THE STABLE-ISOTOPIC VIEW OF TREE-RING SERIES FROM THE GREAT LAKES AREA BETWEEN CA. 12 KA AND 13.8 KA

An extended campaign collected ancient wood preserved in estuarine, glacial, bog and subaqueous deposits and settings throughout the Great Lakes region in order to develop tree-ring chronologies to better understand high-resolution environmental variability during the late Pleistocene deglaciation and the Holocene. Ring-width data were obtained from a network of more than 70 sites (‘GLSTR’, http://greatlakes.ltrr.arizona.edu/) for which radiocarbon dates provided initial age control. Tree-ring crossdating of multiple trees within a site then afforded exact assignment of ring dates within these “floating” chronologies. Stable oxygen and carbon isotope analysis of cellulose was conducted on the annual ring sequence from spruce trees at four of the sites collected in Wisconsin, Michigan and Indiana, two of which were approximately contemporaneous. Each of the chronologies was developed by pooling the rings of four trees, resulting in isotope series ranging from ca. 100 to 200 years in length. Variability in the isotope series is interpreted with respect to temperature and moisture conditions, but other events such as flooding may have also influenced the end of some of the chronologies. Inferences are made using the isotopes as well as ring widths and other climate proxies.