A tentative stalagmite-based multi-proxy reconstruction of environmental changes at the end of Marine Isotope Stage 11 in Uzbekistan, Central Asia

The archaeological record suggests that multiple groups of hominins occupied and dispersed across Central Asia periodically during the middle Pleistocene (Ranov et al., 1995; Derevianko et al. 2003; Vishnyatsky 1999). It is likely that early transcontinental migrations were tightly interwoven with environmental conditions, and especially water availability. To gain insights into the impact of climatic changes and associated regional environmental responses on hominin dispersal in inner Asia, high-resolution palaeoenvironmental reconstructions are vital. Here we utilize a stalagmite-based multi-proxy record from Uzbekistan to shed light on environmental changes in Central Asia during the end of Marine Isotope Stage 11, ca. 390 ka before present.

We analysed stable isotopes (δ¹³C and δ¹⁸O), grey values (reflecting matrix density), and trace elements on a broken stalagmite segment (S-12-4) collected in 2012 in Amir Timur Cave, Uzbekistan. The cave is in the arid westernmost reaches of the Zaravshan mountain ranges south of Samarkand, with hot and arid summers and cold and humid winters. The cave is developed in marble at an altitude of 1813 m a.s.l. and exposed to western air masses. Backward trajectory modelling shows that moisture is derived mainly from the west and north-west. U/Th dating and stable isotope samples were taken at the Max Planck Institute for the Science of Human History, Jena. Six U/Th samples were measured by MC-ICP-MS at the Institute of Global Environmental Change, Xi'an Jiaotong University. Stable isotope analysis was carried out at Northumbria University. The stalagmite covers the period between 405±8 ka BP and 387.8±7 ka BP. To improve the uncertainty of the U-Th chronology we counted 682 visible layers with an average thickness of 71.4 μm that are presumably of seasonal origin. The δ¹³C values vary between -8.21 and -4.14 ‰ VPDB, while δ¹⁸O ranges from -11.06 to -8.5 ‰ VPDB. Both isotope ratios covary on multi-decadal scale and correlate positively with Mg. Stable isotopes, grey values, and trace elements (Sr, U, Ba, and S) reveal changes in local moisture supply, with one prominent drying event at ca. 388±8 kyr BP. Although the cause of this prominent event remains unclear, we hypothesize that it could be the expression of local drying in response to a large volcanic eruption in the northern hemisphere, like that associated with the Campanian cryptotephra TP09-70.45 of Vakhrameeva et al. (2018). Ongoing work focuses on potential changes in seasonality and climate volatility, which might have affected the suitability of this region for middle Pleistocene hominin occupation.

References

Ranov, V. A., Carbonell, E., & Rodriguez, X. P. (1995). Current Anthropology 36, 337-346.

Derevianko, A. P. (Ed.) (2003). Novosibirsk: Institute of Archaeology and Ethnography SB RAS press.

Vishnyatsky, L. B. (1999). Journal of World Prehistory 13, 69-122.

Vakhrameeva et al. (2018). Quaternary Science Reviews 200, 313-333.