@article{fdi:010073043,
  title = {{A}photic {N}-2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical {S}outh {P}acific {O}cean},
  author = {{B}enavides, {M}. and {S}hoemaker, {K}. {M}. and {M}oisander, {P}. {H}. and {N}iggemann, {J}. and {D}ittmar, {T}. and {D}uhamel, {S}. and {G}rosso, {O}. and {P}ujo-{P}ay, {M}. and {H}elias-{N}unige, {S}. and {F}umenia, {A}. and {B}onnet, {S}ophie},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he western tropical {S}outh {P}acific ({WTSP}) {O}cean has been recognized as a global hot spot of dinitrogen ({N}-2) fixation. {H}ere, as in other marine environments across the oceans, {N}-2 fixation studies have focused on the sunlit layer. {H}owever, studies have confirmed the importance of aphotic {N}-2 fixation activity, although until now only one had been performed in the {WTSP}. {I}n order to increase our knowledge of aphotic {N}-2 fixation in the {WTSP}, we measured {N}-2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from {N}ew {C}aledonia to {F}rench {P}olynesia. {B}ecause non-cyanobacterial diazotrophs presumably need external dissolved organic matter ({DOM}) sources for their nutrition, we also identified {DOM} compounds using {F}ourier transform ion cyclotron resonance mass spectrometry ({FTI}-{CRMS}) with the aim of searching for relationships between the composition of {DOM} and non-cyanobacterial {N}-2 fixation in the aphotic ocean. {N}-2 fixation rates were low (average 0.63 +/- 0.07 nmol {N} {L}-1 d(-1)) but consistently detected across all depths and stations, representing similar to 6-88 % of photic {N}-2 fixation. {N}-2 fixation rates were not significantly correlated with {DOM} compounds. {T}he analysis of nif{H} gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. {I}nterestingly, a distinct phylotype from the major nif{H} subcluster 1{G} dominated at 650 dbar, coinciding with the oxygenated {S}ubantarctic {M}ode {W}ater ({SAMW}). {T}his consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. {W}hile 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 {N}-2 fixation activity at all depths sampled during our study suggest that aphotic {N}-2 fixation may contribute significantly to fixed nitrogen inputs in this area and/or areas downstream of water mass circulation.},
  keywords = {{PACIFIQUE}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {15},
  numero = {9},
  pages = {3107--3119},
  ISSN = {1726-4170},
  year = {2018},
  DOI = {10.5194/bg-15-3107-2018},
  URL = {https://www.documentation.ird.fr/hor/fdi:010073043},
}