The claim is that these plants haven’t been exposed for thousands of years, as dated by the C14 isotope. At four different ice caps, radiocarbon dates show the mosses had not been exposed to the elements since at least 44,000 to 51,000 years ago. That might be true, but then again they are long dead, so there wouldn’t be any uptake of new C14 if they were exposed to the open air in the past. There’s no claim that the mosses are now suddenly alive and growing again. So, if they had been “exposed to the elements” since then, they would not have an new C14 in them unless they came back to life and conducted photosynthesis.
Since plant material in the Arctic doesn’t decay like it does elsewhere due to low temperature and low humidity, it could very well remain intact while exposed for quite some time. All I think they can claim is that the plants haven’t been alive for 44,000 to 120,000 years. I don’t think they can’t prove with C14 dating that they have not been exposed then reburied under ice/snow since then. Ice is a funny thing, it can melt due to warmer temperatures or it can sublimate at below freezing temperatures if there’s not enough sustaining precipitation, as we
know from Mount Kilimanjaro. What I’d really like to see is what the receding ice edge looks like. Sublimation leaves a signature that is quite different from melting.
