Black Sea Methane Flares From the Seafloor: Tracking Outgassing by Using Passive Acoustics

Type Article
Date 2021-08
Language English
Author(s) Longo Manfredi1, Lazzaro Gianluca1, Caruso Cinzia Giuseppina1, Radulescu Vlad2, Radulescu Raluca2, Sciré Scappuzzo Sergio Simone1, Birot Dominique3, Italiano Francesco1
Affiliation(s) 1 : Istituto Nazionale di Geofisica e Vulcanologia, INGV, Palermo, Italy
2 : Institutul National de Cercetare - Dezvoltare pentru Geologie si Geoecologie Marina, GeoEcoMar, Constanta, Romania
3 : Département Ressources physiques et Ecosystèmes de fond de Mer (REM), Unité des Géosciences Marines, IFREMER, Brest, France
Source Frontiers In Earth Science (2296-6463) (Frontiers Media SA), 2021-08 , Vol. 9 , P. 678834 (20p.)
DOI 10.3389/feart.2021.678834
WOS© Times Cited 8
Keyword(s) methane, greenhouse gas, passive acoustics, bubbles, multidisciplinary submarine observatory
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.

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Longo Manfredi, Lazzaro Gianluca, Caruso Cinzia Giuseppina, Radulescu Vlad, Radulescu Raluca, Sciré Scappuzzo Sergio Simone, Birot Dominique, Italiano Francesco (2021). Black Sea Methane Flares From the Seafloor: Tracking Outgassing by Using Passive Acoustics. Frontiers In Earth Science, 9, 678834 (20p.). Publisher's official version : https://doi.org/10.3389/feart.2021.678834 , Open Access version : https://archimer.ifremer.fr/doc/00723/83463/