Methane
escaping from the ocean-floor in polar zones. There, under high pressure
and low temperatures, methane can remain captive in cage-like structures
formed of water molecules (called clathrate or gas hydrates) until the
warming of the waters or sea floor movement release it to the atmosphere.
These emissions could have been enormous at some periods in the past.
Methane itself and the carbon dioxide that comes out of its oxidation
in the water or in the atmosphere, cause a “greenhouse” warming
effect. For some, these emissions are key to the deglaciation process.
Values
of carbon 13 (d13C) in different reservoirs. The values are large and
negative in continental and marine organic matter. Methane is poor in
d13C due to its biological origin. Therefore, the periods when the carbon
sediment is poor in this isotope can indicate the existence of large emission
episodes.
