The biological dinitrogen (N₂) fixation process converts atmospheric N2 into biologically available ammonia. In the ocean, it is carried out by a group of microorganisms termed diazotrophs, mainly attributed to cyanobacteria such as <em>Trichodesmium</em>. However, recent studies revealed the wide distribution of non-cyanobacterial diazotrophs (NCDs), which contrary to cyanobacteria, cannot photosynthesise and depend on organic matter to meet their nutritional requirements. While their taxonomy and ecology are yet to be explored, it is thought these groups live associated with organic sinking particles, populated particulate marine-aggregates playing a crucial role in sinking organic matter in deep waters and carbon sequestration. In the context of the relevance that ocean mesoscale structures play in regulating N₂ fixation and sinking particle fluxes, the diversity and relative abundance of the particle-attached NCD community was investigated across an anticyclonic eddy in the Canary Eddy Corridor. Community differences were observed between the core and periphery of the eddy. Such groups were impacted by water mass flows and its unique physicochemical properties, highlighting the importance of an anticyclonic eddy, as an example of a recurrent mechanism of matter transport between surface and deep ocean. The results highlight the key role of NCDs in mesoscale dynamics when determining particle transport, providing new understanding on the functioning of both carbon and nitrogen cycles, as well as on interactions between particle-associated organisms and ocean mesoscale structures.

Primary Presenter: Elena Cerdán, Aix-Marseille Université / Mediterranean Institute of Oceanography (elena.cerdan@mio.osupytheas.fr)

Authors:

Elena Cerdán-García, Aix-Marseille Université  (elena.cerdan@mio.osupytheas.fr)

Xosé Álvarez-Salgado, Instituto de Investigacións Mariñas Vigo (CSIC)  (xsalgado@iim.csic.es)

Javier Arístegui, Instituto de Oceanografía y Cambio Global (IOCAG), Universidad de Las Palmas de Gran Canaria  (javier.aristegui@ulpgc.es)

Mar Benavides, Aix-Marseille Université / Mediterranean Institute of Oceanography  (mar.benavides@mio.osupytheas.fr)