First sighting of active fluid venting in the Gulf of Cadiz

Abstract

The Mercator mud volcano, located in the Gulf of Cadiz off the coasts of Spain, Portugal, and Morocco (Figure 1), may provide an accessible field laboratory for studying local active venting and its possible internal and external controls. The recent discovery of the first active deep ocean ‘brown smoker’ chimney in this area can possibly be linked with the disintegration of a gas hydrate layer between the seafloor and a subsurface level that is dependent on pressure and temperature. For more than a decade, the international marine scientific community has deployed considerable efforts in exploring the Gulf of Cadiz. Since the discovery of the Gulf's first mud volcano in 1999, research cruises have steadily unveiled one mud volcano after another [Gardner, 2001; Pinheiro et al., 2003; Somoza et al., 2003]. These mud volcanoes are clustered in several fields on the Portuguese, Spanish, and Moroccan margins (Figure 1). Extensive geophysical evidence of shallow gas and subsurface fluid flow has been reported in the Gulf of Cadiz [Baraza and Ercilla 1996; Pinheiro et al., 2003].

Anaerobic oxidation of methane in hypersaline cold seep sediments

“…These results are in agreement with previous publications on the geochemistry of the chosen structures (e.g. Van Rooij et al ., ; Niemann et al ., ; Hensen et al ., ; Nuzzo et al ., ; Scholz et al ., ). At Mercator MV Crater Centre, methane concentration decreased from 3 mM at 75 cmbsf to 0.6 mM at the sediment surface.…”

“…At Mercator MV, the observation of shallow subseafloor internal seismic reflectors resembling bottom‐simulating reflectors suggested the presence of gas hydrates near the surface (Depreiter et al ., ). On the basis of these results and on video observations of gas venting from Mercator MV crater (Van Rooij et al ., ), it has been proposed that methane hydrate dissociation could also occur at this site (Van Rooij et al ., ). The present study thus provides new insights on the origin of the gas venting from Mercator MV Crater Centre.…”

Tracing the composition, fluid source and formation conditions of the methane-derived authigenic carbonates in the Gulf of Cadiz with rare earth elements and stable isotopes

“…Extensive work was carried out by several research groups with the objective to study the fluid escape structures and processes in the Gulf of Cadiz, especially within the middle and lower slope over the last years in order to contribute to the knowledge of the margins structure and basins evolution, hydrocarbons potential and the associated dewatering and fluid migration and escape to the seafloor (e.g., the IOC-UNESCO Training-through-Research program, MVSeis, HERMES and SWINGLO) Gardner et al, 2001;Somoza et al, 2002;Díaz-del-Río et al, 2003;Kenyon et al, 2003;Pinheiro et al, 2003;Somoza et al, 2003;Kopf et al, 2004;Depreiter et al, 2005;Henriet et al, 2005;Rooij et al, 2005;Kenyon et al, 2006;Masson and Berndt, 2006). As a result of coring efforts, 55 mud volcanoes were confirmed, and gas hydrates specifically recovered from five.…”

Shallow Microbial Recycling of Deep-Sourced Carbon in Gulf of Cadiz Mud Volcanoes

“…In particular, no traces of intense seepage of CH 4 at the seafloor have been observed at the sites under study at times when samples were recovered. One notable exception is venting of hydrocarbon-rich fluids at the seabed visually observed at Mercator MV on the Moroccan margin (van Rooij et al 2005).…”