THE EFFECT OF LOCAL LACUSTRINE CONDITIONS ON THE EXPRESSION OF REGIONAL HOLOCENE CLIMATE IN THE RUBY MOUNTAINS AND EAST HUMBOLDT RANGE, NEVADA, USA

Climate of the north-central Great Basin currently exhibits a bimodal precipitation pattern, dominated by winter (Nov.-Feb.) precipitation from the eastern Pacific Ocean, augmented by late spring and early summer (May-Jul.) convectional precipitation. PRISM precipitation data indicate that the Ruby Mountains receive more moisture than most other mountain ranges in the central Great Basin; CPC/NOAA data show interannual variability. Reconstruction of past moisture variability has proven difficult due to limited continuous paleoclimate records in this region and the effect of lake-specific and local watershed characteristics.

In order to evaluate the role of local conditions on a ~7600-yr-long climate record collected from Favre Lake, surface sediments were collected from tarns in the northern Ruby Mountains at elevations between 2500 and 3100 m (Lamoille Lake, 6 ha, 20 m deep; Upper Dollar Lake, ~1 ha, 2 m deep; Lower Dollar Lake, ~1 ha, 2 m deep; Liberty Lake, 9 ha, 33 m deep; Castle Lake, 6 ha, 4.6 m deep; Favre Lake, 8 ha, 12 m deep), and East Humboldt Range (Angel Lake, 5 ha, 9 m deep). Individual lake basins are underlain by varying combinations of bedrock and till. Bathymetry, water chemistry and physical properties data collected from Liberty and Favre Lakes indicate that they are continuous cold polymictic lakes. Lamoille and Angel Lakes are also likely continuous cold polymictic lakes, while Upper Dollar, Lower Dollar and Castle Lakes are rarely stratified. Temperature profiles to a depth of ~8 m in Farve and Liberty Lakes include the epilimnion and the upper part of the metalimnion. The warmer surface water and shallower epilimnion-metalimnion boundary (~3 m) in Favre Lake may be due to an extensive shallow shelf in the lake. The larger shift in pH in Favre Lake (~3 m) is indicative of a higher (mesotrophic) nutrient level and increased decomposition of organic matter compared to the change in Liberty Lake (oligotrophic). Lake bathymetry and associated thermal feedback processes that imposed by differences in water depth appear to be the primary factor controlling the composition of the diatom flora in these lakes. The results of these modern lake studies are being applies to study of the Favre lake core and will be useful in planning climate change studies in other nearby subalpine lakes.