From 18,000 to 15,000 years (ka) ago, during the broad Heinrich Stadial 1 interval, the Laurentide ice sheet (LIS) began its largest retreat in North America. However, climatic conditions near ice margins during this recession are poorly understood due to a lack of studies focusing on paleoenvironmental proxies in corresponding sedimentary records. Here, we show that eolian dunes were actively forming in portions of the Upper Mississippi River valley, the Middle Illinois River valley, and the Lower Ohio River valley. In the Upper Mississippi River valley in Illinois, dune fields were examined at the Atkinson (41 degrees 29'N; 90 degrees 01'W), Annawan (41 degrees 28'N; 89 degrees 54'W), Bureau (41 degrees 26'N; 89 degrees 49'W), and Colona (41 degrees 29'N, 90 degrees 21'W) sites. In the Middle Illinois River valley, dune fields were examined at the Manito (40 degrees 22'N and 89 degrees 54'W) and Arenzville (39 degrees 55'N; 90 degrees 22'W) sites. In the Lower Ohio River valley in Indiana a dune field was examined at the Sandridge site (37 degrees 57'N; 87 degrees 10'W). Optically stimulated luminescence (OSL) dates from these sites indicate that dunes in these localities were active between 18.0 and 16.3 ka. This record corresponds with the timing of the last standing arctic dryas (Dryas intergrifolia), a drought resistant plant, that prevailed on the till plain between the Upper Mississippi and Ohio River valleys. It also agrees with peaks in C4 biomass within loess deposits since the last glacial maximum in the Middle Mississippi River valley. The synchronicity of eolian dune activities in three major drainage systems, the predominance of dry tundra ecosystems in northern flood plains, and the highest C4 biomass content in loess along the Mississippi River valley leads us to believe that drought conditions prevailed between 18.0 ka and 16.3 ka in the upper Midwest of the United States.
|Name||American Geophysical Union Fall Meeting|
|Publisher||American Geophysical Union, Washington, DC, United States|