An interlaboratory study of TEX86 and BIT analysis of sediments, extracts, and standard mixtures

Abstract

Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. [2] Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX 86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX 86 values (reproducibility 63– 4 C when translated to temperature) but a large spread in BIT measurements (reproducibility 60.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX 86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX 86 values ranged from 1.3 to 3.0 C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX 86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the ''true'' (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.

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@inproceedings{Hopmans2013AnIS, title={An interlaboratory study of TEX86 and BIT analysis of sediments, extracts, and standard mixtures}, author={Ellen C. Hopmans and Antoni Rosell-Mel{\'e} and Ann Pearson and Pierre Adam and Thorsten Bauersachs and Edouard Bard and Stefan Schouten and Stefano M. Bernasconi and Thomas S. Bianchi and Jochen J Brocks and Laura Truxal Carlson and Sylvie Derenne and Ayça Do grul Selver and K. Dutta and Timothy I. Eglinton and C{\'e}line Fosse and Valier Galy and Kai-Uwe Hinrichs and Yongsong Huang and Arnaud Huguet}, year={2013} }