Springtime contribution of dinitrogen fixation to primary production across the Mediterranean Sea
1Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University,Ramat Gan 52900, Israel
2Israel Oceanographic and Limnological Research, National Institute of Oceanography, Haifa 31080, Israel
3Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, 4600 Elkhorn Avenue, Norfolk, Virginia 23 529-0276, USA
Abstract. Dinitrogen (N2) fixation rates were measured during early spring across the different provinces of Mediterranean Sea surface waters. N2 fixation rates, measured using 15N2 enriched seawater, were lowest in the eastern basin and increased westward with a maximum at the Strait of Gibraltar (0.10 to 2.35 nmol N L−1 d−1, respectively). These rates were 3–7 fold higher than N2 fixation rates measured previously in the Mediterranean Sea during summertime. Moreover, comparisons between N2 fixation rates measured during dark versus natural light incubations (48 h) show higher rates during dark incubations at the eastern Mediterranean stations but lower rates at the western stations. This suggests that heterotrophic diazotrophy has a significant role in the Eastern Mediterranean while autotrophic diazotrophy has a more dominant role in the Western basin.