Monitoring Cold-Seep Emissions at the Shallow Bulgarian Coastal Shelf

The Black Sea experiences widespread methane-rich gas emissions and elevated hydrogen sulfide concentrations, extending from coastal to deep basin areas. The toxicity of hydrogen sulfide and the powerfull greenhouse gas methane, can lead to local acidification, posing threats to ecosystems. Monitoring these compounds is essential for economic growth tied to Black Sea ecosystem services. Also, the rise in seawater temperatures due to climate change increases the risk of the Black Sea releasing methane stored under gas hydrates form into the atmosphere, potentially becoming a important carbon source.The significant release of methane from the seafloor accentuates environmental apprehensions, playing a role in the creation of the Earth's largest anoxic water body (Kosarev, 2007; Riboulot et al., 2017). This underscores the necessity of investigating the dynamics of these gases and closely monitoring their concentrations to gain a comprehensive understanding of their environmental repercussions.

This presentation outlines the fieldwork conducted under the European Project H2020 - DOORS, comprising two field campaigns, METZE and METZE2 (Methane dynamics at Varna lakes and the Zelenska coastal Seeps), which investigated methane dynamics in distinct Black Sea environments, namely Varna Lake and Zelenka gas-seeps. They took place in September 2022 and March 2023. The purpose of this research is to enhance our understanding of the environmental challenges associated with methane concentrations in this unique marine setting. The work initiated a study focused on comprehending methane emissions off the coast of Varna by mapping gas emission sites and measuring their flow rates, taking into account environmental factors such as seasonality and extreme events affecting methane flow rate variability. So, in situ methane sensor deployed for several months at Varna lake indicaticates that the coastal methane fluxes exhibit a noteworthy variability, with daily processes exerting discernible influences on fluxes levels. Also, preliminary findings suggest discernible seasonal fluctuations in both the molecular and isotopic compositions in the water column and sediment pore waters, alongside variations in emission flow rates.

 

Acknowledgements

The authors thank the different projects and programs for their financial supports: DOORS by the EU Project number 101000518, ORAGGE by Interdisciplinary graduate School for the Blue planet (ANR-17-EURE-0015 and "Investissements d'Avenir"), SEAMLESS by INSU LEFE Programme 2022.

References

Kosarev, A. N., 2007, The Black Sea Environment, Springer.

Riboulot, V., Cattaneo, A., Scalabrin, C., Gaillot, A., Jouet, G., Ballas, G., Marsset, T., Garziglia, S., and Ker, S., 2017, Control of the geomorphology and gas hydrate extent on widespread gas emissions offshore Romania: Bulletin De La Societe Geologique De France, v. 188, no. 4.