There is a fundamental gap in our understanding of the events leading up to the abrupt climate change known as the 8,200 yr cold event. The assumed trigger is the sudden introduction of meltwater into high latitudes, yet only preliminary studies undertaken for other purposes have provided evidence for the trigger and its source area. The objective of this project is to confirm or revise the phasing between Laurentide meltwater drainage events and the 8,200 yr cold event. The long-term goal is to understand the nature of interactions between ice sheets and climate change. It is a central hypothesis is that the break-up of the glacier dam holding in glacial Lake Ojibway was a multi-stepped process operating over centuries. The rationale for this work is that a well-constrained age assignment for the glacial lake drainage will either allow for more detailed modeling experiments or force reconsideration of the role of meltwater in not only this climatic shift, but also earlier events such as the Younger Dryas. Limited radiocarbon dates on overlying marine shells currently provide only a younger bracket on the drainage chronology. Direct and replicated dating of this lacustrine sequence as well as modern correlation techniques will place the final drainage event (or events) into absolute time. The youngest portion of the stratigraphy is currently only represented in a few places, and descriptions vary. In the model of a single catastrophic lake drainage, this sequence should not display this variation. By generating new synthetic rhythmite sequences and comparing them to existing ones, it should be possible to describe the nature of meltwater expulsion. Paleomagnetic secular variation stratigraphy, combined with geochemical data generated via X-ray fluorescence scanning, will help to assess the annual nature of the rhythmites and rhythmite thickness correlations. This work is original because it will place the events of the final stages of the Laurentide Ice Sheet into a high resolution time scale. The expected product is a test of a meltwater trigger of the 8,200 year event via annually resolved records, and a critical addition to a growing body of temporally constrained, high resolution records of ice retreat and late-glacial paleohydrology.
Broader Impacts: The Lake Ojibway varves are a time-series that connect discovery and teaching. Data sequences are commonly used to instruct topics such as climate variability, spectral analysis, and geochronology. These particular records aid teaching of these concepts from the introductory to graduate level. This award directly supports interested students via undergraduate and graduate research projects at both the University of Cincinnati and Mercyhurst College. At Mercyhurst College, these data enhance infrastructure via the development of a new laboratory program emphasizing teaching through research. This work helps reintroduce the data's utility and establish a framework for the next generation of deglaciation models. This contribution is significant because it generates a new chronological framework to understand the roles of the Laurentide Ice Sheet and of freshwater flux to the North Atlantic in abrupt climate change. Results will be published and submitted to the National Geophysical Data Center, so that they will be readily available to experts worldwide.
