Dear Lora,
Yes, over the years we have found isotopic data above the meteoric water
line ( assuming delta D is the Y-axis) in a few ground water samples and in
some high altitude snow/ice accumulations but their occurence is rare.. One
thought that has come to me is the following;
The isotopic compositions of  evaporating shallow water bodies go to higher
delta values along trends below the MWL. This in turn means that the
isotopic compositions of the vapour fall above the MWL.  Are there
conditions whereby  the vapour might condense without extensive mixing with
a large reservoir of other vapour prior to condensing or other water after
condensing ? Because of the isotope fractionation during condensation, the
condensate won't necessarily  be above the MWL.  Its location on the delta D
vs delta 18O plot will depend on the extent, rate, and temperate of
evaporation and on the temperature of condensation.
Another possibility which probably does not apply is hydrogen isotope
exchange between water and vast quantities of H2S.

Roy Krouse

Roy Krouse.