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Abstract Great Salt Lake, Utah, is a hypersaline terminal lake in the 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 Archaeol and Caldarchaeol Ecometric (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 ka. 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 ka. Several GDGT metrics show a step shift in microbial communities and limnology at 5.5 ka. Extended archaeol detects elevated salinity during the regional mid-Holocene drought, not readily detected in the ACE record that is often near the upper limit of the index. Wemore »infer that the mid-Holocene GSL was shallower and saltier than the late Holocene. The current drying may be returning the lake to conditions not seen since the mid-Holocene. Plain Language Summary Great Salt Lake in Utah is the remnant of a once much larger lake and is currently at a historically low level. We study a lake sediment core, collected in 2000 from the floor of Great Salt Lake, and recently dated. We take new samples from the core and measure them for molecules made by microbes, whether living in the lake or washed in from the surrounding soils. We reconstruct lake conditions during the last 7,200 years and assess whether lake level fluctuated during that time. Over the past 7,200 years, we find evidence that the lake was shallower from 7,200 to 5,500 years ago but has been relatively stable until the modifications of the lake in the 20th century and the current drying trend.« less

The response of the terrestrial biosphere to warming remains one of the most poorly understood and quantified aspects of the climate system. One way to test the behavior of the Earth system in warm climate states is to examine the geological record. The abundance, distribution, and/or isotopic composition of source-specific organic molecules (biomarkers) have been used to reconstruct terrestrial paleoenvironmental change over a range of geological timescales. Here, we review new or recently improved biomarker approaches for reconstructing ( a) physical climate variables (land temperature, rainfall), ( b) ecosystem state variables (vegetation, fire regime), and ( c) biogeochemical variables (soil residence time, methane cycling). This review encompasses a range of key compound classes (e.g., lipids, lignin, and carbohydrates). In each section, we explore the concept behind key biomarker approaches and discuss their successes as paleoenvironmental indicators. We emphasize that analyzing several biomarkers in tandem can provide unique insights into the Earth system. ▪ Biomarkers can be used to reconstruct terrestrial environmental change over a range of geological timescales. ▪ Analyzing several biomarkers in tandem can provide unique insights into the Earth system. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 50 is Maymore »2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.« less