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This study uses a hydrologic‐balance model to evaluate the range of precipitation and temperature (P‐T) conditions required to sustain Lake Bonneville at two lake levels during the late Pleistocene. Intersection with a second set of P‐T curves determined from glacial modelling in the nearby Wasatch Mountains places tighter climatic constraints that suggest gradually increasing wetness from ~21 to 15 ka. Specifically, during the latter part of the Last Glacial Maximum (LGM) (~21–20 ka), Lake Bonneville approached its highest level under conditions roughly 9.5°C colder but only 7% wetter than modern. As the lake reached its pre‐flood Bonneville level (~18.2–17.5 ka), climate conditions were ~16% wetter and ~9°C colder than modern. Byca. 15–14.8 ka, Lake Bonneville abandoned the overflowing Provo level under conditions that were ~21% wetter and ~7°C cooler. These results suggest that regional LGM highstands were not caused by large increases in precipitation, but rather by a climatic optimum in which moderate wetness combined with depressed temperatures to create a positive hydrologic budget. Later highstands during Heinrich I from 17 to 15 ka were likely achieved under gradual increases in precipitation, prior to a transition to drier conditions after 15 ka.

 

Prominent lunette dunes 500e800 m long, 50e80 m wide, and up to 5 m tall are present on the floor of the Independence Valley in northeast Nevada, USA. These dunes border the downwind margins of circular playas at the end of a drainage descending from the East Humboldt Mountains, which terminates in an ephemeral water body named Little Lake. Gastropod shells from the Little Lake playa yield radiocarbon ages of ~400 cal yr BP, after correction for a hard-water effect. A similar age was obtained for shells from the crest of one of the lunettes. Deeper sediment in this lunette yielded shell ages clustering around 600 cal yr BP. This pattern suggests two intervals of relatively persistent water at Little Lake, both of which ended with lake desiccation and deflation of sediment and shells to the adjacent lunette. Shells from the crest of another lunette yielded radiocarbon ages between 3800 and 1750 cal yr BP. This dune, therefore, is considerably older and accumulated over a much longer stretch of time. Using the Global Surface Water Explorer, years between 1984 and 2018 were identified in which Little Lake contained water in most of the available summer imagery. These years form three clusters: 1984e1987, 1997e2000, and 2017e2018. Snow water equivalent (SWE) is greater in the mountains, snow makes up a greater percent of total annual precipitation, and Palmer Drought Severity Index is more positive in this region, in years when water is present in Little Lake compared with those in which the lake remains dry. Values of the PDO are also higher in years when Little Lake holds water. Although the hydrology of Little Lake may be influenced to an unknown degree by upstream water diversions, this overall pattern implies that the lake and its associated lunettes are a sensitive recorder of late Holocene hydroclimate variability in the northern Great Basin. 

We applied luminescence dating to a suite of shorelines constructed by pluvial Lake Clover in northeastern Nevada, USA during the last glacial cycle. At its maximum extent, the lake covered 740 km2 with a mean depth of 16 m and a water volume of 13 km3. In the north-central sector of the lake basin, 10 obvious beach ridges extend from the highstand to the lowest shoreline over a horizontal distance of ~1.5 km, representing a lake area decrease of 35%. These ridges are primarily composed of sandy gravel and rise ~1.0 m above the alluvial fan surface on which they are superposed. Single grain luminescence dating of K-feldspar using the pIRIR SAR (post-infrared infrared single-aliquot regenerative dose) protocol, corroborated by SAR dating of quartz, indicates that the highstand shoreline was constructed ca. 16–17 ka during Heinrich Stadial I (Greenland Stadial 2, GS-2), matching 14C age control for this shoreline elsewhere in the basin. The lake regressed rapidly during the Bølling/Allerød (GI-1), before the rate of regression slowed during the Younger Dryas interval (GS-1). The lowest shoreline was constructed ca. 10 ka. Persistence of Lake Clover into the early Holocene may reflect enhanced monsoonal precipitation driven by the summer insolation maximum. 

Beach ridges constructed by pluvial Lake Clover in Elko County, Nevada during the Late Pleistocene were investigated with ground-penetrating radar (GPR). The primary objective was to document the internal architecture of these shorelines and to evaluate whether they were constructed during lake rise or fall. GPR data were collected with a ground-coupled 400-Mhz antenna and SIR-3000 controller. To constrain the morphology of the ridges, detailed topographic surveys were collected with a Topcon GTS-235W total station referenced to a second class 0 vertical survey point. GPR transects crossed the beach ridge built by Lake Clover at its highstand of 1725 m, along with seven other ridges down to the lowest beach at 1712 m. An average dielectric permittivity of 5.0, typical for dry sand and gravel, was calculated from GPR surveys in the vicinity of hand-excavations that encountered prominent stratigraphic discontinuities at known depths. Assuming this value, consistent radar signals were returned to a depth of ~3 m. Beach ridges are resolvable as ~90 to 150-cm thick stratified packages of gravelly sand overlying a prominent lakeward-dipping reflector, interpreted as the pre-lake land surface. Many ridges contain a package of sediment resembling a buried berm at their core, typically offset in a landward direction from the geomorphic crest of the beach ridge. Sequences of lakeward-dipping reflectors are resolvable beneath the beach face of all ridges. No evidence was observed to indicate that beach ridges were submerged by higher water levels after their formation. Instead, the GPR data are consistent with a model of sequential ridge formation during a monotonic lake regression.