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Imagerie de la structure thermohaline dans le Golfe de Cadix: Traitement des données sismiques et d'océanographie physique de la Veine d'Eau Méditerranéenne

Abstract : The rediscovery in 2003 by Holbrook et al. that the water column could be imaged by marine seismic reflection data has led to the initiation of the European GO (Geophysical Oceanography) project. This project aims to improve our comprehension of the oceanic meso and submesoscale structure, with particular application to the Gulf of Cadiz. The Gulf of Cadiz has a complex thermohaline structure. The work presented in this thesis is directly related to this project. By reprocessing the historical marine seismics and hydrology data, we began to resuscitate the large database which exists on this area. Thus, we demonstrate that marine seismic data can image the mesoscale to submesoscale oceanographic structures at a horizontal resolution of 10 m. Hydrologic data which have a vertical resolution around 1 m calibrate the seismic data in temperature and salinity. To relate our two databases, we searched a precise definition of the seismic signal, which is the reflection coefficient convoluted with the source wavelet of the acquisition system. However, all the terms are not known and we still have to improve our knowledge of the seismic signal. Nevertheless, the main factor influencing the seismic signal is temperature via the sound speed gradient. Marine seismic and hydrological data from the GO cruise acquired simultanously in the Gulf of Cadiz in April 2007 have been analyzed to determine the physical nature and geometric characteristics of acoustic reflectors in the water column. Seismic data show strong reflectors near the surface, above the Mediterranean Water (MW) undercurrents, above a meddy, and in a submesoscale MW structure. Wavelet analysis of seismic data indicates these reflectors have vertical wavelengths of 16-64 m and are associated with thermo-haline layering. At the edge of a meddy, lateral intrusions of less saline water are revealed by reflectors with 25-75 m thickness. Seismic data reveal that upper and lower boundaries of the layers match to the existence of the fine-scale structures. Marine seismic data (Low Frequency) allow systematic detection and monitoring of mesoscale and submesoscale eddies that hydrological sections identify only occasionally.
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Contributor : Elise Quentel <>
Submitted on : Tuesday, June 29, 2010 - 11:47:45 AM
Last modification on : Wednesday, September 16, 2020 - 9:56:34 AM
Long-term archiving on: : Thursday, September 30, 2010 - 5:43:00 PM

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Elise Quentel. Imagerie de la structure thermohaline dans le Golfe de Cadix: Traitement des données sismiques et d'océanographie physique de la Veine d'Eau Méditerranéenne. Géophysique [physics.geo-ph]. Université de Bretagne occidentale - Brest, 2010. Français. ⟨tel-00495963⟩

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