ARTICLE IN PRESS Quaternary Science Reviews 24 (2005) 533–569 New insights into the Weichselian environment and climate of the East Siberian Arctic, derived fromfossil insects, plants, and mammals$ A.V. Shera,Ã, S.A. Kuzminab, T.V. Kuznetsovac, L.D. Sulerzhitskyd aSevertsov Institute of Ecology and Evolution, Russian Academy of Sciences (RAS), 33 Leninskiy Prospect, 119071 Moscow, Russia bPaleontological Institute, RAS, 123 Profsoyuznaya St., 117868 Moscow, Russia cMoscow State University, Department of Paleontology, Vorobyovy Gory, 119899 Moscow, Russia dGeological Institute, RAS, 7 Pyzhevsky Per., 109017 Moscow, Russia Received 12 March 2004; accepted 24 September 2004 Abstract Multidisciplinary study of a key section on the Laptev Sea Coast (Bykovsky Peninsula, east Lena Delta) in 1998–2001 provides the most complete record of Middle and Late Weichselian environments in the East Siberian Arctic. The 40-m high Mamontovy Khayata cliff is a typical Ice Complex section built of icy silts with a network of large syngenetic polygonal ice wedges, and is richly fossiliferous. In combination with pollen, plant macrofossil and mammal fossils, a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka. The large number of radiocarbon dates from the section, together with an extensive 14C database on mammal bones, allows chronological correlation of the various proxies. The Bykovsky record shows how climate change, and the Last Glacial Maximum in particular, affected terrestrial organisms such as insects and large grazing mammals. Both during the presumed ‘‘Karginsky Interstadial’’ (MIS 3) and the Sartanian Glacial (MIS 2), the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats: the tundra-steppe type. This biome was supported by a constantly very continental climate, caused by low sea level and enormous extension of shelf land. Variations within the broad pattern were caused mainly by fluctuations in summer temperature, related to global trends but overprinted by the effect of continentality. No major changes in humidity were observed nor were advances of modern-type forest or forest-tundra recorded, suggesting a major revision of the ‘‘Karginsky Interstadial’’ paradigm. The changing subtypes of the tundra-steppe environment were persistently favourable for mammalian grazers, which inhabited the shelf lowlands throughout the studied period. Mammal population numbers were lowered during the LGM, especially toward its end, and then flourished in a short, but impressive peak in the latest Weichselian, just before the collapse of the tundra-steppe biome. Throughout MIS 3 and MIS 2, the climate remained very favourable for the aggradation of permafrost. No events of regional permafrost degradation were observed in the continuous Bykovsky sequence until the very end of the Pleistocene. r 2004 Elsevier Ltd. All rights reserved. 1. Introduction came into being only a few thousand years ago, in the early Holocene, when the dramatic rise of global sea- The shallow shelf seas in the East Siberian Arctic level resulted in the rapid inundation of the flat coastal (Laptev, East Siberian, Chukchi) are very recent. They plain (Bauch et al., 2001). Prior to that, during the Late Pleistocene regression, the East Siberian arctic marginal $This paper is dedicated to the memory of Prof. Boris Yurtsev plain extended 400–700 kmnorth, to about 78 1N, and (15.03.1932–14.12.2004), a great Arctic botanist and a strong promoter incorporated all the present-day islands. Although wide- of the tundra-steppe concept. ÃCorresponding author. Tel.: +7 095 238 3875; ranging geological and stratigraphic exploration of fax: +7 095 954 5534. Pleistocene deposits had been done in the area by the E-mail address: [email protected] (A.V. Sher). USSR Geological Survey and other Russian researchers, 0277-3791/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2004.09.007 ARTICLE IN PRESS 534 A.V. Sher et al. / Quaternary Science Reviews 24 (2005) 533–569 and recently by international teams, the past environ- and occasionally ‘‘visited’’ high latitudes, or lived here at ment of the shelf land remains essentially enigmatic and a different time, i.e., that their fossils are not synchro- debatable, except for the almost unanimous opinion that nous with this pollen record. it was never covered by glaciers (Sher, 1995). There is no Such sceptical views have not been supported by the clear knowledge about the dynamics of the environment conveners of the great discussion on tundra-steppe in on the shelf land during the global climatic variations. Beringia (Hopkins et al., 1982). They concluded that Even the last 50 ka, the period within the scope of there was enough evidence confirming the presence of a radiocarbon dating, still raises many questions. For diverse ungulate fauna in Beringia both during the instance, how did the Late Weichselian climate cooling, ‘‘Duvannyy Yar Interval’’ (i.e., MIS 2), and the corresponding to MIS 2 (the Last Glacial Maximum, Boutellier Interval (or Karginskian, MIS 3) (Schweger named here Sartanian after the Sartan Glaciation of the et al., 1982). However, the nihilistic approach to the Verkhoyansk Mountains) affect the environment and concept of a tundra-steppe biome as the favourable life in the high latitudes? Was the climate milder and native environment for mammoth fauna is resilient vegetation richer in the Middle Weichselian (MIS 3) (Colinvaux, 1996), and the main reason for that is our than today? Some researchers believe they were, and insufficient knowledge of the past environment in the reconstruct shrub tundra (Alekseev, 1997) or even taiga Arctic and the details of its history and dynamics. The forest (Igarashi et al., 1995) on the shelf land; they shelf lands of the Laptev and East Siberian Seas, due to traditionally describe this period as a relatively warm their huge extent, extremely northern position, relative ‘‘Karginskian Interstadial’’. Other students suggest that homogeneity of topography and geology and very rich the vegetation of that time did not differ much from fossil record, provide the best area to test these herb-dominated tundra or tundra-steppe of the ‘‘gla- environmental concepts and, even more importantly, cial’’ intervals; it should be noted, however, that real to get more detailed knowledge of variation of the evidence is very poor and scattered (cf. Anderson and tundra-steppe biome in space and time. Lozhkin, 2001 for review). Another unsolved problemis Critical new evidence on the Late Pleistocene envir- the scale of the sea-level rise during MIS 3: the presumed onment of the Arctic shelf land has been obtained in the ‘‘Karginskian Transgression’’ (Saks, 1948; Lomachen- course of multidisciplinary paleoecological research kov, 1966; Kind, 1974), if it existed (cf. discussion in under the German–Russian project ‘‘The Laptev Sea Astakhov, 2001), left almost no traces in the areas of the System2000’’. Here, we introduce someresults of the Laptev and East Siberian Seas. field and lab research conducted in 1998–2002. One of One of the most intriguing facts about the past life on the main objects was the continuous Late Pleistocene the shelf land is the abundance of fossil mammal bones, sequence exposed in the Mamontovy Khayata (MKh) found over the coastal lowlands and on the shelf islands. cliff on the Bykovsky Peninsula (east Lena Delta), where Thousands of fossils of such grazing mammals as woolly the first complete carcass of woolly mammoth (the mammoth, horse, bison, woolly rhino and others ‘‘Adams’ Mammoth)’’ was found in 1799 (Fig. 1). After suggest the richness of the past fauna. Even one of the four seasons of field research, with a broad complex of most stenotopic ungulates, saiga antelope, that now geological and paleontological studies and an extensive inhabits southern steppe and semi-desert, was able to programme of radiocarbon dating, this section provides live on what are now the Lyakhovsky Islands. It seems the most complete record of the environmental and difficult to blend this Late Pleistocene grazing assem- climatic history for the last 50,000 years in whole of blage with the modern Arctic environment. An abun- Arctic Siberia. In this paper, we concentrate on biotic dance of grazing herbivores in high latitudes invites the evidence fromthe record (mostly fossil insects, plants assumption of some pasturable ecosystem, essentially and mammals), which offers new perspectives on the different frommoderntundra; in fact, a non-analogue problems raised above. environment. The concept of such an ecosystem, called ‘‘tundra-steppe’’, was suggested by Tugarinov (1929), and successfully developed in Russia since then. Similar 2. Material and methods concepts emerged in North America under various names (‘‘Arctic steppe’’, ‘‘steppe-tundra’’, or ‘‘mam- 2.1. The study site moth steppe’’). The critics of these concepts argue that the vegetation reconstructed frompollen data did not The 40-mhigh MKh cliff ( Fig. 2) is built by ice differ much from graminoid arctic tundra or even polar saturated silts, sometimes fine silty sands, with a desert, and had such low productivity that it could not polygonal systemof thick syngenetic ice wedges. This support populations of various grazers (Ritchie and syncryogenic (i.e., turning into permafrost as it was Cwynar, 1982). The logical inference would be that the deposited) sedimentary formation, containing up to mammalian grazers did not live permanently in that 80–90% ice (both structure-forming and wedge ice) and environment, and either lived somewhere further south usually called Ice Complex (IC), is extremely widespread ARTICLE IN PRESS A.V. Sher et al. / Quaternary Science Reviews 24 (2005) 533–569 535 5e 5f 5c 1 Laptev 5b 5a Sea 4d 2 4b 4c 3b 3a 4a (A) Kharaulakh Ridge (B) 20 km Fig. 1. Geographic position of the studied section. (A) The regions around the Laptev Sea, where the radiocarbon-dated mammal bones came from (cf.