Climate in the great lakes region between 14,000 and 4000 years ago from isotopic composition of conifer wood

The isotopic composition of ancient wood has the potential to provide information about past environments. We analyzed the delta C-13, delta O-18, and delta H-2 of cellulose of conifer trees from several cross-sections at each of 9 sites around the Great Lakes region ranging from similar to 4000 to 14,000 cal BP. Isotopic values of Picea, Pinus, and Thuja species seem interchangeable for delta O-18 and delta H-2 comparisons, but Thuja appears distinctly different from the other 2 in its delta C-13 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.