Estimates of Arctic land surface temperatures during the early Pliocene from two novel proxies Adam Z. Csank a, ⁎, Aradhna K. Tripati b,c,d , William P. Patterson e , Robert A. Eagle c , Natalia Rybczynski f , Ashley P. Ballantyne g , John M. Eiler c a Department of Geosciences, and Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA b Departments of Earth and Space Sciences and Atmospheric and Oceanic Sciences and Institute of Geophysics and Planetary Physics, University of California–Los Angeles, Los Angeles, CA 90095,USA c Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA d Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK e Saskatchewan Isotope Laboratory, Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5E2 f Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, Ontario, Canada K1P 6P4 g Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA abstract article info Article history: Received 8 August 2010 Received in revised form 15 February 2011 Accepted 16 February 2011 Available online 5 March 2011 Editor: P. DeMenocal Keywords: Pliocene Arctic Palaeoclimate oxygen isotopes ‘clumped’ isotopes During the Pliocene (2.6 to 5 Ma ago) atmospheric CO 2 levels have been estimated as similar to or slightly above present levels (Tripati et al., 2009; Pagani et al., 2010), and yet Earth's climate was considerably different. Recent evidence suggests that although global temperatures were 2–3 °C warmer than pre-industrial, Arctic warming may have been amplified during the Pliocene. Thus precise temperature records of this interval are required to assess the sensitivity of Earth's climate to persistent levels of CO 2 between 365 and 415 ppm.We present records of two independent proxies for terrestrial growing-season temperatures at the Early Pliocene Beaver Pond site on Ellesmere Island. δ 18 O values of cellulose from well-preserved peat constrain the δ 18 O values of meteoric water to -20.7 ± 0.3‰, which we combined with δ 18 Ovalues of aragonitic freshwater molluscs found within the peat in order to calculate mollusc growth temperatures. This approach results in an average growing-season temperature of 14.2±1.3 °C. Temperatures were independently derived by applying carbonate ‘clumped isotope’ thermometry to mollusc shells from the same site, indicating an average growing-season temperature of 10.2 ± 1.4 °C. A one-way ANOVA indicates that the differences between the two techniques are not significant as the difference in mean temperatures between both methods is no different than the difference between individual shells using a single technique. Both techniques indicate temperatures ~11–16 °C warmer than present (May–Sept temperature=-1.6 ± 1.3 °C) and represent the first thermodynamic proxy results for Early Pliocene Ellesmere Island. © 2011 Elsevier B.V. All rights reserved. 1. Introduction An increasing number of studies, including the most recent Intergov- ernmental Panel on Climate Change (IPCC) report, have highlighted the early Pliocene climate as an example of climate conditions that could result from elevated atmospheric CO 2 driven by anthropogenic emissions (Jansen et al., 2007). Models of Pliocene climate suggest temperatures ~2– 3 °C warmer globally and 7–15 °C warmer in the Arctic relative to today (Haywood et al., 2009; Sloan et al., 1996) which is within the range projected for the end of this century (Jansen et al., 2007). The Pliocene configuration of the continents was more similar to today than other periods of climatic warmth, and estimated Pliocene CO 2 levels of ~365– 415 ppm were similar to or slightly above present levels (Pagani et al., 2010; Tripati et al., 2009). Therefore, the Pliocene is, in many respects, an accessible example of near-future temperatures (Haywood et al., 2009; Jansen et al., 2007). However, accurate and detailed constraints on polar temperatures in the Early Pliocene are needed to test Pliocene model predictions, but have been limited to-date. New reconstructions of Pliocene Arctic temperatures are particularly needed, as such data would constrain the extent to which global warming is amplified at high latitudes and help assess the Earth System Sensitivity of global and Arctic climate to changing levels of CO 2 (Lunt et al., 2010). Fossil forest sites in the Canadian Arctic, which contain well-preserved plants, vertebrates and invertebrates, are amenable to the use of two novel proxies to constrain Pliocene polar temperature. The Beaver Pond locality (78º 33′ N; 82º 25′ W) on Ellesmere Island, Canada, so named because of the abundance of beaver-gnawed sticks found at the site (Rybczynski, 2008), is particularly well characterized and is unique in having abundant well-preserved remains of both plants and animals. The study site is located in Central Ellesmere Island near the head of Strathcona Fiord (Fig. 1). Stratigraphically the site lies within the Beaufort Formation, a Earth and Planetary Science Letters 304 (2011) 291–299 ⁎ Corresponding author. E-mail address: csank@ltrr.arizona.edu (A.Z. Csank). 0012-821X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2011.02.030 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl