Ababou F. E. auteur aut IRD Le Moigne F. A. C. auteur aut IRD Grosso O. auteur aut IRD Guigue Catherine auteur aut IRD Nunige S. auteur aut IRD Camps M. auteur aut IRD Bonnet Sophie auteur aut IRD text journalArticle eng text/pdf reformatted digital access Diazotrophs are ubiquitous in the surface (sub)tropical ocean, where they sustain most new primary production. Several recent studies also report the presence of diverse cyanobacterial diazotrophs in the mesopelagic and bathypelagic ocean, suggesting that they gravitationally sink, potentially supporting organic matter export and the biological carbon pump. Yet, the mechanisms leading to their export are not elucidated. Here, we simulated the sinking of diazotrophs in the water column by using rolling tanks, and measured the aggregation capacity and sinking velocities of four globally distributed strains having different sizes, shapes, and abilities to produce transparent exopolymer particles (TEP): two filamentous diazotrophs (Trichodesmium erythraeum, Calothrix sp.) and two unicellular cyanobacterial diazotrophs (UCYN-B, Crocosphaera watsonii) and (UCYN-C, Cyanothece sp.). All diazotrophs tested, regardless their size and shape, were capable of forming aggregates and sunk, albeit at different velocities depending on the aggregation capacity. Overall, UCYN formed aggregates as large as those formed by the filamentous diazotrophs (7000-32,014 mu m ESD, equivalent spherical diameter), and sunk at 100-400 m d(-1), i.e., at the same velocity as filamentous diazotrophs (92-400 m d(-1)). Although TEP are generally considered as enhancers of aggregation, TEP did not clearly influence aggregation rates nor sinking velocities during our study. We conclude that diazotrophs may be important contributors to carbon export in the ocean and need to be considered in future studies to improve the accuracy of current regional and global estimates of export. specialized 034 [Early access] [12 ] 2023 0024-3590 https://www.documentation.ird.fr/hor/fdi:010086813 10.1002/lno.12301 0024-3590 [F B010086813] https://www.documentation.ird.fr/hor/fdi:010086813 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2023-02/010086813.pdf IRD - Base Horizon / Pleins textes 2023-02-08 2026-06-12 fdi:010086813 fre