A CONTINUOUS SEDIMENT RECORD DOCUMENTS THE ONSET AND TERMINATION OF GLACIATION DURING THE LGM AND MIS 4 FROM FISH LAKE, UTAH

The Fish Lake sediment record is a continuous, high-resolution, freshwater paleoclimate archive recording glacial and precipitation-evaporation (P-E) history from a sensitive catchment straddling the boundary between the Colorado Plateau and the Great Basin. The Fish Lake Plateau at >3,600m is sufficiently high to glaciate during stadial periods making it an ideal location to investigate the glacial history of the region. The Fish Lake sediment record is long, continuous, high-resolution (>3.3mm/decade) and contains multiple proxies sensitive to climate and ecosystem response. Successful dating of progressively longer and older cores recovered in 2014, 2020, and 2024 was accomplished by radiometric methods, including ²¹⁰Pb and AMS ¹⁴C of terrestrial macrofossils and charcoal, as well as through tephrochronology, and paleomagnetic measurements. Multiproxy analyses of an 18.5 m-long core with a basal age of ~65ka recovered in February of 2020 includes indicators of glacial erosion and biological productivity indicate the onset of Last Glacial Maximum (LGM) glaciation occurred ~24.5ka. Proxy indicators for glacial erosion include magnetic susceptibility, sediment density, % mineral matter, grainsize, and scanning XRF data; proxies for biological productivity include biogenic silica and organic matter. These proxies indicate the local LGM spanned the period between 24.5-19.5ka. During this time the glaciers reached the shoreline, but did not override the lake nor increase rates of sedimentation above that of the Holocene because increases in glacial erosion were balanced by decreases in productivity in the glaciated catchment and turbid lake. Deglaciation began at 19.5ka and was interrupted by a readvance during the wetter conditions synchronous with Heinrich Stadial 1 before final deglaciation of the catchment ~15ka. After 14.3ka proxies for biological productivity increase rapidly and remain high through the Holocene while proxies for erosion decrease abruptly. In February 2024 additional cores were recovered from a thinner sediment package with the goal for extending the record further back in time to MIS 5. Work is currently in progress on these cores but it appears they penetrate a second glacial phase likely in MIS 4 into sediments that are more characteristic of a warm phase.