NEOGLACIAL EPISODES RECORDED IN A LAKE SEDIMENT CORE FROM THE UINTA MOUNTAINS, UTAH

Considerable paleoclimate research is focused on climatic variability during the Holocene, including the enigmatic period of renewed glaciations known as the Neoglaciation. Alpine lake sedimentary records are particularly useful in Neoglacial studies because they can provide uninterrupted, high-resolution records of environmental changes. This study focused on analysis of biogenic silica, phosphorus, and carbon/nitrogen from an alpine lake sediment record collected in northeastern Utah, adding to an extensive dataset that suggests several periods of Neoglacial activity in the Uinta Mountains. The sediment core, which spans the past 5300 years, was taken from EJOD Lake, a small lake with a maximum depth of 4.3 m, and a surface area of 2.7 ha, located above modern treeline at 3323m. The lake is situated in a large glacial cirque ~500 m downslope from a complex of Neoglacial end moraines. Dry meltwater channels run from these moraines directly into EJOD Lake establishing a clear connection between glacial activity and the lake sediment record. The biogenic silica time series exhibits an overall decreasing trend over the past 5000 years suggesting a gradual shift of the lake environment toward a condition less suitable for an abundant diatom population. Superimposed on this downward trend are smaller-scale fluctuations including intervals of notably low values between 5000 and 5200, 1800 and 2300, and 500 and 800 BP. These intervals are interpreted as times of Neoglacial activity because a reduction in biogenic silica content of the sediment would be expected if delivery of glacial flour and cold meltwater to the lake were increased. These intervals are also synchronous with shifts in color, LOI, bulk density and average grain size in time series previously generated from this core. Results from ongoing phosphorus and carbon/nitrogen analysis will be combined with the biogenic silica data to further develop a Neoglacial chronology from the EJOD Lake sedimentary record.