Eagle-Tripati LaboratoriesGuide for clumped isotope data quality assessment, including measurement flagging December 2022 J. Lucarelli and A. Tripati • Definitions:○ Data quality assessment: the process of assessing if data are reproducible, including identifying if there were statistical outliers that may arise due to incomplete sample digestion, voltage fluctuations, exchange with water, carousel not advancing properly, or other processes relating to sample reaction, purification, and measurement, etc., resulting in an erroneous measurement or non-representative value ○ Flagging: identifying a statistical outlier that you hypothesize is due to an erroneous measurement or is not representative of the sample, that you think should not be included in calculations.■ You need ≥3 replicates to begin flagging. ○ Outlier: an observation that statistically lies an abnormal distance from other values in a random sample from a population. ○ Exclusion: removal of an analysis from the population.■ Before excluding a replicate, talk to Aradhna/Rob and Ben about why it's being excluded -there may be a solution to the issue. ■ You must include detailed notes on the justification in both the run log and in Easotope, after discussion with Aradhna/Rob and Ben ○ Standard deviation: a measure of the amount of variation or dispersion of a set of values.A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while a high standard deviation indicates that the values are spread out over a wider range.
The Cedars is an area in Northern California with a chain of highly alkaline springs resulting from CO-charged meteorological water interacting with a peridotite body. Serpentinization resulting from this interaction at depth leads to the sequestration of various carbonate minerals into veins accompanied by a release of Ca and OH enriched water to the surface, creating an environment which promotes rapid precipitation of CaCO at surface springs. This environment enables us to apply the recently developed Δ-Δ dual clumped isotope analysis to probe kinetic isotope effects (KIEs) and timescales of CO transformation in a region with the potential for geological CO sequestration. We analyzed CaCO recovered from various localities and identified significant kinetic fractionations associated with CO absorption in a majority of samples, characterized by enrichment in Δ values and depletion in Δ values relative to equilibrium. Surface floes exhibited the largest KIEs (ΔΔ: 0.163‰, ΔΔ: -0.761‰). Surface floe samples begin to precipitate out of solution within the first hour of CO absorption, and the dissolved inorganic carbon (DIC) pool requires a residence time of >100 hours to achieve isotopic equilibria. The Δ/Δ slope of samples from the Cedars (-3.223±0.519; 1 SE) is within the range of published theoretical values designed to constrain CO hydrolysis-related kinetic fractionation (-1.724 to -8.330). The Δ/δO slope (-0.009±0.001) and Δ/δC slope (0.009±0.001) are roughly consistent with literature values reported from a peridotite in Oman of -0.006±0.002 and -0.005±0.002, respectively. The consistency of slopes in the multi-isotope space suggests the Δ-Δ dual carbonate clumped isotope framework can be applied to study CO-absorption processes in applied systems, including sites of interest for geological sequestration.
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