Dew, The newspaper writer is probably considering: CH4+O2=CO2+H2O.
The 1st problem is kinetic. While the righthand side of the equation is thermodynamically favored the reaction is quite slow (like diamonds not transforming to graphite as they sit on women's fingers). Without input of a sufficient activation energy you could happily bubble methane and oxygen thru warmish water forever, regardless of the water column's length, and nothing would happen other than some small amount of the gases would dissolve in the water.
The 2nd problem is a simple logical conundrum created by the author, e.g. if methane is not going to be oxidized in the atmosphere it sure isn't going to be oxidized in a more oxygen deficient environment (ignoring the possible intercedence of methanogenic bacteria).
The 3rd problem is more subtle: the methane being considered is derived from decomposition of methane hydrates (a solid). If my memory is correct, these are only stable in pure water below about 16 C (CO2 hydrates are stable below about 10 C). The maximum stability temperature is lowered by the presence of salt in the water. So with regard to the methane hydrates in the Arctic, those that are in shallow water, where ice cover is being lost, are more susceptible to reaching the decomposition point.
The decomposition is not kinetically inhibited and can be explosive with very unhappy consequences under some circumstances (like when some yahoo uses a torch to warm up a pipeline clogged with hydrate). Conversely, the temperature in the deep sea is relatively stable and is below the methane hydrate decomposition point even in seawater. So if there is a leaky hydrocarbon reservoir beneath the seafloor in deepwater, the methane accumulates on the seafloor as it contacts the seawater rock interface rather than bubbling up thru the seawater column (below a few meters of the interface the geothermal gradient maintains the methane as a gas).
As a bit of an aside, an input of mechanical energy can easily be sufficient to cause spontaneous decomposition of hydrates. This combined with a bulk density that is less than seawater could lead to some interesting mass releases of methane (or CO2) from the deepsea. Some folks think these sorts of mass release may explain the disappearances of planes and ships in the "Bermuda Triangle".
On a more practical front of interest to you, formation of these hydrates in seafloor pipelines and infrastructure is a major problem for the development of deepwater hydrocarbon reservoirs.
The stuff you might read about natural hydrates being a economic resource is most likely bunk. Other resources will be much cheaper for far longer than we'll be alive. regards, Charlie
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