Dead Sea pollen provides new insights into the paleoenvironment of the southern Levant during MIS 6–5
Introduction
Connecting Africa with the Arabian Peninsula, the southern Levant is a hotspot for investigating the dispersal of anatomically modern humans (AMH) to the rest of the world, since their emergence in Africa (Gibbons, 2017). Pivotal findings are the AMH remains in Israel (the Skhul and Qafzeh Caves) dated to the time range of 130–90 thousand years ago (Grün et al., 2005; Mercier et al., 1993; Valladas et al., 1988). These findings suggest the occupation by modern humans in the region during the last interglacial (LIG). The present southern Levant is covered by large areas of uninhabitable desert, whereas, in the past, the present desert barrier was probably a migration corridor with sufficient water and food resources during climate ameliorations (Breeze et al., 2016; Vaks et al., 2007).
The southern Levant is located at the boundary between the Mediterranean and the Saharo-Arabian climate zones. The sensitive response of this region to climatic variations has been documented in the geological archives (Bar-Matthews et al., 2017; Stein, 2014). Nevertheless, inconsistences exist among regional paleoenvironmental archives regarding the glacial-interglacial climate conditions. For instance, a relatively active speleothem deposition occurred in the central and southern Negev Desert during the LIG (Vaks et al., 2007). The evidence points to wetter conditions in the LIG than in the glacial periods. However, inverse climate conditions are indicated, due to the significantly lower Dead Sea lake stands during the LIG as compared to the glacial periods (Waldmann et al., 2010). It is prominent that the lake level at ca. 27–24 ka rose to ca. 270 m higher than the present level, resulting in the mergence of the Dead Sea and the Sea of Galilee (Bartov et al., 2003). Controversies are focused on the relative impact of the climate variables, i.e., precipitation, temperature, evaporation, and seasonality (Gasse et al., 2011; Miebach et al., 2017). In this case, more paleorecords involving independent proxies are needed.
The Dead Sea is a remarkable archive for investigating the paleoenvironment of the southern Levant. So far, studies on a series of proxies, such as sedimental lithology (e.g., Neugebauer et al., 2014), geochemistry (e.g., Torfstein et al., 2009), and pollen assemblages (e.g., Litt et al., 2012), show the great potential of the Dead Sea sediments for documenting changes in regional hydroclimate. Nevertheless, compared to the well-studied last glacial and Holocene sediments, the LIG conditions remain elusive due to the limited availability of materials deposited in the lake margin area. In 2010–2011, the Dead Sea Deep Drilling Project (DSDDP) retrieved sediment cores dated back to ca. 220 ka from the deepest part of the basin (Stein et al., 2011; Torfstein et al., 2015). The project successfully recovered LIG sediments consisting of conspicuously thick halite deposits (Neugebauer et al., 2014). Previous analyses for chronology, lithology, and isotope composition suggested that the LIG period was characterized by low lake levels and generally dry conditions (Torfstein et al., 2015).
Despite this progress, the paleovegetation as independent evidence for the LIG paleoenvironment in the southern Levant is largely unknown. Previous palynological studies in the region are mainly confined to the Holocene (e.g., Langgut et al., 2015; Litt et al., 2012; Neumann et al., 2010) and last glacial period (e.g., MIS 2; Miebach et al., 2017), whereas the LIG pollen records are rare, poorly-dated, and fragmentary (e.g., Weinstein-Evron, 1987). In this study, we present a high-resolution pollen record dated to 147–89 ka, based on the DSDDP sediment core. The main objectives are to reconstruct the paleovegetation in the southern Levant and to elucidate the response of vegetation successions to variations in regional climate. Comparisons with other regional records are made in order to provide new insights into the paleoenvironmental setting of the early modern human dispersal.
Section snippets
The Dead Sea and its setting
The Dead Sea is a hypersaline terminal lake (ca. 27.5% salinity; 76 × 17 km; 760 km2; Fig. 1). It occupies the Dead Sea Basin (DSB) in the Dead Sea Transform, which developed due to the breakup of the African and Arabian plates. This process was accompanied by the formation of narrow valleys and the uplifting of their shoulders at the plate boundary (Garfunkel, 1997). The northern DSB is deep, with a bottom depth of 730 m bmsl (below mean sea level) and a water depth of ca. 300 m. The southern
Drilling campaign and stratigraphy
The coring of the DSDDP was conducted in the northern DSB (Stein et al., 2011). The top depth of the borehole 5017-1A (31°30′28.98″ N, 35°28′15.60″ E) was at 297.46 m below lake level. The total drilled length of this borehole was 455.34 m, retrieving 405.83 m sediments with a recovery rate of 89.13% (for details see Neugebauer et al., 2014). The sediments recover four stratigraphic formations (Fm.). The Amora and Lisan Fm., accumulated during the glacials, mainly consist of marl sediments and
Vegetation and climate
The palynological results are illustrated as a simplified pollen diagram (Fig. 3). Halite samples have very low pollen concentrations (a mean of 1511 grains/cm3) due to a rapid accumulation of salt crystals, while laminated marl samples hold a much higher pollen concentration of 39,910 grains/cm3 on average. Therefore, the fluctuations of pollen concentrations mainly point to the shifts of deposit types. The charcoal concentrations (particles/cm3), conventionally used for representing fire
Conclusions
- 1)
This study analyzes pollen, non-pollen-palynomorphs, and charcoal from the deep-drilled Dead Sea 5017-1A sediment core. It reconstructs a detailed vegetation and fire history of the southern Levant at 147–89 ka.
- 2)
The late penultimate glacial (MIS 6) and early last glacial (MIS 5d–5b) were cool and were characterized by steppe and desert expansions. Sub-humid conditions were confined to the mountains, where moderate amounts of deciduous oaks were distributed. The initial warming (early MIS 5e) was
Acknowledgements
We thank all our colleagues from the DSDDP scientific party for the drilling, core opening, and sampling campaign. The project is supported by the Collaborative Research Center 806 “Our way to Europe” (DFG-Sonderforschungsbereich). The Ph.D. scholarship for Chunzhu Chen is provided by the China Scholarship Council (CSC). We are grateful for Karen Schmeling for technical support. We acknowledge Andrea Miebach and Nadine Pickarski for the sampling campaign, as well as for constructive discussions
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