The climate of the southwestern North America has experienced profound changes between wet and dry phases over the past 200 kyr. To better constrain the timing, magnitude and paleoenvironmental impacts of these changes in hydroclimate, we conducted a multiproxy biomarker study from samples collected from a new 76 m sediment core (SLAPP-SRLS17) drilled in Searles Lake, California. Here, we use biomarkers and pollen to reconstruct vegetation, lake conditions and climate. We find that δD values of long chain n-alkanes are dominated by glacial to interglacial changes that match nearby Devils Hole calcite δ18O variability, suggesting both archives predominantly reflect precipitation isotopes. However, precipitation isotopes do not simply covary with evidence for wet-dry changes in vegetation and lake conditions, indicating a partial disconnect between large scale atmospheric circulation tracked by precipitation isotopes and landscape moisture availability. Increased crenarchaeol production and decreased evidence for methane cycling reveal a 10 kyr interval of a fresh, productive and well-mixed lake during Termination II, corroborating evidence for a paleolake highstand from shorelines and spillover deposits in downstream Panamint Basin during the end of the penultimate (Tahoe) glacial (140–130 ka). At the same time brGDGTs yield the lowest temperature estimates (mean months above freezing = 9 ± 3°C) of the 200 kyr record. These limnological conditions are not replicated elsewhere in the 200 kyr record, suggesting that the Heinrich stadial 11 highstand was wetter than that during the last glacial maximum and Heinrich 1 (18–15 ka).

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.

Ice cores and other paleotemperature proxies, together with general circulation models, have provided information on past surface temperatures and the atmosphere’s composition in different climates. Little is known, however, about past temperatures at high altitudes, which play a crucial role in Earth’s radiative energy budget. Paleoclimate records at high-altitude sites are sparse, and the few that are available show poor agreement with climate model predictions. These disagreements could be due to insufficient spatial coverage, spatiotemporal biases, or model physics; new records that can mitigate or avoid these uncertainties are needed. Here, we constrain the change in upper-tropospheric temperature at the global scale during the Last Glacial Maximum (LGM) using the clumped-isotope composition of molecular oxygen trapped in polar ice cores. Aided by global three-dimensional chemical transport modeling, we exploit the intrinsic temperature sensitivity of the clumped-isotope composition of atmospheric oxygen to infer that the upper troposphere (5 – 15 km altitude, effective mean 10 – 11 km) was 4 – 10°C cooler during the LGM than during the late preindustrial Holocene. These results support a minor or negligible steepening of atmospheric lapse rates during the LGM, which is consistent with a range of climate model simulations. Proxy-model disagreements with other high-altitude records may stem from inaccuracies in regional hydroclimate simulation, possibly related to land-atmosphere feedbacks.