GEOLOGY, July 2007 619 Geology, July 2007; v. 35; no. 7; p. 619–622; doi: 10.1130/G23445A.1; 3 figures; 1 table; Data Repository item 2007154. © 2007 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. INTRODUCTION Evidence for synchronous millennial-scale climatic change between the Great Basin of the western United States and the North Atlantic exists mostly as records of Great Basin lake- level fluctuations (Benson et al., 1998; Lin et al., 1998; Oviatt, 1997) and alpine glacier advance and retreat along the west coast (Benson et al., 1996; Clark and Bartlein, 1995). However, robust dating that would allow detailed corre- lations has been problematic. Determining the phase relationships of Great Basin and North Atlantic records is complicated by uncertainties and limits of the radiocarbon method (includ- ing lake water reservoir effects), the difficulty in identifying deflation-related hiatuses in lake sediments, and the high frequency and short duration of Dansgaard-Oeschger (D-O) events. Here we present an oxygen isotope record from stalagmites collected from Goshute Cave, Nevada, United States (40°2′N, 114°47′W), from the last interglacial period (Fig. 1). A robust U-Th chronology allows comparison with Greenland ice core sequences as well as other high-resolution records of climatic vari- ability from western North America and the Northern Hemisphere. MILLENNIAL-SCALE CLIMATE VARIABILITY IN WESTERN NORTH AMERICA D-O events, first identified in Greenland ice records (Dansgaard et al., 1993), have been documented in multiproxy records (e.g., gray scale and foraminiferal oxygen isotopic ratios) of marine sediments in the Santa Barbara Basin off the west coast of the United States (Fig. 1) (Hendy and Kennett, 1999). However, the con- nection from the marine to the continental realm is not necessary straightforward, and no record has unambiguously demonstrated the synchro- neity of D-O events between the North Atlantic and the western United States. Evidence of rapid climate change in the Great Basin comes largely from lake sediments (Benson et al., 2003). Despite the benefits of multiple paleoenviron- mental proxies from a number of lake basins, age-control limitations have hampered the abil- ity to correlate variability in lake records from the western United States with the North Atlan- tic. For example, Grigg and Whitlock (2002) used palynological analysis of Fargher, Carp, and Little Lakes from the Pacific Northwest to demonstrate that temperatures oscillated every 1–3 k.y. during marine isotope stages (MIS) 2–3 (14–60 ka), although age uncertainties do not allow precise correlation among these lakes or with other regional climate records (Fig. 1). Zic et al. (2002) tied fluctuations in isothermal rem- nant magnetization signatures from sediments at Summer Lake, Oregon, to D-O and Heinrich events and Bond cycles, but their chronology is stretched around a single 14 C correlation point. Lin et al. (1998) applied U-Th methods to date interbedded muds and salts at Searles Lake, Cali- fornia, and found that lake levels rose and fell on time scales similar to D-O events from 35 to 24 ka; however, precise correlations were ham- pered by significant corrections for detrital 230 Th. Based on proxy glacial and hydrologic records of Owens Lake, California, and Pyramid Lake, Nevada, Benson et al. (2003) argued that D-O interstades corresponded to relatively warm and wet conditions in the Great Basin; however, the chronology was problematic. In general, these issues derive from the situation that (1) the duration of D-O events is roughly the same as the age uncertainties, and (2) the characteristic asymmetry of D-O events in the Greenland ice δ 18 O record can be difficult to detect in lacus- trine records from the Great Basin. The question has thus remained unresolved as to whether the millennial-scale climatic shifts of the western United States have been synchronous with those of the North Atlantic region. Synchronous millennial-scale climatic changes in the Great Basin and the North Atlantic during the last interglacial Rhawn F. Denniston Department of Geology, Cornell College, 600 1st Street West, Mount Vernon, Iowa 52314, USA Yemane Asmerom Department of Earth and Planetary Science, Northrop Hall, University of New Mexico, Albuquerque, Victor Polyak New Mexico 87131, USA Jeffrey A. Dorale Scott J. Carpenter Department of Geoscience, Trowbridge Hall, University of Iowa, Iowa City, Iowa 52242, USA Charles Trodick Brian Hoye Department of Geology, Cornell College, 600 1st Street West, Mount Vernon, Iowa 52314, USA Luis A. González Department of Geology, 1475 Jayhawk Boulevard, University of Kansas, Lawrence, Kansas 66045-7613, USA ABSTRACT Stalagmites from Goshute Cave, located in the Great Basin of the western United States, preserve ~20,000 yr of millennial-scale oxygen isotopic variability during marine isotope stages 5c and 5b, similar in timing and structure to Dansgaard-Oeschger (D-O) events 23–21 from the Greenland Ice Sheet Project 2 record. That D-O interstades 23–21 were of longer duration than many of the later D-O events, coupled with the asymmetric shape of the D-O oxygen isotope curve, and the direct U-Th dating of the Goshute Cave stalagmites, allows for an improved understanding of the synchroneity of climatic changes between the western continental United States and the North Atlantic. Eastern Pacific–atmosphere interactions are a likely mechanism for transmission of millennial-scale climate variability into the Great Basin. Keywords: speleothem, Great Basin, last interglacial, oxygen, Dansgaard-Oeschger event. SB OP Great Basin 115°W 120°W 40°N 110°W 50°N FL CL LL GC RV SL C P 20% LB OL PL SrL ML SB OP Great Basin 115°W 120°W 40°N 110°W 50°N FL CL LL GC RV SL C P 20% LB OL PL SrL ML Figure 1. Map of western United States show- ing Great Basin (brown area), modern north- ern limit of Southwest Monsoon (blue line; as defined as <20% annual precipitation received during June–August) (Douglas et al., 1993), and modern boundary between continental- dominated and Pacific-dominated moisture (green line) (Houghton, 1969). Studies cited in text: CL—Carp Lake, GC—Goshute Cave, FL—Fargher Lake, LB—Pluvial Lake Bonne- ville, LL—Little Lake, ML—Mono Lake, OL— Owens Lake, OP—Ocean Drilling Program Site 1020, PL—Pyramid Lake, RV—Ruby Val- ley, SB—Santa Barbara Basin, SL—Summer Lake, SrL—Searles Lake.