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These results are preliminary and
unpublished. Please do not cite or distribute.
Based on correlations
with 20th century instrumental records and derivitive indices,
ring-width chronologies from all three of our study sites have
signals for high-frequency variation in growing-season drought
stress. Although the low-frequency variation which is conspicuous
in all chronologies is at a wavelength which approaches the length
of the instrumental record, it appears that those low-frequency
oscillations in the chronologies also contains information about
climatic variability. Although the three chronologies are from
sites spanning 150 km along the Bighorn Basin, and each is from
a different species of tree, they have a substantial amount of
low-frequency variation in common. This similarity is evident
in the graph below of the 25 year cubic-smoothing splines of
the chronologies. The similarity of these geographically and
taxonomically disparate chronologies suggests that their low-frequency
signal is one of regional climate. These chronologies appear
to have a reliable record of decadal-scale periods of climatic
fluctuations, and are expected to be good proxies for droughts
which pre-date the instrumental record. |
