This doctoral dissertation project will investigate the distribution and timing of eolian (wind-blown) sand activity during the last glacial period in central North America. The landscape setting, form, and age of eolian sand deposits indicate past changes in the supply of sand for movement by the wind, wind regime, vegetation cover, and factors that influence vegetation such as temperature and precipitation. This information is important for reconstructing past climate change south of the Laurentide Ice Sheet during the last glacial period as well as for improving boundary condition inputs to climate models. Much of the understanding of environmental conditions in the North American midcontinent over the last 21,000 years relies on biological proxies (e.g., pollen and plant or animal fossils) but eolian sediments provide important additional parameters to complement these data. Determination of an accurate age for eolian activity is an important task in reconstructing past climate change. This project will use optically simulated luminescence (OSL or optical) dating to determine the age of eolian sand. Optical ages provide an estimate of the timing of burial of sand after exposure to light during transportation. The project will address several research questions: 1) Was the timing of eolian sand activity time-transgressive from south to north (i.e., older in the south and younger in the north) as the ice sheet and permafrost (permanently frozen ground) retreated northward after the last glacial maximum ca. 21,000 years ago? 2) Does the chronology and landscape setting of eolian sand indicate a response to abrupt climate change during the last deglaciation? These questions will be addressed by collecting and analyzing samples for optical dating along a ca. 500 km north-south transect from western Wisconsin and southeastern Minnesota to eastern Iowa. The time sequences of eolian activity will provide key insight into the landscape response to climate change during the last glacial period in the North American midcontinent.
Understanding past landscape response to environmental change is an important step in predicting future response and its impact on society. This is especially relevant for dry areas in central North America, which are vulnerable to future warming and increasingly variable precipitation. These conditions may influence eolian sand activity, which has major implications for preserving productive agricultural land as well as human health concerns related to airborne dust. This project investigates the climatic parameters during the most recent past episode of relatively rapid warming (ca. 21-10 thousand years ago) and provides background for predicting future changes in eolian activity in central North America. Results from this project will be presented to academic as well as broader audiences through publication and conference presentations, and also collaboration with private (The Nature Conservancy) and public (Department of Natural Resources of several states) agencies, with an emphasis on outreach at native sand prairie sites. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising student to establish an independent research career.
This project focused on sand dunes of Wisconsin, southeastern Minnesota, eastern Iowa, and northern Illinois, which were actively moving in the wind at some time in the past but are now stable and covered by forest, grassland, or agricultural crops. The most important goal was to understand the past environmental conditions that allowed the dunes to be active, by mapping their distribution and determining their age. More accurate mapping of these dunes should also be useful in interpreting soil patterns that influence natural vegetation and land use. Areas covered by dunes were mapped using soil surveys and new laser-based topographic data, which revealed hundreds of dunes that have never been recognized in the past, because of lower-quality topographic maps and/or forest cover. The image below shows an example of newly mapped dunes in the Central Sand Plain of Wisconsin, an area with unique soils, natural vegetation, and land use issues that can now be better understood as the result of extensive wind-blown sand activity in the past. A method called optically stimulated luminescence dating was used to determine the age of dunes at 17 sites across the region. Most of the dunes were active between 18,000 and 14,000 years ago. At that time, the ice sheet that had covered much of the Midwest was retreating quickly because of a warmer climate, and permanently frozen ground that had developed under the cold glacial climate was thawing. These changes probably made sandy soils much more susceptible to be eroded by the wind, during a fairly short period when dense forest vegetation had not yet covered many areas. This scenario for dune activity is not likely to be repeated in the Midwest in the foreseeable future, but it could take place in the Arctic in response to a warmer climate there. Some dunes were also active around 12,000 to 10,000 years ago, possibly as a result of unusually dry conditions. That possibility should be studied in future research. The dunes were formed by winds from the northwest or west, similar to the most common directions of strong winds today.
