ABRUPT CHANGE IN WIND REGIMES OBSERVED FROM MORPHOLOGY OF PARABOLIC DUNE FIELDS IN NORTHEASTERN NORTH AMERICA

Parabolic dunes are globally widespread in humid and cold-climate environments and are the predominant stabilized dune form in formerly glaciated regions of the northern hemisphere. Abundant stabilized parabolic dunes in northeastern North America attest to widespread eolian transport and deposition following deglaciation, and glacial lake/marine regression. Various parabolic dune forms occur under differing conditions of sediment supply and past sediment-transporting wind regimes. Bidirectional winds, acting in succession, played a significant role in creating modified and compound parabolic dunes throughout the region. Older sediment transporting winds were predominantly from the northeast and younger transporting winds were from the west. Past sediment-transport directions are presented in relation to the timing of deglaciation and lake or sea level changes revealing a complex spatial-temporal pattern. Southern dunes within the Central and Mohawk River valleys record unidirectional westerly winds between 13.6 and 11.5 ka. Dunes in the Champlain Sea basin in northern New York and southern Ontario and Quebec record east-northeasterly winds along the receding margins of the Laurentide Ice Sheet (LIS) between 11 and 8 ka, and subsequent opposing winds originating from the west. Dunes on the Canadian Shield are commonly bidirectional, but those within the Glacial Lake Ojibway basin record only westerly winds. An abrupt change in sediment-transporting winds from glacial-driven anticyclonic circulation to more modern-day circulation is related to the 8.2 ka collapse of the LIS over Hudson Bay, Canada, marking a rapid transition from Late Pleistocene to Holocene climate.