Affiliation:
1. Sorbonne Université CNRS Laboratoire d'Océanographie de Villefranche LOV Villefranche‐sur‐Mer France
2. ACRI‐ST Sophia Antipolis France
3. National Oceanography Centre Southampton UK
4. Institute for Marine and Antarctic Studies University of Tasmania Hobart TAS Australia
5. Freshwater and Oceanic Science Unit of Research (FOCUS) University of Liège Liège Belgium
6. Biology Department Ghent University MarSens Research Group Ghent Belgium
7. Flanders Marine Institute (VLIZ) InnovOcean Campus Ostend Belgium
Abstract
AbstractThe gravitational sinking of particles in the mesopelagic layer (∼200–1,000 m) transfers to the deep ocean a part of atmospheric carbon fixed by phytoplankton. This process, called the gravitational pump, exerts an important control on atmospheric CO2 levels but remains poorly characterized given the limited spatio‐temporal coverage of ship‐based flux measurements. Here, we examined the gravitational pump with BioGeoChemical‐Argo floats in the Southern Ocean, a critically under‐sampled area. Using time‐series of bio‐optical measurements, we characterized the concentration of particles in the productive zone, their export and transfer efficiency in the underlying mesopelagic zone, and the magnitude of sinking flux at 1,000 m. We separated float observations into six environments delineated by latitudinal fronts, sea‐ice coverage, and natural iron fertilization. Results show a significant increase in the sinking‐particle flux at 1,000 m with increasing latitude, despite comparable particle concentrations in the productive layer. The variability in deep flux was driven by changes in the transfer efficiency of the flux, related to the composition of the phytoplanktonic community and the size of particles, with intense flux associated with the predominance of micro‐phytoplankton and large particles at the surface. We quantified the relationships between the nature of surface particles and the flux at 1,000 m and used these results to upscale our flux survey across the whole Southern Ocean using surface observations by floats and satellites. We then estimated the basin‐wide Spring‐Summer flux of sinking particles at 1,000 m over the Southern Ocean (0.054 ± 0.021 Pg C).
Funder
Association Nationale de la Recherche et de la Technologie
HORIZON EUROPE Marie Sklodowska-Curie Actions
Publisher
American Geophysical Union (AGU)
Subject
Atmospheric Science,General Environmental Science,Environmental Chemistry,Global and Planetary Change
Cited by
1 articles.
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