Stable isotopes of a subfossil Tamarix tree from the Dead Sea region, Israel, and their implications for the Intermediate Bronze Age environmental crisis Amos Frumkin ⁎ Department of Geography, The Hebrew University of Jerusalem, 91905, Israel abstract article info Article history: Received 19 December 2007 Available online 28 February 2009 Keywords: Levant paleoclimate Climate deterioration Tree ring isotopes Carbon isotopes Nitrogen isotopes Dead Sea level Cave deposit Radiocarbon Salt karst Sedom Trees growing on the Mt. Sedom salt diapir, at the southern Dead Sea shore, were swept by runoff into salt caves and subsequently deposited therein, sheltered from surface weathering. A subfossil Tamarix tree trunk, found in a remote section of Sedom Cave is radiocarbon dated to between ∼ 2265 and 1930 BCE. It was sampled in 109 points across the tree rings for carbon and nitrogen isotopes. The Sedom Tamarix demonstrates a few hundred years of 13 C and 15 N isotopic enrichment, culminating in extremely high δ 13 C and δ 15 N values. Calibration using modern Tamarix stable isotopes in various climatic settings in Israel shows direct relationship between isotopic enrichment and climate deterioration, particularly rainfall decrease. The subfossil Tamarix probably reflects an environmental crisis during the Intermediate Bronze Age, which subsequently killed the tree ∼ 1930 BCE. This period coincides with the largest historic fall of the Dead Sea level, as well as the demise of the large regional urban center of the 3rd millennium BCE. The environmental crisis may thus explain the archaeological evidence of a shift from urban to pastoral culture during the Intermediate Bronze Age. This was apparently the most severe long-term historical drought that affected the region in the mid-late Holocene. © 2009 University of Washington. All rights reserved. Introduction The isotopic composition of vegetation can be used as a proxy for ancient air, water, and nutrients as well as environmental conditions (Epstein and Krishnamurthy,1990; McCarroll and Loader, 2004). This paper attempts to reconstruct a climatic crisis during a crucial period of human history in the Levant, using variations in the natural abundance of carbon and nitrogen isotopes in stem cellulose of tree rings. Where relative humidity or precipitation are the limiting factors to carbon isotope fractionation in trees, isotopic enrichment of 13 C in wood cellulose is an indicator of drought stress (Garten and Taylor, 1992; Stewart et al., 1995; Chen et al., 2000; Treydte et al., 2001; Warren et al., 2001; Leavitt et al., 2002; Swap et al., 2004; Gagen et al., 2004; McCarroll and Loader, 2004; Liu et al., 2004; Ferrio and Voltas, 2005; Leavitt, 2007). The reason is that under these conditions, relative humidity and soil moisture control stomatal conductance which in turn dominates the ratio of internal to external concentra- tions of CO 2 and the resultant C fractionation. In extremely arid regions such as Mt. Sedom, where the dominant stress factor influencing trees is a combination of high temperature and low precipitation, 13 C enrichment provides a strong indicator of such severe conditions (McCarroll and Loader, 2004). In addition, studies from a variety of climatic regions and plant species reported significant negative correlation between annual rainfall and δ 15 N values of wood cellulose in C3 plants (Heaton, 1987; Swap et al., 2004), although many other processes play a role too. During early historic times, the impact of natural environmental deterioration on society could be significant, but is often debated due to the difficulty to differentiate between anthropogenic and natural effects. Four thousands years ago, anthropogenic impact on the environment was relatively small compared to the impact of natural environmental change on human society. Mt. Sedom, at the south-western edge of the Dead Sea (Fig. 1A), is a unique site to study the pure environmental signal, and its effects on neighboring societies. The mountain itself has no archaeological remains, suggesting that human interventions, such as grazing, agriculture, pollution or habitation are negligible. Therefore, environ- mental conditions are believed to reflect mainly natural factors rather than human impact. In addition, other studied sites often have shallow groundwater reached by tree roots, precluding the determi- nation of local δ 13 C – climate relationship (Lipp et al., 1996). This limitation does not exist at Mt. Sedom, where no freshwater aquifer exists (Frumkin, 1994) and deep infiltration water become salinized, so the only water source is local rainfall and associated runoff. In this study, a subfossil Tamarix tree trunk from Sedom Cave (Fig. 1B) is radiocarbon dated and isotopically analyzed in compar- ison with modern samples, in order to elucidate the nature of the Intermediate Bronze Age cultural crisis in the Dead Sea region. During this crisis the Early Bronze Age urban culture was abandoned and replaced by nomadic or semi-nomadic culture (e.g. Amiran, 1986; Dever, 1989; Finkelstein, 1989; Rast, 1987). The term Quaternary Research 71 (2009) 319–328 ⁎ Fax: +972 25820549. E-mail address: msamos@mscc.huji.ac.il. 0033-5894/$ – see front matter © 2009 University of Washington. All rights reserved. doi:10.1016/j.yqres.2009.01.009 Contents lists available at ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres