Ballu Valerie

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Ballu
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Valerie
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  • Preprint
    Hydrothermal activity along the slow-spreading Lucky Strike ridge segment (Mid-Atlantic Ridge) : distribution, heatflux, and geological controls
    ( 2015-09) Escartin, Javier E. ; Barreyre, Thibaut ; Cannat, Mathilde ; Garcia, Rafael ; Gracias, Nuno ; Deschamps, Anne ; Salocchi, Aura ; Sarradin, Pierre-Marie ; Ballu, Valerie
    We have reviewed available visual information from the seafloor, and recently acquired microbathymetry for several traverses across the Lucky Strike segment, to evaluate the distribution of hydrothermal activity. We have identified a new on-axis site with diffuse flow, Ewan, and anactive vent structure ~1.2 km from the axis, Capelinhos. These sites are minor relative to the Main field, and our total heatflux estimate for all active sites (200-1200 MW) is only slightly higher than previously published estimates. We also identify fossil sites W of the main Lucky Strike field. A circular feature ~200 m in diameter located on the flanks of a rifted off-axis central volcano, is likely a large and inactive hydrothermal edifice, named Grunnus. We find no indicator of focused hydrothermal activity elsewhere along the segment, suggesting that the enhanced melt supply and the associated melt lenses, required to form central volcanoes, also sustain hydrothermal circulation to form and maintain large and long-lived hydrothermal fields. Hydrothermal discharge to the seafloor occurs along fault traces, suggesting focusing of hydrothermal circulation in the shallow crust along permeable fault zones.
  • Article
    The Kallisti Limnes, carbon dioxide-accumulating subsea pools
    (Nature Publishing Group, 2015-07-16) Camilli, Richard ; Nomikou, Paraskevi ; Escartin, Javier E. ; Ridao, Pere ; Mallios, Angelos ; Kilias, Stephanos P. ; Argyraki, Ariadne ; Andreani, Muriel ; Ballu, Valerie ; Campos, Ricard ; Deplus, Christine ; Gabsi, Taoufic ; Garcia, Rafael ; Gracias, Nuno ; Hurtos, Natalia ; Magi, Lluis ; Mevel, Catherine ; Moreira, Manuel ; Palomeras, Narcis ; Pot, Olivier ; Ribas, David ; Ruzie, Lorraine ; Sakellariou, Dimitris
    Natural CO2 releases from shallow marine hydrothermal vents are assumed to mix into the water column, and not accumulate into stratified seafloor pools. We present newly discovered shallow subsea pools located within the Santorini volcanic caldera of the Southern Aegean Sea, Greece, that accumulate CO2 emissions from geologic reservoirs. This type of hydrothermal seafloor pool, containing highly concentrated CO2, provides direct evidence of shallow benthic CO2 accumulations originating from sub-seafloor releases. Samples taken from within these acidic pools are devoid of calcifying organisms, and channel structures among the pools indicate gravity driven flow, suggesting that seafloor release of CO2 at this site may preferentially impact benthic ecosystems. These naturally occurring seafloor pools may provide a diagnostic indicator of incipient volcanic activity and can serve as an analog for studying CO2 leakage and benthic accumulations from subsea carbon capture and storage sites.
  • Article
    Temporal variability and tidal modulation of hydrothermal exit-fluid temperatures at the Lucky Strike deep-sea vent field, Mid-Atlantic Ridge
    (John Wiley & Sons, 2014-04-02) Barreyre, Thibaut ; Escartin, Javier E. ; Sohn, Robert A. ; Cannat, Mathilde ; Ballu, Valerie ; Crawford, Wayne C.
    We deployed autonomous temperature sensors at black smoker chimneys, cracks, and diffuse flow areas at the Lucky Strike hydrothermal field (Mid-Atlantic Ridge, ~37°17'N) between summer 2009 and summer 2012 and contemporaneously measured tidal pressures and currents as part of the long-term MoMAR experiment to monitor hydrothermal activity. We classify the temperature data according to the hydrogeologic setting of the measurement sites: a high-temperature regime (>190°C) representing discharge of essentially unmixed, primary hydrothermal fluids through chimneys, an intermediate-temperature regime (10–100°C) associated with mixing of primary fluids with cold pore fluids discharging through cracks, and a low-temperature regime (<10°C) associated with a thermal boundary layer forming over bacterial mats associated with diffuse outflow of warm fluids. Temperature records from all the regimes exhibit variations at semi-diurnal tidal periods, and cross-spectral analyses reveal that high-temperature discharge correlates to tidal pressure while low-temperature discharge correlates to tidal currents. Intermediate-temperature discharge exhibits a transitional behavior correlating to both tidal pressure and currents. Episodic perturbations, with transient temperature drops of up to ~150°C, which occur in the high-temperature and intermediate-temperature records, are not observed on multiple probes (including nearby probes at the same site), and they are not correlated with microearthquake activity, indicating that the perturbation mechanism is highly localized at the measurement sites within the hydrothermal structures. The average temperature at a given site may increase or decrease at annual time scales, but the average temperature of the hydrothermal field, as a whole, appears to be stable over our 3 year observation period.
  • Article
    Towards comprehensive observing and modeling systems for monitoring and predicting regional to coastal sea level
    (Frontiers Media, 2019-07-25) Ponte, Rui M. ; Carson, Mark ; Cirano, Mauro ; Domingues, Catia M. ; Jevrejeva, Svetlana ; Marcos, Marta ; Mitchum, Gary ; van de Wal, Roderik S.W. ; Woodworth, Philip L. ; Ablain, Michaël ; Ardhuin, Fabrice ; Ballu, Valerie ; Becker, Mélanie ; Benveniste, Jérôme ; Birol, Florence ; Bradshaw, Elizabeth ; Cazenave, Anny ; De Mey-Frémaux, Pierre ; Durand, Fabien ; Ezer, Tal ; Fu, Lee-Lueng ; Fukumori, Ichiro ; Gordon, Kathy ; Gravelle, Médéric ; Griffies, Stephen M. ; Han, Weiqing ; Hibbert, Angela ; Hughes, Chris W. ; Idier, Deborah ; Kourafalou, Vassiliki H. ; Little, Christopher M. ; Matthews, Andrew ; Melet, Angelique ; Merrifield, Mark ; Meyssignac, Benoit ; Minobe, Shoshiro ; Penduff, Thierry ; Picot, Nicolas ; Piecuch, Christopher G. ; Ray, Richard D. ; Rickards, Lesley ; Santamaría-Gómez, Alvaro ; Stammer, Detlef ; Staneva, Joanna ; Testut, Laurent ; Thompson, Keith ; Thompson, Philip ; Vignudelli, Stefano ; Williams, Joanne ; Williams, Simon D. P. ; Wöppelmann, Guy ; Zanna, Laure ; Zhang, Xuebin
    A major challenge for managing impacts and implementing effective mitigation measures and adaptation strategies for coastal zones affected by future sea level (SL) rise is our limited capacity to predict SL change at the coast on relevant spatial and temporal scales. Predicting coastal SL requires the ability to monitor and simulate a multitude of physical processes affecting SL, from local effects of wind waves and river runoff to remote influences of the large-scale ocean circulation on the coast. Here we assess our current understanding of the causes of coastal SL variability on monthly to multi-decadal timescales, including geodetic, oceanographic and atmospheric aspects of the problem, and review available observing systems informing on coastal SL. We also review the ability of existing models and data assimilation systems to estimate coastal SL variations and of atmosphere-ocean global coupled models and related regional downscaling efforts to project future SL changes. We discuss (1) observational gaps and uncertainties, and priorities for the development of an optimal and integrated coastal SL observing system, (2) strategies for advancing model capabilities in forecasting short-term processes and projecting long-term changes affecting coastal SL, and (3) possible future developments of sea level services enabling better connection of scientists and user communities and facilitating assessment and decision making for adaptation to future coastal SL change.