Sub‐Permil Interlaboratory Consistency for Solution‐Based Boron Isotope Analyses on Marine Carbonates

Abstract

Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO2 through Earth’s history. While isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the boron isotopic composition (commonly expressed in δ11B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp‐1 (coral Porites) and JCt‐1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre‐treatment, aimed at removing organic material from carbonate, can influence the resulting δ11B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ11B; and (c) to provide well‐constrained consensus δ11B values for JCp‐1 and JCt‐1. The resultant robust mean and associated robust standard deviation (s*) for un‐oxidised JCp‐1 is 24.36 ± 0.45‰ (2s*), compared with 24.25 ± 0.22‰ (2s*) for the same oxidised material. For un‐oxidised JCt‐1, respective compositions are 16.39 ± 0.60‰ (2s*; un‐oxidised) and 16.24 ± 0.38‰ (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement.

Porites Calcifying Fluid pH on Seasonal to Diurnal Scales

“…(2011), based on the long‐term reproducibility of the JCp‐1 reference material (Okai et al., 2002), and was on average ± 0.25‰ (2 SD). The δ 11 B of the JCp‐1 used in this study was 24.14‰, consistent with both the long term results from JCp‐1 analysis in this laboratory and with results from other laboratories (24.25 ± 0.22; Gutjahr et al., 2021). For trace element ratios, the analytical precision is 5% determined by the reproducibility of several in house standards (Henehan et al., 2015).…”

NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions): Inter‐laboratory δ11B and Trace Element Ratio Value Assignment

“…The simulated marine carbonate solutions comprising NIST RM 8301 will not be subject to CITES limitations restricting distribution of authentic biogenic material and will help minimise analytical artefacts caused by sample pre‐treatment in respective laboratories (e.g., oxidative cleaning and/or dissolution; Gutjahr et al . 2020). NIST RM 8301 (Foram) and NIST RM 8301 (Coral) are therefore valuable tools for evaluating the quality of marine carbonate geochemical analyses, thus improving confidence in palaeoceanographic interpretation.…”

“…In addition, assessment of the full powdered sample processing methodology was performed using the carbonate reference material JCp‐1 (robust mean including robust standard deviation (2 s *) of oxidatively cleaned JCp‐1 from companion inter‐laboratory study: 24.25‰ ± 0.22‰; Gutjahr et al . 2020). Measurements for these additional reference materials at 100 ng g −1 B mass fraction during sample analysis were, respectively, 19.71‰ ± 0.07‰ (2 s ; n = 39; no matrix separation) and 24.18‰ ± 0.39‰ ( n = 6; matrix removed by micro‐columns).…”

“…2013) (see companion inter‐laboratory study by Gutjahr et al . (2020 in press). While many carbonate geochemistry laboratories routinely use these materials in‐house, recent changes to regulations by Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) now restrict the distribution of both biogenic carbonates due to their animal origins.…”

Dichotomy between Regulation of Coral Bacterial Communities and Calcification Physiology under Ocean Acidification Conditions

“…The accuracy and precision of δ 11 B results were assessed using carbonate standards NIST RM 8301 Coral and JCp-1. Measured values for these reference materials during sample analysis were, respectively, 24.35‰ ± 0.26‰ (2 standard deviations; n = 34) and 24.06‰ ( n = 2), which were within uncertainty of interlaboratory consensus values ( 83 , 86 ). Seven total procedural blank measurements were made alongside samples in this study (average of 104 pg of boron).…”