Origin and structure of methane, hydrates and fluid flows in the Black Sea - Cruise No. MSM15/2 - May 10-June 02, 2010 - Istanbul (Turkey)-Piraeus (Greece) (English)

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The aim of the cruise was to perform AUV and ROV pre-site surveys of potential drill sites which are planned to be drilled during a MeBo cruise in 2011 in the Black Sea. The selected locations represented deposits where shallow gas hydrates have already been sampled by gravity and piston coring and where gas emissions to the water column have been detected. For the first time we could acquire AUV bathymetric maps from five gas hydrate sites of the Black Sea in Ukrainian and Georgian waters. In the Sorokin Trough two mud volcanoes, the Dvurechenskii MV and the Helgoland MV were mapped by the AUV, which gave us very detailed information to plan and conduct ROV dives on the mud volcanoes. The maps allowed us to investigate mud pools for the first time in the center of Helgoland MV. Temperature measurements showed clearly higher temperatures in sediments of the Helgoland MV, in contrast to Dvurechenskii MV which showed a constant temperature of 16.5° C between 10-30 mbsf. Since 16.5° C marks the gas hydrate stability boundary the temperature is interpreted as a result of diverse gas hydrate dynamics (decomposition and formation of gas hydrates). Further site surveys have been performed at a new flare site in 1700 m water depth and at Kerch Flare which is a prominent gas emission site in the eastern Sorokin trough at 900 m water depth. Due to restrictions only one seep site in Georgian waters, the Colkheti oil seep on the western side of Kobuleti Ridge could be mapped in detail. The AUV surveys have been accompanied by ROV dives, which were used to quantify gas ebullition from the seabed, acoustic imaging of flares and bathymetric surveys of larger areas of gas hydrate presence.