Celebration of Scholarship and Creative Activity 2023
In March 2022, my advisor and I pulled a single core out of a lake in Wisconsin’s Northern Kettle Moraine State Forest. The goal was to reach the basal sediment and use my funding to date the formation of the lake. Most lakes in this area had already been basally dated; the oldest kettle lake in the region formed around 14,000 years ago. But after spending almost a year studying LiDAR maps, mapping sedimentary geology from well construction records, and conducting an exhaustive literature review of the area, I suspected that this lake was erroneously classified as a kettle lake. My hypothesis was that this long and narrow lake within an interlobate zone is in fact the remnant of a subglacial or proglacial stream dating to the Last Glacial Maximum (LGM), around 20,000 years ago.
In the lab, we subsampled a set of charcoal lenses approximately 36cm from the bottom of the core for radiocarbon dating. Previous research has shown that fires were common after the collapse of the Laurentide Ice Sheet, so a charcoal lens should be a good proxy to approximate when the water body became open-air. Six weeks later, we learned that the age of those charcoal lenses is 27,000-27,122 ybp. This predates the oldest lake in the area by 13,000 years and suggests this lake, located on the eastern edge of the Green Bay ice lobe and 70 miles north of its terminal moraine, may have been pro-glacial 4,000 years before the Last Glacial Maximum.