Study of the radium and actinium 227 isotopes along SWINGS section in the indian sector of the Southern Ocean

• Main Author: Leon, Morgane
• 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), Université Paul Sabatier - Toulouse III, Pieter Van Beek, Virginie Sanial
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Radium isotopes; Actinium-227; Southern ocean; Hydrothermalism; GEOTRACES; Tracers; Isotopes du radium; Océan Austral; Hydrothermalisme; Traceurs; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Antarc*; Antarctic; Southern Ocean
• Online Access: https://theses.hal.science/tel-04631893; https://theses.hal.science/tel-04631893/document; https://theses.hal.science/tel-04631893/file/2023TOU30384.pdf

The Southern Ocean absorbs around 20% of the world's atmospheric CO2, thanks in part to the biological carbon pump, regulated by the abundance of surface nutrients. The interaction of the Antarctic Circumpolar Current with sediments results in significant inputs of chemical elements to the ocean, inducing phytoplankton blooms in the vicinity of the sub-Antarctic islands. As part of the GEOTRACES program, the SWINGS cruise took place in 2021 in the Indian sector of the Southern Ocean to study the distribution, sources and sinks of various trace elements and isotopes, as well as their internal cycles in the Indian sector of the Southern Ocean. Radium isotopes (223Ra, 224Ra, 228Ra and 226Ra) are mainly diffused in the dissolved phase from marine sediments and then dispersed in the ocean. Thanks to their different radioactive half-lives, these isotopes are powerful tracers of the contact of water masses with sediments, enabling the study of processes on various time and space scales. Similarly, 227Ac is mainly released by diffusion from deep sediments, making it a complementary tracer to Ra isotopes. In the first chapter, methodological work has been carried out to improve the estimation of Ra and 227Ac isotope activities from large-volume seawater samples. Two methods for assessing the absorption efficiency of Ra isotopes on pre-concentrated radionuclide cartridges are compared. The first consists in comparing the activities observed on the cartridges with the activities observed on a media where the water has been filtered at less than 1L/min to allow complete adsorption of the radioelements onto the media. A second method involves comparing the activities of two cartridges placed in series. While the Ra efficiencies estimated by the two methods are similar (79.2% and 63.9%), the extraction efficiency of 227Ac is lower (49.3%). The possibility of estimating the extraction efficiency of 227Ac from that of Ra is therefore discussed. Finally, it is recommended to determine the extraction efficiencies of Ra and 227Ac ...