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CLIMATE IN THE GREAT LAKES REGION BETWEEN 14,000 AND 4000 YEARS AGO FROM ISOTOPIC COMPOSITION OF CONIFER WOOD
Abstract
The isotopic composition of ancient wood has the potential to provide information about past environments.
We analyzed the d13C, d18O, and d2H of cellulose of conifer trees from several cross-sections at each of 9 sites around the
Great Lakes region ranging from ~4000 to 14,000 cal BP. Isotopic values of Picea, Pinus, and Thuja species seem interchangeable
for d18O and d2H comparisons, but Thuja appears distinctly different from the other 2 in its d13C composition. Isotopic
results suggest that the 2 sites of near-Younger Dryas age experienced the coldest conditions, although the Gribben
Basin site near the Laurentide ice sheet was relatively dry, whereas the Liverpool site 500 km south was moister. The spatial
isotopic variability of 3 of the 4 sites of Two Creeks age shows evidence of an elevation effect, perhaps related to sites farther
inland from the Lake Michigan shoreline experiencing warmer daytime growing season temperatures. Thus, despite floristic
similarity across sites (wood samples at 7 of the sites being Picea), the isotopes appear to reflect environmental differences
that might not be readily evident from a purely floristic interpretation of macrofossil or pollen identification.
We analyzed the d13C, d18O, and d2H of cellulose of conifer trees from several cross-sections at each of 9 sites around the
Great Lakes region ranging from ~4000 to 14,000 cal BP. Isotopic values of Picea, Pinus, and Thuja species seem interchangeable
for d18O and d2H comparisons, but Thuja appears distinctly different from the other 2 in its d13C composition. Isotopic
results suggest that the 2 sites of near-Younger Dryas age experienced the coldest conditions, although the Gribben
Basin site near the Laurentide ice sheet was relatively dry, whereas the Liverpool site 500 km south was moister. The spatial
isotopic variability of 3 of the 4 sites of Two Creeks age shows evidence of an elevation effect, perhaps related to sites farther
inland from the Lake Michigan shoreline experiencing warmer daytime growing season temperatures. Thus, despite floristic
similarity across sites (wood samples at 7 of the sites being Picea), the isotopes appear to reflect environmental differences
that might not be readily evident from a purely floristic interpretation of macrofossil or pollen identification.