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.

9The application of clumped isotopes ( 47 ) in carbonate minerals as a sensitive temperature proxy in 10 paleo-environments depends on a well-constrained clumped isotope fractionation for the necessary 11 step of phosphoric acid digestion of the carbonate mineral to produce CO 2 . Published estimates for 12 clumped isotope fractionations vary, and the effect of different carbonate mineralogies is still under 13 debate. Differences in the sample preparation design and sample digestion temperatures are 14 potential sources for varying acid fractionations and could be a source for discrepant  47 -15 temperature calibrations observed in different laboratories. To evaluate the clumped isotope acid 16 fractionation at 70 °C and simultaneously account for a potential cation effect we analyzed a set of 17 eight carbonate minerals (calcite, aragonite, dolomite and magnesite) that were driven to a 18 stochastic isotope distribution by heating them to temperatures of 1000 °C. Our study reveals 19 significant cation-and mineral-specific differences for the  47 acid fractionation of carbonate 20 minerals digested at 70 °C or 100 °C. The  47 acid fractionation at 70 °C for calcite is 0.197±0.002 ‰, 21 for aragonite 0.172±0.003 ‰, whereas dolomite has a significantly larger acid fractionation of 22 0.226±0.002 ‰. For magnesite digested at 100 °C we observed a  47 acid fractionation of 23 0.218±0.020 ‰. Projected to an acid digestion at 25 °C, our acid fractionation for calcite of 0.260 ‰ 24 is statistically indistinguishable from existing studies. We further show that the  47 of the calcite 25 standards ETH-1 and ETH-2 of 0.265 ‰ and 0.267 ‰, respectively, are in the range of the 26 determined acid fractionation projected to 25 °C suggesting that they have an identical and near 27 stochastic isotope distribution. The observed differences in the  47 acid fractionation between calcite 28 and aragonite ( 47 = -0.025 ‰) and between calcite and dolomite ( 47 = -0.029 ‰) does not 29 correlate with the phosphoric acid fractionation of oxygen isotopes, but rather depends on the radius 30 of the cation as well as on the mineral structure. Our results reveal that the acid fractionation of 31 dolomite at 70 °C is significantly distinct from the one of calcite, but at 90 °C the two are within error 32 © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ with M being the metal cation of the corresponding carbonate mineral (e.g. calcite and aragonite 52 (CaCO 3 ), dolomite (CaMg(CO 3 ) 2 ), magnesite (MgCO 3 ), siderite (FeCO 3 ), witherite (BaCO 3 )). Having 53 attained equilibrium this exchange reaction (Eq. 1) is thermodynamically controlled and produces an 54 excess in the doubly substituted isotopologue relative to a stochastic isotope distribution (0.5 ‰ at 0 55 °C), which decreases with increasing temperature and approaches a stochastic isotope composition 56 at 1000 °C (Schauble et al., 2006). Ghosh et al. (2006a) demonstrated the feasibility...

Carbonate clumped isotopes offer a potentially transformational tool to interpret Earth's history, but the proxy is still limited by poor interlaboratory reproducibility. Here, we focus on the uncertainties that result from the analysis of only a few replicate measurements to understand the extent to which unconstrained errors affect calibration relationships and paleoclimate reconstructions. We find that highly precise data can be routinely obtained with multiple replicate analyses, but this is not always done in many laboratories. For instance, using published estimates of external reproducibilities we find that typical clumped isotope measurements (three replicate analyses) have margins of error at the 95% confidence level (CL) that are too large for many applications. These errors, however, can be systematically reduced with more replicate measurements. Second, using a Monte Carlo‐type simulation we demonstrate that the degree of disagreement on published calibration slopes is about what we should expect considering the precision of Δ47 data, the number of samples and replicate analyses, and the temperature range covered in published calibrations. Finally, we show that the way errors are typically reported in clumped isotope data can be problematic and lead to the impression that data are more precise than warranted. We recommend that uncertainties in Δ47 data should no longer be reported as the standard error of a few replicate measurements. Instead, uncertainties should be reported as margins of error at a specified confidence level (e.g., 68% or 95% CL). These error bars are a more realistic indication of the reliability of a measurement.

The oxygen isotope composition of siderites can be used to deduce the paleoenvironmental conditions under which the mineral formed. However, it is not clear whether the published fractionation factors (CO2-siderite) for the acid digestion of siderites are appropriate for modern "on-line" sample preparation techniques. This is an important source of uncertainty that has not yet been investigated. To this aim, we obtained new siderite acid fractionation factors for open and closed vessel digestions at 100°C and 70°C, respectively. We find that previous CO2-siderite estimates are appropriate for GasBench-type sealed vessel digestions and propose a revised relationship between CO2-siderite and temperature: This relationship encompasses most practical laboratory digestion temperatures and has a temperature sensitivity of-0.032‰/°C that is similar to other carbonate minerals. The open vessel digestion CO2-siderite at 100°C, on the other hand, is offset from previous estimates by 1‰, with a value of 1000Ln9.79± 0.23 (0.12 se). This estimate is essential for the open vessel digestions that are needed for siderite clumped isotope analyses.

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