Publication Date:
2017-08-03
Description:
Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 5263–5285, doi:10.1002/2013GC004904.
Description:
Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (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 TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 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 TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 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 TEX86 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.
Description:
S.S. thanks the Netherlands Organisation
for Scientific Research (NWO) for financial support through a
VICI grant and Jaap van der Meer for advice and support on
the statistical analysis. A.P. thanks Susan Carter for laboratory
assistance and NSF-OCE for funding. A.R.M. thanks Jordi
Coello and N uria Moraleda for advice and support on the statistical
analysis and Spanish Ministry for research and innovation
(MICIIN) for funding. V.G. thanks Xavier Philippon and
Carl Johnson for technical assistance. K.G. and M.W. thank
the Australian Research Council and John de Laeter Centre
for funding toward the LC-MS system, and ARC Fellowship
awarded to K.G. C.L.Z. thanks the State Key Laboratory of
Marine Geology and the Chinese ‘‘National Thousand Talents’’
program for supporting the LC-MS work performed at
Tongji University.
Description:
2014-06-20
Keywords:
TEX86
;
BIT
;
GDGT
;
Round robin
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
text/plain
Format:
application/msword
Format:
application/pdf
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