Fractionation of soil gases by diffusion of water vapor, gravitational settling, and thermal diffusion

Publication Status is "Submitted" Or "In Press: 
LDEO Publication: 
Publication Type: 
Year of Publication: 
1996
Editor: 
Journal Title: 
Geochimica Et Cosmochimica Acta
Journal Date: 
Mar
Place Published: 
Tertiary Title: 
Volume: 
60
Issue: 
6
Pages: 
1005-1018
Section / Start page: 
Publisher: 
ISBN Number: 
0016-7037
ISSN Number: 
Edition: 
Short Title: 
Accession Number: 
ISI:A1996UA25900008
LDEO Publication Number: 
Call Number: 
Abstract: 

Air sampled from the moist unsaturated zone in a sand dune exhibits depletion in the heavy isotopes of N-2 and O-2. We propose that the depletion is caused by a diffusive flux of water vapor out of the dune, which sweeps out the other gases, forcing them to diffuse back into the dune. The heavy isotopes of N-2 and O-2 diffuse back more slowly, resulting in a steady-state depletion of the heavy isotopes in the dune interior. We predict the effect's magnitude with molecular diffusion theory and reproduce it in a laboratory simulation, finding good agreement between field, theory, and lab. The magnitude of the effect is governed by the ratio of the binary diffusivities against water vapor of a pair of gases, and increases similar to linearly with the difference between the water vapor mole fraction of the site and the advectively mixed reservoir with which it is in diffusive contact (in most cases the atmosphere). The steady-state effect is given bydelta(i) = [i/j/i(0)/j(0) - 1] 10(3) parts per thousand congruent to [(1 - x(H2O)/1 - x(H2O0))((Dj-H2O/Di-H2O)-1) -1] 10(3) parts per thousand,

Notes: 

Ua259Times Cited:26Cited References Count:31

DOI: