%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Bonnet, Sophie
%A Caffin, M.
%A Berthelot, H.
%A Grosso, O.
%A Benavides, Mar
%A Helias-Nunige, S.
%A Guieu, C.
%A Stenegren, M.
%A Foster, R. A.
%T In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N-2 fixation (OUTPACE cruise)
%D 2018
%L fdi:010073224
%G ENG
%J Biogeosciences
%@ 1726-4170
%K PACIFIQUE ; MELANESIE ; ZONE TROPICALE
%M ISI:000438465800001
%N 13
%P 4215-4232
%R 10.5194/bg-15-4215-2018
%U https://www.documentation.ird.fr/hor/fdi:010073224
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers18-08/010073224.pdf
%V 15
%W Horizon (IRD)
%X Here we report N-2 fixation rates from a similar to 4000 km transect in the western and central tropical South Pacific, a particularly undersampled region in the world ocean. Water samples were collected in the euphotic layer along a west to east transect from 160 degrees E to 160 degrees W that covered contrasting trophic regimes, from oligotrophy in the Melanesian archipelago (MA) waters to ultraoligotrophy in the South Pacific Gyre (GY) waters. N-2 fixation was detected at all 17 sampled stations with an average depth-integrated rate of 631 +/- 286 mu mol Nm(-2) d(-1) (range 196-1153 mu mol Nm(-2) d(-1)) in MA waters and of 85 +/- 79 mu mol Nm(-2) d(-1) (range 18-172 mu mol Nm(-2) d(-1)) in GY waters. Two cyanobacteria, the larger colonial filamentous Trichodesmium and the smaller UCYN-B, dominated the enumerated diazotroph community (>80 %) and gene expression of the nifH gene (cDNA > 10(5) nifH copies L-1) in MA waters. Single-cell isotopic analyses performed by nanoscale secondary ion mass spectrometry (nanoSIMS) at selected stations revealed that Trichodesmium was always the major contributor to N-2 fixation in MA waters, accounting for 47.1-83.8% of bulk N-2 fixation. The most plausible environmental factors explaining such exceptionally high rates of N-2 fixation in MA waters are discussed in detail, emphasizing the role of macro- and micro-nutrient (e.g., iron) availability, seawater temperature and currents.
%$ 036