HYDROCLIMATE VARIATIONS OVER THE LAST THREE GLACIAL-INTERGLACIAL CYCLES AT GREAT SALT LAKE AND BEAR LAKE, UTAH, USA

Continental paleoclimate records are vital for understanding the magnitude of climate shifts associated with insolation and greenhouse gas forcing, and, in particular, resolving these changes close to present-day centers of population and agriculture. While abundant evidence on the Holocene and Last Glacial Maximum is accessible in continental archives, much less is known about prior glacial-interglacial variability. Longer records are of interest because successive glacial terminations offer comparisons between recurring warming transitions driven by similar forcings, thus allowing us to delimit the range of variability beyond the Holocene. Continental scientific drilling permits access to these long-term records. Drilling at Great Salt Lake (GSL) and Bear Lake (BL) in 2000 by the Global Lakes Drilling Initiative (GLAD) recovered sediments spanning 2-3 glacial cycles. Here, we revisit these legacy cores with new techniques, applying a suite of biomarkers (plant waxes and microbial membrane lipids) to reconstruct past climate by comparing lower elevation, saline GSL (~1.3 kmasl) with higher elevation, freshwater BL (~1.8 kmasl). While both lakes offer unique climate insights, each has their respective complications, such as fluctuating catchment size at BL and extreme hypersaline conditions at GSL. By using a dual site approach and integrating their environmental information, we disentangle basin dynamics from regional climate signals. We reveal new insights from plant wax evidence on the magnitude of glacial-interglacial precipitation isotope cyclicity (~20‰ in δD) and vegetation water stress (~4‰ in δ¹³C). We also show evidence from microbial membrane lipids for water balance variation (freshening events at GSL) and temperature cyclicity (3°C at BL). To constrain the timing of climatic events, we measure U and Th isotopes on calcium carbonate and halite sequences for potential GSL age model revision. An accurate chronology is essential for linking regional climate to global forcings. Revisiting these deep-drilled cores with novel biomarker and improved geochronology techniques will enable us to 1) test the limits of these techniques in two unique lake systems, and 2) uncover a terrestrial climate history of the western US over multiple recent glacial cycles, which will help expand the global glacial-interglacial climate record.