HOLOCENE CLIMATE IN THE GREAT BASIN: PRELIMINARY RESULTS FROM FAVRE LAKE, NORTHERN RUBY MOUNTAINS, NEVADA

Little is known about Holocene climate variability at high elevations in north-central Nevada. This study aims to assess changes in watershed vegetation, lake levels and limnological conditions in order to understand secular to millennial-scale changes in regional climate. Favre Lake (2,899 m a.s.l.; 12 m deep; 7.7 hectares) is a flow-through lake in the northern Ruby Mountains. Castle Lake (2,989 m a.s.l.) and Liberty Lake (3,077 m a.s.l.) are the primary sources of influent; both appear to be intermittent. There is a single outlet. The bedrock of all three lake basins is early Paleozoic marble and Mesozoic granite and metamorphic rocks.

Bathymetric maps and temperature, pH, salinity, and conductivity profiles have been generated for Favre Lake. Surface samples and a series of cores were also collected using a modified Livingstone piston corer. The presence of the Mazama ash in the basal sediment indicates the record extends to ~7,700 cal yr B.P.

Magnetic susceptibility and loss-on-ignition indicate that the sediments in the lowest part of the core contain primary and reworked Mazama ash. About 2,000 years ago CaCO₃ increases from 2% to 3% of the inorganic sediment. The upper 25 cm of the core are marked by an increase in magnetic susceptibility which may indicate increased erosion due to grazing. During the first 1,500 years of the record, a diverse assemblage of benthic species dominated the diatom flora. The remainder of the core is dominated by members of the Fragilaria “complex,” suggesting that water level rose and flooded the shelf that surrounds the depocenter of the lake. This is supported by changes in the abundance of the aquatic fern ally Isoetes. While the resolution of the pollen data is currently too coarse to infer environmental change, the elevation of the lake (near the modern sagebrush/alpine pine zone boundary) suggests that it should be sensitive to variations in temperature and(or) precipitation. Exposure of the shelf during periods of high evaporation should result in an increase in herbaceous taxa, while increased precipitation should result in an increase in aquatic pollen.

Lastly, future research on sediment cores from Ruby Marsh, a perennial wetland on the eastern edge of the range, will provide a low elevation paleoclimatic counterpoint to this alpine site.