TY - JOUR
T1 - Aphotic N2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical South Pacific Ocean
AU - Benavides, Mar
AU - Shoemaker, Katyanne M.
AU - Moisander, Pia H.
AU - Niggemann, Jutta
AU - Dittmar, Thorsten
AU - Duhamel, Solange
AU - Grosso, Olivier
AU - Pujo-Pay, Mireille
AU - Hélias-Nunige, Sandra
AU - Fumenia, Alain
AU - Bonnet, Sophie
N1 - Funding Information:
Acknowledgements. This is a contribution of the OUTPACE (Oligotrophy from Ultra-oligoTrophy PACific Experiment) project (https://outpace.mio.univ-amu.fr/, last access: May 2018) funded by the French research national agency (ANR-14-CE01-0007-01), the LEFE-CYBER program (CNRS-INSU), the GOPS program (IRD) and the CNES (BC T23, ZBC 4500048836). The OUTPACE cruise (https://doi.org/10.17600/15000900) was managed by MIO (OSU Institut Pythéas, AMU) from Marseilles (France). The authors thank the crew of the R/V L’Atalante for outstanding on-ship operations. Mar Benavides was funded by the People Programme (Marie Skłodowska-Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement number 625185. The NSF OCE-1733610 award to Pia H. Moisander supported Pia H. Moisander and Katyanne M. Shoemaker. Solange Duhamel was funded by National Science Foundation award OCE-1434916 and by support from the Vetlesen Foundation.
Funding Information:
This is a contribution of the OUTPACE (Oligotrophy from Ultra-oligoTrophy PACific Experiment) project (https://outpace.mio.univ-amu.fr/, last access: May 2018) funded by the French research national agency (ANR-14-CE01-0007-01), the LEFE-CYBER program (CNRS-INSU), the GOPS program (IRD) and the CNES (BC T23, ZBC 4500048836). The OUTPACE cruise (https://doi.org/10.17600/15000900) was managed by MIO (OSU Institut Pythéas, AMU) from Marseilles (France). The authors thank the crew of the R/V L'Atalante for outstanding on-ship operations. Mar Benavides was funded by the People Programme (Marie Skłodowska-Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement number 625185. The NSF OCE-1733610 award to Pia H. Moisander supported Pia H. Moisander and Katyanne M. Shoemaker. Solange Duhamel was funded by National Science Foundation award OCE-1434916 and by support from the Vetlesen Foundation.
Publisher Copyright:
© Author(s) 2018.
PY - 2018/5/22
Y1 - 2018/5/22
N2 - The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63±0.07 nmol NL-1 d-1) but consistently detected across all depths and stations, representing ∼6-88% of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed nitrogen inputs in this area and/or areas downstream of water mass circulation.
AB - The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63±0.07 nmol NL-1 d-1) but consistently detected across all depths and stations, representing ∼6-88% of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed nitrogen inputs in this area and/or areas downstream of water mass circulation.
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U2 - 10.5194/bg-15-3107-2018
DO - 10.5194/bg-15-3107-2018
M3 - Article
AN - SCOPUS:85047625278
VL - 15
SP - 3107
EP - 3119
JO - Biogeosciences
JF - Biogeosciences
SN - 1726-4170
IS - 10
ER -