It is also very hard to know what effect methane from melting permafrost will do and if we will encounter significant releases of methane clathrates in ocean sediment. (illconsidered.blogspot.ru)
Could it also be due to anoxia happening when methane clathrates melt — the methane combines with oxygen, forming CO2 and such, depleting the oxygen. (realclimate.org)
The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water, though this is dependent on how many methane molecules «fit» into the various cage structures of the water lattice. (princeton.edu)