Mystery of Methane on Mars

Recently the Curiosity Rover reported very low concentrations of Methane in the atmosphere of Mars at its landing site at the moment in time of the test.

Previously several observational sources (orbital and earth based telescopes) had reported significant amounts of Methane in the atmosphere, some of which was in plumes of high concentration. They even pinpointed those plume sources.

At the moment these two results, which are both considered accurate and true, seem at odds with each other. But if both measurements and results are accurate (which they appear to be), then it leaves us with an even better mystery than just whether Methane exists on Mars... it implies that we need to explain what happens to the Methane in the atmosphere.

http://www.newscientist.com/article/dn24227-mystery-deepens-as-martian-methane-eludes-curiosity.html#.UkHeI2Q4XKl

http://www.newscientist.com/article/dn16429-methane-pockets-may-narrow-search-for-mars-life.html#.UkHegmQ4XKl

If we take all the observational and measured results (from Curiosity) as true and accurate, then we must assume that there is Methane on Mars and that it is not evenly distributed in the atmosphere even though it should take several hundred years to break down. It seems to me that in order for us to observe plumes in concentration and to then measure almost zero content in other locations that we have to start wondering about a process which not only produces Methane and releases it into the atmosphere, but also a process which removes it from the atmosphere (all on very short time intervals similar to seasonal intervals).

From what I gather from the articles I've read, Methane can be produced by organic and inorganic processes. And the removal of Methane can also occur organically or inorganically. However, both the organic and inorganic removal processes are not well defined and purely speculative at this point.

Right now most of the news articles (and NASA articles) I've read seem to be focused on how disappointing it is for Curiosity not to have found Methane, but I think the real story is "where did the Methane go?".

All of the speculation above is subject to the assumption that the two sets of evidence with regard to Methane are true and accurate. So the first question I've been trying to resolve is whether one (or both) of the test/observations are not accurate or true.

The observational evidence reported for almost a decade now seems very strong. Apparently nobody disputes it, but I would like to confirm this. Just how well respected is that observational evidence?

Does anybody think that we're at a point where we need to question the observations/measurements? Or are we now at the next step of explaining what is apparently a Methane Cycle of some type occurring on Mars?

More detailed information:
http://www.sciencedirect.com/science/article/pii/S0019103512004599