Diazotrophic Trichodesmium impact on UV-Vis radiance and pigment composition in the western tropical South Pacific

Type Article
Date 2018-08
Language English
Author(s) Dupouy Cecile1, 2, Frouin Robert3, Tedetti Marc1, Maillard Morgane1, Rodier Martine, Lombard Fabien, Guidi Lionel, Picheral Marc, Neveux Jacques, Duhamel Solange, Charriere Bruno, Sempere Richard
Affiliation(s) 1 : Univ Toulon & Var, Aix Marseille Univ, CNRS, IRD,MIO UM 110, F-13288 Marseille, France.
2 : Ctr IRD Noumea, MIO UM 110, Noumea 98848, New Caledonia.
3 : Univ Calif San Diego, Scripps Inst Oceanog, La Jolla, CA 92093 USA.
4 : Univ Polynesie Francaise, Inst Malarme, Ifremer, Inst Rech Dev,EIO, Papeete, French Polynesi, Fr Polynesia.
5 : Univ Paris 06, UPMC, Sorbonne Univ, CNRS,LOV,Observ Oceanol, F-06230 Villefranche Sur Mer, France.
6 : Univ Paris 06, UPMC, Sorbonne Univ, Lab Oceanog Microbienne LOMIC,Observ Oceanol,CNRS, F-66650 Banyuls Sur Mer, France.
7 : Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY USA.
8 : Ctr Format & Rech Environm Mediterraneens CEFREM, UMR CNRS UPVD 5110, 52 Ave Paul Alduy, F-66860 Perpignan, France.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2018-08 , Vol. 15 , N. 16 , P. 5249-5269
DOI 10.5194/bg-15-5249-2018
WOS© Times Cited 9
Note Special issue Interactions between planktonic organisms and biogeochemical cycles across trophic and N2 fixation gradients in the western tropical South Pacific Ocean: a multidisciplinary approach (OUTPACE experiment) Editor(s): T. Moutin, S. Bonnet, K. Richards, D. G. Capone, E. Marañón, and L. Mémery
Abstract

We assessed the influence of the marine diazotrophic cyanobacterium Trichodesmium on the bio-optical properties of western tropical South Pacific (WTSP) waters (18-22 degrees S, 160 degrees E-160 degrees 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 7093 colonies m(-3)) was well correlated to the trichome concentrations (maximum 2093 trichomes L-1) with an aggregation factor of 600. In the Melanesian archipelago, a maximum of 4715 trichomes L-1 was enumerated in pump samples (3.2 m) at 20 degrees S, 167 30 degrees E. High Trichodesmium abundance was always associated with absorption peaks of mycosporine-like amino acids (330, 360 nm) and high particulate backscattering, but not with high Chl a fluorescence or blue particulate absorption (440 nm). 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 (nL(w)) 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 nL(w) at 305, 325, 340, 380, 412 and 440 nm was strongly correlated to chlorophyll and zeaxanthin, while nL(w) at 490 and 565 nm exhibited lower correlations. These results, as well as differences in the PCA of BIOSOPE data, indicated that nL(w) 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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Dupouy Cecile, Frouin Robert, Tedetti Marc, Maillard Morgane, Rodier Martine, Lombard Fabien, Guidi Lionel, Picheral Marc, Neveux Jacques, Duhamel Solange, Charriere Bruno, Sempere Richard (2018). Diazotrophic Trichodesmium impact on UV-Vis radiance and pigment composition in the western tropical South Pacific. Biogeosciences, 15(16), 5249-5269. Publisher's official version : https://doi.org/10.5194/bg-15-5249-2018 , Open Access version : https://archimer.ifremer.fr/doc/00457/56824/