Acoustical surveys of Methane plumes using the quantitative echo sounder in Japan Sea

Multiple gas reservoirs are responsible for the gas emissions along the Marmara fault network

“…Intensive gas emissions are common and widespread processes in oceanic and continental marine basins. Amongst the areas on Earth where they have been densely observed, one can cite offshore Siberia (Shakhova et al, 2014), the Norwegian continental margin including the well-studied Hakon Mosby Mud Volcano (Gentz et al, 2014;Sauer et al, 2015;Westbrook et al, 2009), the North Sea (Borges et al, 2016;McGinnis et al, 2011;von Deimling et al, 2011), the Black Sea (Klaucke et al, 2006;Roemer et al, 2012a), the Sea of Marmara (Dupré et al, 2012;Dupré et al, 2010a), the Aquitaine Shelf (Dupré et al, 2014;Ruffine et al, 2017), the Central Nile Deep-Sea Fan (Dupré et al, 2010b;Roemer et al, 2014a), the US Atlantic Margin (Skarke et al, 2014;Weinstein et al, 2016), the Gulf of Mexico (Bernard et al, 1976;Hu et al, 2012), the Santa Barbara Basin (Clark et al, 2010), the Hydrate Ridge (Haeckel et al, 2004;Milkov et al, 2005;Philip et al, 2016), the Makran continental margin (Roemer et al, 2012b), the South China Sea (Di et al, 2014;Huang et al, 2009), the Japan Sea (Aoyama et al, 2007), as well as offshore New Zealand (Greinert et al, 2010) and the Southern Ocean (Roemer et al, 2014b). Such phenomena occur either as dissolved or free gases, and they lead to the formation of specific sites called cold seeps (Hovland and Judd, 1988;Suess, 2014;Talukder, 2012).…”

Labile barite contents and dissolved barium concentrations on Blake Ridge: New perspectives on barium cycling above gas hydrate systems

“…These modern "gas hydrate systems" are clearly open, and provide carbon fluxes to the ocean (Dickens, 2003). In several places, notably along faults, CH 4 migrates up from gas hydrate and free gas horizons to the seafloor where it vents to the water column (e.g., Tryon et al, 2002;Wiedicke et al, 2002;Aoyama et al, 2004). For many gas hydrate systems, however, anaerobic oxidation of methane (AOM) in shallow sediment dominates the carbon output (Fig.…”

Ocean Dynamics and Methane Plume Activity in Tatar Strait, Far Eastern Federal District, Russia as Revealed by Seawater Chemistry, Hydroacoustics, and Noble Gas Isotopes

“…Although to date there have not been ROV deployments to directly observe the seafloor seeps in Tatar Strait, the flares themselves (Figure 3) are thought to be comprised of free gas, free gas enclosed in a gas hydrate shell, or gas hydrate flakes similar to those observed elsewhere in related studies including at Umitaka Spur (Aoyama et al, 2007). In these cases, it has been shown that the ascending gas hydrate melts and gas bubbles disperse within the water column before reaching the subsurface (II) and surface (I) waters (e.g., Greinert et al, 2006;Salomatin et al, 2014).…”

“…If the most intense red and orange areas within the hydroacoustic flares (Figure 3) do in fact represent such gas hydrate which forms layers around rising gas bubbles as has been observed elsewhere in the Japan Sea (Aoyama et al, 2007), it is clear that the gas hydrate bubbles could extend into lower intermediate (IIIb) and even upper intermediate (IIIa) water masses, above the predicted range of gas hydrate stability (Figure 7A) as calculated from the equation of Dickens and Quinby-Hunt (1994). Shakirov et al (2019) interpreted some of the shallower gas anomalies as being due to the dissociation gas hydrate bubbles, based on observations by Yapa et al (2001), whereby gas hydrate from seeps which are relatively rich in ethane and propane, with C 1 /(C 2 +C 3 )<6, can remain stable at higher temperatures and shallower depths, even shallower than intermediate waters (IIIa and IIIb) found in Tatar Strait.…”

“…The Tatar Strait plumes differ from plumes situated offshore of NE Sakhalin (Salomatin et al, 2014) and Umitaka Spur (Aoyama et al, 2007) in that the location of gas venting in Tatar Strait is significantly shallower. Plumes at Umitaka Spur, Sea of Japan (Figure 1A) are at 900 m or more (Aoyama et al, 2007;Hiruta et al, 2015), while numerous plumes situated in the Okhotsk Sea to the northeast of Sakhalin Island are mostly found between 500 and 1000 m (Jin et al, 2011). Any gas hydrate forming at 350 m at the base of the Tatar Strait Plumes, would travel a much shorter distance before dissociating and dissipating into the water column.…”