AEOLIAN RECORD OF MEGADROUGHTS FROM A CONTINUOUS LAKE CORE RECORD IN THE GREAT PLAINS

Long term continuous records of hydroclimatic conditions in the midcontinental United States are rare. Geomorphic evidence of dune mobilization, however, suggests that at least 4 periods of profound drought occurred during the last 5000 years (-71 to ~5000 yr BP). The paucity of records from this region means that the nature of these droughts and their regional impacts are not well known. Here, we investigated midcontinental hydroclimate during the last 5000 years using a 12-m-long sediment core from Blybug Lake, NE. This small oxbow lake in Dakota County, NE is situated within the Missouri River floodplain and incorporates sediment from much of the Missouri River watershed when the river is at flood stage. A suite of multi-proxy analyses, including X-Ray fluorescence (XRF), grain size analysis, bulk density (BD), and loss on ignition (LOI), were performed on the Blyburg Lake sediment cores and geochronologically constrained by a radiocarbon-based age model. XRF analysis revealed discrete periods of excess silicon (Si) and aluminum (Al). The Si and Al peaks are interpreted here to indicate an increase in Si-rich aeolian dust within the Missouri River Basin, potentially related to aridity-driven dune activation. We found that these peaks in Si and Al correspond to recorded events of Great Plains aeolian activity dated by optically stimulated luminescence (OSL). Synthesizing these new geochemical data with existing records of regional aridity provides new insight into the impacts and geological indicators of these mid-to-late Holocene “megadroughts.” Continued research on Blyburg Lake will include a higher resolution radiocarbon-based age model to precisely reconstruct sediment accumulation rates and flood recurrence.