Environment and paleoecology of a 12 ka mid-North American Younger Dryas forest chronicled in tree rings

Abstract

Until now, availability of wood from the Younger Dryas abrupt cooling event (YDE) in N. America ca. 12.9 to 11.6 ka has been insufficient to develop high-resolution chronologies for refining our understanding of YDE conditions. Here we present a multi-proxy tree-ring chronology (ring widths, “events” evidenced by microanatomy and macro features, stable isotopes) from a buried black spruce forest in the Great Lakes area (Liverpool East site), spanning 116 yr at ca. 12,000 cal yr BP. During this largely cold and wet period, the proxies convey a coherent and precise forest history including frost events, tilting, drowning and burial in estuarine sands as the Laurentide Ice Sheet deteriorated. In the middle of the period, a short mild interval appears to have launched the final and largest episode of tree recruitment. Ultimately the tops of the trees were sheared off after death, perhaps by wind-driven ice floes, culminating an interval of rising water and sediment deposition around the base of the trees. Although relative influences of the continental ice sheet and local effects from ancestral Lake Michigan are indeterminate, the tree-ring proxies provide important insight into environment and ecology of a N. American YDE boreal forest stand.