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Fig. 6.1 Methodological choices in stable isotope dendroclimatology can be viewed as a flow chart
of options. The aims and objectives of the study should guide: sampling resolution and pooling
options, ring portion sampled (earlywood, latewood, or whole ring), and wood product choice
whilst another does not exchange with trunk water but records evaporative enrich-
ment and the Peclét effect. The isotopic variability between these molecules is not
insignificant; the fractionation of oxygen-2 differs from the average fractionation
of the other molecules by 9‰ (Sternberg et al. 2006 ) . Isolation of those oxygen
molecules that hold the strongest climatic signal is known as 'position-specific anal-
ysis' and has been piloted successfully through the used of derivitized cellulose
(Mullane et al. 1988 ; Sternberg et al. 2006 ) . Complex synthetic organic chem-
istry is required to extract and separate the molecules prior to measurement. Each
molecule, or group of molecules, is chemically exposed or protected in turn in order
to measure its
18 O value (Waterhouse, personal communication). Position-specific
analysis is still in development, and it will be some time before it can be used in
the measurement of long chronologies, but it is potentially an extremely powerful
technique.
With evidence that whole wood, rather than cellulose, might routinely be used
in stable isotope dendroclimatology, there is now scope for developing fully auto-
mated sampling systems. One of the most exciting possibilities is a coupled system
using ultraviolet laser ablation. An ablating laser can be used to sample whole wood
pieces, of just a few microns, from a standard core. Ablation produces an aerosol of
wood particles, suspended in a helium current, which can be streamed directly into
a combustion furnace and gas chromatography-IRMS (GC-IRMS) system (Schulze
et al. 2004 ; Skomarkovaetal. 2006 ) .
δ
 
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