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

Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO(2) 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 delta B-11) 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 delta B-11; (b) to determine to what degree the chosen analytical approach may affect the resultant delta B-11; and (c) to provide well-constrained consensus delta B-11 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 parts per thousand (2s*), compared with 24.25 +/- 0.22 parts per thousand (2s*) for the same oxidised material. For un-oxidised JCt-1, respective compositions are 16.39 +/- 0.60 parts per thousand (2s*; un-oxidised) and 16.24 +/- 0.38 parts per thousand (2s*; oxidised). The consistency between laboratories is generally better if carbonate powders were oxidatively cleaned prior to purification and measurement.

Automated summary

The study focused on analyzing boron isotopes in marine carbonates, with an emphasis on evaluating the influence of oxidative pre-treatment and analytical approaches on the results, and providing consistent boron isotope compositions for two carbonate materials.