InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards.

Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth-system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I-CDES) values for Intercarb-Carbon Dioxide Equilibrium Scale.

Assessment of oceanic productivity with the triple-isotope composition of dissolved oxygen.

Plant production in the sea is a primary mechanism of global oxygen formation and carbon fixation. For this reason, and also because the ocean is a major sink for fossil fuel carbon dioxide, much attention has been given to estimating marine primary production. Here, we describe an approach for estimating production of photosynthetic oxygen, based on the isotopic composition of dissolved oxygen of seawater. This method allows the estimation of integrated oceanic productivity on a time scale of weeks.

Effect of tumor removal on the presence of lymphocytic cortisol metabolism-enhancing factor in plasma of cancer patients.

Because lymphocytic cortisol metabolism-enhancing factor (LCMEF) is absent in the plasma of cancer patients (CP), this study was undertaken to determine the influence of tumor removal on this phenomenon. Known concentrations of human lymphocytes were incubated with cortisol in media containing 50% phosphate-buffered saline (PBS) and 50% of one of the following: a) homologic normal plasma (HP),b) plasma from patients with noncancerous diseases (NCD) before surgery, c) plasma from patients with NCD after surgery, d) plasma from CP before tumor removal, e) plasma from CP after tumor removal, f) plasma from long-surviving CP (LSCP), and g) PBS. With the exception of plasma from the LSCP group, all the plasma had the capacity to enhance the lymphocytic cortisol metabolism (LCM) when compared with that of PBS. There was no significant difference between the metabolism obtained with HP and that obtained with plasma from patients with NCD either before or after surgery. The plasma from CP led to a significant reduction in activity, with no significant difference in conversion rates before and after tumor removal. The plasma from LSCP failed to enhance LCM, had a conversion rate similar to that of PBS and significantly lower than that of the plasma from CP, and appeared to contain no LCMEF. These findings, which showed that the lack of LCMEF in CP is not influenced by tumor removal, may indicate 1) that the lack of LCMEF preceded the appearance of cancer or 2) irreversibility of a possible anti-LCMEF synthesis effect was induced by the tumor.

Conversion of O(2) into CO(2) for High-Precision Oxygen Isotope Measurements.

An improved procedure of (18)O/(16)O ratio measurements by means of oxygen conversion to CO(2) is developed, which allows one to obtain the true δ(18)O values with a precision of ±0.05‰ in oxygen samples down to 7 µmol. The isotopic exchange between quartz glass and oxygen gas was measured in the temperature range of 600-900 °C, and it was found to be less than 0.2%.