Holocene Salinity Variations in Great Salt Lake, Utah: Application &
Calibration of the ACE Salinity Proxy
Abstract
The Great Salt Lake (UT) is a hypersaline terminal lake in the US Great
Basin, and the remnant of the late glacial-pluvial Lake Bonneville.
During the Holocene, hydroclimate variations have been more subtle in
the basin. These variations can be investigated by organic geochemical
methods within the sediment core GLAD1-GSL00-1B, cored in 2000 and
recently well-dated by radiocarbon for the Holocene section (Bowen et
al., 2019) with 11 meters representing 8 ka to present. Sediment samples
every 30 cm (~200 years) were extracted and the total
lipid extracts were analyzed by HPLC-MS to detect the full suite of
microbial membrane lipids, including those responsive to temperature and
salinity. Modern samples were also collected to provide local
calibration for the archaeol-caldarchaeol ecometric (ACE) salinity
proxy, where ACE = archaeol/(archaeol + caldarchaeol). ACE detects the
increase in lipids of halophilic archaea, relative to generalists, as
salinity increases. From currently analyzed data and calibrations, we
find Holocene lake salinity estimates ranged from 239 to 283 psu,
suggesting persistent hypersalinity with < 50 psu variability
across 8 kyr. For comparison, the modern salinity of the lake ranges
from 100 to 160 psu in the southern half, and 240 to 270 psu in the
north. From ~7-6 ka, salinity estimates were relatively
high at 270 to ~280 psu. Following 6 ka, salinity
decreases and reaches its lowest value of 239 psu at 4.8 ka. Afterwards,
salinity increases and varies between ~250 to
~270 psu, remaining at 270 psu in the last 1 kyr. This
new salinity record is compared to available shoreline reconstructions
and regional climate records. The temperature proxy,
MBT’5Me, as calibrated by BayMBT,
suggests mean annual air temperature estimates ranged from 12°C to 24°C
(compared to modern mean temperature of 13°C). This indicates a
substantial, variable complication from salinity in this consistently
hypersaline lake, as recently reported for the MBT’5Me
proxy.