Valérie Chavagnac

Valérie Chavagnac
French National Centre for Scientific Research | CNRS · Observatoire Midi-Pyrénées Toulouse

Ph.D., Research Habilitation

About

121
Publications
23,259
Reads
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2,831
Citations
Additional affiliations
October 2018 - present
French National Centre for Scientific Research
Position
  • Research Director
October 2007 - September 2018
French National Centre for Scientific Research
Position
  • Researcher
December 2000 - August 2007
National Oceanography Centre, Southampton
Position
  • Research Associate

Publications

Publications (121)
Article
Full-text available
The unique ecosystems and biodiversity associated with mid-ocean ridge (MOR) hydrothermal vent systems contrast sharply with surrounding deep-sea habitats, however both may be increasingly threatened by anthropogenic activity (e.g., mining activities at massive sulphide deposits). Climate change can alter the deep-sea through increased bottom tempe...
Article
Full-text available
Lithium (Li) and strontium (Sr) are two economically relevant chemical elements whose oceanic biogeochemical cycles are not fully constrained. In particular, how they disperse and behave from hydrothermal sources into the water column is understudied while hydrothermal systems on the global mid-ocean ridge network (~67,000 km) represent one of the...
Article
It is now clear that, in some parts of the ocean, inputs of hydrothermal iron (Fe) can make a more significant contribution to the Fe inventory than previously thought. While the Fe isotopic signature of seawater has proved useful for distinguishing between inputs of Fe from atmospheric deposition and seafloor sediments, the Fe isotope signature of...
Article
The establishment of the Antarctic Circumpolar Current (ACC) is one of the most important events for both global oceanic circulation and climate of the Cenozoic. The onset of this major current hinges on the opening of two major oceanic passages, the Drake Passage and the Tasmanian gateways that connect Pacific, Atlantic and Indian oceans allowing...
Article
The MAR 13°20’N corrugated detachment fault is composed of pervasively silicified mafic cataclastic breccias, instead of ultramafics and gabbros commonly found at other detachments. These breccias record overplating of hangingwall diabases, with syntectonic silicification due to important influx of silica‐iron‐rich fluids, able to leach alkalis and...
Article
Full-text available
Lost City (mid-Atlantic ridge) is a unique oceanic hydrothermal field where carbonate-brucite chimneys are colonized by a single phylotype of archaeal Methanosarcinales, as well as sulfur-and methane-metabolizing bacteria. So far, only one submarine analog of Lost City has been characterized, the Prony Bay hydrothermal field (New Caledonia), which...
Article
To better constrain the Sr isotope budget in marginal domains without any fluvial inputs, we analyzed the chemical composition and 87Sr/86Sr ratio of waters and shells from four locations: two coastal lagoons, one hemipelagic platform and one open marine shelf. Our results highlight homogeneous 87Sr/86Sr ratios typical of oligotrophic oceanic water...
Article
The first step of ice-sheet build-up on Antarctica at the Eocene-Oligocene boundary was followed by a phase of climate instability culminating during the Miocene with a warming event called the Middle Miocene Climate Optimum (MMCO), that ended with a marked cooling phase identified as the Middle Miocene Climate Transition (MMCT). While numerous ben...
Article
A fiber refractometer with large dynamic range from 1.316 to 1.61 RIU has been realized using a hybrid configuration of a single-mode fiber (SMF) coupled to a stripped-cladding multimode fiber (MMF) as sensing element. An extended analysis of the diffraction principle of a Gaussian beam is specifically developed for this sensor configuration to det...
Article
Metal partitioning between the dissolved and particulate phases is still poorly constrained within the early mixing of hydrothermal fluids and deep seawater. In this study, in situ filtration has been used to collect early buoyant plume fluids. This has provided the unique opportunity to reassess precisely metal partitioning along the mixing gradie...
Article
Full-text available
Iron (Fe) limits primary productivity and nitrogen fixation in large regions of the world’s oceans. Hydrothermal supply of Fe to the global deep ocean is extensive; however, most of the previous work has focused on examining high temperature, acidic, focused flow on ridge axes that create “black smoker” plumes. The contribution of other types of ve...
Article
Full-text available
Iron (Fe) limits primary productivity and nitrogen fixation in large regions of the world's oceans. Hydrothermal supply of Fe to the global deep ocean is extensive; however, most of the previous work has focused on examining high temperature, acidic, focused flow on ridge axes that create "black smoker" plumes. The contribution of other types of ve...
Article
Full-text available
The mixing zone between high temperature hydrothermal fluids and seawater produces redox gradients, promoting the development of unique ecosystems based on chemotrophy. The structure of microbial communities depends on their environment, which can vary according to space and time. Hydrothermal circulation within the oceanic crust determines the che...
Article
Full-text available
Studies of submarine hydrothermal systems in Mediterranean Sea are limited to the southern Italian volcanism, while are totally missing in the Aegean. Here, we report on the geochemistry of high-temperature fluids (up to 220°C) venting at 500 m b.s.l. from the floor of Kolumbo submarine volcano (Hellenic Volcanic Arc, Greece), which is located 7 km...
Conference Paper
Full-text available
The Sr isotope ratio (87Sr/86Sr) of modern seawater is generally considered as homogeneous at global scale because the residence time of this element is longer than the global ocean mixing duration. However, the 87Sr/86Sr ratios of seawater show long-term fluctuations at geological time scales. The study of these variations is of prime importance f...
Article
Full-text available
The reconstruction of past variations in seawater strontium isotope ratios (87Sr/86Sr) from marine carbonate skeletons (MCSs) is based on the assumption that the Sr isotope composition of oceans is homogeneous worldwide. However, fossil materials are mainly from shelf domains whose modern Sr budget is known to be very sensitive to continental Sr fl...
Article
This study aims at characterizing the subseafloor architecture of the Lucky Strike hydrothermal field (LSHF) based on an extensive chemical database of the various vents. Our analysis is motivated by the discovery in 2013 of a new active high-temperature site, named Capelinhos, approximately 1.5 km east of the LSHF. Capelinhos fluids display partic...
Article
While hydrothermal vents are now thought to be a major source of dissolved iron to the oceans, they have always been considered to be a sink for the dissolved rare-earth elements (DREEs). However, true dissolved REE observations in hydrothermal plumes are still lacking. Here we report for the first time the DREE concentrations and neodymium isotopi...
Article
Full-text available
In the Western Tropical South Pacific, patches of high chlorophyll concentrations linked to the occurrence of N2-fixing organisms are found in the vicinity of volcanic islands. The survival of these organisms relies on a high bioavailable iron supply whose origin and fluxes remain unknown. Here, we measured high dissolved iron (DFe) concentrations...
Article
Full-text available
The evolution of the seawater oxygen isotopic composition (δ18O) through geological time remains controversial. Yet, the past δ18Oseawater is key to assess past seawater temperatures, providing insights into past climate change and life evolution. Here we provide a new and unprecedentedly precise δ18O value of −1.33 ± 0.98‰ for the Neoproterozoic b...
Article
Full-text available
We propose and develop a comprehensive model for estimating the refractive index (RI) response over three potential sensing zones in a multimode fiber. The model has been developed based on a combined ray optics, Gaussian beam, and wave optics analysis coupled to the consideration of the injected interrogating lightwave characteristics and validate...
Article
Using a combined approach of seafloor mapping, MAPR and CTD survey, we report evidence for active hydrothermal venting along the 130°-140°E section of the poorly-known South-East Indian Ridge (SEIR) from the Australia-Antarctic Discordance (AAD) to the George V Fracture Zone (FZ). Along the latter, we report Eh and CH4 anomalies in the water column...
Article
Full-text available
Deep-sea hydrothermal venting is now recognized as a major source of iron (Fe), an essential trace element that controls marine productivity. However the reactions occurring during dispersal from buoyant plumes to neutrally-buoyant hydrothermal plumes are still poorly constrained. Here we report for the first time on the dissolved-particulate parti...
Article
p>Microbathymetry data, in situ observations, and sampling along the 13°20′N and 13°20′N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high-a...
Article
Full-text available
Microbathymetry data, in-situ observations, and sampling along the 13°20’N and 13°20’N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high ang...
Article
Full-text available
Travertine are found in ophiolite massifs in association with bicarbonate-depleted hyperalkaline spring waters (pH up to 11.9), in contrast with most continental carbonates (e.g., travertine, tufa, speleothems) that precipitate from calcium bicarbonate-enriched waters. Here travertines formed from bicarbonate-depleted hyperalkaline spring water wer...
Article
Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event pa...
Article
Full-text available
Submarine volcanism represents ~80% of the volcanic activity on Earth and is an important source of mantle-derived gases. These gases are of basic importance for the comprehension of mantle characteristics in areas where subaerial volcanism is missing or strongly modified by the presence of crustal/atmospheric components. Though, the study of subma...
Conference Paper
Full-text available
Submarine volcanism represents ∼80% of the volcanic activity on Earth and is an important ource of mantle-derived gases. These gases are fundamental for the comprehension of mantle characteristics in key sectors where subaerial volcanism is missing or strongly modified by mixing with crustal and atmospheric components. Though, the study of submarin...
Research
Full-text available
Conference paper #OS43A-2031 AGU 2015 To study the hydrothermal forcing on microbial colonization, and impacts on the oceanic crust alteration, an integrated study was led at the Tour Eiffel hydrothermal site (Lucky Strike hydrothermal field, 37°N, MAR). We benefited from an annual survey between 2009 and 2011 of temperatures, along with sampling...
Conference Paper
Full-text available
The operational EMSO-Azores deep-sea observatory provides a unique opportunity combining yearly hydrothermal fluid sampling along with continuous monitoring of physical parameters (temperature, seismicity, pressure,…) to better constrain hydrothermal fluid flow dynamics both in time and space at the Lucky Strike vent field. Repeated sampling at thi...
Conference Paper
Full-text available
Large-offset detachment faults are widespread along the slow-spreading Mid-Atlantic Ridge (MAR), exhume ultramafic rocks, and host a great diversity of hydrothermal systems. During the ODEMAR'13 cruise, the fully developed 13º20'N and 13º30'N oceanic core complexes (OCC) along MAR were investigated to constrain the tectonic, hydrothermal and magmat...
Conference Paper
To study the hydrothermal forcing on microbial colonization, and impacts on the oceanic crust alteration, an integrated study was led at the Tour Eiffel hydrothermal site (Lucky Strike hydrothermal field, 37°N, MAR). We benefited from an annual survey between 2009 and 2011 of temperatures, along with sampling of focused and diffused fluids for chem...
Poster
Full-text available
Newly discovered hydrothermal plumes along the Furious Fifties, South East Indian Ridge (SEIR; 128°E-140°E)
Conference Paper
The Lucky Strike hydrothermal field is situated at the mid-Atlantic ridge, south of the Azores, on top of a central volcano within the axial valley. The volcano is composed of a fossil lava lake surrounded by three volcanic cones. An Axial Magma Chamber (AMC) is reported 3.4km below the seafloor. The active venting sites are situated around the fos...
Article
Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood1, 2. Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The o...
Article
Full-text available
The Voltri Massif is an ophiolitic complex located in the Ligurian Alps close to the city of Genova (Northern Italy) where several springs discharge high pH (up to 11.7), low salinity waters produced by the active serpentinization of the ultramafic basement. Mixing of these hyperalkaline waters with the river waters along with the uptake of atmosph...
Data
Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood (Dittmar and Stubbins, 2014; Hansell, 2013, doi:10.1146/annurev-marine-120710-100757). Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved org...
Article
Full-text available
The terrestrial hyperalkaline springs of Prony Bay (southern lagoon, New Caledonia) have been known since the nineteenth century, but a recent high-resolution bathymetric survey of the seafloor has revealed the existence of numerous submarine structures similar to the well-known Aiguille de Prony, which are also the location of high-pH fluid discha...
Article
The shallow submarine hydrothermal field of the Prony Bay (New Caledonia) discharges hydrogen- and methane-rich fluids with low salinity, temperature (<40°C) and high pH (11) produced by the serpentinization reactions of the ultramafic basement into the lagoon seawater. They are responsible for the formation of carbonate chimneys at the lagoon seaf...
Article
Full-text available
The terrestrial hyperalkaline springs of the Prony bay (southern lagoon, New Caledonia) have been known since the XIXth century, but a recent high resolution bathymetric survey of the seafloor has revealed the existence of numerous submarine structures similar to the well-known Aiguille de Prony, which are also the location of high pH fluid dischar...
Article
Distributions of dissolved and particulate rare earth elements (REEs) and seawater neodymium isotopic composition (εNd) were established in samples from the BONUS GoodHope (BGH) IPY-GEOTRACES cruise in the SE Atlantic sector of the Southern Ocean (36°S-13°E to 57°S-0°, Feb.-Mar. 2008). Close to the South African continent in the subtropical domain,...
Article
We report a measurement procedure to determine simultaneously the major cation concentrations (Na, Ca, K and Mg) of seawater-derived solutions by inductively coupled plasma-atomic emission spectrometry. The best results were obtained when the IAPSO (“standard”) seawater reference material was diluted by thirty times with Milli-Q® water. We obtained...