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Richard C (NZ):
March 26th, 2011 at 8:49 am
The ice core record (Law Dome spliced to Mauna Loa) is a bit dodgy too.
Evidence for molecular size dependent gas fractionation in firn air derived from noble gases, oxygen, and nitrogen measurements
Huber et al 2005
http://icebubbles.ucsd.edu/Publications/Huber_closeoff_EPSL2006.pdf
6. Conclusions
The enrichment of elemental ratios near the close-off region measured in the firn air from Devon Island and NGRIP, can be modeled assuming a constant close-off fractionation factor between closed off air and open pore composition during air enclosure. The strong similarities found at both sites indicate a universal physical process causing this close-off fractionation. Our model approach
is able to explain and predict the general shape of the firn air profiles from various different sites. However, it fails when the firn density structure has impermeable layers that cause large non-diffusive zones at the bottom of the firn. This has to be implemented into a future model.
The bottom of the firn is critical. This is the inclusion zone where firn transforms to solid ice.
Close-off fractionation factors for different gases depend strongly on the diameter.
Except they use an inappropriate diameter. They use collision diameter (molecules colliding with other molecules) when they should be using kinetic diameter (the aperture size that will let a molecule pass, CO2 collision dia 39nm, CO2 kinetic dia 33nm).
The mass of the molecule is less important, since the effect on isotope ratios is very low. The critical size of about 3.6 Å [36nm] seems to be an upper limit up to which molecules fractionate during the close-off process in the firn.
CO2 will pass 36nm if kinetic dia is used.
A possible explanation for this could be the diffusion of molecules through channels in the ice lattice. From our findings we believe that the effect of close-off fractionation is nonexistent or at least very small for isotope ratios and for large molecules, like Xe, Kr, N2, CO2, CH4, and N2O.
They have only considered a simple sieving mechanism. Others, notably Ideka-Fukusawa et al describe a hydrogen bond breaking lattice distorting mechanism where CO2 passes through the ice latice.
http://www.nanonet.go.jp/english/mailmag/2005/054b.html
This is an important confirmation for the integrity of polar ice cores as a climate archive of the ancient atmospheric composition of these gases.
I don’t think so. I would be interested in any comments on this either here or at CCG
http://www.climateconversation.wordshine.co.nz/2011/03/fallen-snow/
This bears repeating at every available opportunity too.
The “correction”:-
……the average age of air was arbitrary decreed to be exactly 83 years younger than the ice in which it was trapped. The “corrected” ice data were then smoothly aligned with the Mauna Loa record (Figure 1 B), and reproduced in countless publications as a famous “Siple curve”. Only thirteen years later, in 1993, glaciologists attempted to prove experimentally the “age assumption”[10], but they failed[9].”
“CO2: The Greatest Scientific Scandal of Our Time”
by Zbigniew Jaworowski, M.D., Ph.D., D.Sc., March 2007
http://www.warwickhughes.com/icecore/
This is the dataset that ALL IPCC climate models use for initialization and subsequent simulations are based on, the results of which became the basis of govt policy.
I'm sure the analysis of what they have in hand is very precise (although that post seems to question exactly that) but have they thought of all the possible factors that could affect those gasses through the centuries? One unsuspected reaction could alter every conclusion they have come to.