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gas diffusion coefficients



OCMIP investigators:

For modelling gas exchange of O2 and CFCs, semi-empirical formulae are 
typically used for the Schmidt number.  There is no need to do this however,
since there are direct measurement of O2 and CFC diffusivities.

For O2, measurements in fresh water made by Jahne (1980), as reported in 
Liss and Merlivat (1986), can be used, after correcting for the effect of
salinity.  An expression for the Schmidt number in seawater derived from such
measurements is: 

Sc = 1638 - 81.83T + 1.483T^2 - 0.008004T^3

where T is in deg C.  The proper references for this formula can be found
in a paper in press in Global Biogeochemical Cycles by R. Keeling et al:
"Seasonal variations in the atmosheric O2/N2 ratio in relation to the kinetics
of air-sea gas exchange."

For CFCs, diffusion measurements and derived Schmidt numbers can be found in
a recent JGR Oceans paper by Zheng et al. (1998): "Measurements of the 
diffusion coefficients of CFC-11 and CFC-12 in pure water and seawater,"
volume 103, page 1375.

Perhaps these CFC and O2 Schmidt number formulae should be adopted as part of
OCMIP protocols.

Ray