LAKE-LEVEL RECONSTRUCTION FOR THE PAST ~2000 YEARS FROM COASTAL STRANDPLAINS

Lake-level fluctuation in Lake Michigan-Huron that occurred after the separation from Lake Superior are climate-driven. Hence, the relation between climate variability and lake-level response is best understood by reconstructing a lake-level record that extends the historical instrumental data to the time of lake separation approximately 1200 to 2000 years ago. Records of lake-level during the past ~2000 years are preserved in beach ridges in coastal embayments along Lakes Michigan and Huron. Vibracores were used to define the modern elevation of the foreshore facies in preserved beach ridges. The geochronologies of beach ridges preserved during the past ~2000 years are constrained through optically stimulated luminescence of foreshore sediments and 14C dating of organics in swales. A lake-level record and estimate of glacio-isostatic adjustment (GIA) have been established for a sequence of ~30 ridges at Bailey's Harbor on the Door County peninsula of Michigan. Data from additional strandplains in Lake Michigan and Alpena, Michigan in Lake Huron are compared to data from Bailey's Harbor to address issues of error associated with dating methodologies, estimates of GIA, and record completeness. This comparison leads us to consider the efficacy of reconstructing records of late Holocene GIA, lake-level fluctuation and climate variability from the geology of strandplains.