DIATOM-INFERRED HYDROCLIMATE VARIABILITY IN MARL LAKE, WI OVER THE PAST 2,000 YEARS

Hydroclimate variability in the Midwest region of the United States has increased over the past few decades, evidenced by increases in average precipitation and frequency of extreme hydroclimate events. Natural lakes in the Midwest are often effective archives of hydroclimate; many have been shown to respond directly to changes in both local and regional climate. We extracted a 4.5-meter sediment core, representing approximately 2,000 years of sediment accumulation, from the deepest part of Marl Lake (Waushara County, Wisconsin). For this study, we identified fossil diatoms from a 3.5-meter segment at 2.5 to 5-year resolution to document shifts in assemblages over time. Changes in the dominant diatom species of Marl Lake reflect important environmental changes such as lake-level fluctuations and changes in lake stratification. The diatom record indicates the lake experienced distinct wet periods in the past. These hydrologic shifts are evidenced by increases in the relative abundance of planktonic taxa including Lindavia michiganiana and Discostella pseudostelligera. Understanding natural climate variability in this region will help us better prepare and mitigate the risks associated with extreme hydroclimate variability. Robust, high-resolution hydroclimate records from the Midwestern United States are relatively sparse so expanding the number of millennial-scale records will provide policymakers with additional critical information needed for future planning.