A 30,000-year continuous record of glacial history and water balance from Fish Lake, Utah documents the onset, development, and demise of LGM glaciation

Fish Lake provides a continuous, high-resolution freshwater paleoclimate archive of glacial and hydroclimate history from a catchment straddling the Colorado Plateau–Great Basin boundary in the western US. At >3600 m, the Fish Lake Plateau glaciates during stadials, making it an ideal site for tracking the region's glacial history. The high-resolution (>3.3 mm/decade) record contains multiple climate- and ecosystem-sensitive proxies. Geochronology relies on ²¹⁰Pb and AMS ¹⁴C measurements on terrestrial macrofossils and charcoal, tephrochronology, and paleomagnetic measurements. Multiproxy analyses include indicators of glacial erosion (magnetic susceptibility, sediment density, % mineral matter, grainsize, scanning XRF) and biological productivity (biogenic silica, organic matter). These proxies show glacial inception during the local Last Glacial Maximum at 25.8 ka, coincident with Heinrich Stadial 2, with maximum down-valley ice expansion between 24.8 and 20.9 ka. Glaciers reached the shoreline but did not override the lake, and sedimentation rates did not exceed Holocene levels, as increased glacial erosion was offset by reduced productivity in the glaciated, turbid lake. Deglaciation began by 18.2 ka, was interrupted by a readvance under wetter conditions synchronous with Heinrich Stadial 1 and concluded with final catchment deglaciation ∼14.1 ka. After 13.7 ka, productivity proxies rise rapidly and remain high through the Holocene while erosion proxies drop abruptly. Comparison with the adjacent Bonneville pluvial lake-level record shows that glacial onset on the Fish Lake Plateau preceded the rise in Bonneville water levels at ∼24 ka by roughly a millennium, implying temperature decreases led P-E increases. Similarly, deglaciation onset preceded falling Bonneville water levels by several centuries.