Basin-wide N2 fixation in the deep waters of the Mediterranean Sea

• Published in: Global Biogeochemical Cycles
• Main Authors: Benavides, Mar, Martínez-Pérez, Alba María, Nieto-Cid, Mar, Álvarez-Salgado, Xosé Antón, Gasol, Josep M., Arístegui, Javier
• Other Authors: Haut Conseil pour la Science et la Technologie (France), Ministry of Science, Technology and Space (Israel), European Science Foundation, Consejo Superior de Investigaciones Científicas (España), Ministerio de Economía y Competitividad (España), European Commission, Institut de Recherche pour le Développement (France)
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Geophysical Union 2016
• Subjects: Benavides; North Atlantic
• Online Access: http://hdl.handle.net/10261/135418; https://doi.org/10.1002/2015GB005326; https://doi.org/10.13039/501100001738; https://doi.org/10.13039/501100000782; https://doi.org/10.13039/501100003339; https://doi.org/10.13039/501100003329; https://doi.org/10.13039/501100000780; https://doi.org/10.13039/100012947

Benavides, Mar. et al.-- 10 pages, 2 figures, 2 tables, supporting information https://dx.doi.org/10.1002/2015GB005326 Recent findings indicate that N2 fixation is significant in aphotic waters, presumably due to heterotrophic diazotrophs depending on organic matter for their nutrition. However, the relationship between organic matter and heterotrophic N2 fixation remains unknown. Here we explore N2 fixation in the deep chlorophyll maximum and underneath deep waters across the whole Mediterranean Sea and relate it to organic matter composition, characterized by optical and molecular methods. Our N2 fixation rates were in the range of those previously reported for the euphotic zone of the Mediterranean Sea (up to 0.43 nmol N L−1 d−1) and were significantly correlated to the presence of relatively labile organic matter with fluorescence and molecular formula properties representative for peptides and unsaturated aliphatics and associated with the presence of more oxygenated ventilated water masses. Finally, and despite that the aphotic N2 fixation contributes largely to total water column diazotrophic activity (>50%), its contribution to overall nitrogen inputs to the basin is negligible (<0.5%) This work was supported by project HOTMIX—“Dark-ocean water mass boundaries and mixing zones as “hot-spots” of biodiversity and biogeochemical fluxes across the Mediterranean Sea and Eastern North Atlantic”—(CTM2011-30010-C02-01 and CTM2011-30010-C02-02) to J.A., X.A.A.S., and J.M.G. M.B. was funded by the Marie Sklodowska-Curie Actions of the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement 625185. S.B. was funded by the Institut de Recherche pour le Développement (IRD). A.M.M.-P. was funded by FPI and short stay fellowships from the Spanish Ministry of Economy and Competitiveness. M.N.-C. was supported by the CSIC Program “Junta para la Ampliación de Estudios” cofinanced by the ESF. I.B-F. was supported by a collaborative grant with S.B. from MOST Israel and the High Council ...