, n = 3) and several others. Conclusions:A new method using a break seal tube was found to be efficient for the clumped isotope analysis of carbonates that require longer reaction time at 25°C. This method yields good precision in Δ 47 analysis and was found to be suitable for acid digestions at any desired temperature.

{CaCO}_{3} + H_{3} {PO}_{4} \leftrightarrow {CaHPO}_{4} + {CO}_{2} + H_{2} normalO

…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Acid digestion of carbonates using break seal method for clumped isotope analysis

Fosu

Ghosh

Mishra

et al. 2018

“…Most laboratories carrying out clumped isotope analyses on carbonates follow analytical methods based on the original publication of Ghosh et al [13] or the automated system described by Passey et al [14] These laboratories dissolve 4 to 15 mg of carbonate powder in a common phosphoric acid bath or digest samples in large-volume vessels (online or offline). The gas is then cleaned and transferred to an isotope ratio mass spectrometer to be measured via the traditional dual inlet (DI) technique (see Spencer and Kim [15] for a detailed overview of different preparation systems). Relatively large sample sizes are needed because the sample bellow of the mass spectrometer must be filled with enough gas (50-200 μmol) for the long ion counting times needed to obtain internal standard errors (SE) of less than ±0.01 ‰ at constant signal intensity.…”

mentioning

confidence: 99%

Carbonate clumped isotope analyses with the long‐integration dual‐inlet (LIDI) workflow: scratching at the lower sample weight boundaries

Müller

Fernández

Radke

et al. 2017

105

122

This study demonstrates that by using a Kiel IV-253 Plus system with LIDI it is possible to achieve the same analytical precision as conventional DI measurements with at least a factor of 40 less sample material. With the new 10 ohm resistor technology there is the potential to reduce the required sample material even more. This opens new avenues of research in paleoceanography, paleoclimatology, low-temperature diagenesis and other currently sample size limited applications. Copyright © 2017 John Wiley & Sons, Ltd.

“…The pretreatment debate is also ongoing among the users of clumped isotopes, 125,126 those working in other isotope systems, 127,128 those focused on abiogenic carbonates, 113,129,130 and those measuring stable isotopes in soft tissues 131 . On‐line geochemistry list‐serves reflect the lack of consensus on what, if any, pretreatment should be used.…”

Section: Discussionmentioning

confidence: 99%

Effect of removal of organic material on stable isotope ratios in skeletal carbonate from taxonomic groups with complex mineralogies

Key

Smith

Phillips

et al. 2020

Rationale Stable oxygen and carbon isotope ratios are one of the most accurate ways of determining environmental changes in the past, which are used to predict future environmental change. Biogenic carbonates from marine organisms are the most common source of samples for stable isotope analysis. Before they are analyzed by mass spectrometry, any organic material is traditionally removed by one of three common pretreatment methods: roasting, bleaching, or with hydrogen peroxide at various strengths and durations. Methods This study compares δ18O and δ13C values in a control with no pretreatment with those from five different pretreatment methods using conventional acid digestion mass spectrometry. The objectives are to: assess the impact of the most common pretreatment methods on δ18O and δ13C values from (1) taxonomically underrepresented groups in previous studies, and (2) those that precipitate a wide range of biomineralogies, in the debate of whether to pretreat or not to pretreat. We analyzed the following biomineralogically complex temperate marine organisms from southern New Zealand: four species of bryozoans, four species of molluscs, two species of arthropods, and one species each of annelid, red alga, brachiopod, and echinoderm (test plates and spines treated separately). These species precipitate aragonite, High‐, Intermediate‐, and/or Low‐Mg calcite (LMC) in their skeletons. We used linear mixed statistical models to compare the effects of the pretreatments and mineralogical composition on their δ18O and δ13C values. Results Roasting was the most effective pretreatment for the removal of organic matter and light H2O2 the least, but the former had corresponding impacts on isotope ratios. δ18O values were not directly affected by wt% MgCO3, but they were significantly affected by the interaction of roasting and wt% MgCO3. This same negative effect of roasting on species with higher wt% MgCO3 occurred in δ13C values, but it was much more pronounced in δ18O values. Both H2O2 pretreatments significantly and negatively affected δ18O values at higher wt% MgCO3. Neither bleaching pretreatment significantly affected δ18O values. δ13C values were most negatively affected in skeletons with high wt% MgCO3. There was also a strong negative roasting effect and more so at higher wt% MgCO3. Bleaching and H2O2 did not significantly affect δ13C values. Conclusions Based on these results, and when using skeletal carbonate of complex mineralogies, we recommend considering the abandonment of pretreatment of biogenic carbonate for stable isotope analysis due to confounded results from previous studies, difficulties with preparation, and/or the absence of significant effects of organic material on isotope ratios. If pretreatment is necessary, avoid roasting especially at higher temperatures and durations, use minimal bleaching, and in general avoid using High‐Mg calcite species in O and C stable isotope studies. If bleaching is used, clearly indicate the concentration and duration of exposure.