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

Mar Benavides, Sophie Bonnet, Nauzet Hernández, Alba María Martínez-Pérez, Mar Nieto-Cid, Xosé Antón Álvarez-Salgado, Isabel Baños, María F. Montero, Ignacio P. Mazuecos, Josep M. Gasol, Helena Osterholz, Thorsten Dittmar, Ilana Berman-Frank, Javier Arístegui

Research output: Contribution to journalArticlepeer-review


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%).

Original languageEnglish
Pages (from-to)952-961
Number of pages10
JournalGlobal Biogeochemical Cycles
Issue number6
StatePublished - 1 Jun 2016
Externally publishedYes

Bibliographical note

Publisher Copyright:
©2016. American Geophysical Union. All Rights Reserved.


  • diazotrophy

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • General Environmental Science
  • Atmospheric Science


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