- 1Ifremer, Univ Brest, CNRS, UMR Geo-Ocean, F-29280 Plouzané, France
- 2IFPEN, Rueil-Malmaison, France
- 3Groupe Spectroscopie Moléculaire, ISM, UMR 5255 CNRS, Univ. de Bordeaux, Talence, France
- 4Univ. Lille, CNRS, UMR 8523, PhLAM – Physique des Lasers, Atomes et Molécules, CERLA – Centre d’Etudes et de Recherche Lasers et Applications, F-59000, Lille, France
- 5Ifremer, Univ Brest, CNRS, UMR BEEP, F-29280 Plouzané, France
In the western Black Sea, gas hydrates are found at water depths greater than 660 m and are often associated with areas of active gas seepages. Their occurrence has been inferred from both geophysical data (1) and coring operations (2). During the GHASS-2 cruise (2021) offshore Romania, gravity cores containing hydrate were recovered from a ridge site and from a newly mapped mud volcano site. This work integrates data from field observations coupled with physico-chemical and geochemical analyses of gas hydrate, pore fluids and sediments in order to explore the local dynamics of gas hydrate and their interplays with geochemical processes. Gas hydrates are mainly composed of methane (99.6%), and are formed by filling subparallel fractures, as networks of interconnected veins, or as agglomerated nodules, resulting from the combined effect of sediment properties and the fault/fractures system. The combination of chloride porewater anomalies and in situ pore pressure and temperature measurements argues in favor of a recent and/or fast hydrate formation at the ridge area. In addition, microstructural analysis by Raman spectroscopy shows local enrichment of H2S in hydrate cages at the mud volcano site. This H2S, trapped in gas hydrates, is interpreted to stem from the anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR) taking place just above the hydrate occurrence zone. Taken together, these results provide new insights onto processes occuring at hydrate areas in the Romanian sector of the Black Sea.
Acknowledgements
The authors thank the different projects and programs for their financial supports: DOORS by the EU Project number 101000518, and BLAME by the ANR (ANR18-CE01-0007).
References
1. Popescu I, Lericolais G, Panin N, De Batist M, Gillet H. Seismic expression of gas and gas hydrates across the western Black Sea. Geo-Marine Letters. 2007;27(2):173-83.
2. Ker S, Thomas Y, Riboulot V, Sultan N, Bernard C, Scalabrin C, et al. Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea. Geochemistry, Geophysics, Geosystems. 2019;20(1):442-59.
How to cite: Agnissan, C. A.-C., Fandino, O., Haidar, R., Giunta, T., Crémière, A., Guimpier, C., Chazallon, B., Desmedt, A., Pirim, C., Brandily, C., Donval, J.-P., Chéron, S., Philippon, X., Riboulot, V., and Ruffine, L.: Physical and geochemical dynamics of shallow hydrates-bearing sediments at two active seepages sites in the western Black Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21766, https://doi.org/10.5194/egusphere-egu25-21766, 2025.
