DECADALLY-RESOLVED HOLOCENE HYDROCLIMATE TRENDS ACROSS THE MIDCONTINENTAL UNITED STATES REVEALED THROUGH MULTI-PROXY ANALYSES OF LACUSTRINE SEDIMENTS

Extreme hydroclimate variability in the midwestern United States, in the form of flood events in the east and droughts in the west, have increased in frequency and magnitude in recent decades in response to rising average global temperatures. These hydroclimatic trends have the potential to affect global economics and food security as this region is a major exporter of corn, soybean, and wheat. However, the potential human, ecological, and economic impacts of future extreme hydroclimate events across the Midwest are poorly understood because instrumental climate records are limited to the last century and high-resolution regional paleoclimate records are sparse. Here, we provide initial results from a high-resolution (decadally resolved), multi-proxy reconstruction of spatiotemporal hydrologic patterns across the Midwest using new sediment records from four lakes; two from northern Indiana (Martin Lake and Pretty Lake), one from Wisconsin (Marl Lake), and one from Iowa (Clear Lake). Preliminary results obtained through measurements of carbonate δ¹⁸O, C:N ratios, sediment bulk density/loss on ignition, grain size, and magnetic susceptibility, combined with existing proxy data from midwestern and western study sites, provide insight into midwestern hydroclimate patterns that extends through the Holocene. With these data, we address two primary hypotheses: (1) Hydroclimate trends in the eastern Midwest are generally antiphased with sites in the western Midwest, with the eastern study sites revealing increasingly wetter conditions through the Holocene, while the western sites are progressively drier; (2) This hydroclimatic dipole is strongly influenced by the Pacific North American teleconnection (PNA), in which PNA-negative conditions increase warm-season precipitation from the Gulf of Mexico and induce wet phases east of the dipole and dry conditions west of the dipole. During PNA-positive modes, precipitation is derived from northwesterly sources and precipitation seasonality is reversed (i.e., greater cold-season and reduced warm-season precipitation).