PALEOHYDROGRAPHIC RECONSTRUCTIONS FROM STRANDPLAINS OF LATE HOLOCENE BEACH RIDGES IN THE UPPER LAURENTIAN GREAT LAKES: PAST MILESTONES, CURRENT STATUS AND VITAL GAPS IN RESEARCH

In the late 1980’s to early 1990’s Thompson established a consistently robust method measuring former lake-level elevations from strandplains of beach ridges that would be applied throughout the upper Laurentian Great Lakes (LGL). Chronologies were initially developed using a select number of radiocarbon dates calculated from basal wetland organics between beach ridges. Paucity of organics in several key locations within strandplains and at certain more-northern strandplains helped develop a new method using a select number of optically stimulated luminescence dates calculated from mineral grains stratigraphically inside beach ridges. To date, six strandplains have been studied in each of the upper LGL (Superior, Michigan and Huron) and are being used to reconstruct basin-wide or outlet paleohydrographs. These paleohydrographs reveal the most detailed account of lake level, glacial isostatic adjustment, and outlet location/conveyance during the late Holocene. Here we present the past key milestones, current status, and vital gaps in paleohydrographic research in the upper LGL. This most-detailed account of past conditions provides an unparalleled context for today as we are experiencing relatively high lake levels and grappling with an uncertain future with both natural and human-induced influences.