Implications of high-precision measurements of 13 C– 18 O bond ordering in CO 2 for thermometry in modern bivalved mollusc shells

Effects of Improved 17O Correction on Interlaboratory Agreement in Clumped Isotope Calibrations, Estimates of Mineral‐Specific Offsets, and Temperature Dependence of Acid Digestion Fractionation

“…By restricting ourselves to studies performed after the adoption of the absolute reference frame, where the gas and/or carbonate standards analyzed concurrently with unknowns were selected with the purpose of tracking changes in the reference frame, we rule out a poorly constrained gas‐based reference frame as a source of uncertainty (although systematic study of the errors associated with conversion to the absolute reference frame has never been carried out, and some suggest that gas‐based reference frames may be inadequate, Bernasconi et al, ). We have also eliminated variations in the temperature dependence of the acid digestion fractionation (Δ* 25‐X ), Δ 47‐TE values, or 17 O correction parameters (which were not uniformly applied across studies in the original publications—e.g., Petrizzo et al, ) as causes of the remaining disagreement. Obvious calibration differences due to methods of sample cleaning (GC versus He‐carrier PPQ versus static PPQ trap), mass spectrometer (Thermo 253 or 253+ versus Isoprime 100 versus Thermo 253 with peak hopping), or background/pressure baseline measurement method (once per day or longer versus once per sample versus once per acquisition versus none at all) are not apparent from comparisons of data generated in different laboratories.…”

Combining soil water balance and clumped isotopes to understand the nature and timing of pedogenic carbonate formation

“…Due to uncertainties based on discrepancies among carbonate temperature calibrations, Δ 47 results are converted to temperatures using the multiple empirical calibrations in Table 2. To date, numerous carbonate clumped isotope temperature calibrations have been developed using a wide range of materials including synthetic calcite and aragonite (Ghosh et al, 2006;Dennis and Schrag, 2010;Zaarur et al, 2013;Grauel et al, 2013;Petrizzo et al, 2014;Wacker et al, 2014;Tang et al, 2014;Defliese et al, 2015), biogenic calcite and aragonite (Ghosh et al, 2006;Ghosh et al, 2007;Tripati et al, 2010;Thiagarajan et al, 2011;Henkes et al, 2013;Eagle et al, 2013), and siderite (Fernandez et al, 2014). It has been observed that these calibrations can be grouped into two broad categories according to the temperature of the phosphoric acid during sample digestion, where studies that digest samples at temperatures > 70°C tend to produce shallower calibration slopes than those that react samples at 25°C (Fernandez et al, 2014).…”

Scale distortion from pressure baselines as a source of inaccuracy in triple‐isotope measurements

“…Typically, i BG is measured when the gas flow is shut off, but several papers have documented shifts in the effective background current i BG when gas enters the instrument, yielding a PBL. Both positive and negative values of i BG have been documented, attributed to incoherent scattering of ions and electrons down the flight tube, respectively . A schematic depiction of this effect is shown in Figure A.…”