TY - JOUR
T1 - Diazotrophic Trichodesmium impact on UV-Vis radiance and pigment composition in the western tropical South Pacific
AU - Dupouy, Cécile
AU - Frouin, Robert
AU - Tedetti, Marc
AU - Maillard, Morgane
AU - Rodier, Martine
AU - Lombard, Fabien
AU - Guidi, Lionel
AU - Picheral, Marc
AU - Neveux, Jacques
AU - Duhamel, Solange
AU - Charrière, Bruno
AU - Sempéré, Richard
N1 - Funding Information:
Acknowledgements. We thank Joséphine Ras, Laboratoire d’Océanologie de Villefranche, and Crystal Thomas, NASA Goddard Space Flight Center, for performing the HPLC analysis, Mireille Pujo-Pay for scientific advice during the cruise, Benjamin Blanc for sorting and validating UPV-5 images, David Varillon, IRD US IMAGO for invaluable technical support, Philippe Gérard (MIO) for Chl a analyses, and the administrative staff of the IRD Center of Nouméa. We thank Rüdiger Röttgers (Helmholtz-Centrum Geesthacht) for helpful discussions during the elaboration of the manuscript. This is a contribution of the OUTPACE (Oligotrophy from Ultra-oligoTrophy PACific Experiment) project (https://OUTPACE.mio.univ-amu.fr/, last access: 20 August 2018) funded by the French National Research Agency (ANR-14-CE01-0007-01), the LEFECyBER program (CNRS-INSU), the GOPS program (IRD) and the Centre National d’Etudes Spatiales (BC T23, ZBC 4500048836). The OUTPACE cruise (https://doi.org/10.17600/15000900) was managed by MIO Institute from Marseille (France). The National Science Foundation supported Sophie Duhamel under grant OCE-1434916. The National Aeronautics and Space Administration supported Robert Frouin under various grants. Finally, we thank the two anonymous reviewers for their useful and constructive comments.
Publisher Copyright:
© Author(s) 2018.
PY - 2018/8/30
Y1 - 2018/8/30
N2 - We assessed the influence of the marine diazotrophic cyanobacterium Trichodesmium on the bio-optical properties of western tropical South Pacific (WTSP) waters (18-22°S, 160°E-160°W) during the February-March 2015 OUTPACE cruise. We performed measurements of backscattering and absorption coefficients, irradiance, and radiance in the euphotic zone with a Satlantic MicroPro free-fall profiler and took Underwater Vision Profiler 5 (UPV5) pictures for counting the largest Trichodesmium spp. colonies. Pigment concentrations were determined by fluorimetry and high-performance liquid chromatography and picoplankton abundance by flow cytometry. Trichome concentration was estimated from pigment algorithms and validated by surface visual counts. The abundance of large colonies counted by the UVP5 (maximum 7093coloniesm-3) was well correlated to the trichome concentrations (maximum 2093trichomesL-1) with an aggregation factor of 600. In the Melanesian archipelago, a maximum of 4715trichomesL-1 was enumerated in pump samples (3.2m) at 20°S,16730°E. High Trichodesmium abundance was always associated with absorption peaks of mycosporine-like amino acids (330, 360nm) and high particulate backscattering, but not with high Chl a fluorescence or blue particulate absorption (440nm). Along the west-to-east transect, Trichodesmium together with Prochlorococcus represented the major part of total chlorophyll concentration; the contribution of other groups were relatively small or negligible. The Trichodesmium contribution to total chlorophyll concentration was the highest in the Melanesian archipelago around New Caledonia and Vanuatu (60%), progressively decreased to the vicinity of the islands of Fiji (30%), and reached a minimum in the South Pacific Gyre where Prochlorococcus dominated chlorophyll concentration. The contribution of Trichodesmium to zeaxanthin was respectively 50, 40 and 20% for these regions. During the OUTPACE cruise, the relationship between normalized water-leaving radiance (nLw) in the ultraviolet and visible and chlorophyll concentration was similar to that found during the BIOSOPE cruise in the eastern tropical Pacific. Principal component analysis (PCA) of OUTPACE data showed that nLw at 305, 325, 340, 380, 412 and 440nm was strongly correlated to chlorophyll and zeaxanthin, while nLw at 490 and 565nm exhibited lower correlations. These results, as well as differences in the PCA of BIOSOPE data, indicated that nLw variability in the greenish blue and yellowish green during OUTPACE was influenced by other variables associated with Trichodesmium presence, such as backscattering coefficient, phycoerythrin fluorescence and/or zeaxanthin absorption, suggesting that Trichodesmium detection should involve examination of nLw in this spectral domain.
AB - We assessed the influence of the marine diazotrophic cyanobacterium Trichodesmium on the bio-optical properties of western tropical South Pacific (WTSP) waters (18-22°S, 160°E-160°W) during the February-March 2015 OUTPACE cruise. We performed measurements of backscattering and absorption coefficients, irradiance, and radiance in the euphotic zone with a Satlantic MicroPro free-fall profiler and took Underwater Vision Profiler 5 (UPV5) pictures for counting the largest Trichodesmium spp. colonies. Pigment concentrations were determined by fluorimetry and high-performance liquid chromatography and picoplankton abundance by flow cytometry. Trichome concentration was estimated from pigment algorithms and validated by surface visual counts. The abundance of large colonies counted by the UVP5 (maximum 7093coloniesm-3) was well correlated to the trichome concentrations (maximum 2093trichomesL-1) with an aggregation factor of 600. In the Melanesian archipelago, a maximum of 4715trichomesL-1 was enumerated in pump samples (3.2m) at 20°S,16730°E. High Trichodesmium abundance was always associated with absorption peaks of mycosporine-like amino acids (330, 360nm) and high particulate backscattering, but not with high Chl a fluorescence or blue particulate absorption (440nm). Along the west-to-east transect, Trichodesmium together with Prochlorococcus represented the major part of total chlorophyll concentration; the contribution of other groups were relatively small or negligible. The Trichodesmium contribution to total chlorophyll concentration was the highest in the Melanesian archipelago around New Caledonia and Vanuatu (60%), progressively decreased to the vicinity of the islands of Fiji (30%), and reached a minimum in the South Pacific Gyre where Prochlorococcus dominated chlorophyll concentration. The contribution of Trichodesmium to zeaxanthin was respectively 50, 40 and 20% for these regions. During the OUTPACE cruise, the relationship between normalized water-leaving radiance (nLw) in the ultraviolet and visible and chlorophyll concentration was similar to that found during the BIOSOPE cruise in the eastern tropical Pacific. Principal component analysis (PCA) of OUTPACE data showed that nLw at 305, 325, 340, 380, 412 and 440nm was strongly correlated to chlorophyll and zeaxanthin, while nLw at 490 and 565nm exhibited lower correlations. These results, as well as differences in the PCA of BIOSOPE data, indicated that nLw variability in the greenish blue and yellowish green during OUTPACE was influenced by other variables associated with Trichodesmium presence, such as backscattering coefficient, phycoerythrin fluorescence and/or zeaxanthin absorption, suggesting that Trichodesmium detection should involve examination of nLw in this spectral domain.
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U2 - 10.5194/bg-15-5249-2018
DO - 10.5194/bg-15-5249-2018
M3 - Article
AN - SCOPUS:85052734427
VL - 15
SP - 5249
EP - 5269
JO - Biogeosciences
JF - Biogeosciences
SN - 1726-4170
IS - 16
ER -