Interlaboratory Comparison of Branched GDGT Temperature and pH Proxies Using Soils and Lipid Extracts

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 25; no. 7
• Main Authors: De Jonge, Cindy, Peterse, Francien, Nierop, Klaas G. J., Blattmann, Thomas M., Alexandre, Marcelo, Ansanay‐Alex, Salome, Austin, Thomas, Babin, Mathieu, Bard, Edouard, Bauersachs, Thorsten, Blewett, Jerome, Boehman, Brenna, Castañeda, Isla S., Chen, Junhui, Conti, Martina L. G., Contreras, Sergio, Cordes, Julia, Davtian, Nina, Dongen, Bart, Duncan, Bella, Elling, Felix J., Galy, Valier, Gao, Shaopeng, Hefter, Jens, Hinrichs, Kai‐Uwe, Helling, Mitchell R., Hoorweg, Mariska, Hopmans, Ellen, Hou, Juzhi, Huang, Yongsong, Huguet, Arnaud, Jia, Guodong, Karger, Cornelia, Keely, Brendan J., Kusch, Stephanie, Li, Hui, Liang, Jie, Lipp, Julius S., Liu, Weiguo, Lu, Hongxuan, Mangelsdorf, Kai, Manners, Hayley, Martinez Garcia, Alfredo, Menot, Guillemette, Mollenhauer, Gesine, Naafs, B. David A., Naeher, Sebastian, O'Connor, Lauren K., Pearce, Ethan M., Pearson, Ann, Rao, Zhiguo, Rodrigo‐Gámiz, Marta, Rosendahl, Chris, Rostek, Frauke, Bao, Rui, Sanyal, Prasanta, Schubotz, Florence, Scott, Wesley, Sen, Rahul, Sluijs, Appy, Smittenberg, Rienk, Stefanescu, Ioana, Sun, Jia, Sutton, Paul, Tierney, Jess, Tejos, Eduardo, Villanueva, Joan, Wang, Huanye, Werne, Josef, Yamamoto, Masanobu, Yang, Huan, Zhou, Aifeng
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01-07-2024; AGU and the Geochemical Society; Wiley
• Subjects: Analytical chemistry; Chemical Sciences; Earth Sciences; Environmental information; GDGT; Geochemistry; Glycerol; interlaboratory comparison; Ionization; Laboratories; Lipids; Marine sediments; Mass spectrometry; Proxies; Reproducibility; round robin; Sample preparation; Sciences of the Universe; Soil; Soil pH; Soils; round robin; interlaboratory comparison; GDGT
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2024GC011583

Ratios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake‐ and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these reconstructions, high analytical reproducibility is required. Based on submitted results by 39 laboratories from across the world, which employ a diverse range of analytical and quantification methods, we explored the reproducibility of brGDGT‐based proxies (MBT′5ME, IR, and #ringstetra) measured on four soil samples and four soil lipid extracts. Correct identification and integration of 5‐ and 6‐methyl brGDGTs is a prerequisite for the robust calculation of proxy values, but this can be challenging as indicated by the large inter‐interlaboratory variation. The exclusion of statistical outliers improves the reproducibility, where the remaining uncertainty translates into a temperature offset from median proxy values of 0.3–0.9°C and a pH offset of 0.05–0.3. There is no apparent systematic impact of the extraction method and sample preparation steps on the brGDGT ratios. Although reported GDGT concentrations are generally consistent within laboratories, they vary greatly between laboratories. This large variability in brGDGT quantification may relate to variations in ionization efficiency or specific mass spectrometer settings possibly impacting the response of brGDGTs masses relative to that of the internal standard used. While ratio values of GDGT are generally comparable, quantities can currently not be compared between laboratories.
Key Points
39 laboratories participated in a round robin to determine the reproducibility of glycerol dialkyl glycerol tetraethers (GDGT) proxy values and quantities
Peak selection impacts the ratio values and there is no apparent systematic impact of the extraction method and sample preparation steps
Quantification of GDGTs remains a problem, and comparison of GDGT concentrations between laboratories requires further method development