Chavagnac Valerie

No Thumbnail Available
Last Name
Chavagnac
First Name
Valerie
ORCID

Filters

2006 - 2009 1 2020 - 2022 1
2
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Article
    Hydrothermal sediments as a potential record of seawater Nd isotope compositions : the Rainbow vent site (36°14′N, Mid-Atlantic Ridge)
    (American Geophysical Union, 2006-09-09) Chavagnac, Valerie ; Palmer, Martin R. ; Milton, J. Andrew ; Green, Darryl R. H. ; German, Christopher R.
    Geochemical compositions and Sr and Nd isotopes were measured in two cores collected ~2 and 5 km from the Rainbow hydrothermal vent site on the Mid-Atlantic Ridge. Overall, the cores record enrichments in Fe and other metals from hydrothermal fallout, but sequential dissolution of the sediments allows discrimination between a leach phase (easily leachable) and a residue phase (refractory). The oxy-anion and transition metal distribution combined with rare earth element (REE) patterns suggest that 1) the leach fraction is a mixture of biogenic carbonate and hydrothermal Fe-Mn oxy-hydroxide with no significant contribution from detrital material, and 2) >99.5% of the REE content of the leach fraction is of seawater origin. In addition, the leach fraction has an average 87Sr/86Sr ratio indistinguishable from modern seawater at 0.70916. Although we lack the εNd value of present day deep water at the Rainbow vent site, we believe that the REE budget of the leach fraction is predominantly of seawater origin. We suggest, therefore, that the leach fraction provides a record of local seawater εNd values. Nd isotope data from these cores span the period of 4-14 ka (14C ages) and yield εNd values for North East Atlantic Deep Water (NEADW) that are higher (-9.3 to -11.1) than those observed in the nearby Madeira Abyssal Plain from the same depth (-12.4 ± 0.9). This observation suggests that either the Iceland-Scotland Overflow Water (ISOW) and Lower Deep Water (LDW) contributions to the formation of NEADW are higher along the Mid-Atlantic Ridge than in the surrounding basins, or that the relative proportion of ISOW was higher during this period than is observed today. This study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water εNd values, and hence deep-water circulation patterns in the oceans, than is possible from other types of sediments.
  • Article
    Integrating Multidisciplinary Observations in Vent Environments (IMOVE): decadal progress in deep-sea observatories at hydrothermal vents
    (Frontiers Media, 2022-05-13) Matabos, Marjolaine ; Barreyre, Thibaut ; Juniper, S. Kim ; Cannat, Mathilde ; Kelley, Deborah S. ; Alfaro-Lucas, Joan M. ; Chavagnac, Valerie ; Colaço, Ana ; Escartin, Javier E. ; Escobar Briones, Elva ; Fornari, Daniel J. ; Hasenclever, Jörg ; Huber, Julie A. ; Laës-Huon, Agathe ; Lantéri, Nadine ; Levin, Lisa A. ; Mihaly, Steven F. ; Mittelstaedt, Eric ; Pradillon, Florence ; Sarradin, Pierre-Marie ; Sarradin, Pierre-Marie ; Sarrazin, Jozée ; Tomasi, Beatrice ; Venkatesan, Ramasamy ; Vic, Clément
    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 temperatures, loss of oxygen, and modifications to deep water circulation. Despite the potential of these profound impacts, the mechanisms enabling these systems and their ecosystems to persist, function and respond to oceanic, crustal, and anthropogenic forces remain poorly understood. This is due primarily to technological challenges and difficulties in accessing, observing and monitoring the deep-sea. In this context, the development of deep-sea observatories in the 2000s focused on understanding the coupling between sub-surface flow and oceanic and crustal conditions, and how they influence biological processes. Deep-sea observatories provide long-term, multidisciplinary time-series data comprising repeated observations and sampling at temporal resolutions from seconds to decades, through a combination of cabled, wireless, remotely controlled, and autonomous measurement systems. The three existing vent observatories are located on the Juan de Fuca and Mid-Atlantic Ridges (Ocean Observing Initiative, Ocean Networks Canada and the European Multidisciplinary Seafloor and water column Observatory). These observatories promote stewardship by defining effective environmental monitoring including characterizing biological and environmental baseline states, discriminating changes from natural variations versus those from anthropogenic activities, and assessing degradation, resilience and recovery after disturbance. This highlights the potential of observatories as valuable tools for environmental impact assessment (EIA) in the context of climate change and other anthropogenic activities, primarily ocean mining. This paper provides a synthesis on scientific advancements enabled by the three observatories this last decade, and recommendations to support future studies through international collaboration and coordination. The proposed recommendations include: i) establishing common global scientific questions and identification of Essential Ocean Variables (EOVs) specific to MORs, ii) guidance towards the effective use of observatories to support and inform policies that can impact society, iii) strategies for observatory infrastructure development that will help standardize sensors, data formats and capabilities, and iv) future technology needs and common sampling approaches to answer today’s most urgent and timely questions.