Palaeogeography, Palaeoclimatology, Palaeoecology 249 (2007) 103–127 www.elsevier.com/locate/palaeo Late Holocene climate reconstructions for the Russian steppe, based on mineralogical and magnetic properties of buried palaeosols ⁎ T. Alekseeva a, A. Alekseev a, , B.A. Maher b, V. Demkin a a Institute of Physicochemical and Biological Problems of Soil Science, Russian Academy of Sciences, Pushchino, Russia b Centre for Environmental Magnetism and Palaeomagnetism, Lancaster Environment Centre, Department of Geography, Lancaster University, Lancaster, LA1 4YB, UK Received 10 April 2005; received in revised form 29 December 2006; accepted 15 January 2007 Abstract Insights into past climate changes, and corresponding evolution of soils and the environment, can be gained by multi- disciplinary studies of palaeosols. Here, we focus on palaeosols buried beneath archaeological monuments, specifically, funerary mounds (kurgans), in the Russian steppe. The kurgans were constructed, and each of the palaeosols buried, over a range of different timesteps from the mid-Holocene to ∼ 600 years before present (yr BP). Integrated magnetic, mineralogical and pedological data were used to obtain estimates of past climate (especially precipitation) changes, through both time and space. A soil magnetism- based climofunction, derived previously from modern steppe soils and modern climate, was applied to each set of palaeosols, to obtain quantitative reconstructions of annual precipitation for the time at which the soils were buried. Independent soil property data (clay mineralogy, salt content, iron mineralogy from Mossbauer analysis, and optical and electron microscopy) were also obtained, in order to test and substantiate the magnetic inferences. The data obtained indicate that the climate of the Lower Volga steppe area has varied from the mid-Holocene onwards. Precipitation minima occurred at ∼ 5000, ∼ 3800, and ∼ 1600 yr BP, with intervals of enhanced precipitation at ∼ 1900 yr BP and ∼ 600 yr BP. These rainfall variations appear to occur synchronously with changes in Middle Eastern precipitation and lake levels, suggesting they are controlled by index changes in the North Atlantic Oscillation. © 2007 Elsevier B.V. All rights reserved. Keywords: Soil magnetism; Soil mineralogy; Palaeoclimate; Archaeologically buried soils; Russian steppe; North Atlantic Oscillation 1. Introduction the kurgans have been considered as objects of study for archaeology, ethnography, or other humanities; they Burial mounds (earth or stone hills), known in the provide key information about the culture of steppe Russian literature as ‘kurgans’, appeared across large inhabitants (Kimball et al., 2000) during the Bronze Age areas of the Eurasian steppe from ∼ 5000 years ago. (III–II millennia BC, ∼ 5000–4000 yr BP), Early Iron Funeral ceremonies with erection of such burial mounds Age (beginning I millennium BC–IV C. AD, ∼ 3000– occurred between 5000 and 600 yr BP. Until recently, 1600 yr BP), and Middle Ages (V–XVI C. AD, ∼ 1500–500 yr BP). However, the kurgans also contain ⁎ Corresponding author. buried soils, which developed in past Holocene time- E-mail address: [email protected] (A. Alekseev). slices and have been preserved by burial up to the 0031-0182/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2007.01.006 104 T. Alekseeva et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 249 (2007) 103–127 present day. Palaeosols can act as integrative records quantitative estimates of annual precipitation across this of past climatic, lithological, geomorphological, geo- region at intervals through the last ∼ 5000 years. We chemical, biological, and hydrological conditions (e.g. also include quantitative magnetic extraction data to Wright, 1986; Retallack, 2001). The palaeosols buried provide information on the pedogenic magnetic miner- by the very large number of kurgans (100s of thousands) als (their mineralogy, composition, grain size, morphol- on the Russian steppe can provide a database of quan- ogy) in palaeosols of different ages. Independent, titative and qualitative characteristics for environmental rapidly developing (i.e. decades to centuries) soil prop- reconstruction at the moment of each kurgan's con- erties studies include the humus content in the upper soil struction. The properties of these buried soils reflect, horizon, depth of easily soluble salts, gypsum and car- particularly, the climate, vegetation, and microrelief and bonate content, and the upper horizon magnetic prop- thus can be used for reconstruction of palaeoenviron- erties. Clay mineralogy was also examined, since clay mental conditions. Because kurgans were constructed at minerals are the main source of soil Fe (Schwertmann different times from the mid-Holocene onwards, they and Taylor, 1989; Alekseeva et al., 1989; Alekseev preserve a range of palaeosols recording past environ- et al., 1996). mental changes through this whole interval; indeed, kurgans of different ages are often sited close to each 2. Materials and methods other, especially on watershed sites. Palaeosol properties sensitive to climatic and environmental change can The study area falls within the Lower Volga basin, include: the concentration and distributions of salts, which includes the Central Russian, Privolzhskaya, and carbonates, gypsum and humus; structures of their Ergeni uplands and the Caspian Lowland, in the microbial communities; and stable isotope compositions southern Russian Plain (∼ 1200–1500 km south of of pedogenic carbonate and humus. So far for the kurgan Moscow, Fig. 1a and b). Modern climatic conditions palaeosols, qualitative changes in climate (especially across the Lower Volga basin are dry and warm, with humidity) have been inferred from carbonate content mean annual precipitation of 350–400 mm and mean and distributions, assuming carbonate accumulation annual temperature of ∼ 11 °C. The modern climate (Bca horizon formation) during arid conditions and reflects the continentality of the region, together with carbonate dispersion during relatively humid intervals some rainshadow influence of the Caucasus range to (e.g. Demkin et al., 1998, 2004). On this basis, a period the south/southwest. Precipitation, which is variably of desiccation has been inferred at ∼ 5000 years BP, distributed through the year, arises in winter from frontal reaching a maximum at ∼ 4000 BP, before wetter activity associated with penetration of moist Atlantic conditions prevailed at ∼ 3000 BP (e.g. Demkin and westerlies and in summer is mainly convectional. Many Ivanov, 1985; Demkin et al., 1989; Khokhlova et al., of the present day soils and the palaeosols are light 2001, 2004). Recently, a quantitative, soil magnetism- (luvic) or dark (haplic) variants of kastanozem profiles based climofunction has been established for the area (FAO/UNESCO classification), i.e. well-drained soils of the Russian steppe (Maher et al., 2002, 2003). For a with brown, humic topsoils (Ah horizons, with N50% of set of 22 modern soils across the loessial plain of the roots concentrated in the upper 25 cm) overlying a Caucasus to the pre-Caspian region, the pedogenic mag- brown/cinnamon, argic (clay-enriched) or cambic netic susceptibility (magnetic susceptibilityBhorizonminus (slightly weathered) subsoil or B horizon with different the magnetic susceptibilityChorizon) was found to be degrees of solonetz features (i.e. often with carbonate strongly correlated (R2 =0.93) with present day values of and/or gypsum accumulation in or below the B horizon). annual precipitation (Fig. 1). A similar correlation be- The modern soil cover is characterized by a mosaic of tween rainfall and magnetic susceptibility was previously kastanozems and solonetzes forming microcatenas, de- obtained for the Chinese Loess Plateau and explained as a termined by surface microtopography. The solonetzes, result of pedogenic formation of magnetite and maghe- which occupy about 40% of the territory (Demkin and mite via oxidation/reduction processes through soil Ivanov, 1985), are confined to flat micro-elevations wetness events (Maher and Thompson, 1999). whereas the light and dark kastanozems are associated Here, we examine the magnetic properties of a with slopes and microdepressions, respectively. range of palaeosols of different ages, preserved beneath Age control on the kurgans and their buried groups of kurgans constructed at five separate locations palaeosols has been gained previously from radiocarbon within the Russian steppe zone. We then apply the dating (AMS, e.g. Alekseev et al., 2002; Alexandrovs- climofunction obtained from the steppe modern soils kiy et al., 2001; LSC, e.g. Shishlina et al., 2000; (Maher et al., 2002, 2003) to obtain, for the first time, Khokhlova et al., 2004) and archaeological artefacts. T. Alekseeva et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 249 (2007) 103–127 105 Fig. 1. a) Site location, including modern steppe soil transect of Maher et al. (2002, 2003); b) individual site location map with sample sites 1 – Abganerovo; 2 – Malyaevka; 3 – Peregruznoe; 4 – Kalmykia; 5 – Avilov; c) Pedogenic magnetic susceptibility versus annual precipitation for the Russian steppe, modern soil transect (R2 =0.93). Table 1 summarises the relationship between distinctive chikov et al., 1995) provide the basis for age deter- archaeological cultures and an absolute, 14C-based mination for particular burial mounds with an accuracy chronology. The distinctive cultures encapsulated within of e.g.