Cam. Brenninkmeijer et al., A LARGE (CO)-C-13 DEFICIT IN THE LOWER ANTARCTIC STRATOSPHERE DUE TO OZONE HOLE CHEMISTRY .1. OBSERVATIONS, Geophysical research letters, 23(16), 1996, pp. 2125-2128
Isotope and concentration measurements are reported for CO and CH4 in
air collected in the upper troposphere and lower stratosphere between
New Zealand and Antarctica in October 1993. The C-13/C-12 ratio of CO
for the stratospheric samples, which are identified using calculated p
otential vorticity and coherent isotope data, like the abundance of (C
O)-C-14 molecules, are much lower than all previously reported atmosph
eric values. The measurements manifest a very steep decrease in delta(
13)C with declining CO, with one sample reaching a delta(13)C value re
lative to V-PDB of -43 parts per thousand at 20 ppbv CO. This large is
otope shift is caused by the local production of several ppbv of extre
mely depleted CO. Not only is CH4 itself a C-13 depleted precursor of
CO, it is specifically the recently discovered large fractionation in
Cl + CH4, and the availability of free Cl during ozone hole conditions
, which causes the effect.