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Lowered ocean levels as a trigger for methane release...



At the last glacial maximum (~19ka bp) ocean levels were reduced ~100m below 
present day levels. This implies a minimum reduction of ~ 10 atmospheres of 
pressure on methane clathrate deposits that previously formed when ocean levels 
were at or above present-day levels. I speculated some time ago that pressure 
reduction from lowered sea levels could trigger methane releases and subsequent 
warming, thereby limiting the amount of water that could be locked up as ice at 
any given time, and acting as a limiter on glaciation/ice ages. Assuming that 
clathrate deposits were abyssal, I decided that the relative change of pressure 
would be unlikely to cause the release of significant methane quantities, and 
moved on.

However, this from wikipedia --

"However, improvements in our understanding of clathrate chemistry and
sedimentology have revealed that hydrates only form in a narrow range
of depths (continental shelves), only at some locations in the range of depths 
where they could occur..." -- Wikipedia

This implies that clathrates form at depths where a 10 atmosphere pressure 
reduction could be relatively significant (eg, at a depth of 1000m, pressure 
would be reduced 10% by a 100m drop in sealevel, or at 500m the reduction would 
be 20%). 

Although I am aware of ocean warming triggered by impacts or volcanism as a 
hypothesized trigger for methane release and subsequent climate excursions, I 
never seen pressure reduction from lowered ocean levels advanced as a trigger 
for methane burps, or as a 'natural' limiter of glaciation. 

Any climate geeks out there got a ref, comment, or falsification?

Don