Dynamics and controls of heterotrophic prokaryotic production in the western tropical South Pacific Ocean: links with diazotrophic and photosynthetic activity
|Author(s)||Van Wambeke France1, Gimenez Audrey1, Duhamel Solange2, Dupouy Cecile1, 3, Lefevre Dominique1, Pujo-Pay Mireille4, Moutin Thierry1|
|Affiliation(s)||1 : Aix Marseille Univ, Univ Toulon, CNRS, MIO,UM 110,IRD, F-13288 Marseille, France.
2 : Columbia Univ, Div Biol & Paleo Environm, Lamont Doherty Earth Observ, POB 1000,61 Route 9W, Palisades, NY 10964 USA.
3 : Aix Marseille Univ, Univ Toulon, CNRS, MIO,UM 110,IRD, Noumea 98848, New Caledonia.
4 : Sorbonne Univ, Lab Oceanog Microbienne LOMIC, CNRS, UMR 7621,Observ Oceanol, F-66650 Banyuls Sur Mer, France.
|Source||Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2018-05 , Vol. 15 , N. 9 , P. 2669-2689|
|WOS© Times Cited||15|
|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|
Heterotrophic prokaryotic production (BP) was studied in the western tropical South Pacific (WTSP) using the leucine technique, revealing spatial and temporal variability within the region. Integrated over the euphotic zone, BP ranged from 58 to 120 mg C m−2 d−1 within the Melanesian Archipelago, and from 31 to 50 mg C m−2 d−1 within the western subtropical gyre. The collapse of a bloom was followed during 6 days in the south of Vanuatu using a Lagrangian sampling strategy. During this period, rapid evolution was observed in the three main parameters influencing the metabolic state: BP, primary production (PP) and bacterial growth efficiency. With N2 fixation being one of the most important fluxes fueling new production, we explored relationships between BP, PP and N2 fixation rates over the WTSP. The contribution of N2 fixation rates to bacterial nitrogen demand ranged from 3 to 81 %. BP variability was better explained by the variability of N2 fixation rates than by that of PP in surface waters of the Melanesian Archipelago, which were characterized by N-depleted layers and low DIP turnover times (TDIP < 100 h). This is consistent with the fact that nitrogen was often one of the main factors controlling BP on short timescales, as shown using enrichment experiments, followed by dissolved inorganic phosphate (DIP) near the surface and labile organic carbon deeper in the euphotic zone. However, BP was more significantly correlated with PP, but not with N2 fixation rates where DIP was more available (TDIP > 100 h), deeper in the Melanesian Archipelago, or within the entire euphotic zone in the subtropical gyre. The bacterial carbon demand to gross primary production ratio ranged from 0.75 to 3.1. These values are discussed in the framework of various assumptions and conversion factors used to estimate this ratio, including the methodological errors, the daily variability of BP, the bacterial growth efficiency and one bias so far not considered: the ability for Prochlorococcus to assimilate leucine in the dark.