Comparison of methods to determine extraction efficiencies of Ra isotopes and 227Ac from large volume seawater samples

• Published in: Marine Chemistry
• Main Authors: Léon, Morgane, van Beek, Pieter, Sanial, Virginie, Souhaut, Marc, Henderson, Paul, Charette, Matthew
• Other Authors: Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), Woods Hole Oceanographic Institution (WHOI), OCE-2048067 National Science FoundationFlotte Océanographique Française, The authors thank Hélène Planquette and Catherine Jeandel, PIs of the SWINGS project and chief scientist of the SWINGS cruise. We also thank the captain, LDA and GENAVIR officers, engineers, technicians and the crew of the R/V Marion Dufresne for their assistance during the SWINGS cruise. The authors also thank Emmanuel de Saint-Léger and Fabien Pérault, Marion Lagarde, Nolwenn Lemaitre, Edwin Cotard, Frederic Planchon for their help during the deployment of the in-situ pumps. We are grateful to Elodie Kestenare, Frederic Vivier, Gérard Eldin, Sara Sergi, Corentin Clerc and Loyd Izard for CTD data acquisition and preparation of Niskin bottles. We thank Thomas Zambardi for his help at the LAFARA underground laboratory. The SWINGS project was supported by the French Oceanographic Fleet, ANR (Agence Nationale de la Recherche; ANR) CNRS/ INSU (Centre Nationale de la Recherche Scientifique/Institut National des Sciences de l'Univers) and ISblue ( ANR-17-EURE-0015 ). This study has been partially supported through the grant EUR TESS N°ANR-18-EURE-0018 in the framework of the Programme des Investissements d'Avenir. M.A.C. was funded by the U.S. National Science Foundation OCE-2048067 ., ANR-17-EURE-0015,ISBlue,Interdisciplinary Graduate School for the Blue planet(2017), ANR-18-EURE-0018,TESS,Toulouse Graduate School of Earth and Space Sciences(2018)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2024
• Subjects: Actinium-227; Extraction efficiency; Methodology; Ocean; Radium; Tracers; [SDE]Environmental Sciences; Southern Ocean
• Online Access: https://hal.univ-brest.fr/hal-04373424; https://doi.org/10.1016/j.marchem.2023.104328

International audience Radium isotopes, other than 226Ra, and 227Ac are typically present at low activities in the open ocean. The analysis of these isotopes thus requires the collection of large volumes of seawater and high sensitivity, low background instruments. To obtain the required large volumes (hundreds to thousands of liters), these radionuclides are typically preconcentrated on cartridge-style filters impregnated with MnO2 (Mn-cartridges) deployed on in-situ pumps. This technique, however, requires the determination of the extraction efficiency of the Mn-cartridges for the radionuclides of interest. For Ra isotopes, we used two methods to estimate the extraction efficiency of these Mn-cartridges at two stations on the South-West Indian Ridge in the Southern Ocean (GEOTRACES GS02). Method (1) compares the 226Ra activities recovered on the Mn-cartridges versus the activities determined in Mn-fibers, through which seawater was passed at a flow rate < 1 L min−1 to quantitatively sorb Ra (Mn-fiber method) while method (2) combines the 226Ra activities determined from two Mn-cartridges placed in series on in-situ pumps (A-B method). The second method is also applied to determine the 227Ac extraction efficiency. We find a relatively wide-range of Ra and 227Ac extraction efficiencies across the dataset (from 44.8% to 99.6% for Ra, and from 23.7% to 77.5% for 227Ac). Overall, the yield of 227Ac extraction is lower than that of Ra (mean value of 49.3 ± 19.0% for 227Ac, n = 10, mean value of 79.2 ± 10.3% for Ra, n = 13, using the Mn-fiber method; and a mean value of 63.9 ± 12.5%, n = 11 using the A-B method). Our dataset suggests that the Ra extraction efficiencies using either the A-B method or the Mn-fiber method are in relatively good agreement. Consequently, the 223Raex, 224Raex and 228Ra activities determined from the Mn-cartridges by applying the two Ra extraction yields are similar. We also show that the 227Ac extraction efficiency can be estimated from the Ra extraction efficiency allowing the use of ...