Éditeur(s) : Gauthier-Villars
Résumé : The distribution and behaviour of nutrients (nitrate, nitrite, ammonia, silicate and phosphate) have been examined over the course of a year in two major Scottish estuaries, the Forth and Tay. Maximum concentrations of nitrate and silicate in both estuaries occur in winter, when mixing is conservative. By contrast maximum phosphate, ammonia and nitrite concentrations (notably in the Forth) are observed in summer, these are related to lower oxygen concentrations both within the water column and sediments. Phosphate, ammonia and nitrite concentrations are high in the Forth relative to the Tay. Phosphate behaviour in plots for both estuaries show some common features including removal at low salinity, mid estuary inputs and simple dilution at high salinity. The results are interpreted on the basis of removal onto particles at low salinity followed by desorption at higher salinity together with an input from sediment porewaters. In the Forth the phosphate flux from sediments during the summer is estimated to be 1.98 +/- 1.25 mmol m-2 day-1. At this time the river input of phosphorus is only 10- 14 % of the mid estuary input. Under low river flow conditions in summer a large turbidity maximum (400-500 mg l-1 suspended solids) develops in the Forth estuary and this results in removal of phosphate. Removal is less dramatic in the Tay estuary as the turbidity is wind generated and therefore rarely exceeds 100 mg 1-1. Water quality in the Forth (as defined by the occurrence of low dissolved oxygen concentrations and the presence of species such as ammonia and nitrite) is inferior to that of the Tay. Relative to contaminated estuaries however concentrations in both estuaries are low. By virtue of its high fresh water discharge the Tay is a more significant source of nitrate to the North Sea during the winter than is the Forth. In the Forth bacterial mineralisation and nitrification of organic nitrogen occurs in the upper estuary, this results in an input of nitrate and consumption of dissolved oxygen. Further downstream broad mid estuarine peaks of nitrite and ammonia are observed indicative of a benthic source. Estimates of this source for ammonia and nitrite are 19-44 and 3.9-8.1 mmol m-2 day-1 respectively. In winter the main source of nitrogen to the Forth is from the river but in summer mid estuarine sources dominate. In the outer Tay a peak in dissolved ammonia is estimated to represent an input of 0.5-1.1 tonnes N day-1, this is attributed to sewer inputs from Dundee.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 3 , P. 261-277

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00100/21160/18779.pdf
http://archimer.ifremer.fr/doc/00100/21160/

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
Résumé : International audience
Previous studies have reported respiratory, cardiac and muscle changes at rest in triathletes 24 h after completion of the event. To examine the effects of these changes on metabolic and cardioventilatory variables during exercise, eight male triathletes of mean age 21.1 (SD 2.5) years (range 17-26 years) performed an incremental cycle exercise test (IET) before (pre) and the day after (post) an official classic triathlon (1.5-km swimming, 40-km cycling and 10-km running). The IET was performed using an electromagnetic cycle ergometer. Ventilatory data were collected every minute using a breath-by-breath automated system and included minute ventilation (V(E)), oxygen uptake (VO2), carbon dioxide production (VCO2), respiratory exchange ratio, ventilatory equivalent for oxygen (V(E)/VO2) and for carbon dioxide (V(E)/VCO2), breathing frequency and tidal volume. Heart rate (HR) was monitored using an electrocardiogram. The oxygen pulse was calculated as VO2/HR. Arterialized blood was collected every 2 min throughout IET and the recovery period, and lactate concentration was measured using an enzymatic method. Maximal oxygen uptake (VO2max) was determined using conventional criteria. Ventilatory threshold (VT) was determined using the V-slope method formulated earlier. Cardioventilatory variables were studied during the test, at the point when the subject felt exhausted and during recovery. Results indicated no significant differences (P > 0.05) in VO2max [62.6 (SD 5.9) vs 64.6 (SD 4.8) ml x kg(-1) x min(-1)], VT [2368 (SD 258) vs 2477 (SD 352) ml x min(-1)] and time courses of VO2 between the pre- versus post-triathlon sessions. In contrast, the time courses of HR and blood lactate concentration reached significantly higher values (P < 0.05) in the pre-triathlon session. We concluded that these triathletes when tested 24 h after a classic triathlon displayed their pre-event aerobic exercise capacity, bud did not recover pretriathlon time courses in HR or blood lactate concentration.
EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY

hal-00720432
https://hal.univ-antilles.fr/hal-00720432
https://hal.univ-antilles.fr/hal-00720432/document
https://hal.univ-antilles.fr/hal-00720432/file/Article_2.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We report trace element concentrations of silicate phases in chondrules from LL3 ordinary chondrites Bishunpur and Semarkona. Results are similar to previously reported data for carbonaceous chondrites, with rare earth element (REE) concentrations increasing in the sequence olivine < pyroxene < mesostasis, and heavy REE (HREE) being enriched by 1–2 orders of magnitude (CI-normalized) relative to light REE (LREE) in ferromagnesian silicates, although no single olivine with very large LREE/HREE fractionation has been found. On average, olivine in type II chondrules is poorer in refractory lithophile incompatible elements (such as REE) than its type I counterpart by a factor of ∼2. This suggests that olivine in type I and II chondrules formed by batch and fractional crystallization, respectively, implying that type II chondrules formed under faster cooling rates (>∼10 K/h) than type I chondrules. Appreciable Na concentrations (3–221 ppm) are measured in olivine from both chondrule types; type II chondrules seem to have behaved as closed systems, which may require chondrule formation in the vicinity of protoplanets or planetesimals. At any rate, higher solid concentrations in type II chondrule forming regions may explain the higher oxygen fugacities they record compared to type I chondrules. Type I and type II chondrules formed in different environments and the correlation between high solid concentrations and/or oxygen fugacities with rapid cooling rates is a key constraint that chondrule formation models must account for.
ISSN: 0016-7037

hal-01174084
https://hal.archives-ouvertes.fr/hal-01174084
DOI : 10.1016/j.gca.2015.02.005

Éditeur(s) : Edp Sciences S A
Résumé : This study was designed to measure responses of four-year-old black-lip pearl oysters (Pinctada margaritifera) to different temperatures and food concentrations and to identify the energy requirements of each sex. Oysters were fed a monospecific microalgal diet of Isochrysis affinis galbana (T-iso). Measurements of oxygen consumption and ingestion rates were carried out at 24 degrees C and 27 degrees C and at two algal (T-iso) concentrations: 5000 and 30 000 cell ml(-1). Glycogen content in adductor muscle, absorption efficiency and scope for growth were also estimated. Females and males responded differently to environmental factors, with food level being the most influential parameter. Oxygen consumption and absorption efficiency were significantly higher in females than in males, but males had significantly higher glycogen content than females. At high food concentration, glycogen content, ingestion rate, oxygen consumption, and scope for growth were significantly higher than at the low food concentration. Only absorption efficiency was significantly higher at the low food concentration. Oxygen consumption was significantly higher at 27 degrees C than at 24 degrees C. These results indicate that females and males have different bioenergetic functioning and that energy demands for reproduction are higher in females.
Aquatic Living Resources (0990-7440) (Edp Sciences S A), 2013-07 , Vol. 26 , N. 3 , P. 263-271

Droits : EDP Sciences, IFREMER, IRD 2013
http://archimer.ifremer.fr/doc/00157/26855/24980.pdf
DOI:10.1051/alr/2013059
http://archimer.ifremer.fr/doc/00157/26855/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
In this work, we have studied quenching of the fluorescence of two well-known oxygen probes, 1-pyrene butyric acid (PBA) and tris(2,2'-bipyridine)ruthenium ([Ru(bpy)(3)](2+)) by reactive oxygen species (superoxide anion, nitric oxide derivative, hydrogen peroxide) and by the O(2) molecule. Both, time-resolved and steady state fluorescence measurements were performed in solution (ethanol, dimethyl sufoxide, water) and in micelles of Sodium Dodecyl Sulfate that serve as a model for membrane-containing biological structures. We have found that only the free radicals and O(2) can actively quench for the two probes, but not the diamagnetic H(2)O(2). Our data correspond to the classical Stern-Volmer equation. H(2)O(2) has an effect only at high molar concentrations (>0.1 M). In contrast, effective concentrations of free radicals and O(2) that lead to quenching are in millimolar range. In conclusion, our methods allows for detecting global ROS that are small free radicals without interference from the reactive hydroxyl radical. Our data suggest that the method can be used for the quantification of ROS in individual living cells based on the measurement of fluorescence lifetime of those probes
ISSN: 1053-0509

hal-01326234
https://hal.archives-ouvertes.fr/hal-01326234
DOI : 10.1007/s10895-008-0425-z

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
High sea surface temperature accompanied by high levels of solar irradiance is responsible for the disruption of the symbiosis between cnidarians and their symbiotic dinoflagellates from the genus Symbiodinium. This phenomenon, known as coral bleaching, is one of the major threats affecting coral reefs around the world. Because an important molecular trigger to bleaching appears related to the production of reactive oxygen species (ROS), it is critical to understand the function of the antioxidant network of Symbiodinium species. In this study we investigated the response of two Symbiodinium species, from contrasting environments, to a chemically induced oxidative stress. ROS produced during this oxidative burst reduced photosynthesis by 30 to 50% and significantly decreased the activity of superoxide dismutase. Lipid peroxidation levels and carotenoid concentrations, especially diatoxanthin, confirm that these molecules act as antioxidants and contribute to the stabilization of membrane lipids. The comparative analysis between the two Symbiodinium species allowed us to highlight that Symbiodinium sp. clade A temperate was more tolerant to oxidative stress than the tropical S. kawagutii clade F. These differences are very likely a consequence of adaptation to their natural environment, with the temperate species experiencing conditions of temperature and irradiance much more variable and extreme.
ISSN: 0140-7791

hal-01546161
https://hal.archives-ouvertes.fr/hal-01546161
DOI : 10.1111/pce.12825

Éditeur(s) : Université Bordeaux 1
Résumé : The mercury cycle was explored in the Petit-Saut reservoir / Sinnamary Estuary continuum in French Guiana. Main processes involve (i) photo-induced reduction, (ii) adsorption and desorption at the particle surfaces, (iii) methylating bacterial activity, (iv) precipitation and dissolution of iron oxyhydroxides and sulfides. Sources of mercury to the Petit-Saut reservoir consist of the partly impacted river-tributaries, the atmospheric deposition and the flooded soils or vegetation. Once into the reservoir, divalent mercury undergoes a large spectrum of transformations including speciation and phase changes. We, here, probe these processes and demonstrate that the Petit-Saut reservoir behaves as a privileged site for atmospheric recycling and in situ methylation. At the air / water interface, the mercury evasion exceeds by 50 % the direct atmospheric deposition. The in situ monomethylmercury (MMHg) production mostly occurs at the water-column chemocline and near the benthic interface. It reaches, for the whole reservoir, 8.1 moles yr-1 which corresponds to a 0.06 % d-1 methylation rate. We calculated that the 2003/04 period MMHg outputs from the reservoir to the Sinnamary Estuary averaged 13.5 moles yr-1 while the inputs were 5.4 moles yr-1. The dynamic Sinnamary Estuary is the genuine geochemical reactor of the continuum. There, the divalent mercury undergoes rapid yet profound partitioning among phases, recycling to the atmosphere and methylation processes. Those mostly originate from the long-scale oxygen paucity of the dam discharged waters. The expression of marked redox gradients and the intense organic matter turnover enhance the production of methylable inorganic mercurial species and tend to favor the sulfate reducing bacteria (methylating agents) activity. As a result, the dynamic Sinnamary Estuary exports 60 % more MMHg than it does import: 27 versus 17 moles yr-1. Further at large, in the saline estuary, we determined: (i) a non conservative behavior of dissolved (< 0.2 µm) mercury, (ii) a lowering of the mercury level of particles during mixing with the Amazon plume and (iii) a gradual dilution of the estuarine mercury concentrations by oceanic waters.
La retenue de Petit-Saut et, à l'aval, l'estuaire du Sinnamary sont deux centres d'altération du cycle naturel du mercure. Les processus sont, entre autres, (i) la photoréduction, (ii) la sorption / désorption en surface des particules, (iii) l'activité méthylante des bactéries, (iv) la dissolution / précipitation des oxyhydroxydes et des sulfures de fer. Les sources de mercure vers la retenue sont variées. Elles regroupent, en premier lieu, les affluents (partiellement orpaillés), l'atmosphère, les sols et la végétation ennoyés. Dans la colonne d'eau, les formes divalentes du mercure subissent un train complet de transformations couplant changements de phase et de spéciation. Nos résultats illustrent ces processus et démontrent que la retenue constitue un site privilégié de recyclage vers l'atmosphère et de méthylation. A l'interface air / eau, les exports en mercure de la retenue excèdent de 50 % le dépôt atmosphérique. La production endogène de monométhylmercure (MMHg) a lieu dans des sites particuliers : la chemocline et l'interface benthique. Elle atteint pour l'ensemble de la retenue 8,1 moles a-1 soit un taux de méthylation de 0,06 % j-1. On estime que la retenue exporte vers l'estuaire du Sinnamary 13,5 moles a-1 de MMHg alors qu'elle n'importe que 5,4 moles a-1. L'estuaire dynamique du Sinnamary constitue le véritable réacteur chimique du système fonctionnant en liaison avec celui de la retenue. Le mercure y décrit un cycle rapide aux processus de partition, de recyclage et de méthylation marqués. Ces processus résultent de l'oxygénation incomplète et durable des masses d'eau anoxiques exportées par la retenue de Petit-Saut. L'expression de gradients rédox prononcés conjuguée à un intense recyclage de la matière organique y favorise la production de formes méthylables de mercure ainsi que l'activité des bactéries sulfatoréductrices (agents de la méthylation). C'est pourquoi, l'estuaire dynamique du Sinnamary exporte 60 % plus de MMHg qu'il n'importe : 27 contre 17 moles a-1. Plus en aval, dans l'estuaire salin, nous avons mis en évidence : (i) un comportement non conservatif du mercure dissous, (ii) un appauvrissement du mercure des particules suite au mélange avec le panache de l'Amazone et (iii) une dilution des concentrations par les masses d'eau océaniques.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/these-1508.pdf
http://archimer.ifremer.fr/doc/00000/1508/

Éditeur(s) : HAL CCSD Mineralogical Society of America
Résumé : International audience
The effect of trace concentrations of Ti on the rate and mechanism of hydrogen diffusion in pure forsterite was investigated experimentally. Forsterite doped with 350–400 ppm Ti (predominantly octahedral Ti3+, minor tetrahedral Ti4+) was prepared by diffusing Ti into pure synthetic forsterite at high temperature (1500 °C), very low oxygen fugacity (~QFM-5) at atmospheric pressure. The Ti-doped forsterite was then diffusively hydroxylated in a piston-cylinder apparatus at much lower temperatures (650–1000 °C) and higher oxygen fugacities, at 1.5–2.5 GPa, with chemical activities buffered by forsterite-enstatite or forsterite-periclase and partial pressure of H2O equal to total pressure. This produced hydrogen concentration-distance profiles of several hundred micrometers in length. Diffusion of hydrogen through the Ti-doped forsterite, even at very high Embedded Image , does not lead to redox re-equilibration of the high Ti3+/ΣTi ratio set during the synthesis of the starting material at extremely reducing conditions—the metastable point defects are partially preserved.Three main hydroxylated point defects are observed; hydroxyl is associated with Ti4+ (titano-clinohumite point defects), Ti3+ (and possibly other trivalent cations), and M-site vacancies. Concentration-distance profiles represent an interplay between diffusion and reaction (i.e., site rearrangement) to form the observed point defects. In all experiments, the concentration-distance profiles of the hydroxylated Ti defects coincide with the concentration-distance profiles of the M-site vacancy substitution, with the same crystallographic anisotropy. This suggests that the macroscopic movement of hydrogen through the crystal is due to one diffusion mechanism (the diffusion of hydroxylated M-site vacancies). The net H diffusion coefficient [logD(ΣH)], between 650–1000 °C, is Embedded Image where the values of logD0(ΣH) parallel to [100] and [001] directions are −3.0 ± 0.4 and −2.2 ± 0.4, respectively; diffusion is therefore around one order of magnitude faster along the c axis than along the a axis. The diffusion of hydrogen is slightly faster in Ti-doped forsterite than in pure forsterite. There is no effect of chemical activity or oxygen fugacity on the rate of diffusion. Hydrogen diffusion profiles represent a complex interplay between the movement of H through the crystal lattice and point-defect reactions to maintain charge balance.
ISSN: 0003-004X

hal-01467402
https://hal.archives-ouvertes.fr/hal-01467402
DOI : 10.2138/am-2016-55681571

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study presents the geochemical composition of superficial sediment under oxic and suboxic bottom water conditions along the Chilean continental margin (SE Pacific), where evidence for benthic chemosynthetic activity associated with diffuse seeping of chemically reduced fluids has been reported. The exploration was carried out at: (1) the Chilean Triple Junction (CTJ), at a water depth of ∼2900 m, with the additional indication of hydrothermal activity near a methane-rich cold-seep area (46°S) (German et al., 2010); and (2) the El Quisco methane seep site (EQSS), at ∼340 m water depth (33°S) (Melo et al., 2007; Krylova et al., 2014). While the deeper CTJ is located within an oxic environment (dissolved oxygen in the bottom waters: 164 μM), the shallower EQSS lies within a suboxic environment (dissolved oxygen in bottom water: 23 μM), located within the lower limit of the SE Pacific oxygen minimum zone (OMZ).Pore water from short cores was analyzed for dissolved major, minor, and trace elements (Cl, Na, Mg, K, Ca, Sr, Si, B, P, Ba, Pb, Mn, Fe, Cd, U, and Mo), δ13DIC, sulfide, sulfate, and methane. The solid sediment fraction was likewise analyzed for total organic carbon (TOC), metals, and redox potential. Elevated sediment temperatures were found in superficial sediments (5–13 °C) at the CTJ site, which could be due to warm fluids associated with the proximity of the ridge, where hydrothermal vents may occur. Reduced fluids were also present here, indicated by higher Mn fluxes toward the water column even in oxidized sediments (RPD > 8 cm), which contrasted with the lower fluxes in reduced sediments of the EQSS site (RPD ∼ 2 cm). 13C-depleted DIC, anomalously low pore water Cl (∼15 ppb), and low concentrations of other major elements may be the result of dilution by fluid seeping and precipitation of major elements, producing authigenic enrichment (Ca, Mg, Sr). The fluid could also: (a) be diluted by pure water produced during methane hydrate dissociation, as observed in other cold-seep areas; and (b) correspond to clay mineral dehydration, as reported in plate subduction systems. The reducing conditions established at the CTJ conduct the Cd enrichment at a similar magnitude of that seen at the shallower suboxic site (EQSS). Evidence of chimney or vent fauna was not observed. At the EQSS, higher TOC and total sulfide contents were consistent with enhanced deposition of organic matter and reducing conditions developed in the OMZ, favoring the authigenic enrichment of Cd, U and Pb. The geochemical evidence, based only on methane concentrations and δ13DIC, is insufficient to establish the presence of methane seeps, as previously reported.
ISSN: 0079-6611

hal-01412700
https://hal.archives-ouvertes.fr/hal-01412700
DOI : 10.1016/j.pocean.2016.09.002

Éditeur(s) : HAL CCSD Ocean Drilling Programm
Résumé : This paper provides a summary of postcruise scientific results from Ocean Drilling Program (ODP) Leg 209 available to date, building upon shipboard observations and syntheses summarized in the Leg 209 Initial Results volume. During Leg 209, 19 holes were drilled at 8 sites along the Mid-Atlantic Ridge from 14°43´ to 15°44´N, mainly in residual mantle peridotite intruded by gabbroic rocks, in order to understand the tectonic and structural processes responsible for formation of oceanic lithosphere with abundant residual peridotite exposed on the seafloor coupled with a relatively low proportion of volcanic rocks. Based on proportions of recovered lithologies, the entire area may be underlain by mantle peridotite with ~20%–40% gabbroic intrusions and impregnations. Impregnated peridotites with olivine + two pyroxenes + plagioclase + spinel that apparently formed in equilibrium probably record crystallization from primitive mid-ocean-ridge basalt at pressures of 0.5–0.6 GPa. Metamorphic equilibria record isobaric cooling to ~1100°C at this pressure. Thus, the conductively cooled thermal boundary layer beneath the Mid-Atlantic Ridge in this region is >15 km thick. Combined crystallization and reaction with residual peridotite formed a series of impregnated peridotites recording increasing Na content at nearly constant Mg#; this process could explain some of the variation in fractionation-corrected Na (e.g., Na = 8.0) observed in mid-ocean-ridge basalts. Clinopyroxene textures and compositions record such impregnation processes, and they are particularly well documented for Site 1274. Other Leg 209 gabbroic rocks formed from extensive crystallization of highly evolved melts, indicating that a substantial proportion of melt entering the thermal boundary layer crystallizes entirely beneath the seafloor, with no volcanic equivalent. Alteration of peridotites occurred over a range of temperatures and is the result of three distinct processes: rock-dominated serpentinization with formation of brucite in olivine-rich lithologies, fluid-dominated serpentinization with formation of magnetite and no brucite, and fluid-dominated talc alteration with addition of SiO2 as well as H2O and oxygen. The latter two processes also exhibit detectable trace element metasomatism that is distinct in its character from the igneous impregnation described in the previous paragraph. Microstructures show that most residual peridotites were not ductilely deformed at temperatures less than ~1200°C. Structural and paleomagnetic data require tectonic rotations of relatively undeformed blocks; some rotations probably exceeded 60° around nearly horizontal axes parallel to the rift axis. Rotations occurred along several generations of high-temperature mylonitic shear zones extending deeper than 15 km depth and numerous faults at lower temperature. Early formed shear zones and faults were passively rotated around later features; such a process could have produced low-angle fault surfaces without slip on low-angle faults. This region provides end-member examples of processes that are common at many or most slow-spreading ridges. Osmium isotope ratios indicate an ancient history of depletion for residual peridotites from the 14°–16°N region along the Mid-Atlantic Ridge. Though depleted Os isotope ratios in peridotite have been reported elsewhere along the global ridge system, the values from this region are among the most depleted. In general, Os isotope ratios from mid-ocean-ridge basalts are systematically more radiogenic than Os isotope ratios from ridge peridotite samples, suggesting a polygenetic heterogeneous source for mid-ocean-ridge basalts. Geochemical studies of zircons from Leg 209 gabbroic rocks and impregnated peridotites, together with other ridge and arc-related zircons, indicate that ridge zircons have systematically lower fractionation-corrected U and Th concentrations compared to arc zircons. This observation provides a tool for interpreting the tectonic provenance of ancient detrital zircons and indicates an arclike provenance for Hadean detrital zircons. Geobiological studies and aerobiological studies were also undertaken during Leg 209. The geobiological work found no measurable microbial enhancement of olivine dissolution rate, possibly because the samples from Leg 209 were sterile. The aerobiological study determined that dust from North Africa, collected from the derrick of the JOIDES Resolution during Leg 209, contains a variety of abundant microorganisms.
Proceedings ODP, scientific results, 209

hal-00407966
https://hal.archives-ouvertes.fr/hal-00407966
DOI : 10.2973/odp.proc.sr.209.001.2007

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The diffusion of titanium along with Ni, Co and Mn in pure synthetic forsterite has been studied as a function of temperature, oxygen fugacity, crystallographic orientation and chemical potentials in the four-component system MgO–SiO2–TiO2–TiO1·5. In over 100 different experimental conditions, no Ti diffusion profiles with the classical shape of the error function were observed. Instead, the profiles vary between ‘stepped’ at high fO2 (probably owing to diffusion on octahedral sites and trapping in tetrahedral sites), to hockey-stick shapes at low fO2 owing to concentration-dependent diffusion. The profile shapes vary systematically between these end-members according to oxygen fugacity. These profile shapes are also reproduced in experiments using natural San Carlos olivine. The change in profile shape is interpreted to be a function of valence-state change from Ti4+ to Ti3+, shown by a sigmoidal log fO2–diffusivity relationship. To distinguish between Ti4+ and Ti3+ in forsterite, a diffusion profile was also investigated using ‘hydroxylation spectroscopy’ whereby a crystal from a diffusion experiment was hydroxylated by annealing in an H2O-rich fluid at moderate pressure and temperature. The point defects associated with the added structural OH were then determined by infrared spectroscopy, providing evidence for the presence of Ti4+ and Ti3+ at intermediate oxygen fugacity. The transition from Ti4+ to Ti3+ occurs at considerably higher fO2 in these diffusion experiments than in equilibrium experiments in similar systems. Titanium diffusion, qualified using a mobility parameter (M), is fastest along the c-axis, at high activity of silica, low oxygen fugacity and high temperature. The rate of Ti diffusion is broadly similar to those of Mn, Ni and Co, and closer to published rates of Mg self-diffusion in olivine than Si self-diffusion. The observed Ti3+ and Ti4+ diffusion occurs on the M-sites. From statistical examination of the large Mn, Ni and Co diffusivity dataset, we determine that there is a 102/3 dependence of diffusion on aSiO2; the cations diffuse more rapidly at high aSiO2. In addition, diffusivity has a 10–1/8 dependence on fO2, suggested to be the result of increased concentration of loosely bound Ti3+–vacancy pairs, which enhance the mobility of other cations. This behaviour is likely to be present in natural systems where trivalent (e.g. Fe3+, Al3+, Cr3+) and divalent cations diffuse together. Consideration should be given to diffusive interference by highly charged, fast-moving cations when extracting time scales from frozen diffusion profiles.
ISSN: 0022-3530

hal-01531344
https://hal.archives-ouvertes.fr/hal-01531344
DOI : 10.1093/petrology/egw067

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Trace metals (Cd, U, Co, Ni, Cu, Ba, Fe, Mn), total organic carbon (TOC) and C and N stable isotope signatures (delta C-313 and delta N-15) were determined in short sediments cores from the inner and outer shelf off Concepcion, Chile (similar to 36 degrees S). The objectives were to establish the effect of environmental conditions on trace metal distributions at two shelf sites, one affected by seasonal oxygenation and the other by permanent low oxygen conditions due to the presence of the oxygen minimum zone (OMZ). We evaluate trace metals as proxies of past changes in primary productivity and the bottom water oxygen regime. Concentrations of pore water sulfides and NH4+ were also measured as indicators of the main diagenetic pathways at each site. Our results for the inner shelf (seasonal suboxia) suggest that the oxidative state of the sediments responds to seasonal pulses of organic matter and that seasonal oxygenation develops during high and low primary productivity in the water column. Here, positive fluxes (to the water column) estimated from pore water concentrations of several elements were observed (Ba, Co, Ni, Fe and Mn). The less reduced environment at this site produces authigenic enrichment of Cu associated with the formation of oxides in the oxic surface sediment layer, and the reduction of U within deeper sediment sections occur consistently with negative estimated pore water fluxes. In the outer shelf sediments (permanent suboxia, OMZ site), negative fluxes (to the sediment) were estimated for all elements, but these sediments showed authigenic enrichments only for Cd, Cu and U. The short oxygenation period during the winter season did not affect the accumulation of these metals on the shelf. The distribution of Cu, Cd and U have been preserved within the sediments and the authigenic accumulation rates estimated showed a decrease from the deep sections of the core to the surface sediments. This could be explained by a gradual decrease in the strength of the OMZ in the last 100 years, in combination with periods of strong oxygenations during El Nino events. (C) 2011 Elsevier Ltd. All rights reserved.
ISSN: 0278-4343

hal-00745672
https://hal.archives-ouvertes.fr/hal-00745672
DOI : 10.1016/j.csr.2011.11.006

Éditeur(s) : HAL CCSD
Résumé : We present high-resolution bulk sedimentary δ 15N data from the southern edge of the present-day oxygen minimum zone of the eastern South Pacific. The record is interpreted as representing changes in water column nitrogen removal during the last 70,000 years. We found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales. These fluctuations were not related to other millennial-scale changes like the Northern Hemisphere's Dansgaard-Oeschger climate swings or local changes in primary productivity, so appear to be dictated by the Southern Hemisphere's climate rhythm. This is preliminarily corroborated by an overall agreement between our δ 15N data and the sedimentary proxy of ice sheet dynamics in Patagonia, which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern South Pacific intermediate waters. Finally, potential implications on late Quaternary changes in atmospheric CO2 concentrations are discussed.
Paleoceanography / PALEOECEANOGRAPHY

hal-00407260
https://hal.archives-ouvertes.fr/hal-00407260
DOI : 10.1029/2006PA001308

Éditeur(s) : Elsevier
Résumé : The main feature of the Congo-Angola margin in the Gulf of Guinea is the Congo (ex-Zaire) deep-sea fan composed of a submarine canyon directly connected to the Congo River, a channel and a [sediment] lobe area. During the multi-disciplinary programme called BIOZAIRE conducted by Ifremer from 2000 to 2005, two CTD-O2 sections with discrete water column samples were performed (BIOZAIRE3 cruise: 2003-2004) to study the influence of the Congo River discharges, both in the surface layer and in the deep and near-bottom layers. The surface layer water is greatly diluted with river water that has a heavy particle load. The deep layer is affected by episodic turbidity currents that flow in the deep Congo channel and reach deep areas far from the coast. Previous studies revealed deep anomalies in oxygen (deficit) and nutrient (excess) concentrations at not, vert, similar4000 m depth and assumed that they resulted from mineralisation of the particulate organic matter from the Congo River. The BIOZAIRE3 sections were designed to explore these phenomena in more detail near the Congo channel. Oxygen and nutrients were measured as well as additional parameters, including stable isotopes of oxygen and carbon, dissolved inorganic carbon and pH. For the surface layer, the effect of the Congo River was studied with reference to salinity. Deviations from the theoretical dilution of various inorganic solutes suggested the occurrence of mineralisation and consumption processes. For the deep layer, the network of CTD-O2 stations gave a more detailed description of the deep anomalies than in previous studies. From the east-west section, anomalies appeared on the bottom at 4000 m depth and became slightly shallower when they spread to the west. They were also present north and south on the bottom along the 4000 m isobath. In these deep waters, the decrease in the o13C values of dissolved inorganic carbon confirmed that the mineralisation of organic matter plays a role in generating these anomalies. The location of the origin of this deep anomaly is debated. Here, arguments are given in favour of mineralisation of the particulate organic matter input that overflows from the Congo channel at not, vert, similar4000 m depth during turbidity current events. Other authors suggest that this input comes from downslope particle transport. Anomalies of the same origin, but weaker, also occurred deeper on the Congo lobe, where the Congo channel ends, but with a significant pH decrease on the bottom which was not seen at 4000 m depth.
Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2183-2196

Droits : 2009 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6737.pdf
DOI:10.1016/j.dsr2.2009.04.002
http://archimer.ifremer.fr/doc/00000/6737/

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Growth hormone (GH) may stimulate water loss during exercise by activating sweating. This study investigated GH secretion and water loss during sequential cycling and running, taking postural changes into account. The two exercise segments had similar durations and were performed at the same relative intensity to determine their respective contributions to water loss and the plasma volume variation noted in such trials. Eight elite triathletes first performed an incremental cycle test to assess maximal oxygen consumption. Then, the triathletes performed one of two trials in randomized order: constant submaximal cycling followed by treadmill running (C 1 –R 2) or an inversed succession of running followed by cycling (R 1 –C 2). Each segment of both trials was performed for 20 minutes at ,75% of maximal oxygen consumption. The second trial, reversing the segment order of the first trial, took place two weeks later. During cycling, the triathletes used their own bicycles equipped with a profiled handlebar. Blood sampling (for GH concentrations, plasma viscosity and plasma volume variation) was conducted at rest and after each segment while water loss was estimated from the post-and pre-measures. GH increases were significantly lower in R 2 than C 2 (72.2650.1 vs. 164.06157 ng.ml 21 .min 21 , respectively; P,0.05). Water loss was significantly lower after C 1 –R 2 than R 1 –C 2 (11056163 and 12356153 ml, respectively; P,0.05). Plasma volume variation was significantly negative in C 1 and R 1 (26.1562.0 and 23.1665.0%, respectively; P,0.05), not significant in C 2 , and significantly positive for seven subjects in R 2 (4.0563.1%). We concluded that the lower GH increases in R 2 may have contributed to the smaller reduction in plasma volume by reducing sweating. Moreover, this lower GH response could be explained by the postural change during the transition from cycling to running. We recommend to pay particular attention to their hydration status during R 1 which could limit a potential dehydration during C 2 .
ISSN: 1932-6203

hal-01136734
https://hal.univ-antilles.fr/hal-01136734
https://hal.univ-antilles.fr/hal-01136734/document
https://hal.univ-antilles.fr/hal-01136734/file/Galy%20et%20al.%20-%202014%20-%20Sequential%20exercise%20in%20triathletes%20Variations%20in%20GH%20and%20water%20loss.pdf
DOI : 10.1371/journal.pone.0096145

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cnidarians living in symbiosis with photosynthetic dinoflagellates (commonly named zooxanthellae) are exposed to high concentrations of reactive oxygen species (ROS) upon illumination. To quench ROS production, both the cnidarian host and zooxanthellae express a full suite of antioxidant enzymes. Studying antioxidative balance is therefore crucial to understanding how symbiotic cnidarians cope with ROS production. We characterized glutathione peroxidases (GPx) in the symbiotic cnidarian Anemonia viridis by analysis of their isoform diversity, their activity distribution in the three cellular compartments (ectoderm, endoderm and zooxanthellae) and their involvement in the response to thermal stress. We identified a GPx repertoire through a phylogenetic analysis showing 7 GPx transcripts belonging to the A. viridis host and 4 GPx transcripts strongly related to Symbiodinium sp. The biochemical approach, used for the first time with a cnidarian species, allowed the identification of GPx activity in the three cellular compartments and in the animal mitochondrial fraction, and revealed a high GPx electrophoretic diversity. The symbiotic lifestyle of zooxanthellae requires more GPx activity and diversity than that of free-living species. Heat stress induced no modification of GPx activities. We highlight a high GPx diversity in A. viridis tissues by genomic and biochemical approaches. GPx activities represent an overall constitutive enzymatic pattern inherent to symbiotic lifestyle adaptation. This work allows the characterization of the GPx family in a symbiotic cnidarian and establishes a foundation for future studies of GPx in symbiotic cnidarians.
ISSN: 0300-9084

hal-01404424
http://hal.upmc.fr/hal-01404424
http://hal.upmc.fr/hal-01404424/document
http://hal.upmc.fr/hal-01404424/file/Pey_Characterization_of.pdf
DOI : 10.1016/j.biochi.2016.10.016

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The ultramafic rocks of the Collo region in northeastern Algeria crop out as “stratified” masses that cut across older metamorphic formations of the Petite Kabylie basement. Based on petrological compositions and mineralogical observations, these rocks are mainly peridotites and serpentinites. The peridotites are identified as lherzolites, but dunites may occur rarely. The lherzolites are composed of olivine, orthopyroxene, clinopyroxene and chromian spinel. Their chemical composition shows high MgO (34.4–37.5 wt%), Cr (0.14–0.27 wt%), Ni (0.14–0.26 wt%) and Co (34–133 ppm) contents and low CaO and Al2O3 concentrations (0.02–2.2 wt% and 0.5 to 2.8 wt%, respectively). The chromite, which represents approximately 1–3% of the rock, is ubiquitous and shows two different generations: primary millimetric euhedral crystals and secondary fine xenomorphic grains and interstitial aggregates. The primary chromites are alumino-ferro-magnesian crystals that show high Al2O3 (25.77%–27.36%) and MgO (10.70%–13.36%). Cr# (100 × Cr/(Al + Cr)) ranges from 45 to 48, and Mg# (100 × Mg/(Mg + Fe2+)) from 49 to 59. The secondary interstitial grains are iron-rich chromites. They show low Al2O3 (4.67%–9.54%) and MgO (4.60%–4.65%). Cr# is relatively high (77–88), whereas Mg# shows relatively low values, ranging from 22 to 25. Primary chromite and whole-rock chemistry show that the Collo ultramafic rocks belong to Alpine-type peridotites that were emplaced within an orogenic setting. The oxygen isotopic composition of both peridotites and chromites is consistent with their derivation from a mantle source (δ18O ranges from +3.0 to +5.9‰). Low δ18O values (<+4.4‰) are recorded in serpentinites and are attributed to the effect of serpentinization processes through high-temperature metasomatic fluids. Magnesite-bearing serpentinites show the lowest δ18O values. These are interpreted as the result of surface water input.
ISSN: 0899-5362

hal-01468003
https://hal.archives-ouvertes.fr/hal-01468003
DOI : 10.1016/j.jafrearsci.2016.10.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
TEM Study of Heavitree quartzite deformed at high temperatures and a pressure of 1.5 GPa with three different preparations: water-added, vacuum dried, and sodium doped show a wide range of dislocation microstructure. The vacuum dried sample has a very heterogeneous dislocation distribution varying from almost no dislocations to very high densities. Dislocation nucleation occurs by cross-slip mechanisms, such as Frank-Read sources and Orowan loops around hard inclusions. Shear bands develop in the basal plane composed of two closely spaced shear planes. Dislocations have straight segments and they are aligned along directions of dense packing, suggesting strong Peierls stress control due to the crystal structure. No voids, bubbles or dislocation walls where observed in the vacuum dried sample. The sodium-doped sample had a homogeneous high dislocation density. The water-added sample has a significantly lower, relatively uniform dislocation density. Bubbles associated with dislocations are seen in every grain. Dislocations were either present in loops around bubbles or as straight dislocations with small bubbles spaced along the dislocation line. Some of the long straight dislocations are aligned parallel to the c-axis. Sub-grains where very frequent, sometimes form cells of about 2 p,m in diameter with straight edges. Analysis of dislocations show 1/3 < a > and [c] dislocations in sub-grain walls and free 1/3 < a > dislocations on prism planes. There is clear evidence for dislocation climb with sub-grain walls, dislocation cells, dislocation junctions and dislocation debris of small loops. The major difference between vacuum dried and water-added samples are the homogeneity of the microstructure and evidence for climb in the water-added sample. Glide is clearly difficult, with a high Peierls stress in the vacuum dried sample as shown by areas of very low and very high dislocation density and the crystallographic control of dislocation line direction. The sodium-doped sample indicates that nucleation was easy by the high homogenous dislocation density, but no climb recovery has taken place. The density is high and the dislocations are strongly interacting causing tangles; no evidence for crystallographic control can be observed at these levels of strain. The activation energy for creep in Heavitree quartzite decreases with inferred water content of the specimens form 185 kJ mol(-1) for vacuum dried to 151 for 0.4 wt% water-added samples. Analysis of diffusion data for oxygen under hydrothermal conditions and inferred diffusion data for the hydrogarnet defect and dislocation velocity suggests activation energies for these processes are similar to the activation energy for the dislocation creep of Heavitree quartzite and other quartz aggregates. For data from the previously published experiments with the highest stress resolution there is a correlation between the A pre-factor in the power law creep equation and the activation energy for creep. It is speculated that the correlation may be due to variable hydrogarnet defect concentrations.
ISSN: 0031-9201

hal-00413112
https://hal.archives-ouvertes.fr/hal-00413112
DOI : 10.1016/j.pepi.2008.07.009

Éditeur(s) : HAL CCSD Thieme Publishing
Résumé : International audience
To determine the effect of triathlete performance level on the cardiorespiratory responses elicited by the cycle-run succession, eight regionally and nationally-ranked (Competitive) and five internationally-ranked (Elite) male triathletes underwent four successive laboratory trials: 1) an incremental treadmill test, 2) an incremental cycle test, 3) 30 min of cycling followed by 20 min of running (C-R), and 4) a 20-min control run (R) at the same speed as the run in C-R. Before and 10 min after the third and fourth trials the triathletes underwent lung function testing: spirometry and diffusing capacity testing for carbon monoxide (DL(CO)). During the C-R trial blood samples were drawn to measure venous lactate concentration. During all trials ventilatory data were collected every minute using an automated breath-by-breath system. The results showed that 1) the oxygen uptake (VO2) of post-cycling running versus running alone was similar for both groups; 2) the ventilatory responses (VE, VE/VO2, VE/VC02 and f) of C-R running versus R were significantly higher (P < 0.005) for the Competitive group; and 3) a significant decrease (P< 0.05) in DL(CO) was also noted after the C-R trial in the Competitive group but not in the Elite group. We concluded that 1) the ventilatory responses during a run subsequent to cycling may be related to the triathlete performance level, and 2) the C-R trial induced specific alterations in pulmonary function that may be associated with respiratory muscle alteration and exercise-induced hypoxemia in the Competitive triathletes.
ISSN: 0172-4622

hal-00720719
https://hal.univ-antilles.fr/hal-00720719