Not sure if you are trolling of really believe this to be true, but for anyone else assuming good faith: The diffusion aspect is (of course) well-modeled, see e.g. references under "past greenhouse gasses" at [0].
They have found some meltwater layers with unexpectedly large quantities of CO2 > 750ppm.
But they also show that there is unexpected heavy diffusion around the meltwater layers. And they argue very compellingly, that the ice core CO2 records have been smoothed through natural diffusion.
Why is this information not given when showing this graph?
Where is it well-modelled? Noble gasses will diffuse differently from CO2. And on-top of diffusion of course CO2 will make hydrogen bonds with water in the ice.
It is well-understood that many ice cores give the same relative shape of peaks of various gasses through time.
Going from there to claiming knowing the absolue concentrations without very large error bars, is just not science.
"Carbon dioxide measurements from older ice in Greenland is less reliable, as meltwater layers have elevated carbon dioxide (CO2 is highly soluble in water)."
[0]: https://www.antarcticglaciers.org/glaciers-and-climate/ice-c...