Methane emission from the seabed into the ocean occurs naturally along most continental margins. Methane release in the form of bubbles commonly escapes the seabed and rises through the water column forming bubble plumes. Since methane is a potent greenhouse gas, understanding which factors influence the methane release rate from submarine sources is important.
Within the scope of the M³ project, funded by the German Ministry for Education and Research (BMBF), and an international collaboration with the University of Washington and the Applied Physics Laboratory, scientists from MARUM have installed a suite of new monitoring instruments at the oceanfloor to monitor methane bubble plumes and to study why their intensity varies over time. The instruments were powered and remotely-operated through the Ocean Observatories Initiative's underwater Regional Cabled Array observatory, for the first time allowing scientists to monitor the bubble plumes at Southern Hydrate Ridge, located in the Northeast Pacific 85 kilometers offshore Oregon at a 780 meter water depth, in near real-time.
Complemented by a UK-led, high-resolution photogrammetric mapping effort of the entire study area, the new study confirms that pressure variations caused by tides affect methane release rate and that bubble plumes are more intense during decreasing tides than rising tides. However, tides are not responsible for all fluctuations, and temporary permeability changes near the sediment-water interface are the most likely cause of the short-term gas emission variability. These findings are significant because they show that methane flux estimations from submarine sources may be largely inaccurate if based on short-term or small-scale measurements.
MARUM produces fundamental scientific knowledge about the role of the ocean and the ocean floor in the total Earth system. The dynamics of the ocean and the ocean floor significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, and create unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society and the marine environment, and in accordance with the Sustainable Development Goals of the United Nations. It publishes its quality-assured scientific data and makes it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperates with commercial and industrial partners in accordance with its goal of protecting the marine environment.