High precision osmium elemental and isotope measurements of North Atlantic seawater

• Published in: J. Anal. At. Spectrom.
• Main Authors: Gannoun, Abdelmouhcine, Burton, Kevin W.
• Other Authors: Laboratoire Magmas et Volcans (LMV), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Department of Earth Sciences Durham, Durham University
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2014
• Subjects: [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; North Atlantic; North East Atlantic
• Online Access: https://hal.science/hal-01134921; https://doi.org/10.1039/C4JA00265B

International audience This study presents new Os isotope and elemental data of seawater from the North Atlantic Ocean. Two techniques have been optimised and used to achieve tracer–seawater equilibration: (i) heating of a seawater–tracer mixture at 100 °C with Br2, CrO3 and H2SO4 in Teflon bombs and solvent extraction of OsO4 with Br2; and (ii) heating of a seawater–tracer mixture to 300 °C with CrO3 and H2SO4 in a sealed glass tube (HPA-S-s) at 125 bars and back extraction with Br2. Both techniques yield similar total procedural blanks in the range of 14–18 fg, and have a total Os yield that ranges from 86 to 92%. For the 200 fg Os standard, the effective ionisation efficiency is between 6 and 10% demonstrating that single filament ionization is capable of achieving significant Os sensitivity. To assess the external reproducibility on the 187Os/188Os ratio, both methods have been systematically applied to a single sample from a water depth of 2000 m and yield an indistinguishable 187Os/188Os ratio of 1.026 ± 0.017 (n = 11) and 1.020 ± 0.013 (n = 3), for techniques (i) and (ii), respectively. The external reproducibility on the 187Os/188Os ratio and Os concentration is 1.6% and 3.7% respectively, demonstrating the capability of both methods for analysing Os in natural water. Both procedures have been applied to a seawater profile from the North East Atlantic Ocean (IB13: 60°29.4′ N, 19°59.2′ W, 2650 m water depth). The results show little measurable variability in either Os concentration or isotope composition with depth and the overall average for the whole profile is 1.024 ± 0.031 (3%) for the 187Os/188Os ratio and 9.68 ± 0.48 (4.9%) pg kg−1 for the Os concentration. Therefore, for this locality at least, Os appears to behave conservatively.