117-7 A Closer Examination of Late Holocene Drought Episodes From a Southern Great Basin Lake Core Record

Abstract:

We combine new high-resolution scanning X-ray fluorescence (5 mm resolution) and clumped isotope derived paleotemperature data with previously reported isotopic (δ¹⁸O, ⁸⁷Sr/⁸⁶Sr, and ²³⁴U/²³⁸U) and total inorganic carbon (TIC) data from Lower Pahranagat Lake (LPAH), a highly alkaline, spring-fed southern Nevada lake to explore three recognized droughts over the past 3.5 ka. The LPAH core record has an excellent radiocarbon age chronology, and we previously established that both carbonate production and δ¹⁸O measured from carbonates are highly responsive to evaporative conditions.   

The Late Holocene Dry Period (LHDP; 3.1-1.8 ka) is an especially interesting climate episode for the LPAH record with the most evaporative conditions for the Late Holocene as indicated by anomalous δ¹⁸O values (isotopic enrichments of >9‰), high TIC, and Sr and U isotopic compositions that show significant reductions in water supply to the lake from the primary aquifer source. The increased resolution of the scanning XRF data indicates that the LHDP was characterized by three multi-century long droughts separated by two wetter intervals of shorter duration in this southern Great Basin location. Clumped isotope derived water temperatures average 14.5 ± 2.2 °C, indicating the LHDP was in relatively cool conditions.   

The Medieval Climate Anomaly (MCA; 1.2 – 0.8 ka) is indicated with a more modest increase in δ¹⁸O values (about 4‰) in the early MCA but two significant TIC peaks and Sr and U isotopic compositions that show reduced water from the primary aquifer, though not as much as for the LHDP. High-res XRF data allows us to better see multiple phases of the MCA. Though it was less evaporative, clumped isotope water temperatures average 18.6 ± 2.3 °C, indicating the MCA was warmer than the LHDP.   

The current drought interval (last ~200 years) is indicated by δ¹⁸O enrichment of 4‰ and a slight rise in TIC. One clumped isotope derived temperature for this interval of 23.2 ± 2.3 °C indicates this is the warmest drought interval for the last 3.5 ka, undoubtedly influenced by ongoing human-induced warming.  

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-21789

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