QUANTIFYING NATURAL LAKE LEVEL FLUCTUATIONS FOR THE IPPERWASH STRANDPLAIN, LAKE HURON: EXAMINING THE CONNECTION BETWEEN THE UPPER AND LOWER GREAT LAKES

The Great Lakes connect the interior of North America to the Atlantic Ocean through a system of natural and engineered waterways. The Port Huron/Sarnia outlet drains Lake Huron and is the only unregulated outlet in the Great Lakes. Identifying natural decadal to millennial trends and patterns of past lake levels, glacial isostatic adjustment and outlet conveyance is required to make effective and informed decisions for the maintenance of the important Port Huron/Sarnia outlet and the stewardship of the Great Lakes as a whole. The Ipperwash strandplain in southern Lake Huron is the nearest strandplain to the Port Huron/Sarnia outlet and chronicles lake level fluctuations and sedimentation patterns over the past several millennia. Forty cores have been collected from the Ipperwash strandplain. These cores were visually described, photographed, sampled and preserved on latex peels made on Masonite sheets. Samples were analyzed for grain size using a laser particle analyzer. The visual descriptions, photographs, preserved peels and grain sizes are compared to define the foreshore contact which is typically composed of very fine to medium sand with horizontal to lakeward dipping laminae with abundant medium to coarse grain mineralogic and shell fragments. The depth to the ancient foreshore is then calculated from the total station topographic survey. Ridges are dated using optically stimulated luminesce and an age model developed across the strandplain to ascertain the age of the ridges cored. With elevations and ages known for all 40 cored beach ridges, lake level variations over the past several millennia can be reconstructed for the Ipperwash strandplain. Cross strandplain changes in foreshore thickness, ridge height and ridge width are also calculated to evaluate how sedimentation patterns have changed over time. Here we combine ancient foreshore elevations and OSL dating to reconstruct lake levels and sedimentation patterns for Ipperwash. With these data we quantify the natural baseline of lake level fluctuations at Ipperwash, a site that contains clues to natural conditions experienced at the only unregulated outlet in the entire Great Lakes, a key hydrologic node between the upper and lower Great Lakes in the world’s largest fresh, surface-water system.