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10. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

Author

Blain, Stephane, Queguiner, Bernard, Armand, Leanne, Belviso, Sauveur, Bombled, Bruno, Bopp, Laurent, Bowie, Andrew, Brunet, Christian, Brussaard, Corina, Carlotti, Francois, Christaki, Urania, Corbiere, Antoine, Durand, Isabelle, Ebersbach, Frederike, Fuda, Jean-Luc, Garcia, Nicole, Gerringa, Loes, Griffiths, Brian, Guigue, Catherine, Guillerm, Christophe, Jacquet, Stephanie, Jeandel, Catherine, Laan, Patrick, Lefevre, Dominique, Lo Monaco, Claire, Malits, Andrea, Mosseri, Julie, Obernosterer, Ingrid, Park, Young-Hyang, Picheral, Marc, Pondaven, Philippe, Remenyi, Thomas, Sandroni, Valerie, Sarthou, Geraldine, Savoye, Nicolas, Scouarnec, Lionel, Souhaut, Marc, Thuiller, Doris, Timmermans, Klaas, Trull, Thomas, Uitz, Julia, van Beek, Pieter, Veldhuis, Marcel, Vincent, Dorothee, Viollier, Eric, Vong, Lilita, and Wagener, Thibaut

Abstract

Author(s): Stéphane Blain (corresponding author) [1]; Bernard Quéguiner [1]; Leanne Armand [1]; Sauveur Belviso [2]; Bruno Bombled [2]; Laurent Bopp [2]; Andrew Bowie [3, 4]; Christian Brunet [5]; Corina Brussaard [...]

Published
2007
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16. Resolving the 'opal paradox' in the Southern Ocean

Author

Pondaven, Philippe, Ragueneau, Olivier, Treguer, Paul, Hauvespre, Anne, Dezileau, Laurent, and Reyss, Jean Louis

Abstract

Author(s): Philippe Pondaven (corresponding author) [1]; Olivier Ragueneau [1]; Paul Tréguer [1]; Anne Hauvespre [1]; Laurent Dezileau [2]; Jean Louis Reyss [2] In the Southern Ocean, high accumulation rates of [...]

Published
2000
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17. Isotopic and elemental compositions reveal density‐dependent nutrition pathways in a population of mixotrophic jellyfish

Author

Djeghri, Nicolas, Pondaven, Philippe, Stockenreiter, Maria, Behl, Stephan, Huang, Jessica Y. T., Hansen, Thomas, Patris, Sharon, Ucharm, Gerda, Stibor, Herwig, Djeghri, Nicolas, Pondaven, Philippe, Stockenreiter, Maria, Behl, Stephan, Huang, Jessica Y. T., Hansen, Thomas, Patris, Sharon, Ucharm, Gerda, and Stibor, Herwig

Abstract

Mixotrophic organisms are increasingly recognized as important components of ecosystems, but the factors controlling their nutrition pathways (in particular their autotrophy–heterotrophy balance) are little known. Both autotrophy and heterotrophy are expected to respond to density‐dependent mechanisms but not necessarily in the same direction and/or strength. We hypothesize that the autotrophy–heterotrophy balance of mixotrophic organisms might therefore be a function of population densities. To investigate this relationship, we sampled mixotrophic jellyfish holobionts (host, Mastigias papua etpisoni; symbiont, Cladocopium sp.) in a marine lake (Palau, Micronesia) on six occasions (from 2010 to 2018). Over this period, population densities varied ~100 fold. We characterized the nutrition of the holobionts using the δ13C and δ15N signatures as well as C:N ratios. δ13C values increased and δ15N values decreased with increasing population densities (respectively, R2 = 0.86 and 0.70, P < 0.05). Although less distinct, C:N ratios increased with increasing population densities (R2 = 0.59, 0.1 > P > 0.05). This indicates that the autotrophy–heterotrophy balance tends toward autotrophy when population densities increase. We propose that the availability of zooplanktonic prey is the main driver of this pattern. These results demonstrate that the autotrophy–heterotrophy balance of mixotrophic jellyfishes can be tightly regulated by density‐dependent mechanisms.

Published
2020
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22. All diatoms are not equal in the biological carbon pump

Author

Tréguer, Paul, Moriceau, Brivaëla, Pondaven, Philippe, Leblanc, Karine, Moriceau, Brivaëla, La pompe biologique de carbone: 2 silicifiés essentiels - - BioPSis2016 - ANR-16-CE01-0002 - AAPG2016 - VALID, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'océanographie et de biogéochimie (LOB), Université de la Méditerranée - Aix-Marseille 2-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), ANR-16-CE01-0002,BioPSis,La pompe biologique de carbone: 2 silicifiés essentiels(2016), and Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2018

23. Benthic Diatoms: What Makes Them Unique

Author

Leynaert, Aude, Fardel, Coline, Beker, Beatriz, Soler, Charlotte, Delebecq, Gaspard, Pondaven, Philippe, Durand, Pierre-Emmanuel, Heggarty, Kevin, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Université de Brest (UBO), Université de Bretagne Sud (UBS), Département Optique (OPT), Université européenne de Bretagne - European University of Brittany (UEB)-Télécom Bretagne-Institut Mines-Télécom [Paris] (IMT), and Télécom Bretagne (devenu IMT Atlantique), Ex-Bibliothèque

Subjects
[SPI.OPTI] Engineering Sciences [physics]/Optics / Photonic, [SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic
Abstract

International audience; Diatoms are found in almost all aquatic environments as long as light is available for their photosynthesis. In coastal ecosystems, pelagic diatoms are extensively studied, but their benthic counterparts, more discreet and more difficult to access, are often ignored. Yet living at much lower light intensities, they are a key compartment of coastal ecosystems functioning, being able to produce as much biomass as pelagic diatoms that live in the well-lit surface waters. Benthic diatoms differ considerably from pelagic forms on several aspects: First, pelagic and benthic diatoms do not follow the same seasonal dynamics: In the bay of Brest, we showed that benthic diatoms are the first to bloom in the season, providing food and energy to the ecosystem right from the beginning of spring (with 60% of the total biomass until April). The system then moves from a system dominated by benthic biomass in early spring to a system where the pelagic biomass dominates. Regarding biodiversity, most benthic diatoms species are different from those found in the water column, they are mostly pennate forms and are far more diverse. On the physiological side, benthic diatoms are incredibly well adapted to low light intensities. However, the mechanisms which result in this adaptation remain unclear. We search for the role of the nanostructure of the frustule in the capture of light, but no difference between pelagic and benthic diatoms could be highlighted so far. Of particular interest is that benthic diatoms able to migrate into the sediment, are adapted to the high Si(OH)4 concentrations found in their surrounding and evidence a multiphasic Si uptake with very high half saturation constant (KS). Their capacity to reverse benthic Si(OH)4 fluxes at the interface indicate the important role they also play in the coastal silica cycle and particularly in controlling the pelagic diatom production. It remains to examine the coupling between carbon and silica at the water/ sediment interface and to determine which factors control the benthic production. Further studies are also needed to understand which evolution has allowed pennate diatoms to colonize so successfully the benthic habitat.

Published
2016

24. Influence of diatom diversity on the ocean biological carbon pump

Author

Tréguer, Paul, primary, Bowler, Chris, additional, Moriceau, Brivaela, additional, Dutkiewicz, Stephanie, additional, Gehlen, Marion, additional, Aumont, Olivier, additional, Bittner, Lucie, additional, Dugdale, Richard, additional, Finkel, Zoe, additional, Iudicone, Daniele, additional, Jahn, Oliver, additional, Guidi, Lionel, additional, Lasbleiz, Marine, additional, Leblanc, Karine, additional, Levy, Marina, additional, and Pondaven, Philippe, additional

Published
2017
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25. Differences in size distribution of marine phytoplankton in presence versus absence of jellyfish support theoretical predictions on top-down control patterns along alternative energy pathways.

Author

Wollrab, Sabine, Pondaven, Philippe, Behl, Stephan, Beker, Beatriz, and Stibor, Herwig

Subjects
MARINE phytoplankton, ALTERNATIVE fuels, PHYTOPLANKTON, MARINE plankton, JELLYFISHES, FRESHWATER phytoplankton, CILIATA
Abstract

While theoretical food web studies highlight the importance of alternative energy pathways in shaping community response to bottom-up and top-down forcing, empirical insight on the relevance of the predicted patterns is largely lacking. In marine plankton food webs differences in food size spectra between ciliates and copepods lead to alternative energy pathways, one expanding from small phytoplankton over ciliates to copepods, the other from large edible phytoplankton directly to copepods. Correspondingly, predation pressure by copepods leads to an increase of small phytoplankton through top-down control of copepods on ciliates, but to a decrease of large phytoplankton through direct predation by copepods. Hence, food web theory predicts a shift from the dominance of large to small algae along an enrichment gradient. This prediction clearly deviates from the general assumption of a shift from small fast growing to larger slow-growing phytoplankton taxa with increasing nutrient availability. However, if copepods themselves are under top-down control by strong predation through planktivores such as fish or jellyfish, dominance of large algae is expected throughout the enrichment gradient. We tested these predictions by analyzing the phytoplankton composition from numerous marine lakes and lagoon sites located on the archipelago of Palau covering a wide range of nutrient levels, comparing sites lacking large numbers of higher trophic levels with sites harboring high densities of jellyfish. The observed patterns strongly support that higher trophic levels influence the phytoplankton size distribution along a nutrient enrichment gradient, highlighting the importance of alternate energy pathways in food webs for community responses. [ABSTRACT FROM AUTHOR]

Published
2020
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26. Marine producers, consumers and climate change: From an ecological stoichiometry perspective

Author

Nugraha, Adi, Pondaven, Philippe, Tréguer, Paul, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Grigorov, Ivo

Subjects
[SDU.STU.OC] Sciences of the Universe [physics]/Earth Sciences/Oceanography, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography
Abstract

participant; Ecological stoichiometry is a rapidly expanding research field investigating how the elemental composition of organisms affects ecological processes. Owing to the fact that the ratios of carbon (C) :nitrogen (N) : phosphorus (P) are different among aquatic organisms, their recycling nutrients may thus affect the supply and the stoichiometry of C, N and P in the ocean. In contrast, the changing ocean (e.g. by climate change and human perturbation) may also affect the C:N:P stoichiometry of the ocean, and eventually the C:N:P of those organisms living in the ocean. Here, we investigated the impact of consumer-driven nutrient recycling (CNR) on oceanic primary production and the distribution of nitrogen (N) and phosphorus (P) in the deep ocean. For this purpose, we used and extended two existing models: a 2-box model of N and P cycling in the global ocean (Tyrrell, 1999), and the model of Sterner (Sterner, 1990) which formalised the principles of CNR theory. The resulting model showed that marine herbivores may affect the supply and the stoichiometry of N and P in the ocean, thereby exerting a control on global primary production. The predicted global primary production was higher when herbivores were included in the model, particularly when these herbivores had higher N:P ratios than phytoplankton. The potential impacts of climate change on the C and nutrient availability in aquatic ecosystems, its consequences for the C:N:P stoichiometry of plankton communities, and its implications for the structure of aquatic food webs are briefly discussed.

Published
2010

27. Towards a new approach of the biological pump

Author

Ragueneau, Olivier, Moriceau, Brivaëla, Schultes, Sabine, Marc, Parenthoen, Pondaven, Philippe, Rivière, Pascal, Mémery, Laurent, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des sciences et techniques de l'information, de la communication et de la connaissance (Lab-STICC), École Nationale d'Ingénieurs de Brest (ENIB)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Télécom Bretagne-Institut Brestois du Numérique et des Mathématiques (IBNM), Université de Brest (UBO)-Université européenne de Bretagne - European University of Brittany (UEB)-École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS), and Moriceau, Brivaëla

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2009

28. A Low Global POC Export Controlled by Seasonality

Author

Ragueneau, Olivier, Moriceau, Brivaëla, Pondaven, Philippe, Nicolas, Dittert, Moriceau, Brivaëla, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), and Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2009

29. Potential phytoplankton responses to iron and stratification changes in the Southern Ocean based on a flexible-composition phytoplankton model

Author

Mongin, Mathieu, Nelson, David, Pondaven, Philippe, Tréguer, Paul, Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC), College of Oceanography, Oregon State University (OSU), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
EXPORT PRODUCTION, LIGHT, FERTILIZATION, GROWTH, BLOOM, SI, ECOSYSTEM MODEL, BIOGEOCHEMISTRY, PACIFIC SECTOR, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, PRIMARY PRODUCTIVITY
Abstract

International audience; Under present climatic conditions, primary production in the Southern Ocean is limited by a combination of grazing pressure, the light/mixing regime, and iron. The response of the ecosystem to a permanent increase of iron supply and/or changes in the mixing regime is analyzed with a flexible-composition phytoplankton model that includes C, N, Si, and Fe cycling. Limitation of phytoplankton growth by light and nutrients ( Si, N, and Fe) is treated through their effects on cellular elemental composition. The model is applied to the KERFIX time series in the subantarctic region. Two physical scenarios are considered, normal and reduced mixed layer depth, with four different aeolian inputs of Fe in each case ranging from 1 to 1000 times the estimated present input. These simulations suggest that Fe supply via dust and rain must be increased by more than a factor of 10 to produce significant changes. Increased Fe supply alone causes the bloom to occur later in the season ( summer rather than spring), and coupled with a decrease in the mixed layer depth it produces drastic changes in the bloom intensity while preserving its present temporal development. Seasonal interaction between light and Fe limitation plays a critical role in controlling the primary and export production. If aeolian Fe input is increased by a factor of 1000, and mixed layer depth is reduced at the same time, export of carbon increases by a factor of 3. Light limitation prevents complete drawdown of nitrate, even if Fe limitation is removed and mixed layer depth reduced. This sets an upper limit on the primary production that can be achieved under the present meteorological conditions in this sector of the Southern Ocean.

Published
2007
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30. New primary production and nitrification in the western subtropical North Atlantic: A modeling study

Author

Martin, Adrian, Pondaven, Philippe, National Oceanography Centre (NOC), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
NITROGEN, NITRATE FLUX, SARGASSO SEA, MESOSCALE EDDIES, TIME-SERIES, EUPHOTIC ZONE, OCEAN DESERTS BLOOM, OXYGEN, EXPORT, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, US JGOFS BERMUDA
Abstract

International audience; The original definition of new primary production rests on the assumption that nitrogenous substrate taken up to fuel algal growth is coming into contact with phytoplankton for the first time that year. Therefore, should the generation of nitrate from ammonium by nitrification turn out to be significant in surface waters then nitrate uptake can no longer be simply ascribed to new production. A modeling study is presented centered on the Bermuda Atlantic Time-series Station, in the oligotrophic subtropical North Atlantic. We quantify the role of nitrification in providing nitrate to fuel primary production through a full annual cycle for the first time. The results confirm previous limited observations suggesting that a major fraction of nitrate uptake in oligotrophic regions ( where nitrification will be most influential), previously ascribed to new production, may actually involve "recycled'' nitrate.

Published
2006
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31. Exploring interacting influences on the silicon isotopic composition of the surface ocean: a case study from the Kerguelen Plateau

Author

Coffineau, N., De La Rocha, C. L., Pondaven, Philippe, Coffineau, N., De La Rocha, C. L., and Pondaven, Philippe

Abstract

This study presents six new water column profiles of the silicon isotopic composition (delta Si-30) of dissolved silicon (DSi) from the Atlantic and Indian sectors of the Southern Ocean and a variable depth box model of silica cycling in the mixed layer that was constructed to illuminate the evolution of surface ocean delta Si-30 over the full course of a year. In keeping with previous observations, delta Si-30 values ranged from +1.9 to +2.4% in the mixed layer (ML), +1.2 to +1.7 parts per thousand in Winter Water (WW), and +0.9 to +1.4 parts per thousand in Circumpolar Deep Water (CDW). These data also confirmed the occurrence of diminished values for ML delta Si-30 at low DSi concentrations in early austral autumn on the Kerguelen Plateau. The box model was used to investigate whether these low, post-growing season values of delta Si-30 were related to input of DSi to the ML from basalt weathering, biogenic silica dissolution (with or without isotopic fractionation), the onset of winter mixing, or some combination of the three. Basalt weathering and fractionation during biogenic silica dissolution could both lower ML delta Si-30 below what would be expected from the extent of biological uptake of DSi. However, the key driver of the early autumn decrease in delta Si-30 appears to be the switch from bloom growth (with net removal of DSi and net accumulation of biogenic silica (BSi) biomass) to steady state growth (when slow but continuing production of BSi prevented significant net increase in DSi concentrations with diffusive input of DSi from WW but not decrease in ML delta Si-30 towards WW values). Model results also indicated that fractionation during dissolution has only a negligible effect on the delta Si-30 of BSi exported throughout the course of the year. However, seasonal changes in export efficiency (e. g. favouring the export of bloom BSi versus the export of BSi produced during other times of the year) should strongly influence the delta Si-30 of BSi a

Published
2014
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32. Quantification of algal iron requirements in the Subantarctic Southern Ocean

Author

Blain , Stéphane, Sedwick , Peter, Griffiths , Brian, Quéguiner , Bernard, Bucciarelli , Eva, Fiala , Michel, Pondaven , Philippe, Tréguer , Paul, Laboratoire d'océanographie et de biogéochimie (LOB), Université de la Méditerranée - Aix-Marseille 2-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Bermuda Biological Station for Research (BBSR), Bermuda Biological Station for Research, Institute of Antarctic and Southern Ocean Studies (IASOS), University of Tasmania [Hobart, Australia] (UTAS), Division of Marine and Atmospheric Research (CSIRO), Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Centre National de la Recherche Scientifique (CNRS)-Université de Brest (UBO), Laboratoire d'océanographie biologique de Banyuls (LOBB), Observatoire océanologique de Banyuls (OOB), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'océanographie et de biogéochimie ( LOB ), Université de la Méditerranée - Aix-Marseille 2-Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Bermuda Biological Station for Research ( BBSR ), Institute of Antarctic and Southern Ocean Studies ( IASOS ), University of Tasmania, Division of Marine and Atmospheric Research ( CSIRO ), Commonwealth Scientific and Industrial Research Organisation [Canberra] ( CSIRO ), Laboratoire des Sciences de l'Environnement Marin (LEMAR) ( LEMAR ), Centre National de la Recherche Scientifique ( CNRS ) -Université de Brest ( UBO ) -Institut Français de Recherche pour l'Exploitation de la Mer ( IFREMER ) -Institut Universitaire Européen de la Mer ( IUEM ), Institut de Recherche pour le Développement ( IRD ) -Université de Brest ( UBO ) -Centre National de la Recherche Scientifique ( CNRS ) -Institut de Recherche pour le Développement ( IRD ) -Université de Brest ( UBO ) -Centre National de la Recherche Scientifique ( CNRS ) -Institut de Recherche pour le Développement ( IRD ), Laboratoire d'océanographie biologique de Banyuls ( LOBB ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Bucciarelli, Eva, Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[ SDU.OCEAN ] Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere, Subantarctic Southern Ocean (Indian sector), algal iron requirements
Abstract

International audience; Shipboard iron-addition incubation experiments were carried out in the Indian sector of the Subantarctic Southern Ocean duringthe Antares-IV campaign in late January–February 1999. The aim of these experiments was to estimate the dissolved iron requirements of the native phytoplankton community in this oceanic region, in order to improve the parameterisation of iron as a limitingnutrient in a coupled 1D physical–biogeochemical ocean model. The experiments were conducted with plankton collected from the upper water column (B20m depth) at three sites in the Crozet Basin between 43–461S and 61–651E: (1) the Polar Front Zone (PFZ, dissolved Fe=0.33 nM), (2) the confluence of the Subantarctic and Subtropical Fronts (SAF/STF, dissolved Fe=0.29 nM), and (3) the southern Subtropical Zone (STZ, dissolved Fe=0.09 nM). Experimental results from each site indicate that algal community growth rates varied as a function of added iron concentration. Monod saturation functions fitted to the experimental data yield estimates for the community half-saturation constant for growth with respect to iron (Km) of 0.41–0.45nM Fe (PFZ), 0.055–0.086nM Fe (SAF/STF) and 0.092–0.093nM Fe (STZ, with macronutrients added), each of which has an estimated uncertainty of 720%. The Km estimate for the SAF/STF site reflects the mixed algal assemblage (diatoms+nanoplankton+dinoflagellates) that grew in the experimental incubations, whereas the Km estimates for the PFZ and STZ sites probably reflect the Fe requirements of the small pennate diatoms such as Pseudo-nitzschia spp., which dominated the algal biomass produced in these experiments. The fact that there are significant differences between the Km estimates for the PFZ and STZ sites suggests that similar diatom assemblages may have quite different iron requirements, perhaps due to differences in environmental conditions (e.g., light, macronutrient levels). We also examine the sensitivity of a onedimensional coupled physical–biogeochemical model to the choice of Km for iron, usingtime-series observations from the KERFIX station close to the Polar Front. The model was best able to simulate the KERFIX observations using a diatom Km value ofB0.1nM Fe, which is considerably less than our experimental estimate ofB0.4nM Fe for the PFZ. This discrepancy probably reflects differences in the iron requirements of diatom populations immediately north and south of the Polar Front in the Kerguelen region, due to differences in diatom species composition, availability of light and silicic acid, or the environmental and physiological histories of the diatom populations.

Published
2002

33. Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

Author

Le Moigne, F. A. C., Boye, Marie, Masson, A., Corvaisier, Rudolph, Grossteffan, E., Gueneugues, A., Pondaven, Philippe, Le Moigne, F. A. C., Boye, Marie, Masson, A., Corvaisier, Rudolph, Grossteffan, E., Gueneugues, A., and Pondaven, Philippe

Abstract

Meridional and vertical distributions of several biogeochemical parameters were studied along a section in the southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer 2008 of the International Polar Year to characterize the biogeochemical provinces and to assess the seasonal net diatom production. Based on analyses of macro-nutrients, ammonium (NH4), chlorophyll a, (Chl a), phaeopigments, biogenic silica (BSi), particulate inorganic carbon (PIC), and particulate organic carbon and nitrogen (POC and PON, respectively), four biogeochemical domains were distinguished along the section: the subtropical Atlantic, the confluence zone of the subtropical and subantarctic domains, the Polar Frontal Zone (PFZ) in the Antarctic Circumpolar Current (ACC), and the north-eastern branch of the Weddell Gyre. The subtropical region displayed extremely low nutrient concentrations featuring oligotrophic conditions, and sub-surface maxima of Chl a and phaeopigments never exceeded 0.5 mu g L-1 and 0.25 mu g L-1, respectively. The anticyclonic and cyclonic eddies crossed in the Cape Basin were characterized by a deepening and a rise, respectively, of the nutrients isoclines. The confluence zone of the subtropical domain and the northern side of the ACC within the subantarctic domain displayed remnant nitrate and phosphate levels, whereas silicate concentrations kept to extremely low levels. In this area, Chl a level of 0.4-0.5 mu g L-1 distributed homogenously within the mixed layer, and POC and PON accumulated to values up to 10 mu M and 1.5 mu M, respectively, indicative of biomass accumulation along the confluence zone during the late productive period. In the ACC domain, the Polar Frontal Zone was marked by a post-bloom of diatoms that extended beyond the Polar Front (PF) during this late summer condition, as primarily evidenced by the massive depletion of silicic acid in the surface waters. The accumulation of NH4 to values up to 1.25 mu M at 100

Published
2013
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34. Atmospheric deposition onto oligotrophic marine systems: new insights from mesocosm studies

Author

Guieu, Cecile, Ridame, Celine, Pulido-Villena, Elvira, Wagener, Thibaut, Bressac, Matthieu, Dulac, Francois, Desboeufs, Karine, Blain, Stephane, Brunet, Christophe, Obernesterer, Ingrid, Wuttig, Kathrin, Ye, Ying, Baudoux, Anne-Clair, Pondaven, Philippe, Biegala, Isabelle, Leblond, Nathalie, Doxaran, David, Bourrin, Francois, Stemman, Lars, Guieu, Cecile, Ridame, Celine, Pulido-Villena, Elvira, Wagener, Thibaut, Bressac, Matthieu, Dulac, Francois, Desboeufs, Karine, Blain, Stephane, Brunet, Christophe, Obernesterer, Ingrid, Wuttig, Kathrin, Ye, Ying, Baudoux, Anne-Clair, Pondaven, Philippe, Biegala, Isabelle, Leblond, Nathalie, Doxaran, David, Bourrin, Francois, and Stemman, Lars

Published
2012

38. KERFIX, a time-series station in the Southern Ocean: a presentation

Author

Jeandel, Catherine, primary, Ruiz-Pino, Diana, additional, Gjata, Elvis, additional, Poisson, Alain, additional, Brunet, Christian, additional, Charriaud, Edwige, additional, Dehairs, Frank, additional, Delille, Daniel, additional, Fiala, Michel, additional, Fravalo, Charles, additional, Carlos Miquel, Juan, additional, Park, Young-Hyang, additional, Pondaven, Philippe, additional, Quéguiner, Bernard, additional, Razouls, Suzanne, additional, Shauer, Bernard, additional, and Tréguer, Paul, additional

Published
1998
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39. Recycling and Uptake of Si(OH)4 when Protozoan Grazers Feed on Diatoms.

Author

Schultes, Sabine, Lambert, Christophe, Pondaven, Philippe, Corvaisier, Rudolph, Jansen, Sandra, and Ragueneau, Olivier

Subjects
DIATOM frustules, BIODEGRADATION, DETRITUS, SILICA, BACTERIAL growth, WASTE recycling, MORTALITY
Abstract

Herbivory of microzooplankton is an emerging key factor of diatom mortality in the ocean. As part of the microbial loop, protozoan grazers also feed on bacteria that accelerate the degradation of diatom detritus. The potentially pivotal effect of microzooplankton grazing on Si(OH)4 recycling was investigated with cultures of single-celled diatoms, Thalassiosira pseudonana and Chaetoceros gracilis, and heterotrophic protozoans, the dinoflagellate Oxyrrhis marina and the ciliate Strombidium sp. Both grazers ingested diatoms and the bacteria in the non-axenic cultures. C. gracilis, whose frustule is “armed” with setae, was less suitable as a prey than T. pseudonana. Ingestion rates of T. pseudonana were comparable for O. marina and Strombidium, but the dinoflagellate produced two orders of magnitude more detrital bSiO2 than the ciliate, due to the higher abundance reached by O. marina. Total net release of Si(OH)4 was lower in the grazing treatments compared to the control possibly due to the reduced bacterial growth by microzooplankton bacterivory, and to the transient protection of detrital bSiO2 in discarded feeding vacuoles. Over the first 24h, microzooplankton grazing even led to enhanced uptake of Si(OH)4 by diatoms, confirming the potential of grazing to influence the silicification of diatom frustules. Subsequently however, the Si dynamics in bottles with grazers turned rapidly from net uptake to net Si(OH)4 release. Protozoan grazers hence tie Si(OH)4 recycling into the microbial loop by producing detrital bSiO2. [Copyright &y& Elsevier]

Published
2010
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40. Le Parlement et la politique extérieure sous la IVe République / Philippe Pondaven,.. ; préface de Georges Berlia

Author

Berlia, Georges (1911-1977). Préfacier, Pondaven, Philippe (1941-....). Auteur du texte, Berlia, Georges (1911-1977). Préfacier, and Pondaven, Philippe (1941-....). Auteur du texte

Abstract

Collection : Travaux et recherches de l'Université de droit, d'économie et de sciences sociales de Paris. Série Science politique ; 2, Collection : Travaux et recherches de l'Université de droit, d'économie et de sciences sociales de Paris ; 2, Contient une table des matières, Avec mode texte

Published
1973

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