High‐nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas). Issue 16 (17th August 2017)

• Record Type: Journal Article
• Authors: Berthelot, H.; Benavides, M.; Moisander, P. H.; Grosso, O.; Bonnet, S.
• Is Part Of: Geophysical research letters. Volume 44:Issue 16(2017)
• Page Start: 8414
• Page End: 8423
• Publication Date: 2017-08-17
• Subjects: diazotrophy -- Trichodesmium -- Crocosphaera -- Cyanothece -- N release; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL073856
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Dinitrogen (N2 ) fixation rates were investigated in the euphotic layer of the Bismarck and Solomon Seas using 15 N2 incubation assays taking into account both the particulate and the dissolved pools. Average depth‐integrated particulate N2 fixation rates were 203 (range 43–399) and 1396 (range 176–3132) μmol N m −2 d −1 in the Bismarck and Solomon Seas, respectively. In both seas, N2 fixation measured in the dissolved pool was similar to particulate N2 fixation, highlighting the potentially substantial underestimation of N2 fixation in oceanic budgets when only particulate N2 fixation is considered. Among the diazotroph phylotypes targeted using quantitative polymerase chain reaction amplification of nifH genes, Trichodesmium was the most abundant. Regression analyses suggest that it accounted for the major proportion of N2 fixation. However, unicellular cyanobacterial and non‐cyanobacterial diazotrophs were also occasionally abundant. This study reports high pelagic N2 fixation rates and confirms that the Western Tropical South Pacific is a hot spot for marine N2 fixation. Key Points: The Bismarck and Solomon Seas are hot spots of dinitrogen fixation in the ocean Dinitrogen fixation is underestimated if the dissolved pool is not taken into account Regression analyses indicate that most of the dinitrogen fixation activity is attributed to Trichodesmium