A 7000-year Lacustrine Record from Angel Lake, Nevada

Angel Lake is a tarn at 2554 m asl in the East Humboldt Mountains of northeastern Nevada. To develop a post-glacial paleoclimate record for the lake, a sediment core was retrieved in June, 2007. The core was retrieved in 9.14 m of water, and extended from the sediment-water interface to a depth of 4.54 m below the lake bottom. The basal sediment of the core contains disseminated shards of Mazama tephra, and that ash, along with 5 AMS radiocarbon dates, supports a depth-age model that spans ~7 ka BP. Multiple proxies were investigated at 1-cm intervals including: water content, loss on ignition (LOI), magnetic susceptibility (MS), reflected light spectrophotometry, grain size distribution, and biogenic silica content. MS values generally decreases upward while LOI and water content show significant transient departures from an overall increasing trend through the record. Biogenic silica and detrended LOI values are notably above average from 1 to 2 ka BP and ca. 7 ka BP, suggesting a warmer, more productive lake environment. A pronounced low in detrended LOI is centered on 3.4 ka BP, suggesting decreased productivity. Mean grain size is highly variable, with spikes in the record reflecting delivery of clastic debris to the coring site by high-energy events. Because the core was retrieved from the opposite side of the depocenter from the inlet stream in water ~2 m shallower than the deepest part of the basin, these clastic layers are not considered evidence of fluvial inputs. Instead, these layers are interpreted to represent avalanche deposits onto the lake ice during the winter and spring. Avalanche events were identified as peaks in mean grain size rising above a background level determined by running a Gaussian smoothing function through the grain size time series. The frequency of avalanches was below average from 1.8 to 3.2 ka BP, overlapping the low in detrended LOI. In contrast, avalanches were quite common, up to 2-times the long-term average, from 3.2 to 3.8 ka BP, from 4.5 to 5.0 ka BP, and ca. 6.4 ka BP. These fluctuations may reflect changes in winter/spring moisture delivery to the northeastern Great Basin. Alternatively, increases in avalanche frequency may indicate more common rain-on-snow events or episodes of rapid warming during the spring thaw, both of which could stimulate wet avalanches and slushflows.