Lake Sensitivity To Late-Holocene Climate Change In The Western Great Lakes Region Based On Diatom-Depth Reconstruction

Abstract

Lake sediments provide an unparalleled source of proxy records of Holocene climate change and landscape response. Existing studies show overall synchrony in the upper Midwest (USA) to major climate periods (e.g., Holocene Thermal Maximum, and cooler/wetter late-Holocene), but less synchrony in response to shorter climate anomalies such as the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We examined a sediment core from Cheney Lake (northwest Wisconsin, USA), a lake positioned high in the landscape to reconstruct regional hydrologic climate response using diatom records to predict lake depth for the last 3500 years. To reconstruct historical changes in lake depth, a single lake diatom-based model was constructed based on species-depth relationships from 18 modern surface samples collected at depths of 0.5 to 5 m from Cheney Lake. Based on redundancy analysis (RDA), lake depth explained ~27% of the variance in diatom community abundance. A transfer function for reconstructing lake depth was developed using weighted averaging (WA) regression with inverse deshrinking. The transfer function was applied to downcore diatom communities in a 93-cm long 14C-dated core collected from a littoral zone site, to estimate lake level changes over the last 3500 years. Results suggest that Cheney Lake was almost 6 m deeper beginning ~3500 cal. yr BP, nearly twice as deep as the modern lake, a condition that persisted for several thousand years. An abrupt decrease in water depth occurred around 1500 cal. yr BP, reaching minimal depths around 700 cal. yr BP during the Medieval Climate Anomaly. Lake levels then rebounded and remained ~4 m above modern lake level until ~0 cal. yr BP (1950 CE). An abrupt decrease in moisture availability is evident in the last ~60 years, when lake levels fell to current low levels.