Chlorine-36 and 14 C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet Julie Brigham-Grette, a, * Lyn M. Gualtieri, b Olga Yu. Glushkova, c Thomas D. Hamilton, d David Mostoller, e and Anatoly Kotov f a Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA b Quaternary Research Center, Box 351360, University of Washington, Seattle, WA 98195-1360, USA c Northeast Interdisciplinary Research Institute, Far Eastern Branch Russian Academy of Sciences, 16 Portovaya St., Magadan 685000 Russia d U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508, USA e Weston & Sampson Engineers, Inc., 195 Hanover Street, Suite 28, Portsmouth, NH 03801, USA f Chukotka Science Center, Anadyr, Chukotka Region, Russia Received 29 June 2002 Abstract The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to 20,000 yr ago. Cosmogenic isotope ages  30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald’s Beringian ice-sheet hypothesis. © 2003 Elsevier Science (USA). All rights reserved. Keywords: Cosmogenic isotopes; Last glacial maximum; Glacial history; Chukotka; Arctic; Beringia Introduction Accurate reconstructions of the glacial history of the Russian arctic are essential if we are to further understand the paleoclimatic history and global context of the circum- arctic. Glacial ice extent across the Russian arctic has been among the more controversial topics facing Arctic Quater- nary scientists over the past decade. The idea of a pervasive Eurasian ice sheet (Grosswald 1988; 1998) during the last glacial maximum (LGM) has been strongly challenged by both Russian and European workers as part of the EU- QUEEN program (European Union-Quaternary Environ- ments of the Eurasian North; Svendsen et al., 1999; Thiede et al., 2001, and references therein). The concept of an East Siberian Sea ice sheet (Grosswald and Hughes, 1995, 2002) has been partially adopted by Peltier (1994) in the ICE-4G ice-sheet reconstructions and perpetuated in climate models as boundary conditions for the LGM (cf., Felzer, 2001). This has happened despite a growing body of field evidence against such an ice sheet (Arkhipov et al. 1986; Vartanyan et al. 1993, Felzer, 2001; Glushkova, 2001; Gualtieri et al., 2000; 2001). The concept of a Beringian ice sheet during the LGM covering all of Chukotka Peninsula and the East Siberian Sea (Grosswald, 1998) has also been perpetuated in the literature (Kotilainen and Shackleton, 1995; Clark et al., * Corresponding author. E-mail address: juliebg@geo.umass.edu (J. Brigham-Grette). R Available online at www.sciencedirect.com Quaternary Research 59 (2003) 386 –398 www.elsevier.com/locate/yqres 0033-5894/03/$ – see front matter © 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0033-5894(02)00000-0