NOAA/WDS Paleoclimatology - Great Salt Lake GDGT Data from the Pleistocene to Present

Great Salt Lake (GSL), Utah, USA, is a large hypersaline lake, but during short-lived (~10 – 20 kyr) pluvials, it had been an expansive freshwater lake. We update the age model of GLAD1-GSL00-4, a 120-m sediment core recovered by the Global Lakes Drilling (GLAD) project, with new U-series measurements, seeking to date evaporites representing the driest times in lake history and provide a new basal age of 236.3 ka (2s uncertainty = 6.7 kyr) during the penultimate interglacial. We measure abundances of microbial membrane lipids (glycerol dialkyl glycerol tetraethers; GDGTs) to reconstruct salinity, stratification, and aquatic productivity over the last two glacial cycles. High and variable salinity precludes use of GDGTs as a proxy for temperature. We detect freshening, increased productivity, and overturning during the “Bonneville” and “Little Valley” deep lake phases, here dated to 30.3 – 16.1 ka (2s = 0.6 – 2.6 kyr) and 140.4 – 134.6 ka (2s = 5.5 – 5.7 kyr). The salinity rise following the last glacial termination pluvial agrees with water balance reconstructions from well-dated lacustrine carbonates. However, the evaporite (thenardite) deposition dates to 12.2 – 16.1 (2s = 0.4 – 0.5 kyr), and contrasts with reports of Holocene deposition elsewhere in the basin. The same sequence of salinity increase and evaporite deposition (halite) occurs in the penultimate glacial termination. Despite disparate halite dates spanning 90 – 160 ka, age model assignment of the preceding Little Valley freshening agrees with U-series dating of shoreline tufa, highlighting cyclical lake expansion/contraction followed by evaporite deposition during glacial terminations, consistent with regional pluvials.