STORMINESS RECORDS FROM AEOLIAN COASTAL DUNES AND ADJACENT LAKES ALONG THE SOUTHEAST SHORE OF LAKE MICHGAN

Most coastal sand dunes along the eastern shore of Lake Michigan record dune mobility starting with the mid-Holocene aged Nipissing high stand. These dunes are present because of prevailing westerly winds, a 70 km fetch across Lake Michigan, and a high sand supply from glacial deposits. The dunes along the southeastern shore of Lake Michigan are found on topographically low lake plains or barrier bars that are only a few meters above modern lake level. With more than 100 radiocarbon dates from paleosols and over 20 OSL dates from dune sand, a general geomorphic history of these dunes has been developed from five separate dune fields along the coast, all of which are in general agreement for the past 5000 years. However, because coastal dune complexes are by their very nature cannibalistic, with older dunes and paleosols eroded, extant dunes are biased towards recording more recent activity. Older and more complete records of aeolian activity are found in lacustrine sediments as allocthonous aeolian sand from upwind dunes. During storms, air-fall sand has been observed hundreds of meters in the lee of active blow-outs. Aeolian sand is found dispersed, laminated, and banded within the lacustrine cores adjacent to dunes and downwind of sandy soils. In northern Europe, the sand signal has been correlated with periods of storminess associated with cold phases in the North Atlantic. In our study area an increase in storminess could be caused by more southerly tracking mid-latitude cyclones during the fall and winter when the dunes are most active. While such wind patterns can drive dune mobility, the trigger that initiated dune mobility remains unknown. We contend that the high-resolution sand signals from sediment cores provide a more complete record of dune activity than just from radiocarbon ages from paleosols and OSL ages from dune sand. Refinement of the sand signal and further testing from additional sites is ongoing.