Abstract
The Black Sea bottom is well known to be earth’s largest anaerobic methane source, hosting a huge amount of cold seeps releasing significant volumes of methane of both thermogenic and biogenic origin. Taking into account the well-known effects of methane concerning global warming, including the warming up of the oceans, an effective monitoring of its output from the Black Sea is nowadays an essential target for interdisciplinary studies. We discuss the results achieved during monitoring campaigns aimed to detect and track methane flares from the seafloor of the Romanian sector of the Black Sea, in order to better constrain the possible mechanisms responsible for its injection from the marine sediments, through the water column, into the atmosphere. In the mainframe of the ENVRI-Plus project, we deployed a multidisciplinary seafloor observatory for short, mid and long time monitoring and collected samples of the water column. The multidisciplinary seafloor observatory was equipped with probes for passive acoustic signals, dissolved CH4 and chemical-physical parameters. The collected data showed a high concentration of dissolved methane up to values of 5.8 micromol/L. Passive acoustics data in the frequencies range 40–2,500 Hz allow us to discriminate different degassing mechanisms and degassing styles. The acoustic energy associated with gas bubbling is interpreted as a consequence of the gas dynamics along the water column while the acoustic range 2–20 Hz reveals vibration mechanisms generated by gas dynamic’s along the cracks and inside the sediments.
Highlights
Methane is the second major contributor to the greenhouse effect after carbon dioxide (Shindell et al, 2009)
The multidisciplinary seafloor observatory, able to operate in extreme environments up to the depth of 4,000 m, has been equipped with probes for passive acoustic signals, dissolved methane, temperature, hydrostatic pressure, conductivity, pH and turbidity
The geochemical features of the dissolved gases along the water column show a methane content which increases in the deep water layers besides lowering of pH down to 7.8 or negative Eh values
Summary
Methane is the second major contributor to the greenhouse effect after carbon dioxide (Shindell et al, 2009). Black Sea Methane by Passive-Acoustics trapped to form natural gas accumulations, and some other is sequestered by the formation of gas hydrates, ice-like mixtures of water and gas. Gas hydrate molecules are trapped within a cagelike framework of hydrogen-bonded water molecules, formed under very specific temperature and pressure conditions where sediments contain both water and an adequate supply of gas. Methane injection into the water column may contribute to the ocean acidification due to its oxidation in shallow shelf areas, like the Black Sea, the CH4 release from the seafloor has a greater potential to enter the atmosphere. During 2019, in the mainframe of ENVRIplus, a Horizon 2020 project bringing together Environmental and Earth System Research Infrastructures, we carried out three oceanographic cruises over the Romanian sector of the Black Sea with the aim to better constrain the possible mechanisms of methane injection into the atmosphere by detecting methane flares at the seafloor and tracking them across the water column
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
