1300-m-high rising bubbles from mud volcanoes at 2080m in the Black Sea: Hydroacoustic characteristics and temporal variability

• Main Authors: Greinert, Jens, Artemov, Y, Egorov, V, De Batist, Marc, McGinnis, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science 2006
• Subjects: Earth and Environmental Sciences; Sorokin Trough; Black Sea; mud volcanoes; bubble seepage; timely variability; hydroacoustic plume – flare; bubble dissolution modeling; Methane hydrate
• Online Access: https://biblio.ugent.be/publication/334182; http://hdl.handle.net/1854/LU-334182

A mud volcano area in the deep waters (>2000m) of the Black Sea was studied by hydroacoustic measurements during several cruises between January 2002 and June 2004. Gas bubbles in the water column give strong backscatter signals and thus can be detected even in great water depths by echosounders as the 38kHz EK500 scientific split-beam system that was used during the surveys. Because of their shape in echograms and to differentiate against geochemical plumes and real upwelling bubble-water plumes, we call these hydroacoustic manifestations of bubbles in the water column ‘flares’. Digital recording and processing of the data allows a 3D visualization and data comparison over the entire observation period, without artefacts caused by changing system settings. During our surveys, we discovered bubble release from three separate mud volcanoes, Dvurechenskiy (DMV), Vodianitskiy (VMV) and the Nameless Seep Site (NSS), in about 2080m water depth simultaneously. Bubble release was observed between 9 June 2003 and 5 June 2004. The most frequently surveyed, DMV, was found to be inactive during very intensive studies in January 2002. The first activity was observed on 27 June 2002, which finally ceased between 5 and 15 June 2004 after a period of continuously decreasing activity. This observed 2-yr bubble-release period at a mud volcano may give an indication for the duration of active periods. The absence of short-term variations (within days or hours) may indicate that the bubble release from the observed mud volcanoes does not undergo rapid changes. The recorded echograms show that bubbles rise about 1300m high through the water column, to a final water depth of about 770m, which is ∼75m below the phase boundary of pure methane hydrate in the Black Sea. With a release depth from 2068m and a detected rise height of 1300m, the flare at VMV is among the deepest and highest reported so far, and gives evidence of highly extended bubble life times (up to 108min) in deep marine environments. To better understand how a ...