Burial and preservation of a 30,000 year old perennial snowbank in Red Creek valley, Ogilvie Mountains, central Yukon, Canada Denis Lacelle a, * , Melanie St-Jean b , Bernard Lauriol b , Ian D. Clark c , Antoni Lewkowicz b , Duane G. Froese d , Stephen C. Kuehn d , Grant Zazula e a Planetary Exploration and Space Astronomy, Canadian Space Agency, St-Hubert, QC, J3Y 8Y9, Canada b Ottawa-Carleton Geoscience Centre, Department of Geography, University of Ottawa, Ottawa, ON, K1N 6N5, Canada c Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, University of Ottawa, Ottawa, ON, K1N 6N5, Canada d Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada e Yukon Palaeontology Program, Government of Yukon, Whitehorse, Yukon, Y1A 2C6, Canada article info Article history: Received 20 April 2009 Received in revised form 1 September 2009 Accepted 14 September 2009 abstract This study describes the origin and age of a body of massive ground ice exposed in the headwall of a thaw slump in the Red Creek valley, central Yukon, Canada. The site is located beyond the limits of Pleistocene glaciation in central Yukon and within the southern limit of the modern continuous permafrost zone. The origin of the massive ground ice, which is preserved under a fine-grained diamicton containing thin layers of tephra, was determined through ice petrography, stable O-H isotope composition of the ice, and gas composition of occluded air entrapped in the ice. The age of the massive ground ice was established by identifying the overlying tephra and radiocarbon dating of a ‘‘muck’’ deposit preserved within the ice. Collectively, the results indicate that the massive ground ice formed by snow densification with limited melting-refreezing and is interpreted as being a buried perennial snowbank. The muck deposit within the ice, which yielded an age of 30,720  340 14 C a BP, and the Dawson tephra (25,300 14 C a BP) overlying the perennial snowbank, indicates that the snowbank accumulated at roughly the transition between marine isotope stages 3 and 2. Dry climatic conditions at this time and possibly high winds enabled the snowbank to accumulate in the absence of extensive local valley glaciation as occurred in the mountains to the south. In addition to documenting the persistence of relict permafrost and ground ice to warming climate in regions where they are predicted to disappear by numerical models, this study presents evidence of an isotopic biosignature preserved in a body of massive ground ice. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. 1. Introduction In western Siberia, Alaska and western Arctic Canada, bodies of relict massive ground ice and icy sediments are commonly preserved in Pleistocene-age permafrost deposits. Most of these relict ground ice sites are situated near the northern limits of Pleistocene glacia- tions and are preserved in the present-day continuous permafrost zone. This spatial distribution and many other lines of evidence have led to most relict ground ice bodies in these regions being interpreted as having a glacial ice (firnified or basal glacier ice) origin (Lorrain and Demeur, 1985; Astakhov, 1986; Karpov, 1986; French and Harry, 1988; Dyke and Savelle, 2000; Murton et al., 2005) or as having formed by ice segregation or injection during permafrost aggradation following deglaciation (Mackay, 1971; Rampton, 1988, 2001; Pollard and Dallimore, 1988; Mackay and Dallimore, 1992; Lacelle et al., 2004). Further south, relict bodies of massive ground ice are also preserved within the modern discontinuous permafrost zone. For example, in the unglaciated interior Yukon, a region where permafrost has been intermittently present since at least the late Pliocene (Pearce et al., 1982; Tarnocai, 1990; Burn, 1993; Lauriol et al., 1997; Froese et al., 2000), relict Pleistocene-age massive ground ice bodies take the form of large near-vertical foliated ice bodies (i.e., ice wedges; French and Pollard, 1986; Kotler and Burn, 2000; Froese et al., 2008), buried firnified ice or snowbanks (French and Pollard, 1986; Lacelle et al., 2007) and surface ice (i.e., aufeis; Froese et al., 2006). According to Meehl et al. (2007), the global mean surface air temperature under a doubling atmospheric CO 2 scenario is expected to rise by 2–4.5  C, with still greater increases in the western Arctic and sub-Arctic regions (ACIA, 2004). This increase in air temperature may lead to major thawing of permafrost, and even its disappearance in the more southerly regions over the next century or sooner, as predicted by Lawrence and Slater (2006) and * Corresponding author. E-mail address: denis.lacelle@asc-csa.gc.ca (D. Lacelle). Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev 0277-3791/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2009.09.013 Quaternary Science Reviews 28 (2009) 3401–3413