We performed detailed 2H isotope diffusion measurements
in the upper 3 m of firn at Summit, Greenland.
Using a small snow gun, a thin snow layer was formed from
2H-enriched water over a 6 × 6 m2
area. We followed the diffusion
process, quantified as the increase of the δ
length, over a 4-year period, by retrieving the layer once per
year by drilling a firn core and slicing it into 1 cm layers and
measuring the δ
2H signal of these layers.
We compared our experimental findings to calculations
based on the model by Johnsen et al. (2000) and found substantial
differences. The diffusion length in our experiments
increased much less over the years than in the model. We
discuss the possible causes for this discrepancy and conclude
that several aspects of the diffusion process in firn are still
poorly constrained, in particular the tortuosity.
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