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Missing nitrogen fixation in the Benguela region

Missing nitrogen fixation in the Benguela region
Missing nitrogen fixation in the Benguela region
Opposing opinions on the importance of nitrogen fixation in the northern Benguela upwelling region provoked us to investigate the magnitude of nitrogen fixation in front of northern Namibia and southern Angola. Measurements of nitrogen fixation rates using the 15N method at 66 stations during seven cruises from 2008 to 2014 showed that, in general, the 15N content in the biomass did not increase after tracer incubation with 15N2, indicating that no nitrogen fixation occurred. Correspondingly, the filamentous nitrogen-fixing cyanobacterium Trichodesmium was almost not present. The abundant picocyanobacteria did obviously not perform nitrogen fixation to a significant degree. The artificial improvement of conditions for nitrogen fixation in mesocosm experiments, including phosphate and iron additions and a warmer temperature, failed to induce nitrogen fixation. A plausible explanation of these findings is a lack of conditioned cells for nitrogen fixation in the Benguela region.
Nitrogen fixation, Trichodesmium, Picocyanobacteria, Mesocosm, Nutrients, Temperature, Benguela upwelling
0967-0637
30-41
Wasmund, Norbert
2fa63b2c-dabf-4af9-88f8-67833afecc5d
Struck, Ulrich
9a1dcd81-7dfe-405c-8baf-2c88bfb6bc09
Hansen, Anja
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Flohr, Anita
1e293a22-bdba-408e-9608-fed8b65e4e79
Nausch, Günther
e30fa05b-d216-4e60-96aa-2aeab1550d71
Grüttmüller, Annett
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Voss, Maren
190eb2cb-ecb9-4dcd-9d92-d7829dc0ac6b
Wasmund, Norbert
2fa63b2c-dabf-4af9-88f8-67833afecc5d
Struck, Ulrich
9a1dcd81-7dfe-405c-8baf-2c88bfb6bc09
Hansen, Anja
d8c02750-37ad-49e2-8ccc-b3b3b6cc786d
Flohr, Anita
1e293a22-bdba-408e-9608-fed8b65e4e79
Nausch, Günther
e30fa05b-d216-4e60-96aa-2aeab1550d71
Grüttmüller, Annett
f7edba47-c855-4b1b-b20b-2cbe29770ea9
Voss, Maren
190eb2cb-ecb9-4dcd-9d92-d7829dc0ac6b

Wasmund, Norbert, Struck, Ulrich, Hansen, Anja, Flohr, Anita, Nausch, Günther, Grüttmüller, Annett and Voss, Maren (2015) Missing nitrogen fixation in the Benguela region. Deep Sea Research Part I: Oceanographic Research Papers, 106, 30-41. (doi:10.1016/j.dsr.2015.10.007).

Record type: Article

Abstract

Opposing opinions on the importance of nitrogen fixation in the northern Benguela upwelling region provoked us to investigate the magnitude of nitrogen fixation in front of northern Namibia and southern Angola. Measurements of nitrogen fixation rates using the 15N method at 66 stations during seven cruises from 2008 to 2014 showed that, in general, the 15N content in the biomass did not increase after tracer incubation with 15N2, indicating that no nitrogen fixation occurred. Correspondingly, the filamentous nitrogen-fixing cyanobacterium Trichodesmium was almost not present. The abundant picocyanobacteria did obviously not perform nitrogen fixation to a significant degree. The artificial improvement of conditions for nitrogen fixation in mesocosm experiments, including phosphate and iron additions and a warmer temperature, failed to induce nitrogen fixation. A plausible explanation of these findings is a lack of conditioned cells for nitrogen fixation in the Benguela region.

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Published date: December 2015
Keywords: Nitrogen fixation, Trichodesmium, Picocyanobacteria, Mesocosm, Nutrients, Temperature, Benguela upwelling
Organisations: Geochemistry

Identifiers

Local EPrints ID: 400923
URI: http://eprints.soton.ac.uk/id/eprint/400923
ISSN: 0967-0637
PURE UUID: f0068a1b-5d63-45d3-99cf-cf9b8e6cf13b
ORCID for Anita Flohr: ORCID iD orcid.org/0000-0002-5018-5379

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Date deposited: 30 Sep 2016 13:15
Last modified: 12 Nov 2019 01:37

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Contributors

Author: Norbert Wasmund
Author: Ulrich Struck
Author: Anja Hansen
Author: Anita Flohr ORCID iD
Author: Günther Nausch
Author: Annett Grüttmüller
Author: Maren Voss

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