New insights on the $^7$Be cycle in the ocean

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Grenier, M., van Beek, P., Lerner, P., Sanial, Virginie, Souhaut, M., Lagarde, Marion, Marchal, O., Reyss, J.L.
• 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), NASA Goddard Institute for Space Studies (GISS), NASA Goddard Space Flight Center (GSFC), Department of Applied Physics and Applied Mathematics New York, Columbia University New York, 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), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Beryllium 7; Suspended particles; Vertical profiles; Open ocean; Solid/solution partitioning; GEOTRACES; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Southern Ocean; Indian; Labrador Sea; North Atlantic
• Online Access: https://hal.science/hal-03969407; https://hal.science/hal-03969407/document; https://hal.science/hal-03969407/file/Grenier-etal_7Be-newInsights_DSR_23.pdf; https://doi.org/10.1016/j.dsr.2023.103967

International audience The cosmogenic radionuclide $^7$Be has been applied as a tracer of dynamical processes in the upper ocean and of atmospheric deposition of trace elements at the sea surface. These applications usually assume that 7Be is entirely in the dissolved form, and that scavenging and downward export of $^7$Be by settling particles can be neglected. In this work, we explore these assumptions and more generally assess the significance of the $^7$Be activity in the particulate fraction, through the generation of vertical profiles of particulate $^7$Be in the open ocean. From detailed measurements obtained from low-background gamma spectrometers placed in underground facilities, we report vertical profiles of $^7$Be activity in suspended particles ($^7$Be$_p$) collected in various oceanic regions: the Mediterranean Sea (DYFAMED station), the Indian Sector of the Southern Ocean (station A3-2 from the KEOPS2 cruise), the Sargasso Sea (OFP station), and the subpolar North Atlantic Ocean (GEOVIDE cruise).We find that, in each oceanic region, $^7$Be$_p$ activities are generally higher in the mixed layer than in the thermocline. They vary in the mixed layer from 3.0 dpm/m3 at DYFAMED to 33.1 dpm/m$^3$ at GEOVIDE cross- over station 51/60, i.e., within a range consistent with previous $^7$Be$_p$ measurements for the open ocean. For the GEOVIDE cruise, the $^7$Be$_p$ activities measured on different filter types at different depths are corrected for filter offsets derived from multiple $^7$Be$_p$ measurements at a near-coastal station in the western Mediterranean Sea. We then combine measurements of total $^7$Be activity (Shelley et al., 2017) with our measurements of $^7$Bep activity to estimate the solid/solution partitioning of $^7$Be. On average, the particulate fraction would represent 6% of total $^7$Be activity at 5-m water depth (n = 6), 22% at 20 m (n = 2) and 9% at 70 m (n = 3). At GEOVIDE stations, $^7$Be$_p$ inventories range from 5% to 19% of the total $^7$Be inventories. In the Labrador Sea, ...