In the remote Southern Ocean (SO) considered as a nutrient “hub” between the Atlantic, Pacific and Indian Oceans, the sources, sinks and processes controlling vital nutrient distribution remain a black-box to date. In this context, SWINGS is a multidisciplinary 4-year project dedicated to elucidate trace element sources, transformations and sinks along a section crossing key areas of the SO. Major French contribution to the international GEOTRACES program (www.geotraces.org), SWINGS involves 78 scientists (19 international laboratories, 6 countries). A 63-day oceanographic cruise in the South Indian Ocean (47 participants on board), process-oriented field studies and integrative modeling experiments will be carried out early 2021 to tackle the following objectives:
1) establish the relative importance of sedimentary, atmospheric and hydrothermal sources of TEIs in the Indian sector of the SO, 2) investigate the drivers of the internal trace element cycles: biogenic uptake, remineralization, particle fate, and export, and 3) quantify TEI transport by the Antarctic Circumpolar Current and the numerous fronts at the confluence between Indian and Atlantic Oceans.
SWINGS strategy relies on the strong coupling between physical oceanography, biogeochemistry and modeling. A major and original focus will be put on the characterization of the physical and chemical particle speciation in suspended and sinking particles that will be collected during SWINGS. Together with a high resolution sampling of the dissolved phases, the resulting SWINGS harvest of data will allow a major step forward in the understanding and quantification of dissolved-particle exchanges, a major recognized bolt for the element cycle modelling. Dedicated tracers (e.g. Th and Pa isotopes) will help to characterize the particle dynamics. Ra isotopes will support the quantification of land-ocean transfers while Nd ones will trace the origin of the dissolved and particulate matter. Specific attention will be paid to the ocean interfaces: atmospheric and land contacts, and a segment of the South West Indian Ridge suspected to be the home of active hydrothermal sites. State of the art in situ mass spectrometer will be deployed for this exploration. The cruise track –at the Atlantic-Indian boundary- will cross up to 6 currents or fronts. These jets are major pathways of the general circulation, critical for chemical specie transport: they will be thoroughly documented. New model experiments will be designed and take place after first data acquisition, in order to evaluate the sensitivity in TEI distributions to the representation of sources and transports and explore the importance of “the island effect” on the TEI distribution around naturally fertilized islands.
SWINGS is structured in 4 tasks: 1) Management of the project, design and management of the cruise, physical parameter measurements and data management; 2) Thorough sampling of particulate and dissolved phases of TEIs all along the track; 3) Characterization of the biological uptake and remineralization mechanisms; 4) Original modelling development, coupling tracer distributions with refine simulations of the circulation to quantify TEI transport and transformation.
The first year (2020) will be fully dedicated to the cruise preparation. The cruise is planned for early 2021 on the R/V Marion-Dufresne. Analyses, data validation, interpretation will start in boreal spring 2021. Post-cruise meetings, communications and peer-reviewed publications will happen until 2024 and likely beyond. SWINGS being a GEOTRACES section (#GS02) will follow the mandatory sampling resolution, intercalibration procedure and data validation: all the acquired data will be granted open access following a rigorous Data Management Plan.
Madame Catherine Jeandel (CNRS, Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS))
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Eidgenössische Technische Hochschule Zürich, ETHZ / Institute for Geochemistry and Petrology
WU-SO Washington University / The School of Oceanography
MPI-CCGD Max Planck Institute for Chemistry / Climate Geochemistry Department
CSIR-SOCCO Council for Scientific and Industrial Research / Southern Ocean Carbon and Climate Observatory
SU-DEAS Stellenbosch University / Department of Earth Sciences
WHOI-MBC Woodshole Oceanographic Institution / Marine Bioiorganic Chemistry
FU-DEOAS Florida University / Department of Earth, Ocean and Atmopsheric Science
BAS-PO British Antarctic Survey / Physical Oceanography
DU-B&E Duke University / Biogeochemistry & Ecophysiology
CNRS-CECI CNRS, Laboratoire Climat, Environnement, Couplages et Incertitudes (CECI)
IRD-LOPS Institut de Recherche pour le développement (IRD), Laboratoire d'Océanographie Physique et Spatialen (LOPS)
CNRS-GET CNRS, Géosciences Environnement Toulouse (GET)
CNRS-LOMIC CNRS, Laboratoire d'Océanographie Microbienne (LOMIC)
CNRS-LOCEAN CNRS,Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
CNRS-LSCE CNRS, Laboratoire des Sciences du Climat et de l'Environnement (LSCE)
CNRS-LEMAR Centre National de la Recherche Scientifique (CNRS), Laboratoire des sciences de l'Environnement Marin (LEMAR)
CNRS-AD2M CNRS, Adaptation et Diversité en Milieu Marin (AD2M)
AMU-MIO Aix Marseille Université (AMU), Institut Méditerranéen d'Océanologie (MIO)
CNRS-LEGOS CNRS, Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (LEGOS)
Help of the ANR 597,570 euros
Beginning and duration of the scientific project: January 2020 - 48 Months