What Makes Lake Michigan’s Coastal Dunes Migrate? Investigating the Triggers of Dune Mobility in Lake Michigan’s Dunes Using a Multi-proxy Study of a Coastal Dune Lake
Professor Suzanne DeVries-Zimmerman, Dr. Edward Hansen, and Dr. Timothy G. Fisher
Aeolian studies of Lake Michigan’s coastal dunes have shown periods of dune mobility and stability in the last 6,000 years. However, the triggering mechanisms for these changes in aeolian activity are not well understood. Small lakes located downwind of dune complexes contain aeolian sand and biological proxies that can provide both dune activity and independent paleoenvironmental data. We undertook a multi-proxy study of a lake-sediment-core collected from Gilligan Lake, located adjacent to a large coastal dune complex in Allegan County, Michigan, to reconstruct these histories. We collected a 7.5-cm-diameter vibracore and subsampled in 1 cm3 aliquots for percent sand, charcoal abundance, and pollen identification analyses. Sand concentrations vary on two different scales. Intervals of generally high, intermediate, and low sand persist for intervals of ~ 300–600 years with smaller fluctuations occurring at intervals of 20–100 years. A pattern between the sand concentrations and the different charcoal morphologies was noted. The period of overall high sand concentration is correlated with low abundance of charcoal threads and sheets and high abundances of charcoal chunks. This increase could indicate an increase in the amount of fire. The larger scale period of high sand concentrations is correlated with relatively high abundances of charcoal chunks, suggesting that periods of higher dune activity may be correlated with a higher incidence of fire. The larger scale period of low sand concentrations is correlated with relatively low abundances of oak, hickory, birch, and fir pollen and high abundances of maple, beech, pine, and spruce pollen. The pollen record suggests an expansion of the maple-beech climax community during periods of low dune mobility. Shorter scale fluctuations in sand concentrations do not correlate with any of the pollen or charcoal proxies investigated.
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