Downloaded from specialpapers.gsapubs.org on September 18, 2012 The Geological Society of America Special Paper 473 2011 Surface runoff to the Black Sea from the East European Plain during Last Glacial Maximum–Late Glacial time Aleksey Yu. Sidorchuk Andrey V. Panin Geographical Faculty, Moscow State University, Vorob’evy Gory, Moscow 119991, Russia Olga K. Borisova Institute of Geography, Russian Academy of Sciences, Staromonetny per., Moscow 119017, Russia ABSTRACT Hydromorphological and hydroclimatic methods were used to reconstruct the former surface runoff from the East European part of the Black Sea drainage basin. Data on the shape and dynamics of the last Fennoscandian ice sheet were used to cal- culate meltwater supply to the headwaters of the Dnieper River. The channel width and meander wavelength of well-preserved fragments of large paleochannels were measured at 51 locations in the Dnieper and Don River basins (East European Plain), which allowed reconstruction of the former surface runoff of the ancient rivers, as well as the total volume of fl ow into the Black Sea, using transform functions. Studies of the composition of fossil fl oras derived from radiocarbon-dated sediments of vari- ous origins and ages make it possible to locate their modern region analogues. These analogues provide climatic and hydrological indexes for the Late Pleniglacial and Late Glacial landscapes. Morphological, geological, geochronological, and palyno- logical studies show that the landscape, climatic, and hydrologic history of the region included: (1) a cold and dry interval close to the Last Glacial Maximum character- ized by high meteoritic surface runoff supplemented by meltwater fl ow from ice-dam lakes; (2) a warmer humid interval at the end of the Late Pleniglacial with very high surface runoff and formation of extremely large meandering channels, combined with a short event of substantial infl ow from the Caspian Sea; and (3) a period from the Oldest Dryas to the Preboreal of nonsteady surface runoff decrease, and trans- formation of large meandering channels into smaller ones against the background of climate warming. Sidorchuk, A.Yu., Panin, A.V., and Borisova, O.K., 2011, Surface runoff to the Black Sea from the East European Plain during Last Glacial Maximum–Late Gla- cial time, in Buynevich, I.V., Yanko-Hombach, V., Gilbert, A.S., and Martin, R.E., eds., Geology and Geoarchaeology of the Black Sea Region: Beyond the Flood Hypothesis: Geological Society of America Special Paper 473, p. 1–25, doi: 10.1130/2011.2473(01). For permission to copy, contact [email protected]. © 2011 The Geological Society of America. All rights reserved. 1 Downloaded from specialpapers.gsapubs.org on September 18, 2012 2 Sidorchuk et al. INTRODUCTION sheet, changes in its volume and meltwater supply into adjacent rivers can be estimated (Kalinin et al., 1966). General information on the variability of climate and water Valuable information about past hydrological river regimes budget in Europe for the period from the Last Glacial Maximum can be derived from the morphology of the former river channels, (LGM), through Late Glacial time (LGT), and into the begin- especially if the former topography differs signifi cantly from ning of the Holocene (ca. 18–10 radiocarbon ka) is controversial. that of the present. Morphological data on the large Late Glacial According to vegetation reconstructions based on palynological paleorivers, which give distinct evidence of high surface runoff, data (Grichuk, 1982), the climate is believed to have been both were fi rst investigated by Dury (1964, 1965) in Western Europe cold and dry (the so-called cryoxerotic stage of the glaciation). and North America, and by Volkov (1960, 1963) in northern The climate of the southern part of the East European Plain drives Kazakhstan and western Siberia. Similar results were obtained changes in the water balance of southern sea and lake basins, for several rivers in the Black Sea basin: for the Seim (Borisova and, thus, most workers correlate the last major drop in the level et al., 2006) and Khoper (Sidorchuk and Borisova, 2000) Rivers of the Caspian Sea and Black Sea to the LGM (Varuschenko et in the Dnieper and Don basins; for the basin of the Danube River al., 1987; Winguth et al., 2000; Dolukhanov et al., 2008; and oth- in Hungary (Borsy and Felegyhazi, 1983; Kasse et al., 2000), ers). To explain such a dramatic drop in sea level, a substantial and in Romania (Howard et al., 2004). Morphological, textural, decrease in river runoff into the seas has been suggested. Var- palynological, and geochronological studies have shown that the uschenko et al. (1987) estimated annual river runoff into the Cas- LGT in Europe was a period of very large, widely spread river pian Sea during the LGM at only 20%–28% of its present value. channels, which presumably were formed by high and powerful Estimates of river runoff into the Caspian and Black Seas during surface runoff. the LGM based on atmospheric general circulation models com- Paleobotany plays an important role in providing data for prise 55% and 59% of the modern values, respectively (Kislov paleoclimatic reconstructions. Late Glacial climatic events and and Toropov, 2006). the chronology of vegetation development in Europe have been On the other hand, extensive dating of the Caspian deposits derived mainly from palynological data later dated through undertaken in the last decade have revealed a Late Glacial age radiocarbon and correlated with the isotopic “events” in the for the highest stage of the Khvalynian transgression (Svitoch Greenland ice-core record (e.g., Walker et al., 1999). To recon- and Yanina, 1997; Leonov et al., 2002; Chepalyga et al., 2008; struct the hydroclimatic conditions that existed at various stages and others), which suggests large surface runoff, at least from of the LGM and LGT, palynological studies of dated alluvium, the Volga River basin. Kalinin et al. (1966) estimated river runoff lake, and peat sediments can be applied. The use of paleobotanic into the Caspian Sea during the maximum stage of the Khvalyn- data for paleoclimatic and paleolandscape reconstruction implies ian transgression at 517 km3 per year, a fi gure that is 1.5 times that fl ora and vegetation are strongly infl uenced by changes in higher than the present value. Similarly controversial reconstruc- the natural environment and by the climate in particular (e.g., tions exist for the Black Sea drainage basin: some researchers Iversen, 1944; Grichuk, 1969). propose a relatively high runoff and a continuous outfl ow from This paper is aimed at (1) analysis of the paleoenvironmental the Black Sea (Lane-Serff et al., 1997), while others believe that conditions and causes for the paleohydrological changes in the the runoff into the Black Sea was low due to the dry climate, and East European part of the Black Sea basin during the LGM and as a result, sea level dropped to –110 m (Ostrovsky, 1982; Aksu LGT, (2) paleohydrological reconstruction of the surface runoff et al., 2002) or even to –150 m (Winguth et al., 2000) because there since the Late Pleniglacial, and (3) discussion of the land- of negative water budget during the LGM. It has also been sug- scape and surface runoff changes in the remaining part of the gested that a massive infl ow of meltwater from the Fennoscan- Black Sea basin during the last ~20,000 yr. dian ice sheet into the Black Sea took place after the LGM (Kva- sov, 1979; Kroonenberg et al., 1997), both directly through the METHODS Dnieper River valley and as an outfl ow from the Caspian Sea through the Manych Straight. A series of meltwater pulses is sug- Paleofl oristic Method of Paleolandscape and gested by isotopic depletion of the Black Sea waters between 18 Hydroclimatic Reconstruction and 15.5 ka (Bahr et al., 2006). Hydromorphological and hydroclimatic methods of paleo- Climate reconstructions usually rely on either the compari- geographic reconstructions allow quantitative estimation of the son of fossil and modern pollen assemblages and their associ- former surface runoff originating from melting glaciers and from ated modern climate, or selected indicator plant species with precipitation over a river basin. The ice volume of the Quaternary specifi c climatic requirements. Paleobotanical data used for such ice sheets can be reconstructed from their area using transform reconstructions are of two main kinds: plant macrofossils (seeds, functions derived from recent glaciological information and the- fruits, leaves, etc.), and pollen and spores. Macrofossils have oretical considerations about ice rheology (Markov and Suetova, the advantage of usually being identifi able to the species level. 1964; Khodakov, 1982; Peltier, 1994). Therefore, with informa- On the other hand, the occurrence of macrofossils is relatively tion on the age of the boundaries of the last Fennoscandian ice restricted, and they usually belong to aquatic and subaquatic Downloaded from specialpapers.gsapubs.org on September 18, 2012 Surface runoff to the Black Sea from the East European Plain 3 plants. Pollen diagrams provide more detailed information on characteristics within these analogues. Furthermore, the accuracy the history of specifi c plant taxa as well as vegetation on the of palynological analysis and the richness of a paleofl ora depend whole. Because plants sensitive to climatic conditions are mainly not only on the palynologist’s personal experience, but also on medium to low pollen producers, suffi ciently detailed pollen data the type of sediment, vegetation type, and the degree of pollen are essential. In the process of pollen identifi cation, the highest preservation. Late Glacial fl oras are usually relatively poor, so possible taxonomic resolution should be achieved to obtain the that not all analyzed samples provide suffi cient data for paleofl o- most complete results. This is possible if well-preserved pollen ristic reconstruction. of arboreal plants, as well as pollen and spores of certain groups Usually, conditions that are suitable for all the species of of herbaceous plants (e.g., Thalictrum, Lycopodium, Equisetum), a given fossil fl ora can be found within a comparatively small can be identifi ed to genus or even species levels.