Potential environmental control of free shallow gas in the seafloor of Eckernförde Bay,Germany |
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| Institution: | 1. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, SOA, Qingdao 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. School of Earth Sciences, China University of Geosciences (Wuhan), Wuhan 430074, China;4. Institute of Geography and Planning, Ludong University, Yantai 264025, China;5. Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China;6. Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;1. Oceanographic Institute of the University of São Paulo, 05508-120 Praca do Oceanográfico, 191 São Paulo, Brazil;2. Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Avenida de las Palmeras 4, Armilla, Spain;3. Dr. Moses Strauss Department of Marine Geosciences, Leon H Charney School of Marine Sciences, University of Haifa, Israel;4. Institute of Energy and Environment of the University of São Paulo, Brazil |
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| Abstract: | The depth of the free methane gas horizon in Eckernförde Bay, Western Baltic Sea, was monitored over 4 months in 1-h intervals with an echo sounder mounted on a tower at the seafloor. The depth to the top of the free gas varied between 50 cm and 100 cm below seafloor. Short-term fluctuations of free gas depth are related for the most part to changes of total pressure (air pressure and water level), the observation period was too short to demonstrate the effect of the annual temperature cycle.The correlation of gas depth changes and total pressure agrees well with theory which predicts a linear influence of pressure fluctuations on gas solubility. Since the methane content in the pore water of Eckernförde Bay is at the saturation limit environmental changes (pressure and temperature variations) cannot be buffered and have an instant impact on free gas presence.The implications of this observation are manifold. Geo-technically, the bearing strength of the seafloor is altered by the presence of gas bubbles. Similarly, sonar systems are influenced by the presence of gas bubbles which alter the acoustic seafloor properties. Of ecological interest is that pressure drops can trigger a sudden ebullition of the greenhouse gas methane from the seafloor into the atmosphere. |
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