Atmospheric gases are trapped in ice sheets. These gases stored in air-bubb
les at shallower depth are gradually transformed into clathrate hydrates be
low the depth where the hydrostatic pressure exceeds the dissociation press
ure of the clathrate hydrates. We measured Raman spectra of air-bubbles and
clathrate hydrates in Vostok Antarctic ice cores in order to determine the
fractionation effects on the concentrations of gases during their transiti
on process. The results showed variations of the N-2/O-2 ratios with depth.
The average N2/O2 ratio in the air-bubbles increases from the atmospheric
value at the beginning of the transition to 11.7 at the end. The average N-
2/O-2 ratio for the clathrate hydrates is 2.0 at the beginning, and asympto
tically approaches the atmospheric value. This fractionation is attributed
to faster diffusion of O-2 than N-2 through the ice lattice.