A new approach to monitor the global climate threat from methane emissions
This story entered on 7th Mar, 2007 09:01:47 AM PST

Using passive acoustics, scientists supported by NURP have developed a new technique to monitor emissions of the potent greenhouse gas, methane, from the seabed. This new approach will allow scientist to understand the climate threat from seabed methane emmisions. Methane is stored in and on the seafloor as hydrate (ice-like) deposits. These deposits are susceptible to catastrophic events, potentially resulting in the direct venting of methane to the atmosphere, raising the atmospheric concentration of this greenhouse gas, and ultimately affecting global warming among other processes.

NURP-funded investigators Ira Leifer (University of California, Santa Barbara) and Dajun Tang (University of Washington) have recently published a manuscript in the Journal of the Acoustical Society of America (January 2007, 121 (1), pp. EL35-EL40). This work began with visual observations of gas bubbles being release from the seafloor during manned submersible dives with the submarine Delta off the southern coast of California in the Santa Barbara Channel. The rate of gas release from this seafloor site is sufficient such that bubbles ascend the water column and escape to the atmosphere.

As part of a multi-disciplanary program, Leifer and Tang mounted a hydrophone on the submersible Delta to quantify the size and distribution of bubbles as they form. Enumerating physical characteristics of bubbles is an issue that confounds a broad spectrum of geophysical and industry applications. In the case of marine hydrate seeps, the primary interest in these parameters is to ascertain the fate of bubbles in the water column and determine the rate at which bubbles escape to the atmosphere. They monitored sound from seabed bubble formation (seabed bubble music) to calculate the size and number of bubbles formed. Their method uses the tone of the bubble to measure its size; bigger bubbles have more bass, and smaller bubbles have more treble. The sound of bubble formation lasts a few tens of a millisecond and the frequency of these sounds allows them to calculate the rate of bubble formation. By listening to seabed music, scientists can determine if bubble formation is increasing or decreasing, allowing them to estimate the quantity of methane being released and that portion of methane that reaches the sea surface.

To learn more about bubbles, marine seeps, and the science of bubbles and to watch short movies of individual bubbles, please go to http://www.bubbleology.com.

Contact information
Name: David Christie
Tel: (907) 474-7836
dchristie@guru.uaf.edu