10-blanc-614 keops 2/kerguelen : comparaison plateau océan 2

Compte-rendu de fin de projet

Référence du formulaire : ANR-FORM-090601-01-01

Projet ANR- 10-BLANC-614

KEOPS 2/Kerguelen : Comparaison Plateau Océan 2

Programme Blanc 2010

A IDENTIFICATION ............................................................... 2 B RÉSUMÉ CONSOLIDÉ PUBLIC .................................................. 3

B.1 Résumé consolidé public en français ......................................... 3 B.2 ENGLISH PUBLIC CONSOLIDATED SUMMARY ............................. 5

C SCIENTIFIC REPORT ........................................................... 7 C.1 Abstract ................................................................................ 7 C.2 Context ................................................................................ 7 C.3 Sampling strategy and summary of methods ............................. 7 C.4 Results ................................................................................. 8 C.5 Exploitation of research results .............................................. 12 C.6 Discussion / Conclusions ....................................................... 13 C.7 References .......................................................................... 13

D LIST OF DELIVERABLES ...................................................... 15 E IMPACT OF THE PROJECT ..................................................... 15

E.1 Impact indicators ................................................................. 16 E.2 List of publications and communications .................................. 16 Publications ................................................................................ 16 Communications .......................................................................... 18 E.3 Valorization elements ........................................................... 21 E.4 Bilan et suivi des personnels recrutés en CDD (hors stagiaires) .. 22 Annex 1 ..................................................................................... 23 Annex 2 ..................................................................................... 25

Référence du formulaire : ANR-FORM-090601-01-01 2/52

A IDENTIFICATION Acronyme du projet KEOPS 2 Titre du projet Kerguelen : Comparaison plateau Ocean2

Coordinateur du projet (société/organisme)

Bernard QUÉGUINER (MIO/OSU Institut Pythéas/Université d’Aix–Marseille)

Période du projet (date de début – date de fin) 03/01/2011 − 02/10/2014

Site web du projet, le cas échéant http://www.obs-vlfr.fr/keops2/index.php?option=com_content&view=article&id=1&Itemid=3

Rédacteur de ce rapport Civilité, prénom, nom Prof. Bernard QUEGUINER Téléphone 04 91 82 91 05 Adresse électronique [email protected] Date de rédaction

Liste des partenaires présents à la fin du projet (société/organisme et responsable scientifique)

1 - MIO (ex LOPB) / Université d’Aix−Marseille (ex Université de la Méditerranée) – Bernard Quéguiner 2 - LOMIC / CNRS Délégation Languedoc-Roussillon – Ingrid Obernosterer 3 - LEGOS / CNRS Délégation Midi-Pyrénées – Catherine Jeandel 4 - LEMAR CNRS Délégation Bretagne - Pays de la Loire − Géraldine Sarthou


B RÉSUMÉ CONSOLIDÉ PUBLIC

B.1 RÉSUMÉ CONSOLIDÉ PUBLIC EN FRANÇAIS

KEOPS 2 : Le fer et la productivité des eaux de l’Océan Austral. Comment la fertilisation en fer stimule−t’elle la pompe biologique du carbone dans les écosystèmes HNLC des hautes latitudes? Objectifs généraux du projet : processus de fertilisation naturelle et réponses de l’écosystème pélagique.

L’Océan Austral est une région–clé dans le cycle global du carbone car il représente un puits important de CO2 dont l’importance reste encore aujourd’hui débattue compte tenu notamment du changement climatique en cours. L’Océan Austral représente par ailleurs la plus vaste zone HNLC (High Nutrient Low Chlorophyll) de l’Océan Global, au sein de laquelle l’utilisation des nutriments majeurs est limitée par la disponibilité du fer. Le projet KEOPS 2 s'est ainsi intéressé aux effets de la fertilisation en fer sur le fonctionnement de la pompe biologique de carbone et le développement de l’écosystème pélagique dans l’Océan Austral. Ce projet a été mené au cours d’une campagne océanographique de longue durée en 2011 et qui a permis d’étudier le laboratoire naturel que constituent les eaux entourant l’archipel des Kerguelen. Cet environnement est en effet naturellement fertilisé en fer par l’interaction entre le courant circumpolaire antarctique (ACC, Antarctic Circumpolar Current) et la topographie et des développements planctoniques y sont observés annuellement de façon récurrente. KEOPS 2 a ainsi pu établir des comparaisons entre la zone fertilisée et les eaux HNLC situées en amont de l’ACC.

Le projet KEOPS 2 est original dans la mesure où la plupart des observations concernant le rôle du fer dans l’Océan Austral ont été obtenues jusqu’ici à partir d’expériences de fertilisation artificielle de l’océan. Ces expériences ont établi que le phytoplancton des zones HNLC répond bien à un ajout de fer qui favorise la prolifération de diatomées, microalgues à paroi siliceuse. Toutefois de grandes incertitudes demeurent sur la transposition de ces résultats à des conditions de fertilisation prolongée telles que celles caractérisant les systèmes naturels.

Méthodologie KEOPS 2 est un projet pluridisciplinaire qui, dans sa composante ANR, a regroupé a regroupé

des partenaires du CNRS, de l’Université Paris VI, de l’Université de Bretagne Occidentale, de l’Université Toulouse III et de l’Université d’Aix−Marseille, aux compétences complémentaires en géochimie, biogéochimie, biologie et écologie pélagique.

Le projet a permis de documenter les processus d’apports en fer grâce à l’utilisation d’outils analytiques permettant la mesure de traceurs géochimiques comme les terres rares et de traceurs radioactifs naturels (isotopes du radium). La spéciation des principaux métaux et leurs distributions dans le milieu naturel ont été également étudiées au moyen de techniques de chimie analytique. Plusieurs compartiments biologiques ont été observés à l’aide de techniques classiques (microscopie, analyse d’image, épifluorescence) mais aussi grâce aux techniques de biologie moléculaire (séquençage) et au déploiement de capteurs optiques in situ capables de restituer les spectres de taille des organismes. Les flux de matières ont été également estimés au moyen de techniques de pointe utilisant une panoplie de traceurs isotopiques stables (15N, 13C et 30Si). Il a ainsi été possible d’étudier l’ensemble des processus responsables de la fertilisation, de la biodisponibilité du fer et de son utilisation au sein des communautés pélagiques de la bactérie au mésozooplancton.

Le projet a été organisé en 4 tâches de recherche :

– Spéciation du fer, – Sources et transport du fer, – Diversité microbienne et couplage des cycles biogéochimiques du carbone et du fer, – Biodiversité et structures spatiales des communautés planctoniques.


Résultats majeurs du projet Dans le mécanisme de fertilisation, les apports atmosphériques sont négligeables tandis que les

processus de ruissellement direct, d’apports par les glaciers et les sédiments du plateau sont des sources importantes de fer dissous à proximité de Kerguelen. La reminéralisation des particules au cours de leur sédimentation explique par ailleurs les concentrations élevées en fer dissous dans les eaux du large. Le puissant courant du Front Polaire est ainsi enrichi en fer dissous et vient alimenter les eaux situées à l’est du plateau de Kerguelen. Les organismes qui se développent ensuite au sein de ces floraisons phytoplanctoniques naturelles présentent des caractéristiques tout à fait différentes des communautés observées lors des expériences de fertilisation artificielle. Ces dernières, réalisées sur de faibles superficies, ne peuvent donc pas être transposées à des situations de fertilisation sur de grandes étendues océaniques, pour lesquelles l’évolution de la structure des communautés est beaucoup plus complexe.

Production scientifique depuis le début du projet Le projet KEOPS 2 a abouti à la publication de 28 articles, directement issus du financement de

l’ANR, dans les meilleurs journaux internationaux. Avec l’ensemble des partenaires du projet, le nombre total d’articles scientifiques d’élève aujourd’hui à plus de 50 articles. Le programme a par ailleurs fait l’objet de trois séries de présentations orales dans une session spéciale du 2013 ASLO Aquatic Sciences meeting à la Nouvelle Orléans (U.S.A) en février 2013. Un numéro spécial de la revue Biogeosciences regroupant 33 articles est en cours de finalisation.

Informations factuelles Le projet KEOPS 2 est un projet de recherche fondamentale coordonné par Bernard Quéguiner.

Il associe aussi le LOMIC (OOB, Université Paris VI), le LEGOS (OMP, Université Toulouse III) ainsi que le LEMAR (IUEM, Université de Bretagne Occidentale). Le projet a commencé en janvier 2011 et a duré 45 mois. Il a bénéficié d’une aide ANR de 1 249 788 € pour un coût global de l’ordre de 3 794 195 €.

Illustration: Extension des blooms de phytoplancton au−dessus et en aval du plateau de Kerguelen révélée par télédétection satellitale de la couleur de l'océan le 11 Novembre 2011, en comparaison de la taille approximative des patches de chlorophylle induits lors des expériences de fertilisation en fer artificielle (Smetacek et al., 2012, rectangle vert) et par l'événement de la fertilisation artificielle «pirate» au large du Canada (Tollefson, 2012;. Xiu et al., 2014) (rectangle jaune).


B.2 ENGLISH PUBLIC CONSOLIDATED SUMMARY

KEOPS 2: Iron and productivity of Southern Ocean waters. How iron fertilization stimulates the biological carbon pump in HNLC high-latitude ecosystems? General objectives of the project: natural fertilization processes and responses of the pelagic ecosystem.

The Southern Ocean is a key region in the global carbon cycle because it is a major sink of CO2 whose importance is still debated today especially given the ongoing climate change. The Southern Ocean is also the largest HNLC (High Nutrient Low Chlorophyll) area of the Global Ocean, in which the use of major nutrients is limited by iron availability. The KEOPS 2 project addressed the effects of iron fertilization on the biological carbon pump functioning and the development of the pelagic ecosystem in the Southern Ocean. This project was conducted during a long-term oceanographic cruise in 2011 which enabled studying the natural laboratory constituted by the waters surrounding the Kerguelen Islands. This environment is indeed naturally fertilized with iron by the interaction between the Antarctic Circumpolar Current (ACC Antarctic Circumpolar Current) and the topography, and annual planktonic developments are observed repeatedly. KEOPS 2 enabled making comparisons between the fertilized area and the HNLC waters upstream of the ACC.

The KEOPS 2 project is original in that most of the observations concerning the role of iron in the Southern Ocean have been obtained so far from artificial fertilization experiments in the ocean. These experiments established that the phytoplankton of HNLC areas respond to an iron addition by promoting the growth silicified microalgae: diatoms. However major uncertainties remain on the transposition of these results to sustained fertilization conditions such as those characterizing natural systems.

Methodology

KEOPS 2 is a multidisciplinary project which ANR component brought together partners from CNRS, Paris VI University, University of Western Brittany, Toulouse III University, and Aix-Marseille University, with complementary skills in marine geochemistry, biogeochemistry, biology and pelagic ecology.

The project documented the processes of iron supply through the use of analytical tools making it possible to measure geochemical tracers such as rare earths and natural radioactive tracer (radium isotopes). Speciation of major metals and their distributions in the natural environment were also studied using analytical chemistry techniques. Several biological compartments were observed using conventional techniques (microscopy, image analysis, epifluorescence) but also thanks to molecular biology techniques (sequencing) and deployment of in situ optical sensors capable of reproducing spectra size organisms. Fluxes were also estimated through advanced techniques using a variety of stable isotope tracers (15N, 13C, and 30Si). It was thus possible to study all the processes responsible of the fertilization process, the bioavailability of iron and its use in the pelagic communities from bacteria to mesozooplankton.

The project was organized into four research tasks:

– Speciation of iron, – Sources and transport of iron, – Microbial diversity and coupling of biogeochemical cycles of carbon and iron, – Biodiversity and spatial structure of plankton communities.

Main results of the project In the fertilization mechanism, atmospheric inputs are negligible while processes like direct

runoff, contributions by glaciers and shelf sediments, are important sources of dissolved iron in the vicinity of Kerguelen. Particle remineralization during their sedimentation also explains the high concentrations of dissolved iron in offshore waters. The powerful Polar Front current is thus enriched


in dissolved iron and feeds the waters east of the Kerguelen Plateau. Organisms that grow in these natural phytoplankton blooms have characteristics quite different from communities observed in artificial fertilization experiments. The latter, carried out on small areas, therefore, cannot be transposed to fertilization situations over large ocean areas, for which changes in community structure are much more complex.

Scientific production since the beginning of the project

The KEOPS 2 project resulted in the publication of 28 articles directly from the ANR funding, in the best international journals. With all project partners, the total number of scientific papers now stands at more than 50 articles. The program has also been the subject of three series of oral presentations in a special session of the 2013 ASLO Aquatic Sciences meeting in New Orleans (USA) in February 2013. A special issue of the journal ‘Biogeosciences’ gathering 33 papers is near completion.

Factual information

The KEOPS 2 project is a basic research project coordinated by Bernard Quéguiner. It also associates LOMIC (OOB, University Paris VI), LEGOS (OMP, University Toulouse III), and LEMAR (IUEM, University of Western Brittany). The project started in January 2011 and lasted 45 months. He received an ANR funding of € 1,249,788 for a total cost of around € 3,794,195.

Illustration: Spatial extent of phytoplankton blooms over and downstream from the Kerguelen plateau as revealed by satellite ocean color on 11th November, 2011, in comparison to the approximate size of chlorophyll patches induced by artificial iron fertilization experiments (Smetacek et al., 2012) (green rectangle) and by the ‘rogue’ artificial fertilization event off Canada (Tollefson, 2012; Xiu et al., 2014) (yellow rectangle).


C SCIENTIFIC REPORT A detailed report is given as Annex 2 at the end of the document. Mémoire scientifique confidentiel : oui / non

C.1 ABSTRACT

The role of iron as the main controlling factor of the various blooms that develop around and on the Kerguelen Plateau has been confirmed. In the fertilization mechanism, atmospheric inputs are negligible while processes like direct runoff, contributions by glaciers and shelf sediments, are important sources of dissolved iron in the vicinity of Kerguelen. Particle remineralization during their sedimentation also explains the high concentrations of dissolved iron in offshore waters. The powerful Polar Front current is thus enriched in dissolved iron and feeds the waters east of the Kerguelen Plateau. Organisms that grow in these natural phytoplankton blooms have characteristics quite different from communities observed in artificial fertilization experiments. They are much more silicified than previously thought and this is attributable to the dominance of phytoplankton communities by highly silicified species in the fertilized area. By comparison, the low Si/C ratios of the HNLC sector are explained by dominance by non–siliceous phytoplankton. The artificial iron fertilization experiments, carried out on small areas, on a short time–scale, therefore cannot be transposed to fertilization situations over large ocean areas, for which changes in community structure are much more complex. The complexity of the natural response is apparent as a mosaic of diatom–dominated systems in the fertilization area which in turn influences the biodiversity of the other components of the pelagic food–web, namely the heterotrophic compartments of bacteria and zooplankton.

C.2 CONTEXT

The KEOPS 2 project has enabled studying the role of iron fertilization in the Southern Ocean on the intensity and nature of the carbon biological pump. The study was conducted in an area of natural fertilization (east of the Kerguelen Plateau) enclosed in an otherwise HNLC (High Nutrient Low Chlorophyll) area. The main topics addressed included biogeochemistry, biodiversity and food web structures. The project focused mainly on the KEOPS 2 cruise (MD188/KEOPS 2), which took place from 8 October to 22 November 2011 on board the RV Marion Dufresne 2. The initial objectives aimed at:

1) studying the processes that provide and maintain bioavailable iron to surface waters and defining the associated time scales,

2) studying the coupling between biogeochemical cycles of major elements (C, N, P, and Si) and the iron availability in a naturally fertilized region enclosed within an HNLC area,

3) characterizing the pathways that lead to the remineralization in ‘surface’ layers (epipelagic and upper mesopelagic zones) or to the export to depths of the organic matter produced by the biological activity in the surface water,

4) highlighting the control of biodiversity at the first trophic levels (up to mesozooplankton) by natural iron fertilization,

5) understanding the seasonal and interannual variabilities of biogeochemical processes in a plankton bloom of the Permanently Open Ocean Zone (POOZ) of the Southern Ocean.

In order to achieve these objectives the annual recurrent blooms that develop east of the Kerguelen Islands were selected as a regional case study.

C.3 SAMPLING STRATEGY AND SUMMARY OF METHODS KEOPS 2 benefited from quasi−real−time satellite data acquisition and processing which

enabled to follow the different bloom situations in the fertilized area. Multisatellite data (altimetry, SST, ocean color) were received daily and analyzed onboard. These data were produced by CLS with support from CNES as an optimized regional product for KEOPS 2. The Lagrangian analysis, also


incorporating 50 drifters’ deployments, thus allowed following the chlorophyll plumes which developed during the cruise. This analysis guided the sampling strategy (Figure 1) which, basically, was composed of two transects and several process study stations.

The KEOPS 2 project was a multi-disciplinary project that involved many techniques, often innovative, in geochemistry (utilization of a variety of tracers to identify the sources and mechanisms of iron fertilization, analytical methods for the speciation of iron and other trace metals), biogeochemistry (use of isotopic tracers in biological activity, and vertical export) and biology (optical, fluorescent probes of cellular activity analysis Images in microscopy, sequencing). All of these methods are detailed in the papers compiled in the special issue in preparation for Biogeosciences (http://www.biogeosciences.net/special_issue164.html).

Figure 1: Location of the sampling stations. Transects from North to South (TNS) and

from west to the east (TEW) are indicated in red and blue, respectively. The blank filled circles correspond to a time-series of a recirculation system (E-1, E-2, E-3, E-4E, and E- 5) (from Lasbleiz et al., 2014).

C.4 RESULTS

Trace metal distribution and speciation (TASK 2) Iron (Fe) has been shown to be an essential trace metal controlling phytoplankton growth

and primary production in about 50% of the World’s oceans (Boyd and Ellwood, 2010) including high nutrient low chlorophyll (HNLC) regions. Within the complex Southern Ocean system, numerous studies have highlighted several sites of natural Fe fertilization including the Kerguelen Plateau (Blain et al., 2007; Blain et al., 2008), all stimulating phytoplankton blooms and enhancing carbon sequestration with varying magnitudes. During the first Kerguelen Ocean Plateau compared Study (KEOPS1) held in late summer 2005, the impact of natural fertilization on primary productivity and carbon export was demonstrated in this area (Blain et al., 2007; Savoye et al., 2008). It was proposed that the development of the bloom was constrained by both iron and silicate availability around Kerguelen Island (Blain et al., 2007; Mosseri et al., 2008; Park et al., 2008). The second cruise, KEOPS2 (Kerguelen Ocean and Plateau compared Study 2), which was approved as a GEOTRACES process study, was designed to study the development of the Kerguelen bloom in early spring 2011 and in the offshore fertilization area further east (Blain et al., 2007), in order to better assess the sources, sinks, and internal cycle of Fe.

Results on dissolved iron (dFe) distribution indicate that atmospheric inputs were negligible during the KEOPS2 cruise while direct runoff, glacial, and sedimentary inputs can be considered as important sources of dFe in the vicinity of Kerguelen Island (Figure 2). Remineralization of sinking


particles can explain the high concentrations of dFe in intermediate waters offshore. The strong jet of the Polar Front (PF) was enriched with dFe from the north of the plateau as it flowed northward close to Kerguelen Island and later eastward to loop back into the recirculation area. This fertilized surface waters of the eastern part of the studied area. Furthermore, filaments crossing the PF allowed a more direct natural Fe fertilization of surface water in the recirculation area. Due to variable water mass origin and variable horizontal advection mechanism (along or across the PF), the recirculation area evidenced strong dFe concentration variability. The PF is an important Southern Ocean feature that should not be neglected with regards to Southern Ocean fertilization offshore from the Kerguelen Plateau through fast lateral Fe transport from the north of the Kerguelen Plateau.

Figure 2: Concentrations of dFe (nmol L−1) over the East–West transect. The PF position is

indicated with black dashed lines (Quéroué et al., 2014).

For bioactive trace metals, linear relationships of dissolved metal concentrations versus dissolved macronutrients in deep waters, below the mixed layer depth, can give access to estimates of remineralization ratios if external sources of metals (and macronutrients) in the deep waters are minimal. Such remineralization ratios reflect phytoplankton metal stoichiometries in surface layers. These estimates of trace metal quotas, associated with evaluation of external sources, discriminated 3 groups of trace metals: 1) Cd, whose vertical profiles are mainly impacted by uptake and remineralization, with seemingly little impact of external sources except at the most coastal stations, 2) Mn which is impacted both by biological activity (and scavenging) and external sources, and 3) Cu, Ni and Co whose vertical profiles seem to be more impacted by external sources than by uptake and remineralization.

Iron transport and sources (TASK 3) Refining the origin of the natural fertilization and quantifying it was an important issue

following the results deduced from KEOPS 1 measurements of geochemical tracers. These tracers suggested a significant input of lithogenic elements due to the dissolution of material weathered from the shelf and the slope of Kerguelen and Heard islands. These inputs lead to enrichments of the surface waters of the Plateau in Ra isotopes, Rare Earth Elements (REE), lithogenic Barium (Ba), lithogenic 232Th (Jacquet et al., 2008; van Beek et al., 2008; Venchiarutti et al., 2008; Zhang et al., 2008). In addition, REE, 228Ra, 230Th and 231Pa isotopes clearly indicated the lateral origin of the enrichments – strongly suspected to result from the weathering of Heard and Kerguelen islands and shelves implying submarine weathering-, raising the difficulty of using 1 dimensional models for establishing element budgets on the Kerguelen plateau.

In this context, the apparent ages of surface waters determined using Ra isotopes sampled offshore of the Kerguelen Islands during KEOPS 2 (Figure 3) suggested a rapid transport of chemical elements between the shelves and offshore waters and highlighted the key role played by horizontal


transport in natural iron fertilization and in defining the extension of the chlorophyll plume in this HNLC region of the Southern Ocean. The apparent ages of surface waters determined using our geochemical tracers are in relatively good agreement with the ages determined using physical methods applied to drifter releases (Sanial et al., 2014).

Figure 3: Apparent radium ages of surface waters derived from the 224Ra/228Ra ratios. The

transit time of the drifter is reported in days along its trajectory (Sanial et al., 2014).

Concerning the sources of seawater fertilization in the Kerguelen area dissolved REE concentration results revealed a so far uncharacterized source of continental material in seawater along the coasts of Kerguelen Island that may contribute to the annual events of natural fertilization in the area. REE results of KEOPS2 coastal samples suggested a recent release of lithogenic material from the Kerguelen margins into the dissolved fraction of seawater. Batch reactor experiments were indicative of a rapid release of Si, Nd (and Sr), likely due to the dissolution of basaltic phases and minerals, an observation reinforced by the mineralogical and SEM analyses. First results of an inverse model simulating Pa, Th, Fe, and Nd isotopes and concentrations also identified the importance of the lateral inputs and that an external source is required to balance the budgets of these tracers on the Kerguelen plateau (de Brauwere et al., submitted).

Microbial diversity and activity in the iron fertilized Southern Ocean (TASK 4) Marine microbes play a pivotal role in the marine biogeochemical cycle of carbon, because

they regulate the turnover of dissolved organic matter (DOM), one of the largest carbon reservoirs on Earth. Microbial communities and DOM are both highly diverse components of the ocean system, yet the role of microbial diversity for carbon processing remains thus far poorly understood. The KEOPS2 cruise offered a unique possibility to explore this question in a mosaic of phytoplankton blooms induced by large-scale natural iron fertilization in the Southern Ocean.

Results showed that in this unique ecosystem where concentrations of DOM are lowest in the global ocean a patchwork of blooms stimulates diverse and distinct bacterial communities (Figure 4). Taxa associated with contrasting blooms based on their preferences in the degradation of DOM of different reactivity were identified. The number and the variability in the identity and phylogeny of the responding OTUs among stations suggest that naturally iron-induced phytoplankton blooms in the Southern Ocean stimulate a large diversity of bacterial groups. Our study extends previous investigations of the southeastern bloom above the Kerguelen plateau (Station A3) that have demonstrated major differences in the bacterial community composition during the late stage of the bloom as compared to HNLC waters (West et al., 2008; Obernosterer et al., 2011).Our results from the Kerguelen region are, however, in contrast to the artificial iron enrichment experiments EisenEx and LOHAFEX performed in the Southern Ocean where minor or no changes in bacterial community


composition were observed in the iron-fertilized patch (Arrieta et al., 2004; Thiele et al., 2012). This suggests that the bacterial response is in part driven by the mode of fertilization that differs drastically between these studies.

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Figure 4: Phylogenetic composition of the bacterial communities in surface waters of the

KEOPS2 study sites. Relative contribution of OTUs is expressed as percent of total sequences.

In the fertilized systems of KEOPS 2, the increased supply of phytoplankton dissolved organic matter (DOM) resulted in an increase in bacterial production associated with a higher number of responding taxa in experiments on the natural communities (continuous culture experiments). This suggests that DOM pools of different reactivities are exploited by distinct and diverse taxa, and that the higher number of responding taxa could reflect an increase in niche availability, with a positive feedback on bulk performance due to resource partitioning.

Plankton community structures and biogeochemical cycles (TASK 5) The structure of pelagic communities determines the strength of the biological pump

(magnitude of biogenic matter escaping the epipelagic domain) and its efficiency (effectiveness in reducing surface nutrients relative to subsurface values) (Sarmiento et al., 2004). Several studies have demonstrated that regional differences exist in the strength, overall export efficiency and depth-dependent export efficiency of the biological pump, and that these differences are driven by the structures of pelagic communities, which ultimately determine the magnitude of the biological sequestration of carbon in the deep ocean and sediments (Quéguiner, 2013). KEOPS 2 project offered the unique possibility to address the links between community structures and biogeochemical cycles, in particular as regards the stoichiometry of the particulate organic matter in various conditions of iron fertilization.


The results of KEOPS 1 (Mosseri et al., 2008) stressed the decoupling between the use of nitrate and silicic acid in the blooms of the fertilized area. During KEOPS2, this property has been studied. The results indicated that, contrary to observations in artificial fertilization experiments (Hutchins & Bruland, 1998; Takeda, 1998) naturally–fertilized systems around Kerguelen have stoichiometric Si/C ratios higher than in the HNLC area (Lasbleiz et al., 2014). The careful examination of phytoplankton populations has led to progress two explanations: 1) the HNLC area is not dominated by siliceous phytoplankton but rather by nanoflagellates (Figure 5), 2) phytoplankton communities that develop in the fertilized area are dominated by highly silicified diatoms and it is this specific property that determines their biogeochemical signature (Lasbleiz, 2014). This has important biogeochemical implications on the efficiency of the biological pump in relation to Fe availability.

HNLC site Iron–fertilized blooms

Figure 5: Relative contribution of different plankton groups to the particulate organic carbon

biomass (in %) in the photic zone at the HNLC reference site (R) and the bloom stations.

Finally, KEOPS 2 unexpected result documented the spatial heterogeneity of the diatom blooms, in term of specie dominance, within the Fe–fertilized area which again contrasted with the artificial Fe–fertilization experiments usually characterized by lightly silicified opportunist species like Pseudo–nitzschia spp.

C.5 EXPLOITATION OF RESEARCH RESULTS The exploitation of results obtained during KEOPS 2 was carried out mainly in the form of

papers published in international journals and communications at international conferences. Several results are still being analyzed. Several datasets are still being processed, including those on biodiversity aspects (for which data acquisitions are very time–consuming) and will be the subject of other publications in the coming months.

Results also served as a basis for at least 8 Doctorate Theses:

1. FOURQUEZ Marion, LOMIC/OO Banyuls/mer, Université Pierre & Marie Curie. Rôle des bactéries hétérotrophes dans le couplage des cycles du fer et du carbone dans l’Océan, 24 September 2012.

2. LANDA Marine, LOMIC/OO Banyuls/mer, Université Pierre & Marie Curie. Linking dissolved organic matter sources and bacterial diversity: insights from continuous culture experiments, 16 September 2013.

3. LASBLEIZ Marine, MIO, OSU Institut Pytheas, Université d’Aix–Marseille. Dynamique nutritionnelle du phytoplancton, cycles biogéochimiqus du carbone et des éléments biogènes associés (N,P, Si) en fonction de la disponibilité du fer dans l’Océan Austral au cours de la campagne KEOPS 2, 15 December 2014.

4. CLOSSET Ivia, LOCEAN, Université Pierre & Marie Curie. Cycle biogéochimique du silicium dans l’Océan Austral par les approches isotopiques, defense planned for 2015.

5. QUÉROUÉ Fabien, LEMAR/IUEM, Université de Bretagne Occidentale/University of Tasmania, Hobart.


Trace metals distributions in the Southern and Pacific Oceans, 23 September 2014.

6. LLORT Joan, LOCEAN, Université Pierre & Marie Curie. Influence des apports de fer sur la variabilité de la production primaire et des flux de CO2 dans l'Océan Austral, 9 January 2015.

7. SANIAL Virginie, LEGOS/OMP Toulouse, Université Paul Sabatier. Traçage des échanges côte-large, de la circulation et du mélange dans deux régions océaniques clés : Panache des îles Kerguelen (Océan Austral) et Mer des Salomon (Océan Pacifique), defense planned in October 2015.

8. GEORGES Clément, LOG, Université du Littoral Côte d’Opale. Protist community structure during early phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean), defense planned in 2015.

C.6 DISCUSSION / CONCLUSIONS

With the carrying out of this project, all foreseen sampling objectives have been achieved. A number of developments have yet to be achieved, including the detailed analysis of biodiversity throughout the food web continuum and the precise vertical structure of pelagic communities from bacteria to mesozooplankton. Moreover, data obtained using particle sensors also raise a new question that was not addressed by KEOPS 2: the high-frequency temporal dynamics in the functioning of pelagic food webs. Again the Kerguelen area is a natural laboratory in which may be considered trophic dynamics studies under different stages of bloom development.

C.7 REFERENCES

Arrieta J.M., Weinbauer M.G., Lute C., Herndl G.J., 2004. Response of bacterioplankton to iron fertilization in the southern ocean. Limnology & Oceanography, 49, 799-808.

Blain S., Quéguiner B., Armand L., Belviso S., Bombled B., Bopp L., Bowie A., Brunet C., Brussaard C., Carlotti F., Christaki U., Corbiere A., Durand I., Ebersbach F., Fuda J.L., Garcia N., Gerringa L., Griffiths F.B., Guigue C., Guillerm C., Jacquet S., Jeandel C., Laan P., Lefèvre D., Lo Monaco C., Malits A., Mosseri J., Obernosterer I., Park Y.H., Picheral M., Pondaven P., Remenyi T., Sandroni V., Sarthou G., Savoye N., Scouarnec L., Souhaut M., Thuiller D., Timmermans K., Trull T.W., Uitz J., van Beek P., Veldhuis M., Vincent D., Viollier E., Vong L., Wagener T., 2007. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean. Nature, 446, 1070-U1071.

Blain S., Quéguiner B., Trull T.W., 2008. The natural iron fertilization experiment KEOPS (KErguelen Ocean and Plateau compared Study): An overview. Deep Sea Research Part II: Topical Studies in Oceanography, 55, 559-565.

Boyd P.W., Ellwood M.J., 2010. The biogeochemical cycle of iron in the ocean. Nature Geoscience, 3, 675-682.

de Brauwere A., C. Jeandel, F. Lacan, P. van Beek, M. Roy-Barman, C. Venchiarutti (2014). Disentangling the geochemical fluxes on the Kerguelen Plateau using an inverse multi-tracer box model (submitted to Deep Sea Research).

Hutchins D.A., Bruland K.W., 1998. Iron-limited diatom growth and Si:N uptake ratios in a coastal upwelling regime. Nature, 393, 561-564.

Jacquet S.H.M., Dehairs F., Savoye N., Obernosterer I., Christaki U., Monnin C., Cardinal D., 2008. Mesopelagic organic carbon remineralization in the Kerguelen Plateau region tracked by biogenic particulate Ba. Deep Sea Research Part II: Topical Studies in Oceanography, 55, 868-879.

Lasbleiz M., 2014. Cycles biogéochimiques (Si, C, N, P) en lien avec la dynamique nutritionnelle du phytoplancton dans la région naturellement fertilisée des Kerguelen. Thèse de doctorat, Aix–Marseille University, 314 pp.

Lasbleiz M., Leblanc K., Blain S., Ras J., Cornet-Barthaux V., Hélias Nunige S., Quéguiner B., 2014. Pigments, elemental composition (C, N, P, and Si), and stoichiometry of particulate matter in the naturally iron fertilized region of Kerguelen in the Southern Ocean. Biogeosciences, 11, 5931-5955.

Mosseri J., Quéguiner B., Armand L.K., Cornet-Barthaux V., 2008. Impact of iron on silicon utilization by diatoms in the Southern Ocean: A case study of Si/N cycle decoupling in a


naturally iron-enriched area. Deep Sea Research Part II: Topical Studies in Oceanography, 55, 801.

Obernosterer I., Catala P., Lebaron P., West N.J., 2011. Distinct bacterial groups contribute to carbon cycling during a naturally iron fertilized phytoplankton bloom in the Southern Ocean. Limnology & Oceanography, 56, 2391-2401.

Park Y.-H., Fuda J.-L., Durand I., Naveira Garabato A.C., 2008. Internal tides and vertical mixing over the Kerguelen Plateau. Deep Sea Research Part II: Topical Studies in Oceanography, 55, 582-593.

Quéguiner B., 2013. Iron fertilization and the structure of planktonic communities in high nutrient regions of the Southern Ocean. Deep Sea Research Part II: Topical Studies in Oceanography, 90, 43–54.

Sanial V., P. van Beek, B. Lansard, F. d'Ovidio, E. Kestenare, M. Souhaut, M. Zhou, S. Blain (2014) Study of the phytoplankton plume dynamics off the Crozet Islands (Southern Ocean): A geochemical-physical coupled approach. Journal of Geophysical Research-Oceans, 119, doi:10.1002/2013JC009305.

Sarmiento J.L., Dunne J., Armstrong R.A., 2004. Do we now understand the Ocean’s biological pump? U.S. JGOFS News, 12, 1–5.

Savoye N., Trull T.W., Jacquet S.H.M., Navez J., Dehairs F., 2008. 234Th-based export fluxes during a natural iron fertilization experiment in the Southern Ocean (KEOPS). Deep Sea Research Part II: Topical Studies in Oceanography, 55, 841-855.

Smetacek V., Klaas C., Strass V.H., Assmy P., Montresor M., Cisewski B., Savoye N., Webb A., d'Ovidio F., Arrieta J.M., Bathmann U., Bellerby R., Berg G.M., Croot P., Gonzalez S., Henjes J., Herndl G.J., Hoffmann L.J., Leach H., Losch M., Mills M.M., Neill C., Peeken I., Rottgers R., Sachs O., Sauter E., Schmidt M.M., Schwarz J., Terbruggen A., Wolf-Gladrow D., 2012. Deep carbon export from a Southern Ocean iron-fertilized diatom bloom. Nature, 487, 313-319.

Takeda S., 1998. Influence of iron availability on nutrient consumption ratio of diatoms in oceanic waters. Nature, 393, 774-777.

Thiele S., Fuchs B.M., Ramaiah N., Amann R., 2012. Microbial community response during the iron fertilization experiment LOHAFEX. Applied & Environmental Microbiology, 78, 8803-12.

Tollefson J., 2012. Ocean-fertilization project off Canada sparks furore. Nature, 490, 458-459. van Beek P., Bourquin M., Reyss J. L., Souhaut M., Charette M.A., Jeandel C., 2008. Radium isotopes

to investigate the water mass pathways on the Kerguelen Plateau (Southern Ocean). Deep Sea Research Part II: Topical Studies in Oceanography, 55, 622-637.

Venchiarutti C., Jeandel C., Roy-Barman M., 2008. Particle dynamics in the wake of Kerguelen Island traced by thorium isotopes (Southern Ocean, KEOPS program). Deep Sea Research Part II: Topical Studies in Oceanography, 55, 1343-1363

West N., Obernosterer I., Zemb O., Lebaron P., 2008. Major differences of bacterial diversity and activity inside and outside of a natural iron-fertilized phytoplankton bloom in the Southern Ocean. Environmental Microbiology, 10, 738-756.

Xiu, P., Thomas, A. C. & Chai, F. Satellite bio-optical and altimeter comparisons of phytoplankton blooms induced by natural and artificial iron addition in the Gulf of Alaska. Remote Sensing of the Environment, 145, 38-46.

Zhang Y., Lacan F., Jeandel C., 2008. Dissolved rare earth elements tracing lithogenic inputs over the Kerguelen Plateau (Southern Ocean). Deep Sea Research Part II: Topical Studies in Oceanography, 55, 638-652.


D LIST OF DELIVERABLES

N° Title Nature Delivery date Partner (in

charge underlined) Planned

initially Replanned Delivery

1 kick-off meeting report progress report 03/04/2011 24/05/2011 MIO (ex LOPB)

2 progress report 6 months report 03/07/2011 25/08/2011 MIO (ex LOPB)

3 first annual meeting progress report 03/09/2011 x MIO (ex LOPB)

4 cruise report progress report 03/01/2012 11/07/2012 MIO (ex LOPB)

5 progress report 18 months report 03/04/2012 03/07/2012 13/07/2012 MIO (ex LOPB)

6 second annual meeting report 03/07/2012 15/09/2012 26/10/2012 MIO (ex LOPB)

7 progress report progress report 03/10/2012 forsaken 1 MIO (ex LOPB)

8 progress report 2012 report 03/01/2013 04/11/2014 MIO (ex LOPB)

9 progress report progress report 03/04/2013 x MIO (ex LOPB)

10 third annual meeting report 03/07/2013 x MIO (ex LOPB)

11 progress report progress report 03/10/2013 04/11/2014 MIO (ex LOPB)

12 progress report progress report not planned 04/11/2014 MIO (ex LOPB)

13 final report rapport 03/01/2014 02/12/2014 26/01/2015 MIO (ex LOPB), LOMIC, LEMAR, LEGOS

1 Not applicable given the proximity to the 18 months report and the report of the second annual meeting

E IMPACT OF THE PROJECT The project KEOPS 2 has confirmed the expertise of the French scientific community in the

field of research on natural iron fertilization in the Southern Ocean, which is evidenced by the involvement of the KEOPS 2 community in major international meetings, including the organization of a special session of the 2013 ASLO Aquatic Sciences meeting (New Orleans, February 2013) organized jointly with German colleagues of the Alfred-Wegener-Institut (Helmholtz–Zentrum). KEOPS 2 has also strengthened the French collaboration with international teams, in particular with Australia (CSIRO), Belgium (VUB) and Chili (COPAS). The KEOPS2 cruise has also enabled validating new field strategies for oceanographic cruise, including on board quasi–real–time access to regional ocean dynamics by combining satellite data (altimetry and ocean color) and drifter deployments in a complex meso–scale environment. Although many scientific publication are already published in high impact journals, the large volume of data acquired during the cruise is still being analyzed, in particular with respect to biological data. Several original data thus demonstrate the complexity of the biological response to large-scale iron enrichment and challenge a number of so far biological and biogeochemical paradigms including the role of the Southern Ocean in the global biogeochemical cycles. The results obtained have been partly included into French national databases (SISMER and CYBER data centers). Biological data are also being transferred to the CYBER database. KEOPS2 already had an essential contribution to the on-going debate on artificial ocean fertilization in the context of global atmospheric CO2 increase and climate change (S. Blain and B. Quéguiner have been involved in the ANR Foresight Workshop REAGIR (systemic reflection on the issues and methods of geo-environmental engineering, http://www.arp-reagir.fr/).


E.1 IMPACT INDICATORS Number of publications and communications (detailed in E.2)

Multi-partner publications Single partner publications

International

Peer reviewed journals 8 20 Books or chapters in

collective books Communications

(conferences) 30

France

Peer reviewed journals Books or chapters in

collective books Communications

(conferences) 4

Actions of dissemination

General audience publications

4

General audience conferences

Other 2

Other scientific valorization (detailed in Erreur ! Source du renvoi introuvable.) Number, year and comments

(proven or probable valuations) International patents registered

International patent applications submitted

National patents registered National patent applications submitted

Exploitation licenses (obtaining / sale)

Formation and spin-off of new companies

New collaborative projects Scientific meetings

Special session "SS51: Iron, carbon cycling, and ecosystem dynamics in the Southern Ocean" of the 2013 ASLO Aquatic Sciences meeting (New Orleans, February 2013)

Other

E.2 LIST OF PUBLICATIONS AND COMMUNICATIONS

PUBLICATIONS

Beier S., M.J. Gálvez., V. Molina, G. Sarthou, F. Quéroué, S. Blain, I. Obernosterer,The transcriptional regulation of the glyoxylate cycle in SAR11 in response to iron fertilization in the Southern Ocean (in revision for Environmental Microbiology Reports).

Blain S., J. Capparos, A. Guéneuguès, I. Obernosterer, L. Oriol (2014) Distributions and stoichiometry of dissolved nitrogen and phosphorus in the iron fertilized region near Kerguelen (Southern Ocean). Biogeosciences Discusssions, 11: 9949-9977

Bowie A.R., P van der Merwe, F. Quéroué, T. Trull, M. Fourquez, F. Planchon, G. Sarthou, F. Chever, A.T. Townsend, I. Obernosterer, J.-B. Sallée, S. Blain (2014) Iron budgets for three distinct biogeochemical sites around the Kerguelen archipelago (Southern Ocean) during the natural fertilisation experiment KEOPS-2 (submitted to Biogeosciences).

Bown J., M. Boyé, P. Laan, A. Bowie, Y.-H. Park, C. Jeandel, D.M. Nelson (2012) Dissolved cobalt, a new tracer of the natural iron fertilization over the Kerguelen Plateau? Biogeosciences, 9, 5279–5290, doi:10.5194/bg-9-5279-2012.


Carlotti F., M.-P. Jouandet, A. Nowaczyk, M. Harmelin-Vivien, D. Lefèvre, Y. Zhu, M. Zhou (2014) Mesozooplankton structure and functioning during the onset of the Kerguelen Bloom during Keops2 survey (submitted to Biogeosciences).

Christaki U., D. Lefèvre, C. Georges, J. Colombet, P. Catala, T. Sime-Ngando, S. Blain, I. Obernosterer (2014) Microbial food web dynamics during spring phytoplankton blooms in the naturally iron fertilized Kerguelen area (Southern Ocean). Biogeosciences, 11: 6739-6753.

de Brauwere A., C. Jeandel, F. Lacan, P. van Beek, M. Roy-Barman, C. Venchiarutti (2014). Disentangling the geochemical fluxes on the Kerguelen Plateau using an inverse multi-tracer box model (submitted to Deep Sea Research).

Farías L., L. Florez-Leiva, V. Besoain, G. Sarthou, C. Fernández (2014). Dissolved greenhouse gases (nitrous oxide and methane) associated with the naturally iron-fertilized Kerguelen region (KEOPS 2 cruise) in the Southern Ocean. Biogeosciences Discusssions, 11, 12531–12569, doi:10.5194/bgd-11-12531-2014.

Grégoire M., R. Anderson, B. Delille, C. Jeandel, S. Speich (2013) Tracer of physical and biogeochemical processes, past changes and ongoing anthropogenic impacts. Journal of Marine Systems, 126, 1–2. doi:10.1016/j.jmarsys.2013.04.012

Fourquez M., I. Obernosterer, D. Davies, T. Trull , S. Blain (2014). Microbial iron uptake in the naturally fertilized waters in the vicinity of Kerguelen Islands: phytoplankton-bacteria interactions. Biogeosciences Discusssions, 11: 15053-15086.

Jeandel C., C. Venchiarutti, M. Bourquin, C. Pradoux, F. Lacan, P. van Beek, J. Riotte (2011), Single Column Sequential Extraction of Ra, Nd, Th, Pa and U from a Natural Sample. Geostandards and Geoanalytical Research, 35: doi: 10.1111/j.1751-908X.2010.00087.x.

Jeandel C., B. Peucker-Ehrenbrink, M. Jones, C.R. Pearce, E. Oelkers, Y. Godderis, F. Lacan, O. Aumont, T. Arsouze (2011) Ocean margins: the missing term for oceanic element budgets? EOS transactions American Geophysical Union, 92, 26, 28 June 2011.

Jeandel C., E. Oelkers (2014) The influence of terrigeneous particulate material dissolution on ocean chemistry and global element cycles. Chemical Geology, in press.

Jones M.T., C.R. Pearce, E.H. Oelker, C. Jeandel, E. Eiriksdottir, S.R. Gislason (2012) Suspended river material as key parameter in the global strontium cycle. Earth and Planetary Science Letter, 355–356, 51–59. doi:10.1016/j.epsl.2012.08.04

Jouandet M-P., G. Jackson, F. Carlotti, L. Stemmann, M. Picheral (2014) Rapid formation of large aggregates during the spring bloom of Kerguelen Island: observations and model comparisons. Biogeosciences, 11: 4393-4406.

Landa M., S. Blain, U. Christaki, S. Monchy, I. Obernosterer (2014) Bacterial community composition and production in a mosaic of phytoplankton blooms in the Southern Ocean (in revision for ISME)

Malits A., U. Christaki, I. Obenosterer, M.G. Weinbauer (2014) Enhanced viral production and virus-mediated mortality of bacterioplankton in a natural iron-fertilized bloom event above the Kerguelen Plateau. Biogeosciences Discusssions, 11: 10827-10862 (accepted for Biogeosciences).

Pearce C.R., M.T. Jones, E.H. Oelkers, C. Pradoux, C. Jeandel (2013) The effect of particulate dissolution on the neodymium (Nd) isotope and Rare Earth Element (REE) composition of seawater. Earth and Planetary Science Letters, doi: 10.1016/j.epsl.2013.03.023i.

Obernosterer I., M. Fourquez, S. Blain (2014) Fe and C co-limitation of heterotrophic bacteria in the naturally fertilized region off Kerguelen Islands. Biogeosciences Discusssions, 11: 15733-15752.

Quéroué F., A.R Bowie, H.F. Planquette, E. Bucciarelli, F. Chever, P. van der Merwe, D. Lannuzel, A.T. Townsend, M. Cheize, S. Blain, F. d’Ovidio, G. Sarthou (2015). Distribution of dissolved trace elements (Mn, Co, Ni, Cu, Cd, Pb) in the Kerguelen Plateau region, Biogeosciences, to be submitted.

Quéroué F., G. Sarthou, H.F. Planquette, E. Bucciarelli, F. Chever, P. van der Merwe, D. Lannuzel, A.T. Townsend, M. Cheize, S. Blain, F. d’Ovidio, A.R Bowie. (2014). Dissolved Fe at the vicinity of the Kerguelen Islands, submitted to Biogeosciences.


Quéroué, F., A. Townsend, P. van der Merwe, D. Lannuzel, G. Sarthou, E. Bucciarelli, A.R. Bowie (2014) Advances in the offline trace metal extraction of Mn, Co, Ni, Cu, Cd, Pb in open ocean seawaters with Sector Field ICP-MS analysis. Anal. Meth., DOI: 10.1039/c3ay41312h.

Sanial V., P. van Beek, B. Lansard, M. Souhaut, E. Kestenare, F. d'Ovidio, M. Zhou, S. Blain (2014) Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen Biogeosciences Discusssions, 11, 14023-14061, doi:10.5194/bgd-11-14023-2014, 2014. (KEOPS-2 Special issue)

Sanial V., P. van Beek, B. Lansard, F. d'Ovidio, E. Kestenare, M. Souhaut, M. Zhou, S. Blain (2014) Study of the phytoplankton plume dynamics off the Crozet Islands (Southern Ocean): A geochemical-physical coupled approach. Journal of Geophysical Research-Oceans, 119, doi:10.1002/2013JC009305

Sarthou G., F. Chever, F. Quéroué, A.R. Bowie, P. van der Merwe, M. Cheize, M. Sirois, E. Bucciarelli (2015). Fe-Cu impact in incubation experiments of natural plankton communities and Fe- and Cu-binding ligand production at the vicinity of the Kerguelen Islands, Southern Ocean, to be submitted.

van der Merwe P., A.R. Bowie, F. Quéroué, L. Armand, S. Blain, F. Chever, D. Davies, F. Dehairs, F. Planchon, G. Sarthou, A.T. Townsend, T. Trull, Sourcing the iron in the naturally‐fertilised bloom around the Kerguelen plateau: particulate trace metal dynamics, 2014. Biogeosciences Discussions, 11: 13389-13432, doi:10.5194/bgd-11-13389-2014.

Venchiarutti C., M. Roy-Barman, R. Freydier, C. Jeandel (2011) 231Pa/230Th ratio as tracer for boundary scavenging and particle dynamics in the wake of Kerguelen Island (Southern Ocean, KEOPS). Biogeoscience, 8, 3187–3201.

Tremblay, J. Caparros, K. Leblanc, I. Obernosterer (2014) Origin and fate of particulate and dissolved organic matter in a naturally iron-fertilized region of the Southern Ocean. Biogeosciences Discusssions, 11: 14097-14132 (accepted for Biogeosciences).

COMMUNICATIONS

Armand L.K., J. Wilks, B. Quéguiner (2013) Southern Ocean diatom assemblages and searching for iron enrichment signature species. 27th annual Australasian Society for Phycology and Aquatic Botany (ASPAB) conference, Sydney November 2013.

Blain S. (2012) KEOPS 2: presentation of the scientific objectives and strategy at sea. TANGGO Meeting, Grenoble (France), May 2012.

Blain S. (2012) Strategies and implementation of pluridisciplinary cruises in the Southern ocean. Invited speaker, International Workshop “Diagnosis of vertical exchanges at submesoscales and their impact on ecosystems, from integrated satellite and in-situ observations”, Institut Polaire Français Paul-Emile Victor, Brest (France), November 2012.

Blain S., B. Quéguiner, KEOPS 2 Team (2013) Spatial and temporal responses of the southern ocean to large scale natural iron fertilization (Kerguelen region). ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Blain S., B. Quéguiner, KEOPS2 Team, OISO Team (2014) Response of the southern ocean to large scale natural iron fertilization (Kerguelen region). 2014 Ocean Science Meeting AGU/ASLO/Oceanography Society, Session 072 ‘The Southern Ocean and Its Role In the Climate System: Observations and Modeling of Physical and Biogeochemical Processes’, Hawaii, February 2014.

Bowie A.R., F. Quéroué, G. Sarthou, F. Chever, P. Van Der Merwe, E. Bucciarelli, A.T. Townsend, S. Blain (2013) Dissolved and particulate trace metals in the vicinity of the Kerguelen islands, southern ocean, during the KEOPS 2 experiment. ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.


Carlotti F., A. Nowaczyk, M.-P. Jouandet, D. Lefèvre, M. Harmelin (2013) Mesozooplankton structure and functioning during the onset of the Kerguelen spring bloom: first results of the KEOPS2 survey. ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Cavagna A.-J., F. Dehairs, B. Quéguiner, C. Fernandez, D. Lefèvre (2012) Regimes of production and potential for carbon export in naturally iron-fertilized waters in the Southern Ocean. 2012 ASLO Aquatic Sciences Meeting, Lac Biwa, Otsu, Shiga (Japon), July 2012.

Cavagna A., B. Quéguiner, F. Planchon, S. Jacquet, I. Closset, F. Dehairs (2013) Production regime and potential for carbon export in the naturally iron fertilized Kerguelen area (Southern Ocean). ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Closset I., M. Lasbleiz, K. Leblanc, B. Quéguiner, J. Navez, D. Cardinal (2013) Comparison of Si biogeochemical budget in contrasted southern ocean regions through silica production-dissolution measurements (KEOPS-2). IBIS: Isotopes in Biogenic Silica 2013 meeting, Helsinki, June 2013.

Closset I., M. Lasbleiz, K. Leblanc, B. Quéguiner, J. Navez, D. Cardinal (2013) Comparison of Si biogeochemical budget in contrasted southern ocean regions through silica production-dissolution measurements (KEOPS-2). ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

de Brauwere A., C. Jeandel, F. Lacan, P. van Beek, C. Venchiarutti, F. Fripiat (2012) Putting the pieces together: A multi-tracer model to quantitatively identify the major processes related to the fertilized bloom on the Kerguelen Plateau. AGU Fall Meeting 2012, Session OS31D ‘Sources, Sinks, and Speciation of Marine Micronutrient Trace Elements’, San Francisco, December 2012.

D’ovidio F., M. Zhou, Y.-H. Park, F. Nencioli, L. Resplandy, A. Doglioli, A. Petrenko, S. Blain, B. Quéguiner (2012) Guiding biogeochemical campaigns with high resolution altimetry: Waiting for the SWOT mission. 20 Years of Progress in Radar Altimetry, Venise (Italy), September 2012.

Grenier M., E. Garcia Solsona, N. Lemaitre, V. Bouvier, C. Jeandel (2014) Rare earth concentrations and neodymium isotopic compositions of seawater around the Kerguelen plateau: tracing land-to-ocean sources and ocean circulation. 2014 Ocean Science Meeting AGU/ASLO/Oceanography Society, Session 072 ‘The Southern Ocean and Its Role In the Climate System: Observations and Modeling of Physical and Biogeochemical Processes’, Hawaii, February 2014.

Jouandet M.-P., L. Guidi, F. Carlotti, L. Stemmann, M. Picheral, M. Zhou, T. Trull, S. Blain (2013) Particle size distributions in response to natural iron fertilisation in the Southern Ocean (Kerguelen island)-implication for carbon export. . ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Landa M., S. Monchy, S. Blain, I. Obernosterer (2014) Responses of heterotrophic bacterial diversity to phytoplankton blooms induced by natural iron-fertilization: is DOM a driving factor? 2014 Ocean Science Meeting AGU/ASLO/Oceanography Society, Session 069 ‘Marine Microbial Ecology: the Relative Role of Dispersal, Interactions, Associations and Other Ecological Processes in Structuring Microbial Communities’, Hawaii, February 2014.

Lansard B., V. Sanial, P. Van Beek, M. Souhaut, F. D’ovidio (2012) What do we learn from radium isotopes about natural iron fertilization off Crozet and Kerguelen Islands, Southern Ocean? 4th International Ra-Rn workshop, Narragansett (USA), June 2012.

Lasbleiz M., I. Closset, B. Quéguiner, K. Leblanc, D. Cardinal, J. Navez (2013) Species–specific contribution of diatoms to Si production in the Fe-fertilized Kerguelen region of the Southern Ocean (KEOPS2). ASLO 2013 Aquatic Sciences Meeting ‘Learning for the


Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Lasbleiz M., I. Closset, B. Quéguiner, K. Leblanc, D. Cardinal, J. Navez, M. Elskens (2013) The biogenic silica cycle in the area of interaction between the Antarctic Polar Front and the Kerguelen Plateau (KEOPS 2). 45th International Liege Colloquium on Ocean Dynamics: “The variability of primary production in the ocean: from the synoptic to the global scale”, Liège, May 2013.

Laurenceau E., T. Trull, D. Davies, C. De La Rocha, S. Blain (2012) Sinking velocity of marine aggregates, from simple theory to complex reality: insights from roller tank experiments in a naturally iron-fertilised area of the Southern Ocean. IWOMA 2012, 2nd International Workshop on Marine Aggregates, “From Molecular Principles to Biochemical Impact”, Bremen (Germany), August 2012.

Laurenceau E.C., T.W. Trull, D.M. Davies, C. De La Rocha, S. Blain (2014) Aggregation processes and phytoplankton morphology in the control of export fluxes from naturally iron fertilised waters near the Kerguelen plateau. ASLO 2014 Ocean Science Meeting AGU/ASLO/Oceanography Society, Session 026 ‘Biological and Physical Controls of Particle Dynamics and Fluxes In the Mesopelagic Layer of the Ocean: Current Understanding and Future Directions’, Hawaii, February 2014.

Quéguiner B. (2012) Iron fertilization and the structure of planktonic communities in high nutrient regions of the Southern Ocean. Invited speaker, EUR-OCEANS Flagship for Polar Ecosystem Change and Synthesis: Identifying key links between biogeochemical processes and food web structure, Alfred Wegener Institute, Bremerhaven (Germany), November 2012.

Quéroué F., A.R. Bowie, D. Lannuzel, P. Van Der Merwe, A.T. Townsend, G. Sarthou, E. Bucciarelli (2012) Physical and biological controls on the distribution of trace metals (Fe, Cu, Mn) around Kerguelen Islands (Southern Ocean), Ocean Science Meeting, Salt Lake City (USA), February 2012.

Quéroué F., A.T. Townsend, D. Lannuzel, P. Van Der Merwe, G. Sarthou, E .Bucciarelli, A.R. Bowie (2013) Trace metal (Fe, Mn, Co, Cu, Pb, Cd, Ni, Al) analysis in open ocean samples using Sector Field ICP-MS, Collaborative on Oceanographic Chemical Analysis Meeting, Hawaii, mars 2013.

Sanial V., P. Van Beek, B. Lansard, M. Souhaut, M. Zhou (2012) Land-Ocean Connectivity : Tracing and quantifying the iron input that fuels phytoplankton blooms off Kerguelen and Crozet Islands. Europole Mer Conference on Land-Ocean Connectivity – from Hydrological to Ecological Understanding of Groundwater Effects in the Coastal Zone, L’Aber Wrac’h (France), September 2012.

Sanial V., P. Van Beek, B. Lansard, M. Souhaut, M. Zhou, F. D’ovidio, E. Kestenare, S. Blain (2013) Study of the natural fertilization off Kerguelen Islands (Southern Ocean) using radium isotopes. Gordon Research Conference - Chemical of the Sea, Biddeford (Main, USA), August 2013.

Sanial V., P. Van Beek, B. Lansard, M. Zhou, E. Kestenare, M. Souhaut (2013) Use of the radium quartet (223Ra, 224Ra, 226Ra, 228Ra) to study the natural iron fertilization off Crozet and Kerguelen islands (Southern Ocean). ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Sarthou G., F. Quéroué, F. Chever, A.R. Bowie, P. Van Der Merve, E. Bucciarelli, M. Fourquez, S. Blain (2012) Dissolved iron in the vicinity of the Kerguelen Islands, Southern Ocean, during the KEOPS 2 experiment. Goldschmidt Conference, Montréal (Canada), June 2012.

van Beek P., V. Sanial, B. Lansard, E. Kestenare, M. Souhaut, F. D’ovidio, M. Zhou, S. Blain (2013) Study of the Natural Iron Fertilization off Crozet and Kerguelen Islands (Southern Ocean) using radium isotopes as tracers. INVITED TALK, Goldschmidt Conference, Florence (Italy), August 2013.

van Beek P., M. Souhaut, V. Sanial, B. Lansard (2012) Study of the ocean using low-background gamma spectrometry, CELLAR meeting, Lingolsheim (France), October 2012.


Zhou M., Y. Zhu, Y., B. Quéguiner, F. Carlotti, Y. Zhang (2014) A continuum size spectrum model for marine plankton. 2014 Ocean Science Meeting AGU/ASLO/Oceanography Society, Session 108 ‘Synthesis and Modeling of Global-Scale Marine Planktonic Ecosystems and Plankton Functional Types’, Hawaii, February 2014.

Zhu Y., M. Zhou, B. Quéguiner, K. Leblanc, F. Carlotti, L. Armand, M.-P. Jouandet, E. Kestenare, T. Trull, S. Blain (2013) Estimates of particle settling and scavenging using LISST-LOPC in Kerguelen plateau regions during the 2011 austral spring KEOPS II cruise. ASLO 2013 Aquatic Sciences Meeting ‘Learning for the Future’, Special session 51 ‘Iron, Carbon Cycling, and Ecosystem Dynamics in the Southern Ocean’, Nouvelle Orleans, February 2013.

Public outreach

« KEOPS 2, des recherches scientifiques vingt milles lieux sous les mers », Wiki 2d La Provence, November 2011,

http://www.wiki2d.org/les-bonnes-pratiques/biosphere-et-biodiversite/mer/keops-2-des-recherches-scientifiques-vingt-milles-lieux-sous-les-mers/

« Des Marseillais au sommet de la pyramide », La Provence, December 2011. « KEOPS 2 », La Lettre de l’Université de la Méditerranée, n° 165, p. 19, December 2011. « Des algues contre l'effet de serre », La Provence, January 2012 (1° prix du développement durable du concours Collégien Reporter 2012 de La Provence, Collège Roquepertuse de Velaux).

Du fer dans l'océan Austral : une oasis de plancton, Sarthou G., F. Planchon F. Chever, IUEM, February 2012.

http://www-iuem.univ-brest.fr/connaitre/actualites-et-evenements/exposition-et-conference-du-fer-dans-locean-austral-une-oasis-de-plancton

« Une fertilisation illégale », interview de S. Blain par H. Marchand, La Recherche, January 2013, 471, p. 8.

E.3 VALORIZATION ELEMENTS The first results of the KEOPS2 project were presented during the special session "SS51: Iron,

carbon cycling, and ecosystem dynamics in the Southern Ocean" of the 2013 ASLO Aquatic Sciences meeting (New Orleans, February 2013) co-organized by Quéguiner B. and S. Blain, as well as by German colleagues from the Alfred Wegener Institute in Bremerhaven (V. Strass and D. Wolf-Gladrow) – see details in annex.

A special issue of Biogeosciences is under preparation. This special issue will gather publications of the results of the KEOPS 2 cruise and will include comparisons with the results of the first KEOPS 1 cruise (January-February 2005) as well as with other previous natural or artificial iron fertilization experiments in the Southern Ocean. – see details in Annex 1.


E.4 BILAN ET SUIVI DES PERSONNELS RECRUTÉS EN CDD (HORS STAGIAIRES)

Identification Avant le recrutement sur le projet Recrutement sur le projet Après le projet

Nom et prénom H/F Adresse email Date des dernières nouvelles

Dernier diplôme obtenu au moment

du recrutement Lieu d'études Expérience

prof. antérieure

Partenaire ayant embauché la

personne

Poste dans le projet

Durée de la mission

(mois)

Date de fin de mission Devenir professionnel Type d’employeur Type d’emploi Lien au

projet ANR Valorisation expérience

BEIER Sara F [email protected]

janvier 2015 PhD UE PhD Thesis LOMIC Post-Doc 23 19 Dec 2013 Post-Doc at the Institute for Baltic Sea Researh (Germany)

Enseignement et recherche publique Post-Doc partenaire

du projet oui

CHEIZE Marie F [email protected] Aujourd’hui Thèse de doctorat France LEMAR Vacataire IE +

Post-doc 15 06 Octobre 2013 Post-doc ANR BITMAP Enseignement et recherche publique Chercheur partenaire

du projet oui

CHEVER Fanny F [email protected] Janvier 2015 Thèse de doctorat France Post-doc LEMAR CDD chercheur 2 Décembre 2011 Post-doc IFREMER EPIC

IFREMER Chercheur partenaire du projet oui

GARCIA SOLSONA Ester F

Ester Garcia <[email protected]>

janvier 2015 doctorat Espagne 1 an post-doc LEGOS Post-doc 6 30 mars 2013 contrat de recherche à l’Université Autonome de Barcelone depuis avril 2013

Enseignement et recherche publique Chercheur contractuel partenaire

du projet oui

GOLBOL Melek F [email protected] juin 2014 Master Paris VI MIO (ex LOPB) Assistante−ing

énieure d’étude 6 31 juillet 2012 CDD Observatoire Océanologique de Villefranche/mer

Enseignement et recherche publique

Assistante−ingénieure d’étude

partenaire du projet oui

GRENIER Mélanie F

melanie grenier <[email protected]>

janvier 2015 Doctorat Toulouse 3 mois de CDD ingénieur LEGOS Post-doc 6 30 sept. 2013

contrat de recherche à l’Université de Tasmanie (2013-2014) puis contrat à univerity of British Columbia Vancouver depuis janvier 2015

Enseignement et recherche publique Post-doc partenaire

du projet Oui

JOUANDET Marie-Paule F jouandetmariep

[email protected] décembre 2014 phD France

ATER (12 mois) Post-doc (12 mois) Ing. de Rech (3 mois)

MIO (ex LOPB) Post-doc 19 31 Mars 2013 CDD et recherche d'emploi permanent

Enseignement et recherche publique

enseignant-chercheur, chercheur, ingénieur.


LANDA Marine F [email protected] janvier 2015 PhD France PhD LOMIC Ingenieure

d’etude 3 15 Dec 2013 CDD enseignement et recherche publique

Contrat postdoctoral à University of Georgia (Athens, USA ; responsable : Prof. Mary Ann Moran)



ANNEX 1

ASLO 2013 Aquatic Sciences Meeting Session SS51 Iron, carbon cycling, and ecosystem dynamics in the Southern Ocean

Slot # 1 : Thursday 21 February 4:00 pm – 6:00 pm Klaas, C.; EIFEX and LOHAFEX shipboard Scientific Party, ; Controls on productivity and biogeochemistry in the Southern Ocean: insights from two iron fertilization experiments in the Polar Front Region (Abstract ID:11567)

Blain, S.; Quéguiner, B.; KEOPS2 Team, ; Spatial and temporal responses of the southern ocean to large scale natural iron fertilization (Kerguelen region) (Abstract ID:10517)

Strass, V.H.; Leach, H.; Prandke, H.; Donnelly, M.S.; Klaas, C.; Bracher, A.; Cheah, W.; Wolf-Gladrow, D.; Physico-biogeochemical differences along the ACC in the Atlantic sector during one late summer - first results obtained from Eddy Pump (Abstract ID:10893) Mitchell, B.G.; Reynolds, R.; Kahru, M.; Hewes, C.; Schieber, B.; Wieland, J.; Seegers, B.; Holm-Hansen, O.; A satellite net primary production (NPP) algorithm for the southern ocean based on the VGPM framework - performance evaluation and time-series applications (Abstract ID:11930)

Tagliabue, A.; Sallee, J.B.; Bowie, A.R.; Boyd, P.W.; Levy, M.; Swart, S.; Towards reconciling iron supply and demand in the Southern Ocean (Abstract ID:11629)

Jones, E.M.; Hauck, J.; Salt, L.A.; Hoppema, M.; van Heuven, S.M.; de Baar, H.J.; Ocean eddies create hotspots of carbon uptake in the Southern Ocean (Abstract ID:11215)

Zhou, M.; d'Ovidio, F.; Park, Y.H.; Zhu, Y.; Durand, I.; Kestenare, E.; Sanial, V.; Van-Beek, P.; Quéguiner, B.; Blain, S.; Estimates of horizontal surface circulation and upwelling using surface drifters in Kerguelen Plateau regions during the 2011 austral spring cruise (Abstract ID:11015) Slot # 2 : Friday 22 February 10:00 am – 12:00 am

Sanial, V.; van Beek, P.; Lansard, B.; Zhou, M.; Kestenare, E.; Souhaut, M.; Use of the radium quartet (223Ra, 224Ra, 226Ra, 228Ra) to study the natural iron fertilization off Crozet and Kerguelen islands (Southern Ocean) (Abstract ID:10749) Bowie, A.R.; Quéroué, F.; Sarthou, G.; Chever, F.; van der Merwe, P.; Bucciarelli, E.; Townsend, A.T.; Blain, S.; Dissolved and particulate trace metals in the vicinity of the Kerguelen islands, southern ocean, during the KEOPS 2 experiment (Abstract ID:10867)

Sedwick, P.N.; McGillicuddy, D.J.; Dinniman, M.S.; Bibby, T.S.; Greenan, B.J.; Hofmann, E.E.; Klinck, J.S.; Marsay, C.M.; Smith, W.O.; Sohst, B.M.; An assessment of iron sources on the Ross Sea continental shelf: initial results from the PRISM project (Abstract ID:10612) Laglera, L.M.; Santos-Echeandía, J.; Klaas, C.; Wolf-Gadrow, D.A.; Iron partition in surface waters of a large-scale summer bloom south of the Antarctic Polar Front (Abstract ID:11292) Lasbleiz, M.; Closset, I.; Quéguiner, B.; Leblanc, K.; Cardinal, D.; Navez, J.; Species–specific contribution of diatoms to Si production in the Fe-fertilized Kerguelen region of the Southern Ocean (KEOPS2) (Abstract ID:10873)

Dinasquet, J.; Swalethorp, R.; Kjellerup, S.; Bertilsson, S.; Nielsen, T.G.; Riemann, L.; Particulate matter and protozoans affect bacterioplankton community structure in the productive Amundsen Sea polynya, Antarctica (Abstract ID:10854) Cavagna, A.; Quéguiner, B.; Planchon, F.; Jacquet, S.; Closset, I.; Dehairs, F.; Production regime and potential for carbon export in the naturally iron fertilized Kerguelen area (Southern Ocean) (Abstract ID:10600)

Closset, I.; Lasbleiz, M.; Leblanc, K.; Quéguiner, B.; Navez, J.; Cardinal, D.; Comparison of Si biogeochemical budget in contrasted southern ocean regions through silica production-dissolution


measurements (KEOPS-2) (Abstract ID:10767)

Slot # 3 : Friday 22 February 1:30 pm – 3:30 pm Dehairs, F.; Trull, T.W.; Fernandez, C.; Davies, D.; Cavagna, A.J.; Piniella, A.E.; Nitrate isotopic composition in the Kerguelen area (Southern Ocean) during KEOPS 2 (Abstract ID:10603) Roca-Martí, M.; Puigcorbé, V.; Masqué, P.; Rutgers van der Loeff, M.; Stimac, I.; Iversen, M.; Strass, V.; Klass, C.; Wolf-Gladrow, D.; Impact of eddy structures and the Polar Front region on carbon export fluxes in the water column of the Southern Ocean (Abstract ID:11069)

Jouandet, M.; Guidi, L.; Carlotti, F.; Stemmann, L.; Picheral, M.; Zhou, M.; Trull, T.; Blain, S.; Particle size distributions in response to natural iron fertilisation in the Southern Ocean (Kerguelen island)-implication for carbon export. (Abstract ID:11246) Zhu, Y.; Zhou , M.; Quéguiner, B.; Leblanc, K.; Carlotti, F.; Armand, L.; Jouandet, M.P.; Kestenare, E.; Trull, T.; Blain, S.; Estimates of particle settling and scavenging using LISST-LOPC in Kerguelen plateau regions during the 2011 austral spring KEOPS II cruise (Abstract ID:11057) Trimborn, S.; Hoppe, C.J.; Brenneis, T.; Norman, L.; Santos-Echeandía, J.; Laglera, L.; Hassler, C.; Role of different iron sources on phytoplankton growth and species composition of the Antarctic Circumpolar Current under ocean acidification (Abstract ID:11212)

Jones, B.M.; Sahin, M.S.; New, A.M.; Kustka, A.B.; Integrating physiology and 3rd generation DNA sequencing to characterize the effect of MCDW, iron and ligands on Ross Sea eukaryotic phytoplankton assemblages (Abstract ID:11872) Bennett, J.M.; Sedwick, P.N.; DiTullio, G.R.; Impact of irradiance and iron on the growth and physiology of the Antarctic diatom Fragilariopsis cylindrus (Abstract ID:10670) Boutorh, J.; Moriceau, B.; Ragueneau, O.; Bucciarelli, E.; Impact of copper starvation and of iron limitation on the frustule composition and dissolution of the Pseudo-Nitzschia diatom (Abstract ID:10934)

Posters Olsen, L.M.; Ardelan, M.V.; Holm-Hansen, O.; Bizsel, N.; Hewes, C.; Reiss, C.; Sakshaug, E.; Vadstein, O.; Microbial communities in the surface water masses surrounding the South Shetland Islands, Antarctica (Abstract ID:11928)

Mosby, A.F.; Smith, W.O.; Delizo, L.M.; Doan, N.H.; Phytoplankton growth rates in the Ross Sea, Antarctica (Abstract ID:10757)

González, M.L.; Oriol, L.; Dehairs, F.; Cavagna, A.J.; Fernandez, C.; Molecular nitrogen fixation in the southern ocean: case of study of the Fe-fertilized Kerguelen region (KEOPSII cruise) (Abstract ID:11473) Carlotti, F.; Nowaczyk , A.; Jouandet, M.P.; Lefèvre , D.; Harmelin, M.; Mesozooplankton structure and functioning during the onset of the Kerguelen spring bloom: first results of the KEOPS2 survey. (Abstract ID:12061)

Kruse, S.; Pakhomov, E.A.; Hunt, B.P.; Trophic interactions between Themisto gaudichaudii and Salpa thompsoni in the Antarctic Polar Frontal Zone (Abstract ID:10994)

Jacquet, S.H.; Dehairs, F.; Cavagna, A.J.; Planchon, F.; Closset, I.; Cardinal, D.; Seasonal variability of mesopelagic organic carbon remineralization in the naturally iron-fertilized Kerguelen area (Southern Ocean) (Abstract ID:10642) Ardelan, M.V.; Olsen, L.M.; Bizsel, N.; Bizsel, K.C.; Co-limitation by iron and light at deep Chl a maximum in the Southern Ocean (Abstract ID:11905)


ANNEX 2

KEOPS 2 – ANR FINAL DETAILED REPORT

I. ABSTRACT

The Southern Ocean is a key region in the global carbon cycle because it is a major sink of CO2 whose importance is still debated today especially given the ongoing climate change. The Southern Ocean is also the largest HNLC (High Nutrient Low Chlorophyll) area of the Global Ocean, in which the use of major nutrients is limited by iron availability. The KEOPS 2 project addressed the effects of iron fertilization on the development of the pelagic ecosystem in the Southern Ocean. This project was conducted during a long-term oceanographic cruise in 2011 which enabled studying the natural laboratory constituted by the waters surrounding the Kerguelen Islands. This environment is indeed naturally fertilized with iron by the interaction between the Antarctic Circumpolar Current (ACC Antarctic Circumpolar Current) and the topography, and annual planktonic developments are observed repeatedly. KEOPS 2 enabled making comparisons between the fertilized area and the HNLC waters upstream of the ACC.

The KEOPS 2 project is original in that most of the observations concerning the role of iron in the Southern Ocean have been obtained so far from artificial fertilization experiments in the ocean. These experiments established that the phytoplankton of HNLC areas respond to an iron addition by promoting the growth silicified microalgae: diatoms. However major uncertainties remain on the transposition of these results to sustained fertilization conditions such as those characterizing natural systems.

KEOPS 2 is a multidisciplinary project that brought together partners from CNRS, Paris VI University, University of Western Brittany, Toulouse III University, and Aix-Marseille University, with complementary skills in marine geochemistry, biogeochemistry, biology and pelagic ecology.

The project documented the processes of iron supply through the use of analytical tools making it possible to measure geochemical tracers such as rare earths and natural radioactive tracer (radium isotopes). Speciation of major metals and their distributions in the natural environment were also studied using analytical chemistry techniques. Several biological compartments were observed using conventional techniques (microscopy, image analysis, epifluorescence) but also thanks to molecular biology techniques (sequencing) and deployment of in situ optical sensors capable of reproducing spectra size organisms. Fluxes were also estimated through advanced techniques using a variety of stable isotope tracers (15N, 13C, and 30Si). It was thus possible to study all the processes responsible of the fertilization process, the bioavailability of iron and its use in the pelagic communities from bacteria to mesozooplankton.

The project was organized into four research tasks:

- Speciation of iron, - Sources and transport of iron, - Microbial diversity and coupling of biogeochemical cycles of carbon and iron, - Biodiversity and spatial structure of plankton communities.

Results indicate that, regarding the fertilization mechanism, atmospheric inputs are negligible while processes like direct runoff, contributions by glaciers and shelf sediments, are important sources of dissolved iron in the vicinity of Kerguelen. Particle remineralization during their sedimentation also explains the high concentrations of dissolved iron in offshore waters. The powerful Polar Front current is thus enriched in dissolved iron and feeds the waters east of the Kerguelen Plateau. Organisms that grow in these natural phytoplankton blooms have characteristics quite different from communities observed in artificial fertilization experiments. The latter, carried out on small areas, therefore, cannot be transposed to fertilization situations over large ocean areas, for which changes in community structure are much more complex.

II. STATE OF THE ART AND OBJECTIVES

The Southern Ocean is a key region in the global carbon cycle because it represents an important CO2 sink. The magnitude of this sink in the present and in the past is still highly debated. In


a recent study, Le Quéré et al. (2007) have shown that the Southern Ocean CO2 sink has weakened between 1987 and 2004 by 0.08 pg C yr-1, very likely due to the increase of Southern Ocean winds related to climate change. Theory and model studies also point out the sensitivity of atmospheric CO2 to changes in ocean biology in the Southern Ocean (e.g. Marinov et al., 2008). This sensitivity is related to nutrient utilization in the surface waters. It is expected that increasing the deep ocean ventilation due to increased vertical mixing or due to an enhancement of Southern Ocean winds results in an increase in the atmospheric CO2. By contrast, stratification of the Southern Ocean decreases the atmospheric CO2 due to surface nutrient depletion. In the surface waters of the Southern Ocean, the utilization of nutrients is first limited by the availability of iron, as demonstrated by artificial and natural iron fertilisation experiments (Blain et al., 2007; Boyd et al., 2007; Coale et al., 2004; Pollard et al., 2007). Therefore, fertilisation (natural or artificial) of this region is expected to have in principle a large impact on atmospheric CO2. However, other properties like elemental ratios (i.e. C:P) and gas exchange (Gnanadesikan & Marinov, 2008) are important in this context.

Except for a few locations where natural iron fertilisation was clearly demonstrated, the source of iron supporting higher productivity in the Southern Ocean is a matter of debate (see for example the case for an aeolian source in Boyd & Mackie (2008) and Cassar et al. (2007, 2008)).

The previous KEOPS and CROZEX projects have demonstrated that natural fertilization in the Southern Ocean results in dramatic changes in the functioning of the ecosystem with large impacts on the biogeochemical cycles. We also learned from both projects that the responses can largely differ from one site to another. These projects highlighted the interest of natural laboratories in the context of iron fertilisation of the ocean, but they could cover only a small part of the potential new findings in this area.

The KEOPS 2 project has enabled studying the role of iron fertilization in the Southern Ocean on the intensity and nature of the carbon biological pump. The study was conducted in an area of natural fertilization (east of the Kerguelen Plateau) enclosed in an otherwise HNLC (High Nutrient Low Chlorophyll) area. The main topics addressed included biogeochemistry, biodiversity and food web structures. The project focused mainly on the KEOPS 2 cruise (MD188/KEOPS 2), which took place from 8 October to 22 November 2011 on board the RV Marion Dufresne 2. The initial objectives aimed at :

1) studying the processes that provide and maintain bioavailable iron to surface waters and defining the associated time scales,

2) studying the coupling between biogeochemical cycles of major elements ( C, N, P, and Si) and the iron availability in a naturally fertilized region enclosed within an HNLC area,

3) characterizing the pathways that lead to the remineralization in ‘surface’ layers (epipelagic and upper mesopelagic zones) or to the export to depths of the organic matter produced by the biological activity in the surface water,

4) highlighting the control of biodiversity at the first trophic levels (up to mesozooplankton) by natural iron fertilization,

5) understanding the seasonal and interannual variabilities of biogeochemical processes in a plankton bloom of the Permanently Open Ocean Zone (POOZ) of the Southern Ocean.

In order to achieve these objectives the annual recurrent blooms that develop east of the Kerguelen Islands were selected as a regional case study.

III. TECHNICAL AND SCIENTIFIC APPROACHES

Sampling strategy KEOPS 2 benefited from quasi−real−time satellite data acquisition and processing which enabled to follow the different bloom situations in the fertilized area. Multisatellite data (altimetry, SST, ocean color) were received daily and analyzed onboard. These data were produced by CLS with support from CNES as an optimized regional product for KEOPS 2. The Lagrangian analysis, also incorporating 50 drifters’ deployments, thus allowed to follow the chlorophyll plumes, which developed during the cruise. This analysis guided the sampling strategy (Fig. 1) which, basically, was composed of two transects and several process study stations. Two process stations sampled the eastern bloom (F-L and F-S stations) in the polar front zone (PFZ), and the southeastern bloom (A3 station) over the Kerguelen Plateau. The latter was visited twice (A3-1 in October and A3-2 in November) at a reference station that had been already studied during the KEOPS1 cruise. For comparison, the process station R2 was considered to be representative of the HNLC off-plateau area.


A temporal evolution study of the northeastern Kerguelen bloom was led on the complex recirculation system located in a stationary meander of the PF. This site (referred as process stations E including E-1, E-2, E-3, E-4E and E-5) was visited five times in the course of the cruise. Finally, across this complex system, two transects were sampled to get a detailed description of the biogeochemical parameters of the eastern Kerguelen area. The first transect, oriented south to north (TNS), was sampled from 21 to 23 October; the second transect, oriented west to east (TEW), was sampled from 31 October to 2 November.

Fig. 1: Location of the sampling stations. Transects from North to South (TNS) and from

west to the east (TEW) are indicated in red and blue, respectively. The blank filled circles correspond to a time-series of a recirculation system (E-1, E-2, E-3, E-4E, and E- 5). The stations F-L and F-S are located in the eastern bloom in the polar front zone. A3 and E-4W are the reference southeastern Kerguelen Plateau bloom and the reference eastern flank of the Kerguelen Plateau, respectively. Both were visited twice (1–2). R2 is the HNLC reference station. The dotted line represents the approximate location of the southern branch of the polar front (from Lasbleiz et al., 2014).

Trace–metal distributions and speciation. Depth profiles were realized at more than 15 stations for dissolved Fe, Cu, Mn, Co, Ni, Zn, and Cd, as well as incubation experiments on natural plankton communities at 3 different stations. Together with geochemical tracers (Task 3) this allowed a better understanding of the nature and magnitude of the iron sources, and of the modes of transport. The determination of trace metal concentrations and speciation is a difficult task due to their very low concentrations in seawater. During KEOPS 2 we have used a panel of different techniques to advance our understanding on this issue:

– Dissolved Fe (< 0.2 µm) was measured on board by flow injection analysis with chemiluminescence detection (following Obata et al., 1993; Quéroué et al., 2014a).

– The other dissolved trace metals (Cu, Mn, Co, Ni, Zn, and Cd) were measured back to the laboratory using a method developed by F. Quéroué during his PhD in co-tutelle with the University of Tasmania (Quéroué et al., 2014b).

– Fe and Cu organic speciation were measured back to the laboratory by cathodic stripping voltammetry (Fe, Croot and Johanson, 2000; Cu, Leal et al., 1999).

Radium isotopes, REE and Nd isotopes, in situ studies (cruise samples, analyses). For REE and Nd isotopic composition (IC) analysis, filtered and particulate samples were collected at the following stations: R2; A3 and G1 (A3 sampled for pre-bloom: A3-1 and 20 days later for the post-bloom: A3-2); TNS4; E1, E3, E4_W and E5; TEW1, G2, TEW3, TEW7 and NPF_L, TEW1 and G2 being dedicated to the lithogenic source characterization. Each station was sampled at several depths covering the whole water column from 30 m to 2700 m. After filtration, the so-collected 111 water samples were acidified to pH=2 with twice-distilled HCl and stored at room temperature, and 97 Nd IC samples were already pre-concentrated on board (Shabani et al., 1992). Large volumes (from 65 to


1200 L) of seawater were pumped using In Situ Pumps from different depths through SUPOR filters of 142 mm diameter and 0.8 mm pore size, allowing the collect of 54 suspended particle samples. After pumping, filters were dried in the clean lab with a vacuum pump. A ceramic blade was used to cut the filter in two portions, which will be devoted to 1) Nd isotopes, REE concentrations and Fe isotopes and 2) Si isotopes (D. Cardinal team). Back to the laboratory, dissolved REE concentrations and Nd IC were determined following Garcia-Solsona et al. (2014). Analyses of suspended particles are ongoing. Laboratory experiments on lithogenic micronutrient supply and dissolution. The potential impact of lithogenic sediment dissolution on seawater was experimentally quantified using different well-constrained batch reactor experiments (Jones et al, 2012; Pearce et al, 2013). Basaltic particulate material was used in all the experiments; among the samples tested, top core sediment originating of the Kerguelen plateau collected at 140 m depth was dried and put in contact for 4 months with filtered seawater originating from the mid-depth in the Southern Ocean (the other 2 sediments have been collected in an Iceland river and an Iceland estuary, Iceland basalts being close to the Kerguelen ones). The particulate–seawater interaction experiments were run in 30 l closed-system polypropylene reactors with an initial water/rock ratio of ∼1000. The reactors were stored at room temperature (∼21°C) and manually shaken at regular intervals throughout the experiment. Aliquots were collected for Si, REE, Nd isotope analysis; pH and oxygen content regularly checked. The mineralogical composition (XRD) and Scanning Electron Microscope (SEM) images of the samples were taken before and after the experiments. Fe-uptake rate was investigated using the iron radiotracer 55Fe. Seawater samples were collected with 10-Liters Niskin 1010X-bottles set up on the autonomous Trace Metal Rosette 1018 (TMR) especially adapted for trace metal work. Within less than 2 hours after sample collection, the seawater was dispersed into 500 mL acid-washed polycarbonate (PC) bottles, spiked with 55FeCl3 (0.2 nM final concentration, specific activity 1.83 x 103 Ci mol-1, Perkin Elmer), and incubated for 24h at 75%, 25% and 1% surface PAR. At the end of the incubation, the samples were sequentially filtered on 0.8 µm and 0.2 µm polycarbonate filters and rinsed with TiCl3-EDTA to remove extracellular iron. The radioactivity on the filter was measured onboard with a Tricarb® scintillation counter. Size fractionation after incubation was used to determine the contribution of bacteria, pico-nanoplankton and microplankton to total iron uptake rates. Size fractionation before 55Fe addition was used to investigate the competition for iron between bacteria and phytoplankton. These experiments were conducted at stations R-2, A3-2, F-L, E-2, E-3, E-4E, E-4W and E-5. Fe-C limitation was studied using dose-addition incubations. The samples were collected as described in the previous section and dispersed in 300 mL polycarbonate bottles. Iron and glucose, alone or in combination, were added to the sample and incubated in the dark for up to 7d. Incubation bottles were sampled at different time points to determine bacterial abundance (flow cytometry) and production (3H-leucine incorporation). These experiments were conducted at stations R-2, E-3, E-4W and E-5. Prokaryotic diversity was determined for 3 different size-fractions (< 0.8 µm, considered free-living ; > 0.8 µm and > 3 µm, considered particle-attached) using 454 pyrosequencing (for the free-living community) and Illumina sequencing (for the particle-attached community). Seawater was 25 µm pre-filtered with a Nylon screen, and the seawater was then sequentially filtered through 3 µm and 0.8 µm polycarbonate filters and the free living cells were concentrated on a 0.2 µm cartridge (Sterivex, Millipore). A combined DNA-RNA extraction was performed on all size fractions after lysis and purification steps (Landa et al., 2014). Genomic DNA was sent to the Molecular Research DNA laboratory and to the Fasteris platform for sequencing. Bioinformatics analyses were conducted as described previously (Landa et al., 2013). Briefly, raw data was denoised with AmpliconNoise (Quince et al., 2011) run through Mothur (Schloss et al., 2009), and the denoised reads were clustered into Operational Taxonomic Units (OTUs) with a 97% cutoff using Usearch 5.2.326 (Edgar, 2010). At this stage potential chimeras were removed using de novo and reference-based chimera detection in Uchime. Taxonomy was assigned as described previously (Landa et al., 2013) using the Greengenes database released in August 2013. The diversity of the free-living bacterial community was determined at stations R-2, A3-1 and A3-2, E-1, E-3, E-5, E-4E, E-4W and F-L at 4 depths (upper 300m). Two surface samples collected at the station A3 during KEOPS1 wee also analyzed. The diversity of the particle-attached community (0.8 µm and 3 µm) was determined at stations R-2, A3-2,


F-L and E-5 at 4 depths (upper 300m). The analyses of the particle attached bacterial community is presently under progress. Prokaryotic activity – carbon and iron: To determine the activity of specific groups of Bacteria and Archaea in the utilization of varying organic matter substrates, microautoradiography coupled to fluorescence in situ hybridization (MICRO-CARD-FISH) was applied. We used a radiolabeled amino acid (3H-leucine) and chitin (3H-Di-acetylchitobiose) to identify the bacterial groups incorporating these compounds of contrasting biological availability. We also used 55Fe to identify the bacterial groups actively taking up iron. Incubations with unfiltered seawater were done aboard, and MICRO-CARD-FISH was performed in the home lab, using an automated image analyses system. These analyses were done at stations R-2, A3-2, F-L, E-2, E-3, E-4E, E-4W and E-5 in surface waters, and at stations R-2, A3-2, F-L and E-5 at 4 depths (upper 300m). To investigate the expression of the gene encoding for the isocitrate lyase, a key enzyme in tricarboxylic acid (TCA) cycle, we designed specific group primers in the common and ubiquitous SAR11 clade. We determined the expression of isocitrate lyase by a quantitative PCR approach on DNA and RNA extracted from large volume filtrations (20L) at stations R-2, E-1, E-4W and F-L in surface waters. Further large volume filtrations were also performed for metagenomic and metatranscriptomic analyses of both the prokaryotic and eukaryotic microbial communities. This work is presently under progress.

LISST:

LOPC

Fig. 2: Mounting of LISST and LOPC at the base of the CTD−rosette. The UVP 5 is positioned in between the hydrological bottles.

Planktonic particle size spectrum and planktonic diversity structure A two–track approach was introduced: 1) Three captors counting and measuring particles were mounted on the CTD rosette (Fig. 2): a Laser In-Situ Scatterometer and Transmissometer (Sequoia LISST–100X), for measuring particle size distribution and volume concentration of particles from 1 to 250 µm, a Laser Optical Plankton Counter (ODIM Brooke Ocean LOPC), for measuring particle size distribution and volume concentration of particles from 100 µm to 35 mm, and Underwater Vision Profiler 5 (UVP 5 Sn002, Laboratoire d’Océanographie de Villefranche sur mer), for measuring particle size distribution and volume concentration of particles > 52 µm and counting and observation of macrozooplankton (> 2 mm); 120, 103 and 53 vertical profiles were taken respectively by UVP 5, LISST and LOPC. Those measurements provided the spatial and temporal distributions of size structured plankton communities between 1 µm and 35 mm with high spatial and size resolutions. The time series of size spectra can be further applied to study primary production, trophic interaction and carbon export. 2) 42 plankton 0 to 250 m depth net tows (Double–net BONGO device) were performed in order to analyze the taxonomic and size structure of mesozooplankton. Net tow samples from all stations were processed using ZOOSCAN (www.zooscan.com) to determine the size structure of the zooplankton communities, whereas binocular observations allowed species and genus identification of zooplanktonic organisms.


Particulate matter analyses Bulk measurements of C, N, P, and Si in the particulate matter were performed by different analytical methods (combustion method and measurements on a EA 2400 CHN Analyzer for C and N, wet oxidation method followed by colorimetric measurements for P, and sequential NaOH/HF extractions followed by colorimetric measurements for Si). Pigments were analyzed by HPLC. Phytoplankton production measurements Isotopic enrichment were performes on natural populations which were incubated under simulated in situ light in an on–deck incubator. Isotopic tracers were added to the samples to measure the uptake of nitrogen forms (15NH4

+, 15NO3–) and the isotopic measurements were

performed at the laboratory on an elemental analyzer-isotope ratio mass spectrometer (EA-IRMS). For silicon production and dissolution measurements the method of isotopic dilution of 30Si tracer was used with measurements performed on a high-resolution sector field inductively coupled plasma mass spectrometer (HR−SF−ICP−MS). Phytoplankton taxonomical analyses and cell−specific activities of diatoms Phytoplankton samples were enumerated and identified under an inverted microscope. The measurements of individual biovolumes enables the estimation of the carbon biomass associated with each taxon. For silicifying organisms an incubation with PDMPO (a fluorescent probe of silicic acid deposition) was performed in parallel to production experiments. PDMPO analyses enabled the determination of active cells as well as the degree of silicification of actively growing diatoms and silicoflagellates.

IV. RESULTS

1. Trace metal distribution and speciation (TASK 2) Iron (Fe) has been shown to be an essential trace metal controlling phytoplankton growth

and primary production in about 50% of the World’s oceans (Boyd and Ellwood, 2010) including high nutrient low chlorophyll (HNLC) regions. Within the complex Southern Ocean system, numerous studies have highlighted several sites of natural Fe fertilisation including the Kerguelen Plateau (Blain et al., 2007; Blain et al., 2008), all stimulating phytoplankton blooms and enhancing carbon sequestration with varying magnitudes. During the first Kerguelen Ocean Plateau compared Study (KEOPS1) held in late summer 2005, the impact of natural fertilisation on primary productivity and carbon export was demonstrated in this area (Blain et al., 2007; Savoye et al., 2008). It was proposed that the development of the bloom was constrained by both iron and silicate availability around Kerguelen Island (Blain et al., 2007; Mosseri et al., 2008; Park et al., 2008). The second cruise, KEOPS2 (Kerguelen Ocean and Plateau compared Study 2), which was approved as a GEOTRACES process study, was designed to study the development of the Kerguelen bloom in early spring 2011 and in the offshore fertilisation area further east (Blain et al., 2007), in order to better assess the sources, sinks, and internal cycle of Fe.

The bioavailability of iron and therefore the degree of limitation of the phytoplankton community is controlled in part by the speciation of iron, which is largely dominated by organic complexation (Gledhill and Buck, 2012). Moreover, the acquisition of iron by some organisms is likely to be co-limited by another element, copper (Cu). Indeed, it has been shown that Cu could play a crucial role in iron acquisition via the multi-copper oxidase enzyme (Maldonado et al., 2006). Some other elements also serve as essential micronutrients, being involved in many metabolic processes of marine organisms (e.g. Mn, Co, Ni, Zn, and Cd, Sunda, 1994; Morel and Price, 2003; Middag et al., 2011) or can serve as tracers for Fe sources (Chase et al., 2005). The poor knowledge of their cycles is a major drawback for the understanding of their biogeochemical impact on the food web and a multi-proxy approach as encouraged by the GEOTRACES program is crucial to improve our knowledge.

Within this general context, in order to better constrain the biogeochemical cycle of trace metals and their impact on the carbon cycle our scientific objectives during KEOPS2 were:

1) To determine the trace metal (Fe, Cu, Mn, Co, Ni, Zn, and Cd) distribution and speciation. 2) To study the co-impact Fe-Cu on the natural plankton communities.


1.1. Dissolved Fe distribution in the vicinity of the Kerguelen Island

This work has been published in Biogeosciences Discussions for publication in the KEOPS2 special issue (Quéroué et al., 2014a). We present the dissolved Fe (dFe) concentrations and discuss their distributions in relation to potential new and regenerated sources and to the biological uptake of Fe. The combined suite of KEOPS2 Fe results is presented in two other papers on particulate trace metal distribution and on Fe budgets, in the special issue (van der Merwe et al., 2014; Bowie et al., 2014).

During the KEOPS2 cruise, 149 seawater samples from 15 stations were collected. Dissolved Fe (dFe) concentrations ranged from 0.06 nmol L–1 in offshore, Southern Ocean waters, to 3.82 nmol L–1 within Hillsborough Bay, on the north-eastern coast of Kerguelen Island (Fig. 3). At near-coastal stations, the elevated dFe concentrations are most certainly indicative of Fe sources from the islands. This source is most likely a combination of direct island runoff, glacial melt and resuspended sediments. Above the Plateau, significant deep dFe enrichments were observed close to the seafloor. Non reductive dissolution of resuspended sediments is a potentially important source of dFe as observed at near-coastal stations (e.g. Homoky et al., 2013). Diffusion from pore waters is another important possible source of Fe for the benthic boundary layer (BBL, Elrod et al., 2004).

Fig. 3: Vertical distribution of dFe concentrations measured at near-coastal stations (cluster

1, a), above the Plateau (cluster 2, b), in the recirculation area (cluster 3, c), north of the Polar Front (cluster 4, d) and in the HNLC area (cluster 5, e), showing the median dFe (solid line with crosses). The interquartile range defined as the range around the median containing 50% of the data is given between the two dotted lines.

A significant decrease was observed in dFe concentrations in the SML between A3-1 (20 October, early bloom conditions) and A3-2 (17 November, large diatom bloom, Lasbleiz et al., 2014). Taking into account the decrease in dFe stock and the increase in POC stock, the Fe:C ratio of the biomass that developed between the two visits could be estimated to equal 34 µmol mol-1, a ratio consistent with literature values for diatoms in Fe-replete waters of the Southern Ocean (Sunda and Huntsman, 1995; Sunda, 1997;Twining et al., 2004; Sarthou et al., 2005). Although this is a rough estimate which does not take into account any additional inputs or removal processes, this result indicates that the dFe decrease between the two visits could be due, at least partly, to biological uptake.

In the recirculation area, a rapid transfer towards offshore waters of dissolved sediment-derived Fe from the Plateau was suggested as observed for radium isotopes (Sanial et al., 2014). Within the waters characterized by an oxygen minimum, remineralization of sinking organic matter


may exert a primary control on dFe distribution. The positive correlation for all the stations between dFe and the apparent oxygen utilization (AOU) suggested that remineralization was likely a significant source of dFe at these depths. The net Fe:C ratio for the remineralization process was estimated to be equal to 2.6-2.9 µmol mol-1, which is very similar to Fe:C ratios of Fe-limited diatoms from culture studies and in-situ Southern Ocean data (Martin et al., 1987; Sunda, 1997; Sarthou et al., 2005).

For the stations north of the Polar Front, a decrease in dFe concentrations within the surface waters, around 35-40 m depth, was observed, as a potential result from biological uptake. This is confirmed by the high biomass and the composition of suspended particles reported at these stations (Lasbleiz et al., 2014; van der Merwe et al., 2014). The relatively high dFe concentrations in this region could be explained by the fact that a portion of the water masses found there likely interacted more with both the plateau and shallow coastal waters of Kerguelen Island than the water masses from the recirculation area (Park et al., 2014; d'Ovidio et al., 2014). As for the recirculation area, dFe concentrations in the mesopelagic zone may also reflect remineralization processes. The slope of dFe vs. AOU is not significantly different from the slope in the recirculation area, suggesting that Fe and C are remineralized at the same rates in both regions (Fe:C ~ 2 µmol mol-1).

At the HNLC station, the maximum observed at 500 m could be due to some lithogenic inputs. Indeed, while sea-surface lithogenic silica concentrations (Lasbleiz et al., 2014) were low at station R-2 (< 0.042 µmol L-1), they were maximum at 500 m depth (0.12 µmol L-1). Particulate Fe, manganese and aluminum enrichments were also observed at 500 m (van der Merwe et al., 2014). These authors also observed a unique particulate trace metal composition signature at this station, which could originate from the Leclaire rise, contrasting with the basaltic signature observed above the Kerguelen Plateau (Doucet et al., 2005). The Leclaire Rise is a remarkable oceanic feature that consists of a submerged volcano with an area of 6,500 km2, with the shallowest depth up to 100 m. It is located 75 km north west of R-2 and could release dissolved and particulate material. Moreover, remineralization may also partly explain dFe concentrations in the mesopelagic zone. Fe and C are also remineralized at the same rates as above and the intercept, significantly different from zero, confirms the hypothesis of dFe sedimentary inputs at this station.

To sum up our results on dFe distribution, this third cruise over the Kerguelen Plateau allowed new insight into dFe sources and internal cycling. Atmospheric inputs were negligible during the KEOPS2 cruise while direct runoff, glacial and sedimentary inputs can be considered as important sources of dFe in the vicinity of Kerguelen Island. Remineralization of sinking particles can explain the high concentrations of dFe in intermediate waters offshore. The strong jet of the PF was enriched with dFe from the north of the plateau as it flowed northward close to Kerguelen Island and later eastward to loop back into the recirculation area. This fertilised surface waters of the eastern part of the studied area. Furthermore, filaments crossing the PF allowed a more direct natural Fe fertilisation of surface water in the recirculation area. Due to variable water mass origin and variable horizontal advection mechanism (along or across the PF), the recirculation area evidenced strong dFe concentration variability. The PF is an important Southern Ocean feature that should not be neglected with regards to Southern Ocean fertilisation offshore from the Kerguelen Plateau through fast lateral Fe transport from the north of the Kerguelen Plateau.

1.2. Distribution of dissolved trace elements (Mn, Co, Ni, Cu, and Cd) in the Kerguelen Plateau region

This part will be published in Biogeosciences Discussions in the following months (Quéroué et al., 2015). We report for the first time the analysis of a suite of trace metals in this area. The impact of biological uptake and remineralization on the vertical distribution of dissolved Mn (dMn), Co (dCo), Ni (dNi), Cu (dCu), and Cd (dCd) is discussed, as well as the potential origin of these trace metals, namely atmospheric inputs, freshwater inputs, sediment resuspension and anthropogenic sources.

A total of 17 stations were sampled for dissolved trace metal analysis. Two additional stations, compared to the dFe study, were sampled in the recirculation area (E-1 and E4-E). Dissolved trace metals were analyzed one year after sample collection by solid phase trace metal extraction onto Nobias-Chelate PA1 resin (Hitachi High-Technologies) followed by Sector Field Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis (Quéroué et al., 2014b).

Dissolved Mn (dMn) concentrations ranged from 0.06 nmol L-1 to 5.40 nmol L-1 at near-coastal stations, as illustrated on Fig. 4.


Fig. 4: Concentrations of dMn (nmol L–1) over the East-West transect.

The other trace metals ranged from 28 pmol L-1 to 284 pmol L-1 for dCo, from 5.4 nmol L-1 to 7.5 nmol L-1 for dNi, from 1.1 nmol L-1 to 2.6 nmol L-1 for dCu, and 0.23 nmol L-1 to 0.96 nmol L-1 for dCd.

Consistent with Fe results, atmospheric inputs were negligible for the other studied trace metals. Manganese was the only element with Fe showing enhanced dissolved concentrations at TEW-1 compared to TEW-2. Input of dMn by freshwater inputs was previously observed in the Arctic Ocean by Middag et al. (2011b) revealing high dMn concentrations at levels up to 6 nmol L-1 due to fluvial runoff and melting sea-ice. For Mn, as for Fe, high concentrations at near-coastal stations are likely due to a combination of direct island runoff, glacial melt and resuspended sediments.

Over the Kerguelen Plateau, at A3-2, increase in dMn concentrations up to 1.12 nmol L-1 near the seafloor was observed. This is the highest concentration observed during our study with the exception of the coastal area. It is also at this station and at this depth that the highest dFe concentration over the plateau was observed, most likely due to sediment resuspension and associated pore water release (Quéroué et al., 2014a). However the dMn increase was not observed at G-1 and TEW-3 even if enhanced dFe concentrations were observed at depth at TEW-3 and G-1. This might be due to a more intense sediment resuspension or different pore water concentration observed at A3 compared to the other stations of the plateau (Quéroué et al., 2014a). Surprisingly, over the plateau, no significant dCo deep water concentrations were observed, indicating that this part of the Kerguelen Plateau is not a major source of dCo. During KEOPS1, high dCo concentrations (> 100 pmol L-1) were attributed to lateral advection of Co rich seawater at surface and deep waters from lithogenic source in the vicinity of Heard Island, in the southern part of the Kerguelen Plateau (Bown et al., 2012).

In the recirculation area, drifters data and radium isotopes studies have showed that water masses from the coastal area were transported to the recirculation area after crossing it or flowing with it doing a loop to join the recirculation area (Zhou et al., 2014; Sanial et al., 2014). Increased in lithogenic particulate Fe (PFe) and lithogenic Si concentrations at E stations also suggest lateral transport of enriched waters from the plateau (Lasbleiz et al., 2014; van der Merwe et al., 2014). Since high dNi and dCo concentrations were observed in the coastal area, the enhanced surface dCo and dNi concentrations may indicate enhancement mechanisms by lateral advection. Although, dissolved Mn, amongst all the trace metals, showed the highest concentrations in the coastal area, no significant surface water enhancement was observed in the recirculation area. This might be due to the scavenging of Mn onto settling particles (Noble et al., 2012) or biological uptake of incoming sources.

For bioactive trace metals, linear relationships of dissolved metal concentrations versus dissolved macronutrients in deep waters, below the mixed layer depth, can give access to estimates of remineralization ratios if external sources of metals (and macronutrients) in the deep waters are minimal. Such remineralization ratios reflect phytoplankton metal stoichiometries in surface layers. These estimates of trace metal quotas, associated with evaluation of external sources, discriminated 3 groups of trace metals: 1) Cd, whose vertical profiles are mainly impacted by uptake and remineralization, with seemingly little impact of external sources except at the most coastal stations, 2) Mn which is impacted both by biological activity (and scavenging) and external sources, and 3) Cu, Ni


and Co whose vertical profiles seem to be more impacted by external sources than by uptake and remineralization.

1.3. Fe-Cu impact on natural plankton communities and Fe- and Cu-binding ligand production

This work was also carried out (and partially funded) in the framework of the ANR-ICOP (ANR- 10-JCJC-606) which aims at better understanding how the Fe-Cu co-impact influences phytoplankton growth, competition among different species, and major biogeochemical cycles in the ocean. It will be submitted to Biogeosciences Discussions within the next few months (Sarthou et al., 2015).

The limiting role of trace metals and particularly iron (Fe) in controlling phytoplanktonic production and the structure of the planktonic community has now been largely admitted in the Southern Ocean (Boyd et al., 2007, Blain et al., 2007). Other metals, such as copper (Cu), also play a key role in the biological pump of carbon. Recent studies showed that the biological demand for iron might be linked to Cu (Peers et al., 2005). Our own studies, conducted during the international Bonus-Goodhope cruise in the Southern Atlantic Ocean (Feb.-March 2008), clearly indicate that Cu not only partly controls the intensity of the Fe impact, but also may even control primary production by itself (Sarthou et al., 2009).

Fig. 5: Iron-limitation indices (ILI) determined from Chl-a (white bars), BSi (light grey

bars), POC (dark grey bars), and PON (black bars), for stations R2, A3-1 and E-3. ILI are calculated by normalizing the Chl-a, BSi, POC, and PON concentrations at the end of each experiment to the respective value in the control

During KEOPS2, we carried out on-board Fe-Cu incubations at three stations (A3-1, R2, and E3), with additions of Fe (+ 1 nM) and Cu (+ 0.5 nM). During the course of the experiment (9-14 days), subsamples for the following measurements were taken: concentrations of chlorophyll-a (Chl-a), biogenic silica (BSi), particulate organic carbon (POC), particulate organic nitrogen (PON), and Cu organic speciation.

At R2 station, at the end of the experiment, Chl-a, BSi, POC, and PON in the Fe-amended treatments were higher than in the control (Fig. 5).

At A3-1 station, no significant difference was observed for Chl-a, BSi, POC, and PON (Fig. 5). At station E-3, at the end of the experiment (12 d), Chl-a concentrations reached values similar to R2 station (11 µmol L-1) in the Fe-amended treatments, which was ~ 2 times higher than in the control (Fig. 3). These results clearly highlight the presence of three different Fe regimes: A strongly Fe-limited regime in the HNLC area South-West of the Kerguelen Plateau, a mild limitation in the recirculation area (station E-3) and no limitation above the Plateau (station A3-1).

No significant difference between the control and + Cu treatments and between the + Fe and + Fe + Cu treatments were observed over the course of the experiment for all stations. Results for the Cu speciation showed that the Cu-binding ligand concentrations (LCu) increased with time in all treatments, up to values as high as 150 nM. When normalized to particulate organic carbon, very low

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variations were observed, strongly suggesting a biological origin of these ligands. The maximum values were observed at R2 station, suggesting a link between Cu-binding ligands production and Fe-limitation or phytoplankton community.

2. Iron transport and sources (TASK 3) Refining the origin of the natural fertilization and quantifying it was an important issue

following the results deduced from KEOPS 1 measurements of geochemical tracers. These tracers suggested a significant input of lithogenic elements due to the dissolution of material weathered from the shelf and the slope of Kerguelen and Heard islands. These inputs lead to enrichments of the surface waters of the Plateau in Ra isotopes, Rare Earth Elements (REE), lithogenic Barium (Ba), lithogenic 232Th (Jacquet et al., 2008; van Beek et al., 2008; Venchiarutti et al., 2008; Zhang et al., 2008). In addition, REE, 228Ra, 230Th and 231Pa isotopes clearly indicated the lateral origin of the enrichments – strongly suspected to result from the weathering of Heard and Kerguelen islands and shelves implying submarine weathering-, raising the difficulty of using 1 dimensional models for establishing element budgets on the Kerguelen plateau.

By contrast, iron was depleted in surface waters above the plateau (Blain et al., 2008). This could reflect:

1) that sediment dissolution was not as efficient for iron as for REE, Ba and 232Th,

2) similar dissolution rates, but a more rapid biological consumption and/or an immediate scavenging of Fe,

If confirmed submarine weathering might impact other elements as macronutrients and micronutrients, essential for the biological pump (Jeandel et al., 2011). We use a multi-tracer approach to study the mechanisms of iron fertilization eastward of the Kerguelen Plateau.

2.1. Radium isotopes :

We used radium isotopes (224Ra, T1/2 = 3.66 d; 223Ra, T1/2 = 11.4 d; 228Ra, T1/2 = 5.75 y; 226Ra,

T1/2 =1600 y) to provide information on the origin of iron fertilization and on the timescales of the

transfer of sediment-derived inputs (including iron and other micronutrients) towards offshore waters. We studied two areas visited during the KEOPS2 project (the Kerguelen Islands and the Crozet Islands), using an original approach that combines our geochemical tracers and physical observations (drifter released off the islands and outputs of a model based on altimetry data). Our results provide constrains on the mechanisms of the iron fertilization that take place in these two regions of the Southern Ocean. We report significant 224Ra and 223Ra activities in the near vicinity of the Kerguelen Islands (in agreement with the short half-lives of these isotopes), but more surprisingly in offshore waters up to 200 km downstream of the islands and sometimes also south of the Polar Front (Fig. 6). These observations thus clearly indicate i) that the sediment-derived inputs are rapidly transferred towards offshore waters (on timescales in the order of several days up to several weeks) and ii) that the Polar Front is not a physical barrier for the chemical elements released from the sediments of Kerguelen Plateau. Iron and other micronutrients released by the shallow sediments of the Kerguelen margins may thus contribute to fuel the phytoplankton bloom downstream of the islands, despite the presence of the Polar Front (Sanial et al., Biogeosciences, accepted providing minor revisions).

The apparent ages of surface waters determined using Ra isotopes offshore of the Kerguelen Islands (Fig. 7) also suggest a rapid transport of chemical elements between the shelves and offshore waters and highlight the key role played by horizontal transport in natural iron fertilization and in defining the extension of the chlorophyll plume in this HNLC region of the Southern Ocean. The apparent ages of surface waters determined using our geochemical tracers are in relatively good agreement with the ages determined using physical methods (drifter released off the islands and outputs of a model based on altimetry data). The results of this latter study were published in JGR (Sanial et al., 2014).


Fig. 6 : 224Ra (A) and 228Ra (B) activities in surface waters offshore of the Kerguelen Islands (Sanial et al., accepted for Biogeosciences, KEOPS-2 Special Issue).

Fig. 7 : Apparent radium ages of surface waters derived from the 224Ra/228Ra ratios. The

transit time of the drifter is reported in days along its trajectory (Sanial et al., 2014).

2.2 REE and Nd isotopes

Two original information are revealed by the dissolved REE concentrations results obtained on KEOPS2 seawater samples. The first result concerns the sources of seawater fertilization in the Kerguelen area; the second one is about the impact of the bloom over the REE marine cycle.

Signatures of Kerguelen lithogenic material supplies in seawater Dissolved REE concentration results have revealed a so far uncharacterized source of

continental material in seawater along the coasts of Kerguelen Island that may contribute to the annual events of natural fertilization in the area.

REE results of KEOPS2 coastal samples (stations TEW1, G2) likely suggest a recent release of lithogenic material from the Kerguelen margins into the dissolved fraction of seawater. This can be observed by comparing the PAAS-normalized REE patterns of the coastal samples (yellow and orange patterns in Fig. 8–a) with the upstream surface samples of the HNLC reference station R2 (red pattern). Beyond the higher REE concentrations, the occurrence of recent lithogenic supply was supported by the relatively flat coastal REE patterns, their associated weak negative Ce anomaly and a significant negative Eu anomaly.

A less pronounced but significant negative Eu anomaly was also found offshore in NPF_L surface samples (black pattern in Fig. 8–a), suggesting a direct and fast pathway of the Kerguelen coastal waters in the northern portion of the Polar Front (see the red arrow just north of Polar Front in Fig. 8–d). Except at this offshore station, the negative Eu anomaly seemed to be rapidly eroded.


Surprisingly, a contrasting positive Eu anomaly was found in seawater close to Heard Island during the KEOPS1 cruise (station C1, light green pattern in Fig. 8–b, Zhang et al., 2008). This latter was suggested to be due to REE release from Heard margin basaltic sediments, characterized by a positive Eu anomaly. This second lithogenic source may predominate south of the Polar Front and participate to the erosion of the northern Kerguelen signature. Another process that could potentially erode the Kerguelen negative Eu anomaly is the ubiquitous release of REE by desorption or dissolution from the particulate marine fraction, particles being mainly derived from basaltic material and characterized by a positive Eu anomaly (see the grey pattern of unfiltered Kerguelen beach water in Fig. 8–b).

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Fig. 8 : PAAS-normalized REE patterns of: (a) HNLC reference station R2 (red pattern), Kerguelen coastal stations TEW1 (yellow) and G2 (orange), and offshore station NPF-L (black); (b) Kerguelen coastal stations (yellow and orange), Heard Island coastal station C1 (green; from Zhang et al., 2008), and unfiltered Kerguelen beach water (gray); (c) Kerguelen basalts (brown), Heard basalts (green), and rhryolite and trachyte of the area (black patterns). d: Map – schematic pathways of the lithogenic supplies (white contoured orange and red arrows) and location of main stations, of the Kerguelen and Heard Islands, the Kerguelen Plateau and the polar Front.

As Kerguelen and Heard coastal samples had opposite Eu anomaly, it seems that the continental supplies occurring in each area are derived from continental supplies characterized by different geological natures. In the Kerguelen coastal area, we suspect some release of lithogenic REE coming from Kerguelen flood basalts constituted of rhyolite or trachyte veins (black continuous pattern in Fig. 8–c), these latter being themselves characterized by a negative Eu anomaly.

REE fractionation at different stages of a bloom Over and downstream the Plateau, some temporal fractionations among the dissolved REE in

locations sampled several times and considered as time-series seemed to be related to biological processes and bring new insights about the REE marine cycle. Fig. 9 illustrates the decoupling of La and Eu fractionations that may occur during an austral ocean bloom life, the former being related to the barite cycle and the latter to the Si cycle (Akagi et al., 2011).


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Fig. 9 : (top) Schematic La and Eu biological fractionation during the bloom development on the Kerguelen Plateau. The temporal evolution of the La and Eu anomalies are represented by the green and red curves, respectively, while grey and black curves represent the temporal evolution of the primary and export productions. Black dashed vertical lines represent the sampled phases of the bloom.

(bottom) Schematic illustration of the chemical processes that govern these fractionations. We suggest a decoupling role of barite and opal cycles.

Fig. 10 : Left: SEM images of the particulate phases before and after a dissolution

experiment. Right: Changes in silicic acid content of seawater during a dissolution experiment – comparison of particles colletced uring KEOPS 1 and samples from W Iceland river and coastal area (Figures from Pearce et al., 2013).


Batch reactor experiments (Jones et al., 2012; Pearce et al., 2013) were performed on Solid material representative of the basaltic particulate material of the Kerguelen Plateau. SEM images revealed the absence of any biogenic silica in the samples studied and that solid particles display smooth surfaces and well defined sharp edges before the experiments (Fig. 10 left) while the surfaces became irregular with rounded edges at the end. In addition, differences in the XRD particulate spectra (not shown) before and after the experiments allowed us to identify the loss of Olivine and plagioclase during the course of the experiment. These different and independent characterizations of the solid material argue in favor of the dissolution of lithogenic material during these batch experiments

Three main features are observed in the course of the experiments (Pearce et al., 2013):

1) the silicic acid concentration increases in all 3 experiments, including the one conducted on the Kerguelen plateau core top (Fig. 10 right),

2) the Nd isotopic compositions (expressed as εNd) of the seawater increase on a rapid monthly time scale from its initial value (close to -10) to reach the value of the different basalts that have been in contact with the water (-1.8 for the Kerguelen sample1) , Fig. 11−A),

3) the Nd concentrations simultaneously decrease (Fig. 11−B) –note that the delay of one week before sampling the first aliquot doesn’t allow seeing the release of Nd that would conduct to the isotopic change−, while the REE patterns are changing from a “typical seawater one” to a typical basaltic one. Note that in parallel experiments, Sr showed similar changes in isotopic signature together with a drop in Sr concentration (Jones et al., 2012).

These results are indicative of a rapid release of Si, Nd (and Sr) that explains the change of isotopic values, likely due to the dissolution of basaltic phases and minerals: a hypothesis reinforced by the mineralogical and SEM analyses. Thermodynamic calculations suggest that the secondary phase precipitate are phosphate minerals as for example rhabdophane, that would dime the impact of the dissolution of this lithogenic material on the global ocean. Nevertheless, dissolution of lithogenic material remains a significant additional source of chemical elements to the ocean, including iron (Jeandel et al., 2011) and cobalt, also clearly visible along the Kerguelen shelf (Bown et al., 2012). The Kerguelen top core sediment are releasing 0.04% of its Nd content while the dissolutions are occurring on a short time scale, on the order of a few weeks

Fig. 11: A: Changes in the Nd isotopic composition (εNd) of the particulate phase (open

symbols) and seawater (closed symbols) during typical dissolution experiments. B: Changes in the concentration of Nd in seawater during dissolution experiments. Decreases in Nd abundance from the starting concentration of ∼24 pmol/kg are thought to reflect the incorporation of Nd into precipitating secondary phases such as rhabdophane. Grey symbols indicate samples with anomalous REE patterns (Figures from Pearce et al., 2013).


2.3 Global impact of the lithogenic sediment dissolution and models

The potential impact of the dissolution of a tiny fraction of the sediments deposited on the margins by the submarine weathering can be significant for some elements as discussed in details in Jeandel et al. (2011) and Jeandel and Oelkers (in press). Note that Tagliabue et al. (2014) underline the importance of the “sedimentary source” of iron on the atmospheric CO2 variability. More locally, an inverse model was developed following a collaboration between the geochemists working in the KEOPS program and Anouk de Brauwere (University of Louvain la Neuve). Simultaneous simulations of Pa, Th, Fe, Nd isotope and concentrations reinforce the identification of the importance of the lateral inputs and that an external source is required to balance the budgets of these tracers on the Kerguelen plateau (de Brauwere et al., submitted).

3. Microbial diversity in the iron fertilized Southern Ocean

3.1. Bacterial community composition and production in a mosaic of phytoplankton blooms in the Southern Ocean (TASK 4)

Marine microbes play a pivotal role in the marine biogeochemical cycle of carbon, because they regulate the turnover of dissolved organic matter (DOM), one of the largest carbon reservoirs on Earth. Microbial communities and DOM are both highly diverse components of the ocean system, yet the role of microbial diversity for carbon processing remains thus far poorly understood. The KEOPS2 cruise offered a unique possibility to explore this question in a mosaic of phytoplankton blooms induced by large scale natural iron fertilization in the Southern Ocean. We showed that in this unique ecosystem where concentrations of DOM are lowest in the global ocean a patchwork of blooms stimulates diverse and distinct bacterial communities (Fig. 12).

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Fig. 12 Phylogenetic composition of the bacterial communities in surface waters of the

KEOPS2 study sites. Relative contribution of OTUs is expressed as percent of total sequences. The stations are ordered according to a UPGMA clustering built from a weighted UNIFRAC distance matrix. The numbers at each node of the cluster indicate the percent of dissimilarity. Blue nodes correspond to a bootstrap support of 50 to 75% and red nodes correspond to a bootstrap support higher than 75%. Alphaproteobacteria are shown in blue, Gammaproteobacteria are shown in green and Bacteroidetes are shown in red shades.

By using an original experimental tool, onboard continuous cultures, we identified taxa associated with contrasting blooms based on their preferences in the degradation of DOM of different reactivity. We used the spatial and temporal variability provided by this natural laboratory to


demonstrate that the magnitude of bacterial production is linked to the extent of compositional changes (Fig. 13). Our results suggest that partitioning of the DOM resource could be a mechanism that structures bacterial communities with a positive feedback on carbon cycling. Our study, focused on bacterial carbon processing, highlights the potential role of diversity as a driving force for the cycling of biogeochemical elements.

The number and the variability in the identity and phylogeny of the responding OTUs among stations suggest that naturally iron-induced phytoplankton blooms in the Southern Ocean stimulate a large diversity of bacterial groups. Our study extends previous investigations of the southeastern bloom above the Kerguelen plateau (Station A3) that have demonstrated major differences in the bacterial community composition during the late stage of the bloom as compared to HNLC waters (West et al., 2008; Obernosterer et al., 2011).Our results from the Kerguelen region are, however, in contrast to the artificial iron enrichment experiments EisenEx and LOHAFEX performed in the Southern Ocean where minor or no changes in bacterial community composition were observed in the iron-fertilized patch (Arrieta et al., 2004; Thiele et al., 2012). This suggests that the bacterial response is in part driven by the mode of fertilization that differs drastically between these studies. In contrast to the Southern Ocean, bacterial community composition associated with phytoplankton blooms has been extensively studied in other ocean regions, however, with focus on a single bloom event (González et al., 2000; Fandino et al., 2001; Riemann & Winding, 2001; Larsen et al., 2004; Rink et al., 2007). Our study brings novel perspectives on the subject, through the concurrent exploration of a patchwork of blooms provided by a large scale natural laboratory in the Southern Ocean. The overall low overlap of the responding OTUs between distinct stations or bloom stages suggests that the conditions set by each site or stage favored a given community, dominated by OTUs adapted to the environmental conditions.

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Fig. 13 Regression analysis between bacterial heterotrophic production and the number of

responding OTUs identified at each bloom site (A) and between bacterial heterotrophic production and the intensity of the response (B), determined as the sum of the relative abundances of the responding OTUs identified at each bloom site. For bacterial heterotrophic production, the mean value ±SD in the mixed layer is given.

3.2. Is DOM a driver of the changes in bacterial community composition?

To explore this question we used an original experimental tool, continuous cultures run with an ambient bacterial community aboard the research vessel during the KEOPS2 cruise. This experiment provided evidence that DOM properties are a strong factor shaping bacterial community composition, each tested condition sustaining diverse but comparatively distinct OTUs. We propose that the OTUs responsive in the seawater treatment are competitive when most of the carbon pool is constituted of semi-labile and refractory compounds. By contrast, the OTUs responsive to the diatom-DOM treatment are probably competitive at increased concentrations of labile compounds of phytoplankton origin. The combined experimental and in situ observations suggest that at least some of the abundant bacterial taxa exhibit distinct metabolic preferences with respect to degradation of DOM of variable origin and reactivity. These preferences could lead to partitioning of the available resource between active members of the community at a given site. To support this idea, we have documented relationships based on a subset of the bacterial community, composed of 42 taxa that through their capacity to respond to an environmental change, were major drivers of composition shifts and were associated with up to 40-fold variability in bacterial production. Within this community, the diversity of the responding OTUs, driven by both their number and their relative abundances, were key ecological features sustaining the relationship. This suggests that an increase in bacterial production, driven by an increased supply of phytoplankton DOM, was associated with a


higher number of responding taxa. If, as suggested by our continuous culture experiment, DOM pools of different reactivities are exploited by distinct and diverse taxa, the higher number of responding taxa could reflect an increase in niche availability, with a positive feedback on bulk performance due to resource partitioning.

3.3. The response of Archaea to natural Fe fertilization of the Southern Ocean.

Even though Archaea make up about one third of total prokaryotes in the ocean, little is known on their ecology and contribution to carbon cycling. Up to date, no study has investigated the effect of natural iron fertilization on archaeal abundance and activity. To gain insights into the distribution, abundance and activities of Archaea and Crenarchaeota, we used MICRO-CARD-FISH using radiolabelled leucine and chitin as substrates. Interestingly, Archaea were more abundant in Fe-fertilized waters (up to 34% of total prokaryotes) as compared to HNLC waters (< 10% % of total prokaryotes). Archaea constituted only a small fraction of the community incorporating leucine at the HNLC site (about 3% of total prokaryotes taking up leucine), and this relative contribution was slightly higher in Fe-fertilized waters (5-15% of total prokaryotes taking up leucine). An original observation was the dominant contribution of Archaea to the utilization of chitin (45-93% of total prokaryotes utilizing chitin). Taken together, these results suggest the stimulation of Archaea in the phytoplankton blooms induced by natural iron-fertilization, and they highlight the importance of Archaea in the degradation of high-molecular-weight organic substrates. This latter ecological trait could explain the relatively high abundance of Archaea in surface waters of the Southern Ocean, where highly refractory compounds from deep waters have a major contribution to surface DOM.

Fig. 14 Relationship between the C-normalized bacterial iron uptake in the absence of

microplankton (ρFe:POC)<25µm (a) or in the absence of micro- and pico-nanoplankton (ρFe:POC)<0.8µm (b) and euphotic zone integrated primary production. Empty symbol represents the reference station R-2 and filled symbols represent the fertilized stations.

4. Microbial Fe- and C-cycling in the naturally fertilized Southern Ocean (TASKS 4 & 5) It has univocally been shown that iron is the primary limiting nutrient for phytoplankton

metabolism in HNLC oceans, yet, the question of how this trace metal affects heterotrophic microbial activity is far less understood. We addressed this issue at different levels by asking the following questions:

1) What are the interactions between phytoplankton and heterotrophic bacteria for the uptake of Fe?

2) Are heterotrophic bacteria Fe- or C-limited? 3) Is isocitrate lyase an indicator gene for bacterial Fe and C limitation?

4.1. What are the interactions between phytoplankton and heterotrophic bacteria for the uptake of Fe?

Total Fe uptake in surface waters was on average 34±6 pmol Fe L–1 d–1, and microplankton (>25µm size-fraction; 40-69%) and pico-nanoplankton (0.8-25 µm size-fraction; 29-59%) were the main contributors. The share of heterotrophic bacteria (0.2-0.8 µm size-fraction) to total Fe uptake was low at all stations (1-2%). Fe uptake rates normalized to C biomass were highest for pico– and


nanoplankton above the Kerguelen plateau and for microplankton in the downstream plume. We also investigated the potential competition between heterotrophic bacteria and phytoplankton for the access to Fe. Bacterial Fe uptake rates normalized to C biomass were highest when bacteria were incubated in the absence of both micro- and pico–/nanoplankton. The absence of microplankton resulted in a decrease in bacterial Fe uptake rates by up to 20-fold, while in incubations with the whole microbial community, bacterial uptake rates were reduced by 2- to 8-fold. In Fe-fertilized waters, the bacterial Fe uptake rates normalized to C biomass were positively correlated with primary production (Fig. 14). Taken together, these results demonstrate that heterotrophic bacteria are outcompeted by small sized phytoplankton cells for the access to Fe during the spring bloom development, most likely due to the limitation by organic matter. We conclude that the Fe and carbon cycles are tightly coupled and driven by a complex interplay of competition and synergy between different members of the microbial community.

4.2. Are heterotrophic bacteria Fe- or C-limited?

We investigated the role of Fe for bacterial heterotrophic production and growth at three contrasting sites in the naturally Fe-fertilized region east of Kerguelen Islands and at one site in HNLC waters. Our results showed that single and combined additions of Fe and C stimulated bulk and cell-specific bacterial production at all sites, while bacterial growth was enhanced only in two out of four occasions. The extent of stimulation of bulk bacterial heterotrophic production by single Fe or C additions increased with increasing in situ bacterial Fe uptake rates in the surface mixed layer (Fig. 15).

Fig. 15 Relationship between the maximum extent of stimulation of bacterial heterotrophic

production by Fe- or C-addition and in situ bacterial Fe uptake rates as determined by 24h incubations of the microbial community with 55Fe.

Our results provide evidence that both Fe and C are present at limiting concentrations for

bacterial heterotrophic activity, in HNLC and fertilized regions, in spring. The observation that the extent of stimulation by both elements is related to Fe-uptake rates highlights the tight interaction between the C- and Fe-cycles through bacterial heterotrophic metabolism in the Southern Ocean.

4.3. Is isocitrate lyase an indicator gene for bacterial Fe and C limitation?

The tricarboxylic acid (TCA) cycle is a central metabolic pathway that is present in all aerobic organisms and initiates the respiration of organic material. The glyoxylate cycle is a variation of the TCA cycle, where organic material is recycled for subsequent assimilation into cell material instead of being released as carbon dioxide. Despite the importance for the fate of organic matter, the environmental factors that induce the glyoxylate cycle in microbial communities remain poorly understood.

Previous studies that were based on transcriptional or proteomic responses in cultures suggest an up-regulation of the glyoxylate cycle in the diatom Thalassiosira oceanica (Lommer et al., 2012), in members of the SAR11 clade (Smith et al., 2010) and in the gammaproteobacterium Alteromonas macleodii (Fourquez et al., 2014) also in response to iron limitation. In these studies, the


authors found an increase of the enzyme involved in the initiation of the glyoxylate cycle (isocitrate lyase) in iron depleted cultures by means of gene transcripts (Smith et al., 2010; Lommer et al., 2012) or proteins (Fourquez et al., 2014). The aim of our study was to investigate the TCA to glyoxylate cycle switch by means of isocitrate lyase gene expression in members of the abundant SAR11 clade inhabiting areas characterized by contrasting trophic conditions and iron availability of the Southern Ocean.

Fig. 16 Isocitrate lyase gene expression, concentrations of chlorophyll a and dissolved iron at

the reference site in HNLC waters (R-2) and in naturally iron-fertilized waters off Kerguelen Island.

The cell-specific transcriptional regulation of the glyoxylate cycle, as determined by the ratio between copy numbers of isocitrate lyase gene transcripts and isocitrate genes, was consistently higher in iron fertilized vs. HNLC waters (by 2.4- to 16.5-fold). The SAR11 cell-specific isocitrate lyase gene transcription showed a trend inverse to chlorophyll a and dissolved iron (Fig. 16). We conclude that the glyoxylate cycle is a metabolic strategy for SAR11 that is highly sensitive to the degree of iron and carbon limitation in the marine environment. Metatranscriptomics analyses to get further insight on the question of how widespread the use of the glyoxylate shunt is among diverse prokaryotic taxa is presently in progress.

5. Particle size distribution and volume concentration (TASK 5) During the KEOPS1 cruise, the origin and fate of the elevated phytoplankton biomass in

naturally iron-fertilized waters over the Kerguelen plateau (South-East area) was examined (Blain et al., 2008). Throughout the decline phase (January–February 2005) of the natural long-term bloom (>3 months), the mesozooplankton populations were already well established, with no significant spatial and temporal changes in biomass and species composition (Carlotti et al., 2008), but a subsequent increase of carbon export until 400 m depth (Jouandet et al., 2010) was recorded. Direct exports of diatoms was pointed out as the main export pathway from microscopic analyses of the sediment trap whereas observations from the gel trap indicated an indirect export through copepods fecal pellets. (Ebersbach and Trull, 2008).

The global objectives of the group working on planktonic particle size spectrum and planktonic diversity structure was to:

– Characterize the plankton community structures and dynamics in response to the early phase of the bloom in connection to mesoscale features and iron enrichment on the Kerguelen plateau and the near North-East oceanic deep waters ;

– Quantify the magnitude of carbon export in deep water from changes in particle size spectra in the water column.

The different analysis of the planktonic size spectrum and diversity and particle size spectrum were closely linked to other biogeochemical, biological and physical measurements to study the role of plankton in the bloom process and temporal evolution of plankton communities at time series stations.


5.1 Particle settling and scavenging using LISST-LOPC

The combination of size spectra obtained from LISST and LOPC provided continuous combined spectra of particles from 0.5 µm to 3 mm (Fig. 17–A). The continuity of the spectra confirms the reliability of the measurements.

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Fig. 17 A. Combined size spectrum of particles obtained form LISST and LOPC data

(station E–1). B. Total biovolume (µL L–1) distribution from LISST measurements along the south–north transect indicated by te red line in the insert.

The continuity of the spectra confirms the reliability of the measurements. Contrasted situations were observed on the south–north transect (Fig. 17–B) with an area of high biomass located in the region of the southeastern Kerguelen Plateau and an oligotrophic situation at the north in the subantarctic zone. In between, in the iron−fertilized recirculation area the biovolume distribution tended to be patchier. A similar transition was also observed along a west-east transect with enhanced particle concentrations for all size classes along the shelf break region, a deep pool of ~1 µm particles of in the deep waters at the off-shelf region, and deep export of 10 to 20 µm–sized particles in the middle of the transect.

Fig. 18 Distribution of particle size classes obtained from LISST data on a east-west transect (black line in Fig. 17–B).

5.2 Analysis of particle size spectra and macrozooplankton community based on UVP5 data

Vertical profiles of particle size distributions from the UVP 5 were analyzed. The total particle numerical abundance was more than 4 fold higher in early spring as the result of the 2-weeks bloom development compared to late winter situation observed at the very beginning of the cruise.


The maximum of temporal variability was observed over the 48 hours observations. Indeed, the profiles of particle volumes showed an increase of total volume from 3 mm3 L–1 to 25 mm3 L–1

from 15 to 17 November at the base of the mixed layer. The observed increase was associated with the increase of the abundance of wide particles (> 0.5 mm) during 48 hours. The rapid formation of large particles and their accumulation at the base of the mixed layer was observed as indicated by the total particles volume profiles. These profiles show sinking of particles from the mixed layer to 200 m depth, but little change deeper than 200 m (Fig. 18).

The comparison of observations and outputs from a model of particle dynamics (Jackson, 1995) adapted to the study area (Fig. 19) demonstrates the role of the physical aggregation in the rapid formation of large aggregates over the southeastern Kerguelen Plateau (Jouandet et al., 2014). The comparison with the results of KEOPS 1 as well as of other experiences of fertilization highlight the role of the physical aggregation as the main process for carbon export during the initial phase of iron fertilized blooms. In the Polar Frontal area, the profiles of particle volume and abundance were characterized by the presence of a sub-surface maximum in agreement with the maxima of fluorescence and biogenic silica observed, demonstrating the key role of diatoms in the building of particles. Uniform abundances and volumes in the mixed layer characterized the stations of the recirculation meander. The temporal sampling of the bloom within the meander indicated an increase of the particle abundance by a factor 4 in the course of the bloom development although the biovolume increase was less important (x 0.5). This situation, different from the evolution observed over the plateau, reflects the necessary extension for the building of wide particles by physical aggregation (Jouandet et al., 2014).

Fig. 19 Observed (A) and modeled (B) volume distribution size spectra along vertical axis on

17 November at 1.10 a.m. (from Jouandet et al., 2014).

6. Plankton community structures and biogeochemical cycles (TASK 5) The structure of pelagic communities determines the strength of the biological pump

(magnitude of biogenic matter escaping the epipelagic domain) and its efficiency (effectiveness in reducing surface nutrients relative to subsurface values) (Sarmiento et al., 2004). Several studies have demonstrated that regional differences exist in the strength, overall export efficiency and depth-dependent export efficiency of the biological pump, and that these differences are driven by the structures of pelagic communities, which ultimately determine the magnitude of the biological sequestration of carbon in the deep ocean and sediments (Quéguiner, 2013). KEOPS 2 project offered the unique possibility to address the links between community structures and biogeochemical cycles, in particular as regards the stoichiometry of the particulate organic matter in various conditions of iron fertilization.

In the late 1990’s and early 2000’s a classical view of the effect of iron on the structuration of pelagic ecosystems has progressively emerged in the context of mesoscale iron fertilization experiments. However, while these experiments have resulted, most of the time, in phytoplankton growth enhancement in the surface waters, they failed to demonstrate an enhancement of C export to depth. One the reasons invoked is the artificial context of such experiments where dominant phytoplankton (usually diatoms) would not be representative of natural populations but rather


reflecting opportunist species development (see review in Quéguiner, 2013). In a same way, it has been currently admitted that diatom developing under iron stress are characterized by unusually high C/N/Si ratios (Hutchins & Bruland, 1995; Takeda, 1995). In this context, we have investigated the stoichiometry of the particulate matter produced by different natural plankton communities growing under iron–replete (bloom) or iron–limited (HNLC) conditions.

6.1 Characterization of particulate organic matter (C/N/Si/P stoichiometry)

The complex mesoscale circulation in the iron-fertilized region was characterized by a patchy distribution of particulate matter during the early bloom phase studied during KEOPS 2. Integrated concentrations over 200m ranged from 72.2 to 317.7 mg m−2

for chlorophyll a, 314 to 744 mmol m−2

for biogenic silica (BSi), 1,106 to 2,268 mmol m−2 for particulate organic carbon (POC),

215 to 436 mmol m−2 for particulate organic nitrogen (PON), and 29.3 to 39.0 mmol m−2

for particulate organic phosphorus (POP)(Lasbleiz et al., 2014). Three distinct high biomass areas were identified: the coastal waters of Kerguelen Islands, the easternmost part of the study area in the polar front zone, and the southeastern Kerguelen Plateau (Fig. 20).

Fig. 20: Distribution of depth-integrated total chlorophyll a (a) and contributions of micro-

(b), nano- (c), and picophytoplankton (d) communities to total biomass, as deduced from HPLC data analysis (from Lasbleiz et al., 2014).

As expected from previous artificial and natural iron-fertilization experiments, the iron-fertilized areas were characterized by the development of microphytoplankton dominated by large diatoms, whereas the iron–limited reference area was associated with a low biomass dominated by a mixed (nanoflagellates and diatoms) phytoplankton assemblage (Fig. 21).


Fig. 21: Relative contribution of different plankton groups to the particulate organic carbon biomass (in %) in the photic zone at the HNLC reference site (R) and the bloom stations: A3–2 (Southeastern Plateau bloom), E4W (Final northeasthern meander bloom) and F–L (Polar Front bloom), showing major contribution of nanoflagellates (olive green) under HNLC conditions and diatoms (dark blue) under iron–replete conditions (from Lasbleiz, 2014).

Contrary to our expectations and contrary to most of the previous artificial iron fertilization studies we observed much higher Si:C, Si:N, and Si:P ratios (0.31± 0.16, 1.6± 0.7 and 20.5± 7.9, respectively) in the iron-fertilized areas compared to the iron-limited reference station (0.13, 1.1, and 5.8, respectively) (Fig. 22).

Fig. 22: Si:C ratios of the particulate matter in the HNLC and the fertilized areas (red dotted

line represnts the value of the ‘classical’ Brzeiznski’s ratio).

The second major finding was the patchy response of the elemental composition of phytoplankton communities to large scale natural iron fertilization, which reflected the mosaic of diatom communities under iron–replete conditions (see § 6.3).

Comparison to the previous KEOPS1 cruise also allowed to address the seasonal dynamics of phytoplankton bloom over the southeastern plateau. From particulate organic carbon (POC), particulate organic nitrogen (PON), and BSi evolutions, we showed that the elemental composition of the particulate matter also varies at the seasonal scale. This temporal evolution follows changes in the phytoplankton community structure resulting in major changes in the nutrient stocks progressively leading to silicic acid exhaustion at the end of the productive season.

6.2 Biogeochemical fluxes (C, N, Si)

Iron fertilization was found to stimulate primary production, with integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m−2 d−1 and up to 0.31 d−1, respectively) compared to the HNLC reference site (12 mmol C m−2 d−1 and 0.06 d−1, respectively). Primary production was mainly sustained by nitrate, with f ratio (corresponding to NO3

− uptake/(NO3

− uptake + NH4+ uptake)) lying in the upper end of the observations for the Southern

Ocean (up to 0.9) (Cavagna et al., 2014).

Biogenic silica production rates (ρSi) measured during KEOPS 2 are among the highest reported so far in the Southern Ocean (up to 47.9 mmol m−2

d−1 in the southeastern bloom). Although


significant (10.2 mmol m−2 d−1 on average), dissolution rates (ρDiss) were generally much lower than

ρSi (Fig. 23).

Fig. 23: Vertical distribution of Si uptake (ρSi, a) and biogenic silica dissolution (ρDiss, b)

rates. Open symbols represent the base of the euphotic layer (1% of photosynthetically active radiation) for each station (from Closset et al., 2014).

Fig. 24: Seasonal evolution of the silicon cycle in the mixed layer above the Kerguelen

Plateau (detailed explanations in Closset et al., 2014).

Major nutrient uptake ratios (ρSi:ρC and ρSi:ρN) reflected the dominance by diatoms in the bloom areas. At the bloom onset, decreasing dissolution-to-production ratios indicate that the remineralization of silica could sustain most of the low silicon uptake and that the system progressively shifts toward a silica production regime that is mainly supported by ‘new’ source of silicic acid. By comparing results from KEOPS 2 (spring 2011) and the previous KEOPS 1 (summer 2005), a seasonal evolution of the processes decoupling Si and N cycles in the area was proposed. In this conceptual model, the consumption of H4SiO4 standing stocks occurs only during the growing stage of the bloom when strong net silica production is observed, contributing to higher H4SiO4 depletion relative to NO3

−. The decoupling of H4SiO4 and NO3− is mainly controlled by the more

efficient nitrogen recycling relative to Si via ammonification and/or nitrification within the surface layer, the latter point still to be confirmed. As previously mentioned for the Si and N particulate


stocks, gross Si:N uptake ratios were also unexpectedly higher in the Fe rich regions compared to the high-nutrient low-chlorophyll (HNLC) area, again reflecting the mosaic of diatom communities. Finally, KEOPS 2 results enabled building the first seasonal estimate of the Si biogeochemical budget above the Kerguelen Plateau based on direct measurements (Fig. 24).

6.3 Phytoplankton community structures and diatom activities

One of the major results obtained during KEOPS 2 was the documentation of the spatial heterogeneity of the diatom blooms within the Fe–fertilized area (Fig. 25). This contrasted with the artificial Fe–fertilization experiments usually characterized by lightly silicified opportunist species like Pseudo–nitzschia spp. KEOPS 2 dominant diatoms were highly silicified which, partly, explained the unusually high Si:C and Si:N ratios measured in the bulk particulate matter.

Fig. 25: Synthetic map of the dominant phytoplankton species in terms of carbon biomass (in %) in the photic layer in the HNLC area (station R) and at the bloom stations (Lableiz, 2014).

Fig. 26: Degree of silicification of individual diatom species under various Fe environments (from Lasbleiz, 2014).


The use of PDMPO tracer enabled to observe the degree of silicification of the different component of the diatom communities. Surprisingly the individual responses of diatoms to Fe fertilization were very diverse and did not always reflect the classical paradigm of higher silicification under Fe limitation (Fig. 26).

Finally, the study of the elemental composition (Si:C ratios) of diatoms at the cell level highlighted the variability of cellular responses of different species to iron limitation. The differences in the stoichiometry of the particulate matter between stations would thus be attributed to the specific composition of diatom assemblages and their intrinsic response to environmental conditions, rather than the only iron availability. The lower Si:C ratios of the HNLC area (as compared to the bloom areas) are paradoxically characterized by strongly silicified diatoms, which, however, are not dominant in terms of carbon biomass within the phytoplankton assemblage.

The observation of elevated Si:C diatom ratios in naturally Fe–fertilized environments suggests that, in natural environments, the control of stoichiometric ratios is much more complex than has been commonly accepted as a result of the works of Takeda (1998) and Hutchins and Bruland (1998). The impact of iron availability on the silicification then seems unique to each species of diatom.

6.4 Study of the mesozooplankton structure and functioning during the onset of the Kerguelen bloom

The size structure of the large mesozooplankton community was studied from net samples through Zooscan analyses as well as binocular examinations, and from > 700 µm particles identified from the UVP 5. The mesozooplankton stocks observed at the beginning of the cruise were around 2 g C m−2 both above the plateau and in oceanic waters. Zooplankton biomasses in oceanic waters were maintained in average below 2 g C m−2 all over the study period, except for one station in the Polar Front Zone, whereas zooplankton biomasses were around 4 g C m−2 on the plateau at the end of the cruise (Fig. 8).

The taxonomic composition and stable isotope ratios of size-fractionated zooplankton indicated the strong domination of herbivores. The most remarkable feature during the sampling period was the stronger increase in abundances in the oceanic waters (25 103 to 160 103 ind m−2) than on the plateau (25 103 to 90 103 ind m−2). The size structure and taxonomic distributions revealed a cumulative contribution of various larval stages of dominant copepods and euphausiids particularly in the oceanic waters, with clearly identifiable stages of progress during the pseudo–Lagrangian survey.

The different results during KEOPS2 suggested that the zooplankton community was able to respond to the growing phytoplankton blooms on the plateau earlier than in oceanic waters. Copepods were generally essentially distributed in the first 200 meters. Mesoscale-related initial ephemeral blooms in oceanic waters sustained the reproduction and early development stages of dominant species but individual growth was still food-limited and zooplankton biomass stagnated. On the contrary, zooplankton abundances and biomasses on the plateau were both in a growing phase, with slightly different rates, due to suboptimal conditions of growth and reproduction. Combined with KEOPS 1 data, the present results deliver a consistent understanding of the spring changes in zooplankton abundance and biomass over the Kerguelen Plateau.

Fig. 27 Abundance and biomass values for the different stations visited during KEOPS 2.


6.5 Provisional conclusion

Our observations suggest that the specific response of phytoplankton communities under natural iron fertilization is much more diverse than what has been regularly observed in artificial iron fertilization experiments and that the elemental composition of the bulk particulate matter reflects phytoplankton taxonomic structure rather than being a direct consequence of iron availability. The diatom response to natural Fe fertilization appears much more complex than previously thought, and natural iron fertilization does not necessarily decrease Si:N uptake ratios. This undermines the classical view of the Southern Ocean functioning in the course of the successive glaciation–deglaciation events during the Holocene.

10-blanc-614 keops 2/kerguelen : comparaison plateau océan 2

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