Hi All
Recently we have been using the oxygen isotope ratios of a cellulose 
derivative (Phenylglucosazone, see Sternberg et al. (2007) Geochimica 
Cosmochimica Acta 71: 2463-2473) as a  proxy for environmental water.  
This oxygen isotope ratio of the derivative is much more fateful to the 
oxygen isotope ratio of environmental waters.  We have done a tree ring 
sequence with very promising results.  However, we need more tree ring 
sequences to confirm the validity of this method.  Here is what we need:
A tree ring sequence (7 or more years) having more than 25mg of 
cellulose per annual ring (It would be easier if you have extracted the 
cellulose already).  Each of the year must have a recorded annual 
amount-weighed average oxygen isotope ratios of precipitation.  If you 
would like to contribute to this effort, please contact me directly.
Thanks.
Leo.