Interlaboratory Comparison Study of Calibration Standards for Foraminiferal Mg/Ca Thermometry


M. Greaves, University of Cambridge
N. Caillon, avenue de la Terrasse
H. Rebaubier, avenue de la Terrasse
G. Bartoli, Kiel University
S. Bohaty, University of California
I. Cacho, University of Barcelona
L. Clarke, Bangor University
M. Cooper, National Oceanography Centre
C. Daunt, University of Cambridge
M. Delaney, University of California
P. deMenocal, Columbia University
A. Dutton, Australian National University
S. Eggins, Australian National University
H. Elderfield, University of Cambridge
D. Garbe-Schoenberg, Kiel University
E. Goddard, University of South Florida
D. Green, National Oceanography Centre
J. Groeneveld, University of Bremen
D. Hastings, Eckerd College
E. Hathorne, University of Bremen
K. Kimoto, Institute of Observational Research for Global Change
G. Klinkhammer, Oregon State University
L. Labeyrie, avenue de la Terrasse
D. W. Lea, University of California
T. Marchitto, University of Colorado
M. A. Martínez-Botí, Universitat Autònoma de Barcelona
P. G. Mortyn, Universitat Autònoma de Barcelona
Y. Ni, University of Bristol
D. Nuernberg, IFM-GEOMAR
G. Paradis, University of California
L. Pena, University of Barcelona
T. Quinn, University of South Florida
Y. Rosenthal, University of New Jersey
A. Russell, University of California
T. Sagawa, Kochi University
S. Sosdian, University of New Jersey
L. Stott, University of South California
K. Tachikawa, Europôle Méditerranéen de l'Arbois
E. Tappa, University of South Carolina
R. Thunell, University of South Carolina
P. A. Wilson, European Way

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Mg/Ca thermometry, intercalibration, reference materials, paleoceanography, carbonates

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An interlaboratory study of Mg/Ca and Sr/Ca ratios in three commercially available carbonate reference materials (BAM RS3, CMSI 1767, and ECRM 752-1) was performed with the participation of 25 laboratories that determine foraminiferal Mg/Ca ratios worldwide. These reference materials containing Mg/Ca in the range of foraminiferal calcite (0.8 mmol/mol to 6 mmol/mol) were circulated with a dissolution protocol for analysis. Participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories. Statistical analysis was performed in accordance with the International Standardization Organization standard 5725, which is based on the analysis of variance (ANOVA) technique. Repeatability (RSDr%), an indicator of intralaboratory precision, for Mg/Ca determinations in solutions after centrifuging increased with decreasing Mg/Ca, ranging from 0.78% at Mg/Ca = 5.56 mmol/mol to 1.15% at Mg/Ca = 0.79 mmol/mol. Reproducibility (RSDR%), an indicator of the interlaboratory method precision, for Mg/Ca determinations in centrifuged solutions was noticeably worse than repeatability, ranging from 4.5% at Mg/Ca = 5.56 mmol/mol to 8.7% at Mg/Ca = 0.79 mmol/mol. Results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility. Additionally, the study confirmed the suitability of these solid standards as reference materials for foraminiferal Mg/Ca (and Sr/Ca) determinations, provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases.

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Citation / Publisher Attribution

Geochemistry, Geophysics, Geosystems, v. 9, issue 8