Éditeur(s) : Université des Antilles AREBio Groupe de recherche BIOSPHERES : BIOlogie, Sciences Physiques & Humaines pour les énergies Renouvelables, l
Extrait de : 1er colloque international BIOSPHERES, du 18 au 20 juin 2019. Université des Antilles
Description : Antarctica is a continent of enigmas. Stunning geographic beauty belies its inhospitable climate. Covered a mile thick in ice, it is the world's largest desert. Fossil ferns found in its mountains speak of its prehistory as a tropical rainforest, but now is largely devoid of life. Its most famous inhabitant, the penguin, is thought of as a flightless bird, but soars underwater much as a falcon glides the sky. Perhaps one of the greatest enigmas is the contrast between the terrestrial and marine environments. On land, monochromatic snow and ice support little life, yet the sea teams with life, life that expresses itself with the full rainbow of colors. Color is but one manifestation of chemical ecology. The Antarctic benthos supports an extensive community of predators and prey, competitors and facilitators. A harsh geographic history has contributed to marine diversification and enhanced what we now recognize as a rich flora and fauna, commensurate in some instances with temperate kelp forests and even approaching the richness of tropical marine environments. Not surprisingly, Antarctic benthic ecology is highly dependent on chemical mediation of interspecific interactions, interweaving chemodiversity with biodiversity in a classical yin and yang feedback loop. The evolution of selective chemical defenses facilitates drug discovery research, producing suites of metabolites that inform structure-activity studies and add breadth to bioactivity profiles. This presentation will focus on recent and contextual research from our lab which has demonstrated the potential for new biomedical lead molecules and scaffolds from these difficult to access biological resources.

Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V19067
V19067

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : From 10 to 8 ka BP (thousand years before present), paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere. During this interval, temperatures estimated from proxy data decrease by 0.8 degrees C over Antarctica and 1.2 degrees C over the Southern Ocean. In order to study the causes of this cooling, simulations covering the early Holocene have been performed with the climate model of intermediate complexity LOVECLIM constrained to follow the signal recorded in climate proxies using a data assimilation method based on a particle filtering approach. The selected proxies represent oceanic and atmospheric surface temperature in the Southern Hemisphere derived from terrestrial, marine and glaciological records. Two mechanisms previously suggested to explain the 10-8 ka BP cooling pattern are investigated using the data assimilation approach in our model. The first hypothesis is a change in atmospheric circulation, and the second one is a cooling of the sea surface temperature in the Southern Ocean, driven in our experimental setup by the impact of an increased West Antarctic melting rate on ocean circulation. For the atmosphere hypothesis, the climate state obtained by data assimilation produces a modification of the meridional atmospheric circulation leading to a 0.5 degrees C Antarctic cooling from 10 to 8 ka BP compared to the simulation without data assimilation, without congruent cooling of the atmospheric and sea surface temperature in the Southern Ocean. For the ocean hypothesis, the increased West Antarctic freshwater flux constrainted by data assimilation (+100 mSv from 10 to 8 ka BP) leads to an oceanic cooling of 0.7 degrees C and a strengthening of Southern Hemisphere westerlies (+6 %). Thus, according to our experiments, the observed cooling in Antarctic and the Southern Ocean proxy records can only be reconciled with the reconstructions by the combination of a modified atmospheric circulation and an enhanced freshwater flux.
Climate Of The Past (1814-9324) (Copernicus Gesellschaft Mbh), 2013 , Vol. 9 , N. 2 , P. 887-901

Droits : Author(s) 2013. CC Attribution 3.0 License.
http://archimer.ifremer.fr/doc/00181/29203/27584.pdf
DOI:10.5194/cp-9-887-2013
http://archimer.ifremer.fr/doc/00181/29203/

Éditeur(s) : Elsevier Sci Ltd
Résumé : This study analyses the impact on the oceanic mean state of the evolution of the oceanic component (NEMO) of the climate model developed at Institut Pierre Simon Laplace (IPSL-CM), from the version IPSL-CM4, used for third phase of the Coupled Model Intercomparison Project (CMIP3), to IPSL-CM5A, used for CMIP5. Several modifications have been implemented between these two versions, in particular an interactive coupling with a biogeochemical module, a 3-band model for the penetration of the solar radiation, partial steps at the bottom of the ocean and a set of physical parameterisations to improve the representation of the impact of turbulent and tidal mixing. A set of forced and coupled experiments is used to single out the effect of each of these modifications and more generally the evolution of the oceanic component on the IPSL coupled models family. Major improvements are located in the Southern Ocean, where physical parameterisations such as partial steps and tidal mixing reinforce the barotropic transport of water mass, in particular in the Antarctic Circumpolar Current) and ensure a better representation of Antarctic bottom water masses. However, our analysis highlights that modifications, which substantially improve ocean dynamics in forced configuration, can yield or amplify biases in coupled configuration. In particular, the activation of radiative biophysical coupling between biogeochemical cycle and ocean dynamics results in a cooling of the ocean mean state. This illustrates the difficulty to improve and tune coupled climate models, given the large number of degrees of freedom and the potential compensating effects masking some biases.
Ocean Modelling (1463-5003) (Elsevier Sci Ltd), 2013-12 , Vol. 72 , P. 167-184

Droits : 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00170/28102/26612.pdf
DOI:10.1016/j.ocemod.2013.09.001
http://archimer.ifremer.fr/doc/00170/28102/

Éditeur(s) : HAL CCSD
Résumé : International audience
Cytogenetics provides a unique platform to study in situ structural, functional, and evolutionary aspects of the genome. As such it holds powerful promise in decoding mechanisms and processes of genome architectural changes and their role in organism's diversification and evolution. Since the early 80s, such an approach has been applied to the study of the Antarctic notothenioid fishes. In almost three decades, the cytogenetic information has expanded to cover half of the known species inhabiting the high Antarctic waters. Although started 10 years later, cytogenetic studies of species from the Ross sea region have provided valuable contributions to this bulk of knowledge. Here, we synthesize the currently available cytogenetic information on Antarctic notothenioid fishes from the Ross Sea Region, inclusive of both conventional karyotyping and gene mapping. In addition, new karyotypic data on four species (Lepidonotothen squamifrons, Trematomus scotti, T. loennbergii, and T. lepidorhinus) are provided. In discussing these data, specific focus is made on the patterns and subtleties of cytogenetic diversity at inter- and intra-specific levels aiming at contributing to the refinement of the knowledge of fish diversity in a region, the Ross Sea area, whose primary ecological value is widely recognized.
Hydrobiologia

hal-01544905
https://hal.archives-ouvertes.fr/hal-01544905
DOI : 10.1007/s10750-015-2355-5

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : The distributions of the bio-essential trace element dissolved cobalt (DCo) and the apparent particulate Co (PCo) are presented along the GEOTRACES-A02 deep section from 64(o) N to 50(o) S in the western Atlantic Ocean (longest section of international GEOTRACES marine environment program). PCo was determined as the difference between total cobalt (TCo, unfiltered samples) and DCo. DCo concentrations ranged from 14.7 pM to 94.3 pM, and PCo concentrations from undetectable values to 18.8 pM. The lowest DCo concentrations were observed in the subtropical domains, and the highest in the low-oxygenated Atlantic Central Waters (ACW), which appears to be the major reservoir of DCo in the western Atlantic. In the Antarctic Bottom Waters, the enrichment in DCo with aging of the water mass can be related to suspension and redissolution of bottom sediments a well as diffusion of DCo from abyssal sediments. Mixing and dilution of deep water masses, rather than scavenging of DCo onto settling particles, generated the meridional decrease of DCo along the southward large-scale circulation in the deep western Atlantic. Furthermore, the apparent scavenged profile of DCo observed in the deep waters likely resulted from the persistence of relatively high concentrations in intermediate waters and low DCo concentrations in underlaying bottom waters. We suggest that the 2010 Icelandic volcanic eruption could have been a source of DCo that could have been transported into the core of the Northeast Atlantic Deep Waters. At intermediate depths, the high concentrations of DCo recorded in the ACW linearly correlated with the apparent utilization of oxygen (AOU), indicating that remineralization of DCo could be significant (representing up to 37% of the DCo present). Furthermore, the preferential remineralization of phosphate (P) compared to Co in these low-oxygenated waters suggests a decoupling between the deep cycles of P and Co. The vertical diffusion of DCo from the ACW appears to be a significant source of DCo into the surface waters of the equatorial domain. Summarizing, the dilution due to mixing processes rather than scavenging of DCo and the above-mentioned remineralization could be the two major pathways controlling the cycling of DCo into the intermediate and deep western Atlantic.
Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2014 , Vol. 11 , N. 6 , P. 1561-1580

Droits : Author(s) 2014. CC Attribution 3.0 License.
http://archimer.ifremer.fr/doc/00241/35223/33727.pdf
DOI:10.5194/bg-11-1561-2014
http://archimer.ifremer.fr/doc/00241/35223/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
A new genus and species of deep-sea eelpout (Zoarcidae), Barbapellis pterygalces, is herein described from a single adult female specimen carrying eggs and measuring 204 mm in total length. It was collected on the eastern Antarctic continental slope, off Terre Ad,lie, at ca. 1,200 m depth, on muddy bottom. Barbapellis is placed in the subfamily Gymnelinae and can be distinguished from all other genera by morphological characters unusual in zoarcids as well as by molecular barcoding. The genus is characterized by the presence of a complex system of cephalic skin crests and flaps, especially well developed around the mouth. A new terminology is proposed for the eleven crests and sevenfolds described. The skin folds may be used for foraging on muddy sea bottoms. The genus is also characterized by large, flexible, and highly palmate pectoral fins. The designation of the new genus is discussed.
ISSN: 0722-4060

hal-01544913
https://hal.archives-ouvertes.fr/hal-01544913
DOI : 10.1007/s00300-011-1057-3

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
In this study, the cellular organization of the gill that harbors symbiotic bacteria is described in the thyasirid Thyasira falklandica collected from South Shetlands in Antarctic. Sections of the gills revealed that T. falklandica belongs to the gill type 3, as described by Dufour (Biol Bull, 208:200-212, 2005), with an elongated lateral zone along the frontal-abfrontal axis of the gill Wlaments. The ciliated and intermediary zones looked similar to those described in symbionts-bearing bivalves. The lateral zone is more complex in T. falklandica than in other Thyasiridae already described. Such a zone is composed of four different cell types. Bacteriocytes are abundant in the frontal and abfrontal positions, while the middle part of the lateral zone is occupied mostly by numerous granule cells devoid of bacteria. All along the lateral zone, TEM and SEM observations show some ciliated cells, which are regularly interspersed between bacteriocytes and/or granule cells. Such cells, according to the long double ciliary roots of their cilia, should have a sensory function. Intercalary cells, which have never been observed between bacteriocytes, are restricted to the middle part of the lateral zone where their expansions overlap the adjacent granule cells. Bacterial symbionts occur only extracellularly among long microvilli diVerentiated by the bacteriocytes. They are abundant, usually spherical in shape (around 0.7 m length), and covered by the glycocalix from bacteriocyte microvilli. According to TEM views, the empty vesicles located in the periplasmic space should be sulfur storage, as known for other sulfur-oxidizing symbionts.
ISSN: 0720-213X

hal-00755289
https://hal.univ-antilles.fr/hal-00755289
DOI : 10.1007/s00435-007-0034-4

Éditeur(s) : Yale University
Résumé : Data from a hydrographic section carried out in January-March 1994 offshore from the eastern coast of South America from 50S to 10N, are used to quantify the full-depth exchanges of water between the western boundary currents and the ocean interior. In the upper and intermediate layers, the westward transport associated with the southern branch of the South Equatorial Current was 49 Sv at the time of the cruise. The transports of the central and northern branches in the upper 200 m were 17 Sv and 12 Sv, respectively. After subtraction of the parts that recirculate in the subtropical, subequatorial, and equatorial domains, the fraction of the South Equatorial Current that effectively contributes to the warm water export to the North Atlantic is estimated at 18 Sv. The poleward boundary of the current southern branch is at 31S through the whole thickness of the subtropical gyre, but the latitude of the northern boundary varies from 7 degrees 30'S at the surface to 27S at 1400 m depth. The estimated latitude of its bifurcation into the Brazil Current and North Brazil Undercurrent also varies downward from about 14S at the surface to 28S at a depth of 600 m.In the North Atlantic Deep Water, eastward flows exceeding 10 Sv are observed at 3 degrees -4 degrees of latitude in both hemispheres, at 10S, and at 34S-30S. Between 4S and 17S, a net westward flow with an estimated transport of 19 Sv reinforces the southward deep western boundary current. Cyclonic circulations of Antarctic Bottom Water along the western boundaries of the Argentine and Brazil basins have amplitudes of 15 Sv and 13 Sv, respectively, exceeding those of the interbasin exchanges. The net alongshore transport of this water mass between the hydrographic section and the continental slope reverses to a southward direction from 13S to 27S, probably in relation with an eastward shift of the equatorward near-bottom boundary current at these latitudes.
Journal of Marine Research (0022-2402) (Yale University), 2000-11 , Vol. 58 , N. 6 , P. 1007-1039

Droits : 2000 Yale University
http://archimer.ifremer.fr/doc/2000/publication-803.pdf
DOI:10.1357/002224000763485782
http://archimer.ifremer.fr/doc/00000/803/

Résumé : This expedition was arranged on the initiative of Professor Erik Stensiö of Stockholm to collect fossil specimens for the British Museum (Natural History), the Palaeontologisk Museum, Oslo, and the Hiksmuseum , Stockholm. The chief object was to explore the Old Red Sandstone deposits in the geologically little known Wood Bay area and also in the neighbouring fjords on the north coast. The plans were given in The Polar Record, No. 18, and the final party, which was led by Professor E. A. Steusic with the support of A. Heintz of Oslo, consisted of E. Jarvik (Stockholm), G. Wangsjo (Uppsala), Sven Foyn and K. Aarhus (Oslo), X. Delle (Riga), E. I. White and W. N. Croft (London), J . A. Moy-Thomas (Oxford) and J. Brough (Manchester). C. Andreasen, a sealer from Tromso, brought the collecting party up to twelve. [NOT CONTROLLED OCR]

Droits : Scott Polar Research Institute, Cambridge, UK
http://archimer.ifremer.fr/doc/1940/publication-7341.pdf
http://archimer.ifremer.fr/doc/00000/7341/

Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : The Chile-Argentina Patagonian Cordillera is a natural laboratory to study the interactions between oceanic and continental lithosphere during the subduction of an active spreading ridge beneath a continent. Subduction of the South Chile spreading ridge, which separates the Nazca plate from the Antarctic plate, started around 15–14 Ma at the southern tip of Patagonia. Presently, the southernmost segment of the Chile Ridge enters the Peru-Chile trench at 46°S, at the site of the Chile Triple Junction (CTJ). We review the main events which occurred on land in the CTJ region (46–47°S), related with processes of ridge subduction. We summarize tectonic, sedimentary, and magmatic features in a 30 Ma-to Present chronological table. A preridge subduction stage, from 30 to 15 Ma, is characterized by the onset and growth of Patagonian relief and by a shift from marine to continental detrital sedimentation in the foreland at 20–22 Ma. The change from pre-ridge subduction to ridge subduction is marked on land by a transition from calc-alkaline to alkaline volcanism, at 14–12 Ma, and by the onset of eruption of very large fl ood basalt provinces (future volcanic plateaus) following rapid erosion of the eastern foreland belt. Post-plateau basaltic volcanism (<4 Ma) is coeval with a period of tectonic and morphological rejuvenation during which the eastern foreland of the Cordillera has been affected by extensional/transtensional tectonics. We place these events in the framework of a tectonomagmatic model involving the opening of slab windows due to both slab tear and ridge axis subduction.
Subduction Zone Geodynamics

hal-00421053
https://hal.archives-ouvertes.fr/hal-00421053
DOI : 10.1007/978-3-540-87974-9_12

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Since the first molecular study of the suborder Notothenioidei in 1994, many phylogenetic studies have been published. Among these, those with a sufficient number of taxa have all suggested that the Nototheniidae, as currently defined, is monophyletic only with the inclusion of the Channichthyidae, Artedidraconidae, Bathydraconidae and Harpagiferidae. This is corroborated by more recent studies including more taxa, but in these studies either the number of nuclear markers or the number of taxa included remained low. We obtained sequences for a large sampling covering most nototheniid genera for five markers described previously for other samplings (COI, Rhodopsin retrogene, Pkd1, HECW2, and SSRP1) and one nuclear marker never used before in phylogenetic inference (PPM1d). The topology for the combined analysis of the nuclear coding genes, as well as the topology for SSRP1 (non-coding) and the combined analysis for all markers all support the paraphyly of Nototheniidae, the genus Notothenia (including Paranotothenia) is the sister group of the clade Channichthyidae, Artedidraconidae, Bathydraconidae and Harpagiferidae, and genus Gobionotothen is a sister group to both. As in previous studies, Trematomus, Lepidonotothen and Patagonotothen form a clade that also includes Indonotothenia cyanobrancha. The position of Pleuragramma antarctica, Dissostichus species and Aethotaxis mitopteryx remains unstable and dependant on markers and analyses. We therefore propose the inclusion of the four families of the High Antarctic clade in the Nototheniidae, and their transformation into subfamilies. We transfer Paranotothenia magellanica to the genus Notothenia, as Notothenia magellanica.
ISSN: 1874-7787

hal-01544914
https://hal.archives-ouvertes.fr/hal-01544914
DOI : 10.1016/j.margen.2012.02.003

Éditeur(s) : HAL CCSD Hindawi Publishing Corporation
Résumé : International audience
Two genes, that is, 5S ribosomal sequences and antifreeze glycoprotein (AFGP) genes, were mapped onto chromosomes of eight Antarctic notothenioid fish possessing a X1X1X2X2/X1X2Y sex chromosome system, namely, Chionodraco hamatus and Pagetopsis macropterus (family Channichthyidae), Trematomus hansoni, T. newnesi, T. nicolai, T. lepidorhinus, and Pagothenia borchgrevinki (family Nototheniidae), and Artedidraco skottsbergi (family Artedidraconidae). Through fluorescence in situ hybridization (FISH), we uncovered distinct differences in the gene content of the Y chromosomes in the eight species, with C. hamatus and P. macropterus standing out among others in bearing 5S rDNA and AFGP sequences on their Y chromosomes, respectively. Both genes were absent from the Y chromosomes of any analyzed species. The distinct patterns of Y and non-Y chromosome association of the 5S rDNA and AFGP genes in species representing different Antarctic fish families support an independent origin of the sex heterochromosomes in notothenioids with interesting implications for the evolutionary/adaptational history of these fishes living in a cold-stable environment.
ISSN: 2314-6133

hal-01544911
https://hal.archives-ouvertes.fr/hal-01544911
DOI : 10.1155/2013/243938

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The teleost suborder Notothenioidei is restricted to the Southern Ocean and has been described as a species flock spanning the whole of it. Within the suborder, the subfamily Trematominae is important for coastal Antarctic ecosystems. The eleven Trematomus species occupy a large range of ecological niches. The genus is monophyletic if the genus Pagothenia (two additional species) and Cryothenia amphitreta. also nested within it, are included. Although the Trematominae have received much interest, the relationships among these fourteen species are still unclear. Several recent studies have tried to resolve these interrelationships; however no complete and clear picture has emerged, probably because of the use of a low number of insufficiently variable markers. The only common results places T. scotti as the sister-group of the rest of the subfamily and T. loennbergi close to T. lepidorhinus. We use here more variable markers. Four nuclear markers, two of which are new, and a mitochondrial marker for the biggest trematomine sampling ever gathered (14 species, 78 specimens). We found that several nuclear haplotypes are shared by several species (mostly in very closely related species). The haplotype patterns coupled with the cytogenetics of the subfamily suggest that a phenomenon of incomplete lineage sorting (ILS) is likely to be at play. Using a calibration linked to fossil evidence, we evaluate the relative ages of each clade within the Trematominae to assess the proximity of the speciation events to one another. The main trematomine diversification was recent and sudden.
ISSN: 1055-7903

hal-01544915
https://hal.archives-ouvertes.fr/hal-01544915
DOI : 10.1016/j.ympev.2012.05.032

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : Three methods for automatic detection of mesoscale coherent structures are applied to Sea Level Anomaly (SLA) fields in the South Atlantic. The first method is based on the wavelet packet decomposition of the SLA data, the second on the estimation of the Okubo-Weiss parameter and the third on a geometric criterion using the winding-angle approach. The results provide a comprehensive picture of the mesoscale eddies over the South Atlantic Ocean, emphasizing their main characteristics: amplitude, diameter, duration and propagation velocity. Five areas of particular eddy dynamics were selected: the Brazil Current, the Agulhas eddies propagation corridor, the Agulhas Current retroflexion, the Brazil-Malvinas confluence zone and the northern branch of the Antarctic Circumpolar Current (ACC). For these areas, mean propagation velocities and amplitudes were calculated. Two regions with long duration eddies were observed, corresponding to the propagation of Agulhas and ACC eddies. Through the comparison between the identification methods, their main advantages and shortcomings were detailed. The geometric criterion presents the best performance, mainly in terms of number of detections, duration of the eddies and propagation velocities. The results are particularly good for the Agulhas Rings, which have the longest lifetimes of all South Atlantic eddies.
Ocean Science (1812-0784) (Copernicus Gesellschaft Mbh), 2011 , Vol. 7 , N. 3 , P. 317-334

Droits : Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. EGU
http://archimer.ifremer.fr/doc/00039/15051/12378.pdf
DOI:10.5194/os-7-317-2011
http://archimer.ifremer.fr/doc/00039/15051/

Éditeur(s) : Elsevier
Résumé : A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600-1050dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200-2050dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW` mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7Sv across 16 degrees N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow. (C) 2009 Elsevier Ltd. All rights reserved.
Deep Sea Research Part I: Oceanographic Research Papers (0967-0637) (Elsevier), 2009-10 , Vol. 56 , N. 10 , P. 1615-1632

Droits : 2009 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6815.pdf
DOI:10.1016/j.dsr.2009.06.002
http://archimer.ifremer.fr/doc/00000/6815/

Éditeur(s) : Elsevier Science Bv
Résumé : For many trace elements, continental margins are the location of intense exchange processes between sediment and seawater, which control their distribution in the water column, but have yet to be fully understood. In this study, we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium. We determined dissolved and total dissolvable (TD) concentrations for REE and well-established tracers of fluid seepage (CH4, TDFe, TDMn), and Nd isotopic compositions in seawater samples collected above cold seeps and a reference site (i.e. away from any fluid venting area) from the Niger Delta margin. We also analyzed cold seep authigenic phases and various core-top sediment fractions (pore water, detrital component, easily leachable phases, uncleaned foraminifera) recovered near the hydrocast stations. Methane, TDFe and TDMn concentrations clearly indicate active fluid venting at the studied seeps, with plumes rising up to about 100 m above the seafloor. Depth profiles show pronounced REE enrichments in the non-filtered samples (TD concentrations) within plumes, whereas filtered samples (dissolved concentrations) exhibit slight REE depletion in plumes relative to the overlying water column and display typical seawater REE patterns. These results suggest that the net flux of REE emitted into seawater at cold seeps is controlled by the presence of particulate phases, most probably Fe-Mn oxyhydroxides associated to resuspended sediments. At the reference site, however, our data reveal significant enrichment for dissolved REE in bottom waters, that clearly relates to diffusive benthic fluxes from surface sediments. Neodymium isotopic ratios measured in the water column range from epsilon(Nd) similar to-15.7 to -10.4. Evidence that the epsilon(Nd) values for Antarctic Intermediate waters (AAIW) differed from those reported for the same water mass at open ocean settings shows that sediment/water interactions take place in the Gulf of Guinea. At each site, however, the bottom water epsilon(Nd) signature generally differs from that for cold seep minerals, easily leachable sediment phases, and detrital fractions from local sediments, ruling out the possibility that seepage of methane-rich fluids and sediment dissolution act as a substantial source of dissolved Nd to seawater in the Gulf of Guinea. Taken together, our data hence suggest that co-precipitation of Fe-Mn oxyhydroxide phases in sub-surface sediments leads to quantitative scavenging of dissolved REE at cold seeps, preventing their emission into bottom waters. Most probably, it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine Nd cycle at the Niger Delta margin. (C) 2011 Elsevier B.V. All rights reserved.
Earth And Planetary Science Letters (0012-821X) (Elsevier Science Bv), 2011-12 , Vol. 312 , N. 3-4 , P. 443-452

Droits : 2011 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00066/17754/15571.pdf
DOI:10.1016/j.epsl.2011.10.008
http://archimer.ifremer.fr/doc/00066/17754/

Éditeur(s) : Gauthier-Villars
Résumé : Moored current measurements carried out from 31 March 1990 to 15 September 1991 in two stages at a point (near 6 degrees N) located over the mid-continental slope off French Guiana are presented. Six current meters were positioned between 200 and 2700 m depth. Upper level mean current data showed a northwestward flowing North Brazil Current (NBC) with mean velocity values decreasing from 10 cm/s in the range 200-250 m to almost zero at 800 m depth, the level of the Antarctic Intermediate Waters. In the range 500-800 m, the current reversed in spring in the presence of the southeastward Western Boundary Under Current (WBUC); the mean velocity from February to June 1991 is around 2 cm/s. Deep currents over the continental rise show a strong southeastward Deep Western Boundary Current extending from around 1000 m depth to the bottom (3000 m depth in this case) with mean core speeds of 20 cm/s at 2000-2070 m depth. Transport estimates based on these data and a few Pegasus sections for the mean vertical and lateral extensions of the DWBC yield a value of 21 x 10(6) m(3)/s at that location. Low-frequency current fluctuations were dominated by a well-defined 50- to 70-day period oscillation with peak-to-peak northwestward velocity amplitude of around 90 cm/s at the upper level. The mean vertical eddy kinetic energy distribution showed an abrupt decrease of the energy down to 800 m depth and a slight decrease below and down to the bottom.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1994 , Vol. 17 , N. 4 , P. 345-354

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00098/20897/18510.pdf
http://archimer.ifremer.fr/doc/00098/20897/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Chile Triple junction is a natural laboratory to study the interactions between magmatism and tectonics during the subduction of an active spreading ridge beneath a continent. The MLBA plateau (Meseta del Lago Buenos Aires) is one of the Neogene alkali basaltic plateaus located in the back-arc region of the Andean Cordillera at the latitude of the current Chile Triple junction. The genesis of MLBA can be related with successive opening of slabs windows beneath Patagonia: within the subducting Nazca Plate itself and between the Nazca and Antarctic plates. Detailed Ar-40/Ar-39 dating and geochemical analysis of bimodal magmatism from the western flank of the MLBA show major changes in the back-arc magmatism. which occurred between 14.5 Ma and 12.5 Ma with the transition from calc-alkaline lavas (Cerro Plomo) to alkaline lavas (MLBA) in relation with slab window opening. In a second step, at 4-3 Ma, alkaline felsic intrusions were emplaced in the western flank of the MLBA coevally with the MLBA basalts with which they are genetically related. These late OIB-like alkaline to transitional basalts were generated by partial melting of the subslab asthenosphere of the subducting Nazca plate during the opening of the South Chile spreading ridge-related slab window. These basalts differentiated with small amounts of assimilation in shallow magma chambers emplaced along transtensional to extensional zones. The close association of bimodal magmatism with extensional tectonic features in the western MLBA is a strong support to the model of Patagonian collapse event proposed to have taken place between 5 and 3 Ma as a consequence of the presence of the asthenospheric window (SCR-1 segment of South Chile Ridge) below the MLBA area.
ISSN: 0377-0273

hal-00475648
https://hal.archives-ouvertes.fr/hal-00475648
DOI : 10.1016/j.jvolgeores.2009.11.022

Éditeur(s) : Royal Soc
Résumé : Since its description from the Galapagos Rift in the mid-1980s, Archinome rosacea has been recorded at hydrothermal vents in the Pacific, Atlantic and Indian Oceans. Only recently was a second species described from the Pacific Antarctic Ridge. We inferred the identities and evolutionary relationships of Archinome representatives sampled from across the hydrothermal vent range of the genus, which is now extended to cold methane seeps. Species delimitation using mitochondrial cytochrome c oxidase subunit I (COI) recovered up to six lineages, whereas concatenated datasets (COI, 16S, 28S and ITS1) supported only four or five of these as clades. Morphological approaches alone were inconclusive to verify the identities of species owing to the lack of discrete diagnostic characters. We recognize five Archinome species, with three that are new to science. The new species, designated based on molecular evidence alone, include: Archinome levinae n. sp., which occurs at both vents and seeps in the east Pacific, Archinome tethyana n. sp., which inhabits Atlantic vents and Archinome jasoni n. sp., also present in the Atlantic, and whose distribution extends to the Indian and southwest Pacific Oceans. Biogeographic connections between vents and seeps are highlighted, as are potential evolutionary links among populations from vent fields located in the east Pacific and Atlantic Oceans, and Atlantic and Indian Oceans; the latter presented for the first time.
Proceedings Of The Royal Society B-biological Sciences (0962-8452) (Royal Soc), 2013-11 , Vol. 280 , N. 1770 , P. 1-9

Droits : 2013 The Author(s) Published by the Royal Society. All rights reserved.
http://archimer.ifremer.fr/doc/00157/26814/24961.pdf
DOI:10.1098/rspb.2013.1876
http://archimer.ifremer.fr/doc/00157/26814/