RECONSTRUCTION OF THE WATER-LEVEL RECORD FOR LITTLE MOLAS LAKE, SOUTHERN COLORADO, USING VARIOUS LAKE BED SEDIMENT ANALYSES

Water is a vital resource and its abundance is affected by climate change. Severe drought brought on by climate change affects water availability in the western U.S. Analyzing Holocene water-level responses to climate change may provide suggestions for water resource managers.

The purpose of this project is to generate a lake-level record for Little Molas Lake (LML) in south-central CO using various lake-bed sediment analyses. This will help identify trends in moisture availability for the western U.S. Recent studies suggest El Nino-Southern Oscillation (ENSO) is a possible driver for latitudinal shifts in western storm tracks, producing a north-south precipitation dipole anomaly in the western U.S. (N and S of central CO).

The lake-level record generated from this research is compared to existing lake-level data in the Rocky Mountain region, including Lake of the Woods, WY, Little Windy Hill Pond, WY, and Emerald Lake, CO, to determine Holocene trends in moisture availability. LML provides a southern lake-level site to assist in determining if a N-S contrast in precipitation variability exists in the western U.S. This anomaly could exist due to variations in the intensities and frequencies of ENSO, affecting snowpack and causing changes in water availability in the western U.S.

Accelerated Mass Spectroscopy radiocarbon dating, grain size analysis, and loss-on-ignition was conducted on a near-shore core from LML to establish age constraints on sand intervals (interpreted to represent drought), percent sand content, and percent organic content, respectively. Comparing the percent sand and organic content with lake-level reconstructions from the aforementioned lakes, we observe evidence for the N-S precipitation dipole anomaly at 3 ka (ka = thousands of calibrated radiocarbon years before 1950 AD). To more accurately assess this observation, several other cores from LML are being analyzed and other lakes are being considered for addition to the N-S transect to determine its spatial extent.

Ocean core data suggests ENSO frequencies began to increase ca. 5 ka, possibly contributing to the two southern transect sites reflecting opposite changes in water-levels ca. 3 ka, and lending some support to the idea of the N-S precipitation dipole, however, analysis of more cores and sites will clarify this relationship.