And I'll bet the CO2 in ice core bubbles doesn't degrade one little bit being in contact with all that frozen and often liquid H2O for all that millenia, no sirree. Can you insure that those ice cores came from glaciers in which no liquid water occured in the time the CO2 was trapped?
Why should it degrade? The ice cores are from Greenland or Antarctic ice caps. If you want to know more, try searching on the subject. I have extreme confidence that the CO2 concentrations measured in ice core bubbles are accurate, because they've been independently determined from more than one ice core.