1. A Multi-proxy Paleolimnological Reconstruction of Holocene Climate Conditions in the Great Basin, United States 1 Department of Geography, The Ohio State University 2 Department of Geography-Geology, Illinois State University Introduction Alterations to the hydroclimatological regime of the Great Basin will be significant given how important and potentially limiting water resources are in this region. The Great Basin has experienced large fluctuations in its thermal and precipitation regimes during the late Quaternary. Understanding the nature and causes of this variability will help water resource managers plan for future needs. The remains of chironomids (Fig. 1) and diatoms, preserved in the sediment of Stella Lake, a small climatically sensitive lake located in Great Basin National Park (GBNP) were used to quantitatively and qualitatively reconstruct long-term changes in the temperature regime of the region Scott Reinemann 1, David Porinchu 1, Amy Bloom 2, Bryan Mark 1 and Jason Box 1 Study Site and Methodology A 328 cm sediment core was recovered from Stella Lake (Fig. 3), a small (~ 3ha), shallow (2.0m), high elevation (3,150m) lake in August 2007 Loss-on-Ignition (LOI) analysis was conducted at 0.5 cm resolution following Heiri et al. (2001). Conclusions Acknowledgements: We would like to thank Gretchen Baker (Staff Ecologist, Great Basin National Park, GBNP) and Cindy Nielsen (Superintendent, GBNP) for providing access to the research sites and facilitating our research, and Terry and Debbie Steadman for providing logistical support and local knowledge. We would also like to thank Adam Herrington and Jim DeGrand for their unyielding assistance in the field. We acknowledge The Western National Park Association (WPNA) and Department of Geography at The Ohio State University for funding this research. Results and Discussion Table 1: AMS 14 C dates for the Stella Lake. A total of 11 midge taxa were identified in the Stella Lake core (Fig. 4). The midge community experienced significant compositional turnover throughout the ~7000 yr record. The major taxa comprising the mid-Holocene midge community are: Corynoneura/Theinemaniella, Procladius and Tanytarsus. The overall diatom-community composition at Stella Lake (Fig. 5) was suggestive of shallow, cool, alkaline, oligotrophic waters with extensive ice cover. The midge-based MJAT inferences indicate that during the mid-Holocene (7,000 to 4,000 cal yr BP) the central Great Basin was characterized by relatively high temperatures, with a maximum of ~11.0ºC occurring at ~5200 cal yr BP (Fig. 6) Fig. 4 Chironomid relative abundance diagram for Stella Lake. Fig. 6 Loss-on-Ignition (LOI, green and blue lines), chironomid-inferred MJAT (red line with circles), LOWESS smooth (span = 0.10) of chironomid-inferred MJAT (thick red line). Fig.1: Photomicrograph of a Dicrotendipes head capsule (scale bar is 50  m). VMP = ventromental plate VMP Fig.2: (a) Map of study site and locations of other regional records. Stella Lake = SL. (b) Stella Lake study site (x = coring location). Fig. 3 Stella Lake, Great Basin N. P. (August 2007) A regional signal of maximum warmth and extreme aridity occur at ~5200 cal yr BP (Fig. 7) evidenced at multiple sites in the Great Basin, including Pyramid Lake. The interval between 5000 cal yr BP and 1800 cal yr BP was characterized by a decreasing midge-inferred MJAT reaching a minima of ~9.5°C at ~1800 cal yr BP. MJAT increased relatively rapidly during the post-1800 interval reaching a core maxima of 11.1ºC at ~ 100 yr BP (Fig. 6). Lab Code Depth in core (cm)Material 14 C yr BP ± 1σ 2σ age Range (cal yr BP) Relative area under Distribution Calibrated Age (cal yr BP) OS-6466133 Conifer Needle185 ± 30137 - 2240.556180.5 OS-64648112.5 Plant/Wood2080 ± 351985 - 21450.9552065 OS-64661233 Plant/Wood3920 ± 354242 - 44380.9904340 OS-64649320.5 Plant/Wood5970 ± 406713 - 69020.9626810 Fig. 7 Summary diagram of existing selected Great Basin paleoclimate records and data from Stella Lake. Chronological control was provided by four 14 C AMS dates on terrestrial macro-fossils (Table 1) Sub-fossil midge remains were identified and enumerated (n =100, 20 year resolution) Diatoms were analyzed from 46 samples at approximately 10-cm intervals throughout the core. A chironomid-based Mean July Air Temperature (MJAT) inference model designed specifically for use in the Great Basin was developed using a weighted-averaging partial least squares (WA-PLS) approach. Fig. 5 Diatom relative abundance diagram and Simpson’s Index of Diversity for the diatoms from Stella Lake. This study provides further support that the Great Basin was characterized by a warm and arid mid-Holocene, a cool and moist “Neoglacial” and a return to warm conditions during the late Holocene. The Stella Lake record broadens our knowledge of the thermal conditions that existed during the Holocene in the Great Basin by providing an independent quantitative reconstruction of MJAT.