@article{fdi:010072818,
  title = {{N}-2 fixation as a dominant new {N} source in the western tropical {S}outh {P}acific {O}cean ({OUTPACE} cruise)},
  author = {{C}affin, {M}. and {M}outin, {T}. and {F}oster, {R}. {A}. and {B}ouruet-{A}ubertot, {P}. and {D}oglioli, {A}. {M}. and {B}erthelot, {H}. and {G}uieu, {C}. and {G}rosso, {O}. and {H}elias-{N}unige, {S}. and {L}eblond, {N}. and {G}imenez, {A}. and {P}etrenko, {A}. {A}. and de {V}erneil, {A}. and {B}onnet, {S}ophie},
  editor = {},
  language = {{ENG}},
  abstract = {{W}e performed nitrogen ({N}) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical {S}outh {P}acific ({WTSP}) {O}cean during austral summer conditions ({F}ebruary{M}arch 2015). {U}sing a {L}agrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. {W}e quantified all major vertical {N} fluxes both entering ({N}-2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate {N} export). {T}he three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic {M}elanesian archipelago ({MA}, stations {LD} {A} and {LD} {B}) than in the ultra-oligotrophic waters of the {S}outh {P}acific {G}yre ({SPG}, station {LD} {C}). {N}-2 fixation rates were extremely high at both {LD} {A} (593 +/- 51 mu mol {N} m(-2) d(-1)) and {LD} {B} (706 +/- 302 mu mol {N} m(-2)d(-1)), and the diazotroph community was dominated by {T}richodesmium. {N}-2 fixation rates were lower (59 +/- 16 mu mol {N} m(-2) d(-1)) at {LD} {C}, and the diazotroph community was dominated by unicellular {N}-2-fixing cyanobacteria ({UCYN}). {A}t all stations, {N}-2 fixation was the major source of new {N} (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. {N}-2 fixation contributed circa 1318 % of primary production in the {MA} region and 3 in the {SPG} water and sustained nearly all new primary production at all stations. {T}he e ratio (e ratio articulate carbon export / primary production) was maximum at {LD} {A} (9.7 ) and was higher than the e ratio in most studied oligotrophic regions (< 5), indicating a high efficiency of the {WTSP} to export carbon relative to primary production. {T}he direct export of diazotrophs assessed by q{PCR} of the nif{H} gene in sediment traps represented up to 30.6 of the {PC} export at {LD} {A}, while their contribution was 5 and < 0.1 % at {LD} {B} and {LD} {C}, respectively. {A}t the three studied stations, the sum of all {N} input to the photic layer exceeded the {N} output through organic matter export. {T}his disequilibrium leading to {N} accumulation in the upper layer appears as a characteristic of the {WTSP} during the summer season.},
  keywords = {{PACIFIQUE} {SUD} {OUEST} ; {ZONE} {TROPICALE} ; {NOUVELLE} {CALEDONIE} ; {NIUE} ; {COOK} {ILES}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {15},
  numero = {8},
  pages = {2565--2585},
  ISSN = {1726-4170},
  year = {2018},
  DOI = {10.5194/bg-15-2565-2018},
  URL = {https://www.documentation.ird.fr/hor/fdi:010072818},
}