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| Grenier, M.; Della Penna, A.; Trull, T. W.. |
| Natural iron fertilisation from Southern Ocean islands results in high primary production and phytoplankton biomass accumulations readily visible in satellite ocean colour observations. These images reveal great spatial complexity with highly varying concentrations of chlorophyll, presumably reflecting both variations in iron supply and conditions favouring phytoplankton accumulation. To examine the second aspect, in particular the influences of variations in temperature and mixed layer depth, we deployed four autonomous profiling floats in the Antarctic Circumpolar Current near the Kerguelen Plateau in the Indian sector of the Southern Ocean. Each "bio-profiler" measured more than 250 profiles of temperature (T), salinity (S), dissolved oxygen,... |
| Tipo: Text |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00296/40724/39725.pdf |
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| Fourquez, M.; Obernosterer, I.; Davies, D. M.; Trull, T. W.; Blain, S.. |
| Iron (Fe) uptake by the microbial community and the contribution of three different size fractions was determined during spring phytoplankton blooms in the naturally Fe-fertilized area off the Kerguelen Islands (KEOPS2). Total Fe uptake in surface waters was on average 34 +/- 6 pmol Fe L-1 d(-1), and microplankton (>25 mu m size fraction; 40-69%) and pico-nanoplankton (0.8-25 mu m size fraction; 29-59 %) were the main contributors. The contribution of heterotrophic bacteria (0.2-0.8 mu m size fraction) to total Fe uptake was low at all stations (1-2 %). Iron uptake rates normalized to carbon biomass were highest for pico-nanoplankton above the Kerguelen Plateau and for microplankton in the downstream plume. We also investigated the potential competition... |
| Tipo: Text |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00295/40598/39535.pdf |
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| Fripiat, F.; Elskens, M.; Trull, T. W.; Blain, S.; Cavagna, A. -j.; Fernandez, C.; Fonseca-batista, D.; Planchon, F.; Raimbault, P.; Roukaerts, A.; Dehairs, F.. |
| Nitrification, the microbially mediated oxidation of ammonium into nitrate, is generally expected to be low in the Southern Ocean mixed layer. This paradigm assumes that nitrate is mainly provided through vertical mixing and assimilated during the vegetative season, supporting the concept that nitrate uptake is equivalent to the new primary production (i.e., primary production which is potentially available for export). Here we show that nitrification is significant (~40–80% of the seasonal nitrate uptake) in the naturally iron-fertilized bloom over the southeast Kerguelen Plateau. Hence, a large fraction of the nitrate-based primary production is regenerated, instead of being exported. It appears that nitrate assimilation (light dependent) and... |
| Tipo: Text |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00296/40704/39700.pdf |
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| Van Der Merwe, P.; Bowie, A. R.; Queroue, F.; Armand, L.; Blain, S.; Chever, Fanny; Davies, D.; Dehairs, F.; Planchon, F.; Sarthou, G.; Townsend, A. T.; Trull, T. W.. |
| The KEOPS2 project aims to elucidate the role of natural Fe fertilisation on biogeochemical cycles and ecosystem functioning, including quantifying the sources and processes by which iron is delivered in the vicinity of the Kerguelen Archipelago, Southern Ocean. The KEOPS2 process study used an upstream high-nutrient, low-chlorophyll (HNLC), deep water (2500 m), reference station to compare with a shallow (500 m), strongly fertilised plateau station and continued the observations to a downstream, bathymetrically trapped recirculation of the Polar Front where eddies commonly form and persist for hundreds of kilometres into the Southern Ocean. Over the Kerguelen Plateau, mean particulate (1-53 mu m) Fe and Al concentrations (pFe = 13.4 nM, pAl = 25.2 nM)... |
| Tipo: Text |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00256/36676/35276.pdf |
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| D'Ovidio, F.; Della Penna, A.; Trull, T. W.; Nencioli, F.; Pujol, M. -i.; Rio, M.-h; Park, Y. -h.; Cotte, C.; Zhou, M.; Blain, S.. |
| Field campaigns are instrumental in providing ground truth for understanding and modeling global ocean biogeochemical budgets. A survey however can only inspect a fraction of the global oceans, typically a region hundreds of kilometers wide for a temporal window of the order of (at most) several weeks. This spatiotemporal domain is also the one in which the mesoscale activity induces through horizontal stirring a strong variability in the biogeochemical tracers, with ephemeral, local contrasts which can easily mask the regional and seasonal gradients. Therefore, whenever local in situ measures are used to infer larger-scale budgets, one faces the challenge of identifying the mesoscale structuring effect, if not simply to filter it out. In the case of the... |
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| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00296/40722/39723.pdf |
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