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.
Name: David Christie
Tel: (907) 474-7836