PROGRESS IN USING TREE-RING CHRONOLOGIES TO RECONSTRUCT LAURENTIAN GREAT LAKE LEVELS

Researchers have been reconstructing North American Great Lake levels using tree-rings for over 35 years. Here we review the progress in these efforts including the challenges of lake level reconstruction based on leveraging North American climate teleconnections, the nonstationary relationships between these teleconnections, and the alternating influence of the North Pacific and North Atlantic on large-scale atmospheric forcing on the hydrologic budgets in the lake basins. Tree rings are annually resolved records of past climate, and these series can be calibrated with the remarkable monthly observational record for the Great Lakes that extends back to 1860 CE. This observational record is one of the longest records of hydroclimate for North America and coupled with growing networks of North American tree-ring, this unique combination, has the growing potential for developing long reconstructions of lake-level changes.

For example, Lake Erie water levels are primarily determined by climate, and their variability greatly impacts the region's infrastructure and littoral ecosystems and according to a well-verified tree-ring based reconstruction back to 1600 CE, Lake Erie experienced record lows in the 1930s during the American Dustbowl years and a record high level in 2020. Such extremes are not evident in the reconstruction prior to human impact in the basin and, furthermore, decadal variability is superimposed on a persistent secular lake-level rise that began in the mid-1900s coinciding with a growing influence of the Atlantic sector. Recent work in the Huron basin based on drowned trees indicates a possible abrupt lake level change in the late 1690s CE. This interval coincides with a volcanically-forced shift in the Northern Pacific evident in tree-ring based temperature reconstructions along the Gulf of Alaska. Reconstructing Lake Michigan-Huron lake-levels using tree rings can help independently verify this event. Further dendroclimatic work to reconstruct Great Lake levels will contribute to better understanding of the drivers and history of lake levels, and to an improved ability to anticipate future lake levels.