ARE COASTAL DUNE ACTIVATION CYCLES IN THE GREAT LAKES (USA) LINKED WITH THOSE AT CAPE COD (USA) AND NORTHERN EUROPE DURING THE LATE HOLOCENE? (Invited Presentation)

Numerous geomorphic investigations conducted on coastal dunes along Lake Michigan, USA during the past ~20 years resulted in a clear regional record of growth and stability since 5 ka. A probability density function (PDF) derived from over 150 OSL ages reported from these studies shows that coastal dunes were constructed during basin-wide, millennial-scaled cycles. Dune activation was identified as PDF highs formed when eolian sand was mobilized, while PDF lows marked intervals of dune stability when few OSL age occurred. The record is particularly interesting after the ~2 ka mobilization of eolian sand when a widespread, several hundred years long stability period occurred. This interval is marked by both a paucity of OSL ages in dunes and an Inceptisol (Holland Paleosol) buried in dunes along the lake’s southeastern shore. Subsequent mobilization of dunes at ~1 ka and ~.5 ka may relate to instability during the Medieval Climatic Optimum and Little Ice Age, respectively, but may also be linked with complex interactions between local environmental factors and lake-level fluctuations.

Although previous investigations focused on regional patterns of dune evolution, potential chronological correlations may also occur on a hemispheric scale. These relationships appear to be particularly strong after 2 ka when PDF highs and lows from Lake Michigan become coincident with similar representations of coastal dune activation and stability at Cape Cod, USA, and northern Europe. Prior to then, dune activation intervals were mostly out of sync, which suggests that drivers for dune formation across the hemisphere became linked after 2 ka. The reasons for this hypothetical linkage remains unclear at this time. Possible important linked drivers include ENSO, Arctic & North Atlantic Oscillations, (AO & NAO), Pacific-North American and Pacific Decadal Oscillation (PNA, PDO) among others. Which are most significantly interlinked is unknown, but given the deep time differences between competing climate-driver reconstruction (e.g., ENSO), regional or larger geomorphic responses constructed using meta-analyses of large data sets to show long distance patterns, as described here, may provide a better way to understand climate linkages and test competing reconstructions.