RECONSTRUCTING LAKE HOLOCENE PRODUCTIVITY AT COLUMBINE LAKE, COLORADO THROUGH ANNUALLY LAMINATED SEDIMENTS

Understanding past variations in precipitation and temperature can help contextualize long-term natural climate variability. There is a scarcity of high-resolution Holocene-length paleoclimate reconstructions from the southwest United States, and even fewer in the San Juan Mountains in southern Colorado. Understanding natural climate variability in the southern Rocky Mountains is critical because they provide water for much of the southwestern United States. Changes in summer flow in snow-dominated watersheds can have dramatic impacts for water supply for the Western United States. Here we present initial results from a lake sediment core from Columbine Lake, an alpine lake about 10 km northwest of Silverton, CO. The Columbine Lake sediment cores are finely laminated, and those laminations are annual (varves), potentially providing a very high-resolution age chronology for analyses. Varved sediments are a powerful tool in understanding climate variability because they provide an annual-scale chronology to extend instrumental records back in time. Through a preliminary investigation of varved sediment and a variety of productivity analyses, a new array of sedimentary reconstructions of productivity have been developed. Results from loss on ignition (LOI), hyperspectral imagery, and biogenic silica show a recent increase in aquatic productivity in the lake over the past few hundred years, likely indicative of an increase in the length and warmth of the summer growing season. Reconstructing climate of the past 3000 years will help to constrain climate and environmental history of the southern Rocky Mountains in the late Holocene.