How much of the greenhouse gas methane is transported from the seafloor to the atmosphere is unclear. Here, we present data describing an extensive ebullition event that occurred in Eckernförde Bay, a shallow gas-hosting coastal inlet in the Baltic Sea, in the fall of 2014. A weak storm induced hydrostatic pressure fluctuations that in turn stimulated gas ebullition from the seabed. In a finely tuned sonar survey of the bay, we obtained a hydroacoustic dataset with exceptionally high sensitivity for bubble detection. This allowed us to identify 2849 bubble seeps rising within 28 h from the seafloor across the 90 km² study site. Based on our calculations, the estimated bubble-driven episodic methane flux from the seafloor across the bay is 1,900 μMol m−2 d−1. Our study demonstrates that storm-associated fluctuations of hydrostatic pressure induce bulk gas-driven ebullitions. Given the extensive occurrence of shallow gas-hosting sediments in coastal seas, similar ebullition events probably take place in many parts of the Western Baltic Sea. However, these are likely to be missed during field investigations, due to the lack of high-quality data acquisition during storms, such that atmospheric inputs of marine-derived methane will be highly underestimated.
Bibliographical noteFunding Information:
This project was initially funded by the Cluster of Excellence 80 “The Future Ocean”. The “Future Ocean” was funded within the framework of the Excellence Initiative by the Deutsche Forschungsgemeinschaft (DFG) on behalf of the German federal and state governments. We appreciate the support by Svend Mees during the calibration of the EK60, and the support from Olaf Lautenschläger (KONGSBERG) and want to thank the crew of R/V ALKOR. Validations of the event based findings were provided by the yearly geophysical lectures on R/V ALKOR conducted by the Marine Geophysics and Hydroacoustics working group of Kiel University. The research supporting this manuscript additionally received funding from BONUS, funded jointly by the European Union’s Seventh Programme for research through grant no. FKZ 03F0768 (BONUS ECOMAP). We acknowledge financial support by DFG-Open Access-Publikationsfonds.
© 2020, The Author(s).
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