@article{fdi:010073962,
  title = {{D}iazotrophic {T}richodesmium impact on {UV}-{V}is radiance and pigment composition in the western tropical {S}outh {P}acific},
  author = {{D}upouy, {C}{\'e}cile and {F}rouin, {R}. and {T}edetti, {M}arc and {M}aillard, {M}. and {R}odier, {M}artine and {L}ombard, {F}. and {G}uidi, {L}. and {P}icheral, {M}. and {N}eveux, {J}. and {D}uhamel, {S}. and {C}harriere, {B}. and {S}empere, {R}.},
  editor = {},
  language = {{ENG}},
  abstract = {{W}e assessed the influence of the marine diazotrophic cyanobacterium {T}richodesmium on the bio-optical properties of western tropical {S}outh {P}acific ({WTSP}) waters (18-22 degrees {S}, 160 degrees {E}-160 degrees {W}) during the {F}ebruary-{M}arch 2015 {OUTPACE} cruise. {W}e performed measurements of backscattering and absorption coefficients, irradiance, and radiance in the euphotic zone with a {S}atlantic {M}icro{P}ro free-fall profiler and took {U}nderwater {V}ision {P}rofiler 5 ({UPV}5) pictures for counting the largest {T}richodesmium spp. colonies. {P}igment concentrations were determined by fluorimetry and high-performance liquid chromatography and picoplankton abundance by flow cytometry. {T}richome concentration was estimated from pigment algorithms and validated by surface visual counts. {T}he abundance of large colonies counted by the {UVP}5 (maximum 7093 colonies m(-3)) was well correlated to the trichome concentrations (maximum 2093 trichomes {L}-1) with an aggregation factor of 600. {I}n the {M}elanesian archipelago, a maximum of 4715 trichomes {L}-1 was enumerated in pump samples (3.2 m) at 20 degrees {S}, 167 30 degrees {E}. {H}igh {T}richodesmium abundance was always associated with absorption peaks of mycosporine-like amino acids (330, 360 nm) and high particulate backscattering, but not with high {C}hl a fluorescence or blue particulate absorption (440 nm). {A}long the west-to-east transect, {T}richodesmium together with {P}rochlorococcus represented the major part of total chlorophyll concentration; the contribution of other groups were relatively small or negligible. {T}he {T}richodesmium contribution to total chlorophyll concentration was the highest in the {M}elanesian archipelago around {N}ew {C}aledonia and {V}anuatu (60 %), progressively decreased to the vicinity of the islands of {F}iji (30 %), and reached a minimum in the {S}outh {P}acific {G}yre where {P}rochlorococcus dominated chlorophyll concentration. {T}he contribution of {T}richodesmium to zeaxanthin was respectively 50, 40 and 20% for these regions. {D}uring the {OUTPACE} cruise, the relationship between normalized water-leaving radiance (n{L}(w)) in the ultraviolet and visible and chlorophyll concentration was similar to that found during the {BIOSOPE} cruise in the eastern tropical {P}acific. {P}rincipal component analysis ({PCA}) of {OUTPACE} data showed that n{L}(w) at 305, 325, 340, 380, 412 and 440 nm was strongly correlated to chlorophyll and zeaxanthin, while n{L}(w) at 490 and 565 nm exhibited lower correlations. {T}hese results, as well as differences in the {PCA} of {BIOSOPE} data, indicated that n{L}(w) variability in the greenish blue and yellowish green during {OUTPACE} was influenced by other variables associated with {T}richodesmium presence, such as backscattering coefficient, phycoerythrin fluorescence and/or zeaxanthin absorption, suggesting that {T}richodesmium detection should involve examination of n{L}w in this spectral domain.},
  keywords = {{PACIFIQUE} ; {ZONE} {TROPICALE} ; {MELANESIE} ; {FIDJI}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {15},
  numero = {16},
  pages = {5249--5269},
  ISSN = {1726-4170},
  year = {2018},
  DOI = {10.5194/bg-15-5249-2018},
  URL = {https://www.documentation.ird.fr/hor/fdi:010073962},
}