MASSIVE DUNE BUILDING IN INTERIOR EASTERN UPPER MICHIGAN USA IS TEMPORALLY CORRELATED WITH THE HYDROLOGIC CLOSURE OF THE UPPER GREAT LAKES AND SPATIALLY CONFINED BELOW 245 M ASL

Episodic eolian activity within grasslands of the North American high plains has been linked with changes in vegetation cover during periods of Holocene aridity. The thousands of dunes scattered across interior eastern Upper Michigan (EUM), more than 500 km east of the forest prairie boundary, must reflect an analogous but more complex climate signal. The destruction of forests extant in the early Holocene must have occurred but expected successional trajectories have not been modeled, much less detected in the robust regional paleorecord. To test and build upon earlier work, we mapped dunes throughout EUM using 10 m DEMs and derived optical ages from samples of quartz sand from the crests of 65 dunes using SAR protocol. In contrast with an earlier finding of a mid-Holocene (~7.0-5.5 ka) maximum, 1-sigma cumulative probability plots of our optical ages suggest that widespread eolian activity peaked in the early Holocene, ~10.5-7.5 ka. This time frame has been identified as one of rapid/drastic environmental change across the upper Midwest (e.g., peak meltwater flux to and from the Superior Basin ~ 9.3 ka; hydrologic closure of the upper Great Lakes ~8.9 ka). Given this correspondence, dune chronology seems intuitive but dune distribution and modeling of sand supply change do not. It is clear that sand was supplied to dunes primarily from presently wet, sandy landscapes below a rebound-adjusted surface ~245 m asl and that early Holocene pine forests on uplands >~245 m changed in composition but remained largely intact (no dunes formed). Our data record massive dune building in EUM during the driest known period of the Holocene. Nonetheless, they require an integrated biogeomorphic/physical model that accommodates dune building that is tightly stratified among landscape segments underlain by similar sandy substrates.