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Southampton Marine and Maritime Institute

New tool for measuring frozen gas in ocean floor sediments

Published: 19 March 2013Origin: Engineering

A new collaboration between the University of Southampton and National Oceanography Centre (NOC) is seeking to improve geophysical remote sensing of seafloor methane gas and hydrate through innovative laboratory experimental and theoretical studies.

Researchers will develop a new laboratory instrument capable of simulating the high pressures and low temperatures needed to create methane hydrate in sediment samples and carry out acoustic and electrical properties experiments. The results will be used to develop theory for modelling geophysical survey data in terms of seafloor gas and hydrate content.

Professors Tim Leighton and Paul White from the University of Southampton’s Institute of Sound and Vibration Research (ISVR) and Dr Angus Best of NOC have been awarded a grant of £0.8 million by the Natural Environment Research Council (NERC) to investigate methods for assessing the volume of methane gas and gas hydrate locked in seafloor sediments.

Dr Best, who is leading the project, explains: “Natural methane, a greenhouse gas, is trapped in sediments beneath the seafloor on continental shelves and slopes around the world, sometimes as methane hydrate - a solid, ice-like material. Currently, there are only very broad estimates of the amount of seafloor methane and hydrate. Improvements to geophysical remote sensing methods, especially acoustic methods, offer a way to better assess this important store of greenhouse gas.”

Apart from the possible impact on ocean acidification and global warming if seafloor methane were released in to the water column or atmosphere, methane hydrates are a potentially important energy resource. This week it was announced that for the first time, natural gas has been extracted from frozen methane hydrate in a pilot production project off the Japanese coastline, and other countries are also exploring options for exploiting this energy resource. Methane hydrates may also contribute to geo-hazards such as seafloor landslides – it is thought that earthquakes and the release of gas hydrates caused the largest-ever landslide, the Storegga Slide, around 8,000 years ago.

The team plan a series of experiments on a range of sediment types, such as sand and mud. They intend to map out the acoustic and electrical properties of differing amounts of free methane gas and frozen solid methane hydrate.

The laboratory-based approach adopted by the team will involve the development of a major new Acoustic Pulse Tube instrument at NOC. Using acoustic techniques and theories developed by the ISVR team, they aim to provide improved geophysical remote sensing capabilities for better quantification of seafloor gas and hydrate deposits in the ocean floor.

Professor Leighton says: “Not much is known about the state of gas morphology – bubbles. Muddy sediments show crack-like bubbles, while sandy sediments show spherical bubbles. Only dedicated lab experiments can hope to unravel the complex interactions. By creating our own ‘cores’ of sediment material in a controlled environment where we know the concentrations of methane, we can create models to help us with in situ measurements on the seafloor.”

Professor Leighton adds: “The three of us have collaborated in recent years in an experiment that used acoustics to take preliminary measurements of gas in the muddy sediments revealed at low tide. Those measurements, and the acoustic theory we developed to interpret the data, provided exactly the foundation we needed to undertake this critically important study that will be relevant to the seabed in somewhat deeper waters.

“As a greenhouse gas, methane is 20 times more potent per molecule than carbon dioxide. There is the potential for climate change to alter sea temperatures and cause more methane gas to be released from seabed hydrates into bubbles which reach the atmosphere. It is therefore vital that we have the tools to quantify and map the amount of methane that is down there.”

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Notes for editors

 

With over 23,000 students, around 5,000 staff, and an annual turnover well in excess of £435 million, the University of Southampton is acknowledged as one of the country's top institutions for engineering, computer science and medicine. We combine academic excellence with an innovative and entrepreneurial approach to research, supporting a culture that engages and challenges students and staff in their pursuit of learning.

The University is also home to a number of world-leading research centres, including the National Oceanography Centre, Southampton, the Institute of Sound and Vibration Research, the Optoelectronics Research Centre, the Centre for the Developmental Origins of Health and Disease, the Mountbatten Centre for International Studies and the Southampton Statistical Sciences Research Institute

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