Quaternary Science Reviews 131 (2016) 193e210 Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev Holocene paleoclimate history of Fallen Leaf Lake, CA., from geochemistry and sedimentology of well-dated sediment cores * Paula J. Noble a, , G.Ian Ball b, Susan H. Zimmerman c, Jillian Maloney d, Shane B. Smith a, Graham Kent e, g, Kenneth D. Adams f, Robert E. Karlin a, Neil Driscoll g a Department of Geological Sciences and Engineering, University of Nevada, Reno, NV 89557, USA b Chevron Energy Technology Company, 1500 Louisiana Street, Houston, TX 77002, USA c Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA d Department of Geological Sciences, San Diego State University, San Diego, CA 92182, USA e Nevada Seismological Laboratory, University of Nevada, Reno, NV 89557, USA f Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, NV 89512, USA g Scripps Institute of Oceanography, Geosciences Research Division, La Jolla, CA 92093, USA article info abstract Article history: Millennial-scale shifts in aridity patterns have been documented during the Holocene in the western Received 8 June 2015 United States, yet the precise timing, severity, and regional extent of these shifts prompts further study. Received in revised form We present lake sediment core data from Fallen Leaf Lake, a subalpine system at the southern end of the 19 October 2015 Lake Tahoe basin for which 80% of the contemporary inflow is derived from snowpack delivered by Accepted 23 October 2015 Pacific frontal storm systems. A high quality age model has been constructed using 14C ages on plant Available online xxx macrofossils, 210Pb, and the Tsoyowata tephra datum (7.74e7.95 cal kyr BP). One core captures the transition from the Late Tioga-younger Dryas glaciolacustrine package to laminated opaline clay at Keywords: Holocene 11.48 cal kyr BP. Early Holocene sedimentation rates are relatively high (~1.9 mm/year) and cooler winter Lake cores temperatures are inferred by the presence of pebbles interpreted to be transported out into the lake via Geochemistry shore ice. There is a geochemically distinct interval from ~4.71 to 3.65 cal kyr BP that is interpreted as a Paleoclimate late Holocene neopluvial, characterized by depleted d13C and lower C:N that point to reduced runoff of Lake Tahoe basin terrigenous organic matter, increased winter precipitation, and increased algal productivity. The largest Great Basin Holocene signal in the cores occurs at the end of the neopluvial, at 3.65 cal kyr BP, and marks a shift into Neopluvial a climate state with variable precipitation, yet is overall more arid than the neopluvial. This new climate state persists for ~3 ka, until the Little Ice Age. Low sedimentation rates (0.5 mm/year), the homogeneous opaline sediment, and steadily increasing contributions of terrestrial vs. algal organic matter in these cores suggest that the lowstand state of Fallen Leaf Lake may have been the norm from 3.65 to 0.55 cal kyr BP, punctuated by short term high precipitation years or multi-year intervals capable of rapid short duration lake level rise. Fallen Leaf Lake is strongly influenced by changes in winter precipitation and temperature, manifested largely by the geochemical proxies, and highlights unique advantages of subalpine lakes in regional paleoclimate reconstructions. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction northern Sierra Nevada and western margin of the Great Basin over the last ~13 ka. Fallen Leaf Lake (FLL) is a hydrologically open Here we characterize the Holocene sedimentary package of a oligotrophic subalpine system situated at the southern margin of glacially derived subalpine lake in the Lake Tahoe basin to better Lake Tahoe. Presently, the basin experiences a typical montane Si- constrain the timing and nature of major paleoclimatic shifts in the erra Nevada climate dominated by Pacific frontal storm systems bringing precipitation largely in the winter (Hanes, 1981; O'Hara, 2007), however the intensity and position of synoptic scale climate patterns may have varied throughout the Holocene (Barron * Corresponding author. and Anderson, 2011), contributing to significantly different annual E-mail address: [email protected] (P.J. Noble). http://dx.doi.org/10.1016/j.quascirev.2015.10.037 0277-3791/© 2015 Elsevier Ltd. All rights reserved. 194 P.J. Noble et al. / Quaternary Science Reviews 131 (2016) 193e210 precipitation patterns. Most Holocene climate reconstructions for the Sierra Nevada and western Great Basin have been derived from the alkaline terminal lakes of endorheic basins (e.g., Pyramid, Owens, Mono, Walker lakes) whereas relatively few have come from higher elevation and potentially more climatically sensitive alpine environments (Osleger et al., 2009; Smith et al., 2013; Street et al., 2012, 2013). Alkaline terminal lakes produce endogenic car- bonates particularly suited to d18O analysis and reconstruction of basin-scale water budgets governed by past changes in the relative magnitudes of precipitation and evaporation. However, the lack of macrofossils and variable and unknown reservoir effects on car- bonates in these endorheic systems has complicated the con- struction of age-models used as a basis for interpreting the timing and periodicity of the climatic events. In contrast, subalpine lakes may offer higher fidelity records of past climatic change. They are usually rich in macrofossils that can be 14C-dated, enabling the creation of reliable high-resolution age models, and their low drainage-area to lake-surface ratio should be more responsive to hydrologic cycle perturbations. Climatic effects relating to the strength and degree of winter precipitation can also have discernible effects on subalpine lake productivity and its organic geochemical record, resulting from changes in amounts of lake mixing and the development of stratification. This study provides an opportunity to identify and calibrate the subalpine response to major climate signals affecting the northern Sierra Nevada and western Great Basin, and to inform the timing of regional climate events using a high-resolution age model. 2. Setting and previous work on FLL sediments Fallen Leaf Lake (FLL) is a low conductivity, circumneutral (pH ¼ 6.5e7.5) deep subalpine lake situated ~2 km south of Lake Fig. 1. Digital elevation map showing the location of Fallen Leaf Lake in the southern Tahoe in Glen Alpine Valley at an elevation of 1942 m, 45 m above part of the Lake Tahoe basin, and core localities. Lake Tahoe (Fig. 1). The northern end is bounded by terminal mo- raines left during the retreat of Tioga-, and possible Tahoe-age the upper ~1 m of sediments. The upper ~1 m was not recovered in glaciers (Saucedo et al., 2005). the 2006 coring campaign because of over-penetration. The 2006 The southwestern margin of FLL is bounded by the steep cores were proximally positioned to the West Tahoe-Dollar Point escarpment of the West Tahoe-Dollar Point fault (Brothers et al., Fault and captured debris and gravity driven flows, including one fl 2009). The principal source of water and sediment in ow is Glen ascribed to the most recent seismic event (FLLS1). One core also fl Alpine Creek on the southern end of the lake. Out ow is at the captured the Tsoyowata tephra that, along with sparse macrofossil fl north end through Taylor Creek and subsurface ow through the 14C dating provided a rough portrait of the sedimentologic char- end moraine into Lake Tahoe (Fig. 1; Kleppe et al., 2011). The acter, sedimentation rates, and distribution of datable macrofossils 2 watershed for FLL is ~42 km of steep montane areas in the Deso- in FLL. lation Wilderness, and is ~8 times the surface area of FLL (Kleppe, The piston cores collected in 2010 were also used to constrain 2005). Mean annual precipitation in the watershed ranges from the ages of debris and gravity-driven deposits observed in CHIRP 0.75 m to 1.5 m, the majority of which falls in the winter as snow data. It was hypothesized that these flows were triggered by (Hanes, 1981). Lake levels have been observed to rise quickly seismic events and, as such, were used to expand the paleoseismic following periods of high precipitation, and have been inferred to history of the West Tahoe-Dollar Point Fault (Maloney et al., 2013). drop to the level of Tahoe during prolonged drought periods, Radiocarbon dates from these cores were presented in Maloney including a lowstand during the Medieval Climate Anomaly circa et al. (2013), although in the context of the paleoseismological e 1.0 0.7 cal kyr BP (Kleppe et al., 2011; Mann et al., 2009). Bathy- history. The major seismic events dated by this effort are termed fi metric pro les show that the lake is crossed by a series of reces- FLLS1 (4.71 ± 0.14 cal kyr BP), FLLS2 (7.75 ± 0.14 cal kyr BP), and sional moraines that divide the lake into northern and southern FLLS3 (11.48 ± 0.17 cal kyr BP), and are represented in the piston sub-basins. The deepest end of the lake is to the south with a cores by turbidite deposits that act as marker beds to correlate maximum depth of 116 m (Maloney et al., 2013), and the northern stratigraphy between cores and CHIRP data (Maloney et al., 2013). end is filled with a series of moraine ridges averaging about 70 m depth. Side scan sonar, Compressed High Intensity Radar Pulse (CHIRP) 3. Materials and methods surveys, and a piston coring campaign were conducted in 2006 to assist with reconstructing the frequency and origins of past 3.1. Coring earthquakes in the Lake Tahoe Basin (Brothers et al., 2009; Maloney et al., 2013). This previous subsurface imaging delimited gross Four coring sites were targeted based on previous seismic sur- sedimentologic packages and enabled identification of suitable lo- veys (Brothers et al., 2009; Maloney et al., 2013), two in the cations for a subsequent 2010 coring campaign that sought to northern sub-basin, and two in the southern (Fig.