PALEO-STORMINESS IN THE SOUTHERN LAKE MICHIGAN BASIN, AS RECORDED BY EOLIAN SAND DOWNWIND OF DUNES

The Grand Mere Lakes are a set of three shallow, closely spaced, embayed lakes—North, Middle, and South, which are part of a coastal wetland complex in Berrien County, MI, along southeastern Lake Michigan. Two sediment cores were extracted from each lake to determine if sand peaks within the cores record periodicity of past eolian activity, and thus may be an effective proxy for paleoclimate in the southern Lake Michigan basin. Studies from farther north in Michigan, and from Sweden indicate that peaks in eolian sand within lake sediments correspond to climatic and lake-level fluctuations. Variations in weight percentage of sand with depth in lacustrine sediments, the sand signal, were determined through multi-step laboratory procedures based on 1cm-sampling intervals. High-resolution magnetic susceptibility analysis on each core was found to be a reasonable proxy for terrigenous sediments. Spectral analysis of the sand signal data using the multi-taper method indicates a strong periodicity between sand peaks and depth intervals. A model of the depth-to-time relationship is being developed, pending radiocarbon dating of terrestrial macrofossils within lake sediments. The model is used to reconstruct periodicity of past storminess, and for comparing derived cycles to climatic variability as represented by lake-level fluctuations. Results from this study are compared to results from other coastal lakes within the Lake Michigan basin, the Lake Michigan beach ridge record, and other regional studies to determine if any common periodicity patterns exist. The developed sand signal record will elucidate synchronicity of paleo dune activity along the Michigan coastline, and observed cycles may be used to predict future storminess in the Lake Michigan basin based on geologic evidence of past climatic fluctuations.