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,
MBTʹ5Me, 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.