Holocene water balance variations in Great Salt Lake, Utah: application of GDGT indices and the ACE salinity proxy

Abstract

Great Salt Lake (UT) is a hypersaline terminal lake in the US Great Basin, and the remnant of the late glacial Lake Bonneville. Holocene hydroclimate variations cannot be interpreted from the shoreline record, but instead can be investigated by proxies archived in the sediments. GLAD1-GSL00-1B was cored in 2000 and recently dated by radiocarbon for the Holocene section with the top 11 m representing ˜7 ka to present. Sediment samples every 30 cm (˜220 years) were studied for the full suite of microbial membrane lipids, including those responsive to temperature and salinity. The ACE index detects the increase in lipids of halophilic archaea, relative to generalists, as salinity increases. We find Holocene ACE values ranged from 81-98, which suggests persistent hypersalinity with <50 g/L variability across 7.2 kyr. The temperature proxy, MBT' 5Me , yields values similar to modern mean annual air temperature for months above freezing (MAF = 15.7°C) over the last 5.5 kyr. Several GDGT metrics show a step shift at 5.5 ka before which temperature estimates are unreliable due to the shift in lake ecology and likely shallow depth. The step change in lake conditions at 5.5 ka and additional variations within the late Holocene are compared to regional climate records. We find evidence for a dry mid-Holocene in GSL, corroborating other records.

Lateral and temporal constraints on the depositional history of the Bonneville Salt Flats, Utah, USA

“…Regionally, this period shows declining aridity (Steponaitis et al, 2015;Lachniet et al, 2020). The timing of this increase in moisture aligns with a GSL shift to wetter conditions and lower salinities at 5.5 cal ka BP (So et al, 2023). This observation supports our second hypothesis that the saline pan (in its halite-depositing state) formed as the climate shifted from arid to wet.…”

“…7A), had a pronounced desiccation period from 8.3 to 6.5 ka (Louderback and Rhode, 2009). GSL was saltier at this time (7.2 to 5.5 cal ka BP; So et al, 2023). A compilation of Great Basin lakes showed an increasing proportion of lakes at low levels from 8 to 6 cal ka BP; lakes generally became deeper after 5.5 cal ka BP (Steponaitis et al, 2015).…”