Seafloor geological studies above active gas chimneys off Egypt (Central nile deep sea fan)

Type Article
Date 2007-07
Language English
Author(s) Dupre StephanieORCID1, Woodside J1, Foucher Jean-Paul2, De Lange G3, Mascle J4, Boetius A5, Mastalerz V3, Stadnitskaia A6, Ondreas Helene2, Huguen C7, Harmegnies Francois2, Gontharet Swanne8, Loncke L9, Deville E10, Niemann H5, Omoregie E5, Olu Karine11, Fiala Medioni A12, Dahlmann A3, Caprais Jean-Claude11, Prinzhofer A10, Sibuet Myriam11, Pierre C8, Damste J6
Affiliation(s) 1 : Vrije Univ Amsterdam, Fac Earth & Life Sci, Sedimentol & Marine Geol Dept, Amsterdam, Netherlands.
2 : Ifremer, Brest Ctr, Dept Geosci Marines, Plouzane, France.
3 : Univ Utrecht, Geosci Dept, Utrecht, Netherlands.
4 : Geosci Azur, Villefranche Sur Mer, France.
5 : Max Planck Inst Marine Microbiol, Bremen, Germany.
6 : NIOZ, Texel, Netherlands.
7 : Univ Perpignan, Perpignan, France.
8 : LOCEAN, UPMC, Paris, France.
9 : Univ Amiens, Amiens, France.
10 : Inst Francais Petr, Rueil Malmaison, France.
11 : Ifremer, Ctr Brest, Lab Environm Profond, F-29280 Plouzane, France.
12 : UPMC, Observatoire Océanologique de Banyuls, France
Source Deep Sea Research Part I: Oceanographic Research Papers (0967-0637) (Elsevier), 2007-07 , Vol. 54 , N. 7 , P. 1146-1172
DOI 10.1016/j.dsr.2007.03.007
WOS© Times Cited 73
Keyword(s) Seafloor morphology, Methane, Authigenic carbonate precipitation, Gas chimneys, Mud breccia, Mud volcanoes, Fluid seepage, Nile fan
Abstract Four mud volcanoes of several kilometres diameter named Amon, Osiris, Isis, and North Alex and located above gas chimneys on the Central Nile Deep Sea Fan, were investigated for the first time with the submersible Nautile. One of the objectives was to characterize the seafloor morphology and the seepage activity across the mud volcanoes. The seepage activity was dominated by emissions of methane and heavier hydrocarbons associated with a major thermal contribution. The most active parts of the mud volcanoes were highly gas-saturated (methane concentrations in the water and in the sediments, respectively, of several hundreds of nmol/L and several mmol/L of wet sediment) and associated with significantly high thermal gradients (at 10 m below the seafloor, the recorded temperatures reached more than 40 °C). Patches of highly reduced blackish sediments, mats of sulphide-oxidizing bacteria, and precipitates of authigenic carbonate were detected, indicative of anaerobic methane consumption. The chemosynthetic fauna was, however, not very abundant, inhibited most likely by the high and vigorous fluxes, and was associated mainly with carbonate-crust-covered seafloor encountered on the southwestern flank of Amon. Mud expulsions are not very common at present and were found limited to the most active emission centres of two mud volcanoes, where slow extrusion of mud occurs. Each of the mud volcanoes is fed principally by a main narrow channel located below the most elevated areas, most commonly in the centres of the structures. The distribution, shape, and seafloor morphology of the mud volcanoes and associated seeps over the Central Nile Deep Sea Fan are clearly tectonically controlled.
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Dupre Stephanie, Woodside J, Foucher Jean-Paul, De Lange G, Mascle J, Boetius A, Mastalerz V, Stadnitskaia A, Ondreas Helene, Huguen C, Harmegnies Francois, Gontharet Swanne, Loncke L, Deville E, Niemann H, Omoregie E, Olu Karine, Fiala Medioni A, Dahlmann A, Caprais Jean-Claude, Prinzhofer A, Sibuet Myriam, Pierre C, Damste J (2007). Seafloor geological studies above active gas chimneys off Egypt (Central nile deep sea fan). Deep Sea Research Part I: Oceanographic Research Papers, 54(7), 1146-1172. Publisher's official version : https://doi.org/10.1016/j.dsr.2007.03.007 , Open Access version : https://archimer.ifremer.fr/doc/00000/4455/