The extent of the Barents Kara ice sheet during the Last Glacial Maximum

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1 Quaternary Science Reviews 21 (2002) The extent of the Barents Kara ice sheet during the Last Glacial Maximum Jan Mangerud a, *, Valery Astakhov b, John-Inge Svendsen c a Department of Geology, University of Bergen, All!egt 41, N-5007 Bergen, Norway b Geological Faculty, Petersburg University, Universitetskaya 7/9, St. Petersburg, Russian Federation c Centre for Studies of the Environment and Resources, University of Bergen, Hyteknologisenteret, N-5020 Bergen, Norway Received 30 January 2001; accepted 18 July 2001 Abstract It has been a long-standing discussion whether the Barents Kara Ice Sheet expanded onto mainland Russia during the Last Glacial Maximum (LGM). In this paper, we describe many well-dated (by conventional and AMS 14 C methods and optically stimulated luminescence) sedimentary sequences in the controversial area of Northern Russia. The sequences discussed are not covered by till, and yet all predate the LGM. The deposits consist mostly of aeolian or lacustrine, easily deformable soft silt and fine sand. Two sites feature frozen mammoth carcasses and three sites contain Palaeolithic artefacts and mammalian bones. We emphasise that these formations show no sign of having been overridden by an ice sheet. At several sites, deposition of aeolian sediments and formation of ice wedges took place during the LGM time span. These observations present unambiguous proof that the Barents Kara Ice Sheet did not cover mainland Russia during LGM, with a possible exception for the northern tip of the Taimyr Peninsula. r 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction Results of different methods of estimating the total volume of glacial ice on earth during the Last Glacial Maximum (LGM) were extensively discussed during the EPILOG symposium. The principal method is to calculate volumes of individual ice sheets by using their mapped areas and modelled ice thicknesses. Therefore, empirical geological evidence of the extent of the ice sheets is needed. In the present paper, we describe and discuss data constraining the southern extent of the Barents Kara Ice Sheet during the LGM. The time of the LGM is used in the sense of EPILOG; i.e. as the time slice C kyr or about 21 24,000 cal yr BP. An ice sheet centred over the Barents and Kara seas (hereafter the Barents Kara Ice Sheet) expanded onto the Russian mainland several times during the Quaternary (e.g. Astakhov, 1976). At its Quaternary maximum extent, this ice sheet covered vast areas of West Siberia and European Russia (Arkhipov et al., 1986; Arkhipov *Corresponding author. Tel.: ; fax: address: jan.mangerud@geol.uib.no (J. Mangerud). et al., 1995). However, the dimension of the Barents Kara Ice Sheet during the LGM has been controversial over the last decades. Ice sheets of widely different sizes have been suggested (CLIMAP, 1981; Denton and Hughes, 1981; Grosswald, 1993, 1998; Peltier, 1994; Velichko et al., 1997; Svendsen et al., 1999; Petit-Maire et al., 2000), although in all reconstructions the LGM ice sheet boundary is located well inside the maximum Quaternary drift limits. In the reconstructions of Svendsen et al. (1999, submitted), which we presented at the EPILOG symposium (Fig. 1), the western and northern margins of the ice sheet are localised along the edge of the continental shelf (Landvik et al., 1998), which agrees well with the corresponding limits in Grosswald s (1993) reconstruction. This is also the maximum feasible extent for a grounded ice sheet because beyond the shelf break the water depth becomes so deep that the ice front would float. A possible expansion of this ice sheet into the deep sea as a floating ice shelf would not contribute to a lowering of the global sea level. Therefore, if the Barents Kara Ice Sheet was significantly larger than that shown in Fig. 1, the additional ice must have resided on mainland Russia, especially in the Pechora Lowland and the West Siberian Plain (Figs. 1 and 2) /02/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S (01)

2 112 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) Fig. 1. Limits of the Barents Kara Ice Sheet during the LGM according to Svendsen et al. (submitted), which is a slightly revised version of the map in Svendsen et al. (1999). It should be noted that except for the southern part, the precise position of the ice limit in the Kara Sea is uncertain. This has indeed been suggested in many of the earlier published reconstructions of the LGM ice sheets (CLIMAP, 1981; Denton and Hughes, 1981; Grosswald, 1993, 1998; Peltier, 1994; Petit-Maire et al., 2000). During the EPILOG symposium Grosswald again presented an LGM reconstruction with an ice limit located far to the south on the Russian mainland (Fig. 2), arguing that glaciological modelling supports that alternative. Russian, Western European and American field geologists who presently work in the Russian Arctic, on the other hand, maintain that the existing field observations and geochronometric data falsify Grosswald s hypothesis (Astakhov et al., 1999; Forman et al., 1999; Larsen et al., 1999; Mangerud et al., 1999; Svendsen et al., 1999; Polyak et al., 2000). However, the discussion at the EPILOG symposium shows that Grosswald s idea is still considered as a viable alternative among researchers from other disciplines of Quaternary science, or by those who have not studied this region themselves. Therefore, we will here present a few selected key observations, in a simplified form, that formed the basis for the LGM reconstruction by Svendsen et al. (1999), supplemented by some results obtained later. We emphasise that all the stratigraphic sections and geomorphological features described below are located within the ice limits proposed by Grosswald (Fig. 2). All sediments and landforms predate the time of LGM but none of the sites show any sign of glacial overriding. Some sections also show deposition of non-glacial sediments at LGM time. The observations are therefore incompatible with Grosswald s and other similar reconstructions of a large LGM ice sheet in this area. Details on the sections, methods, dating results, etc, are contained in the referred literature. 2. Pechora Lowland and Pechora Sea The Pechora River runs from the large lowland in the NE corner of Europe into the SE part of the Barents Sea, sometimes named the Pechora Sea (Figs. 1 and 2).

3 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) Fig. 2. Map of Northern Russia showing the proposed limits for the Barents Kara Ice Sheet during the LGM according to Grosswald (1993, 1998) and Svendsen et al. (submitted). Sites described in the text and for which obtained dates and the stratigraphy or morphology demonstrates that they have not been overrun by a LGM glacier are marked. Grosswald (1993, 1998) placed the LGM glacial limit in the southern part of the Pechora Lowland (Fig. 2) Palaeolithic sites The Byzovaya Palaeolithic site (Locality no. 1, Fig. 2) has been known for decades. Recently, we have made large excavations in order to improve our knowledge about the archaeological remains and the sediments (Mangerud et al., 1999; Heggen, 2000). We have obtained 25 radiocarbon dates on bones and mammoth tusks from the cultural layer, which all yielded ages in the range ka, except for one date that yielded 3372 ka. Only some of the dates are plotted in Fig. 3. The layer with bones and artefacts is blanketed by a 10 m thick sequence of unconsolidated aeolian sand and silt, in places intercalated with beds deposited by solifluction or debris flows from the valley slopes. A series of optically stimulated luminescence (OSL) dates from the aeolian sediments have yielded ages in the range ka, indicating that wind-blown sand, intercalated with solifluction deposits, accumulated here during the LGM (Fig. 3). At the Mamontavaya Kurya Palaeolithic site (no. 2, Fig. 2), many bones of large mammals, mostly mammoth, and a few artefacts were found in a cross-bedded gravel, interpreted as river-channel deposits (Mangerud et al., 1999; Pavlov et al., 2001). The 14 C dates from the bones yielded ages of ka (Fig. 3). The gravel is covered by alluvial sand, interpreted as a point-bar sequence. A series of AMS 14 C dates on terrestrial plant remains (leaves, mosses, etc.) from these alluvial sediments yielded ages in the range ka. The sequence is capped by undisturbed aeolian fine sand/ coarse silt OSL-dated to ka (Fig. 3). Just like the Byzovaya site wind-blown sediments accumulated here during the LGM. At the Pymva Shor site (no. 3, Fig. 2), several shallow pits have been excavated (Mangerud et al., 1999). Here, animal bones have yielded radiocarbon dates traversing the LGM time slice: 26.2, 21.9, 20.0, 16.9, 16.5, 16.5 and 15.8 ka Early Weichselian shorelines Shorelines of the large, pro-glacial, ice-dammed Lake Komi mapped by aerial photography are morphologically expressed as many kilometre long knicklines or sand bars following the 100 m altitude contour across most of the Pechora Lowland (Fig. 2) (Astakhov et al.,

4 114 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) Fig. 3. Simplified logs from sites described in the text plotted in an N S profile from the Pechora Sea to the southern Pechora Lowland. Locations on the map in Fig. 2 are given as site nos. (in parentheses) above each log. For Byzovaya the log gives a synthesis of the excavations and is based on Mangerud et al. (1999), Heggen (2000) and unpublished results. Only 14 of the 25 radiocarbon ages from the cultural layer are listed; all the rest also yielded ages ka. For Mamontovaya a simplified log of the section in Pavlov et al. (2001) is shown. The log for the Kolva River terraces is a synthesis of two sections (Mangerud et al., 1999). A simplified log of the section in Mangerud et al. (1999) is given for the Timan Beach, with OSLdates slightly corrected for a different water content (27%). The log from the southern Pechora Sea is based on the boreholes B with several AMS ages added (the right hand row) from borehole B-234 with a similar stratigraphy (Polyak et al. 2000).

5 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) ). Several sections through the shorelines show that they consist of loose beach sand and gravel (Mangerud et al., 1999). The lake was formed in front of an advancing Barents Kara Ice Sheet that blocked the Pechora River. The Byzovaya and Mamontovaya sites described above are incised into the floor of Lake Komi, providing a minimum age for the shorelines of Cka. Optically stimulated luminescence dates of beach sand (Locality no. 4, Fig. 2) yielded ages in the range ka (Fig. 4) (Mangerud et al., 2001) River terraces In the Pechora Lowland, we have studied several river terraces that predate the LGM; here, we will only discuss one of them. The River Kolva (the river on which site no. 5, Fig. 2, is located) starts some 50 km south from the Barents coast and runs southwards before joining the Pechora River. Along much of the River Kolva course there is a terrace about 20 m above the flood plain. Sections in the terrace show mainly cross-bedded fluvial sand, interpreted as braided river deposits (Mangerud et al., 1999). Many bones and mammoth tusks are found in the lower part of the sand. Six radiocarbon dates from two sites gave ages ka (Fig. 3). A thin mantle of loess-like silt covers the terrace Exposures along the Barents Sea coast Sections in a wave-cut cliff have been investigated on the Timan Beach (no. 6, Fig. 2) (Mangerud et al., 1999). Fig. 4. OSLdates of beach sand from sections in Lake Komi shorelines (no. 4 in Fig. 2). The dates are plotted according to increasing age. Open squares show three dates considered as outliers. Dates are shown with one standard deviation. Adapted from Mangerud et al. (2001). The lower part of the section is laminated lacustrine sand that interfingers with solifluction deposits. Both facies are rich in plant remains, from which four AMS 14 C dates yielded non-finite ages (Fig. 3). Three OSL dates from the sand yielded ages in the range ka. Above follows a >3-m thick unit of flat-bedded aeolian cover sand. Two AMS dates from tiny plant remains in this sand also yielded non-finite dates, but the small organic particles were probably eroded from the underlying organic-rich unit and redeposited in the aeolian sand. Two OSLdates yielding 21 ka have been obtained from the aeolian sand. Ice wedge casts and a thin fluvial gravel show a break in aeolian sedimentation before deposition of several metres of a second aeolian sand OSL-dated to ka. A Holocene peat caps the sequence Sediments on the sea floor In the southern part of the Pechora Sea, the youngest till is overlain by thick marine sediments (Gataullin et al. 2001). A series of 14 C dates, mainly on molluscs and foraminifera collected from cores (no. 7, Fig. 2) yielded ages in the range ka (Fig. 3), proving that the unit predates the LGM (Polyak et al., 2000). The top of the unit is cut by an erosional unconformity which is traced to submerged shorelines m below the present sea level, and is interpreted to result from the global sealevel fall during the LGM (Gataullin et al., 2001). 3. Urals The northern Urals were partly invaded by the Barents Kara Ice Sheet according to Grosswald s (1993, 1998) LGM reconstruction, whereas in the minimalist reconstruction of Velichko et al. (1997) an ice cap was centred over these mountains. The youngest mountain glaciers that reached the foothills from the Polar Urals can be identified from distinct lobate end-moraines along the western and eastern flanks of the mountain chain (Astakhov, 1979; Astakhov et al., 1999). The western of these piedmont glaciers collided with a contemporaneous ice lobe from the Barents Kara Ice Sheet. The latter deposited the Harbei moraines dated to the Early Weichselian at about 90 ka (Mangerud et al., 2001). The morphologically well-expressed Harbei moraines have been traced around the northern tip of the Urals where the ice sheet flowed up valleys to an altitude of 560 m a.s.l. (no. 8, Fig. 2) (Astakhov et al., 1999). Nowhere along the Urals were the Early Weichselian moraines overrun by younger glacier advances. This implies that LGM glaciers of the Urals were confined to the mountain valleys. These findings are incompatible with the LGM

6 116 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) reconstructions of both Grosswald (1998) and Velichko et al. (1997). 4. West Siberian Plain The largest discrepancy between Grosswald s (1993, 1998) and Svendsen et al. s (1999) reconstructions is on the West Siberian Plain (Fig. 2). However, it should be noted that also Grosswald s ice limit is inside the maximum extension of the Barents Kara Ice Sheet during the Quaternary Yamal Peninsula This Peninsula, as well as much of northern West Siberia, is covered by thick terrestrial sediment. Two well-dated sequences will be outlined here. Many radiocarbon and OSLdates were recently obtained from the large Marresale section on western Yamal (no. 9, Fig. 2) (Forman et al., 1999). Above the youngest till that cantains fossil glacier ice there are lacustrine and aeolian sediments from which 16 AMS radiocarbon dates yielded ages in the range ka. Five OSLdates are consistent with these radiocarbon ages. Apparently there was a break in deposition during the LGM, at which time large ice wedges were formed. This latter surface is covered by another unit of aeolian sediments dated to ka by means of 12 AMS dates. In eastern Yamal, there is an important and wellstudied section named Syo-Yakha (no. 10, Fig. 2). This section displays a more than 20-m thick sequence of Yedoma-like silt (mainly aeolian in our opinion) with thin moss-mat layers. Altogether 14 radiocarbon dates (AMS and conventional dating) with ages ranging from 37 to 17 ka in the correct stratigraphic order have been obtained on plant material from this section (Fig. 5) (Vasilchuk et al., 1984, 2000). The sedimentary sequence is pierced by two generations of thick, syngenetic ice wedges, which grew simultaneously with sediment accretion. Radiocarbon AMS dates of minute organic remains from ice in the wedges yielded ages in the range ka, whereas dates on alkali extracts from the same samples yielded slightly higher ages ka (Vasilchuk et al., 2000). Measured oxygen isotope values in the ice are about 23 per mil (Fig. 5), as compared to 17 for Holocene wedge ice in this area. Vasilchuk et al. (2000) interpreted this difference to indicate that winter temperatures during ice wedge formation were 6 91C lower than today. For the theme of the present paper, the most important result is that sediments accumulated continuously between 37 and 17 ka and that ice wedges were growing here during the LGM. Fig. 5. The Syo-Yakha section on the eastern coast of Yamal (no. 10, Fig. 2). Simplified from Vasilchuk et al. (2000).

7 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) Yenisei region End moraines with blocks of fossil glacier ice are exposed in sections situated where the Polar Circle crosses the Yenisei River (Fig. 2) (Astakhov and Isayeva, 1988). The moraines were formed by a lobe of the Barents Kara Ice Sheet that flowed southward along the river valley. North of the moraines there is a plain built of glaciolacustrine sediments. Thermokarst lakes, which developed on this plain, were subsequently filled with silty sediments. Radiocarbon dates from wellpreserved tree logs collected in sinkhole silts in the observation pit at the Igarka Permafrost Station (no. 11, Fig. 2), yielded ages of 35, 39 and 50 ka (Kind, 1974), indicating that the latest glaciation of this area occurred more than 50 kyr ago. This age estimate is consistent with radiocarbon dates of around 31 and 32 ka that were obtained on well-preserved plant material from a fluvial terrace incised into the glaciolacustrine plain (Astakhov, 1998). In the extreme north of the Yenisei region, there are several findings of frozen mammoth carcasses which were buried in surficial sediments not covered by till. Radiocarbon dates on mammoth flesh from two sites along the rivers Mokhovaya (no. 12, Fig. 2) and Gyda (no. 13) yielded ages of 35.8 and 33.5 ka, respectively (Heintz and Garutt, 1965). A fresh-looking knee of mammoth collected directly from the permafrost at a site near Leskino (no. 14, Fig. 2) was dated to 30.1 ka and plant remains from the enclosing silt to 29.7 ka (Astakhov, 1998). 5. Taimyr Peninsula The section at Cape Sabler, Lake Taimyr (no. 15, Fig. 2) features one of the best-dated Weichselian sedimentary formations in the Russian Arctic. The sequence consists of laminated silt and sand with peaty interlayers. The silt is similar to the Yedoma formation, which covers much of NE Siberia. Long syngenetic ice wedges propagate through the section (Derevyagin et al., 1999). Kind and Leonov (1982) and Isayeva (1984) obtained nine successive radiocarbon dates in the range ka from the Cape Sabler section. In a more recent study, M.oller et al. (1999) obtained another 21 successive AMS ages in the range ka, demonstrating ice-free conditions during the LGM. The old age of the latest glaciation of the southern Taimyr is confirmed by a study on the northern shore of Lake Labaz (no. 16, Fig. 2). Here, 21 samples from postglacial sediments yielded radiocarbon ages in the range from >48 to 20 ka (Siegert et al., 1999). Additionally, a non-finite date (53 ka) has been obtained from a frozen mammoth carcass found in a river terrace nearby (Arslanov et al., 1980). On northern Taimyr, Alexanderson et al (2001) mapped an end moraine formed by ice moving in from the Kara Sea and dated to LGM by means of two radiocarbon dates on marine shells included in glacial ice. The moraine could show either an outlet glacier from the Barents Kara Ice Sheet or a minor dome on the shelf. As discussed below, we are sceptical it is a lobe from the LGM Barents Kara Ice Sheet, because then a major ice-dammed lake should be formed. 6. Discussion Above we have described stratigraphic sequences and geomorphological features from the Arctic Russia, which are all dated to 20 ka or older. The best-dated sediment successions are located hundreds of km inside the LGM ice limit proposed by Grosswald (1993, 1998). Many more sites with similar stratigraphic sequences have been observed in these areas. Most of the described deposits consist of easily deformable, loose silt or fine sand, and some contain fragile artefacts and bones, or frozen mammoth carcasses. However, none of the sites shows any sign of glacial overriding. At some sites, deposition of non-glacial sediments and/or formation of ice wedges took place during the LGM. The inevitable conclusion, reached by us and other researchers, is that the LGM ice sheet did not overrun the sites described. Astakhov (1998) examined the stratigraphic and geochronometric basis for Grosswald s (1993) reconstructed ice sheet in West Siberia. Only 23% of the total 208 radiocarbon dates in West Siberia that yielded finite ages in the time range ka came from subdiamicton sediments, and many of them were obtained from interglacial strata. Therefore, Astakhov (1998) concluded that the samples had been contaminated by younger carbon. The remaining 73% of the ka dates were derived from sedimentary successions with no signs of glacial overriding, like the sites described in this paper. The sections that Grosswald (1993, 1998) used as evidence for LGM and even Younger Dryas ice advances onto the Pechora Lowland have been reexamined (Tveranger et al., 1995; Astakhov et al., 1999; Mangerud et al., 1999; Henriksen et al., 2001). These investigations showed that the youngest sediments beneath the uppermost till are older than ka, not about 10 ka as postulated by Grosswald. Concerning samples yielding old radiocarbon ages, it is useful to keep in mind that such dates are insensitive to contamination by old carbon, but very sensitive to contamination by young carbon. For example, a sample contaminated with 10% of infinite old carbon appears only about 850 yr old, whereas a contamination of an infinitely old sample by only 1% of modern carbon would yield a date of about 37 ka. In practice, this means that if the discussed dates are erroneous due to

8 118 J. Mangerud et al. / Quaternary Science Reviews 21 (2002) contamination, that has to be contamination by younger carbon, and the real ages are higher than assumed. This would not reverse our conclusion because the samples were collected above the latest till. On the other hand, contamination of samples collected beneath a till would result in very young ages for the till. We consider that the main source of error in the dates used in this paper is redeposition from older sediments. However, this cannot be the case for frozen mammoths, peat, vascular plants in situ, or most of the bones and artefacts. It can neither be applied to the Lake Komi shorelines dated by OSL. Also, it is unlikely that reproducible dates in correct stratigraphic order (Cape Sabler, Yamal) could result from redeposition. The restricted LGM ice sheet extent given in Fig. 1 is also consistent with the lack of raised Late Weichselian or Holocene shorelines along the southern coast of the Kara and Barents seas (Troitsky and Kulakov, 1976; Forman et al., 1999; Mangerud et al., 1999). The deposition of aeolian sediments close to sea level during the LGM also demonstrates that relative sea level was low. Just as important, these aeolian sediments deposited near sea level at LGM also demonstrate that extensive ice-dammed lakes did not exist in front of the ice sheet. This implies that there was an open drainage pathway across the floor of the present Kara Sea to the Arctic Ocean for the Pechora, Ob, Yenisei and other rivers and thus that the ice sheet did not impinge on Taimyr (Fig. 1). However, it should be noted that a LGM moraine is mapped on northern Taimyr, as described above (Alexanderson et al., 2001). The sites described in this paper unambiguously demonstrate that the LGM Barents Kara Ice Sheet invaded neither the Pechora Lowland or West Siberian Plain nor the central Taimyr. There are no documented observations contradicting this conclusion. Our main conclusion has been verified and supported by several independent studies in this region in the last few years (Astakhov et al., 1999; Forman et al., 1999; Larsen et al., 1999, 2001; Mangerud et al., 1999; Svendsen et al., 1999, submitted; Polyak et al., 2000; Alexanderson et al., 2001). It should be mentioned that the Barents Kara Ice Sheet was much larger and expanded onto the Russian mainland twice during the earlier phases of the Weichselian, at around 90 and 60 ka (Mangerud et al., 2001). However, both of these ice advances terminated far to the north of Grosswald s LGM ice limit. 7. Conclusions 1. During the LGM the Barents Kara Ice Sheet was much smaller than postulated in most of the earlier reconstructions used to calculate its contribution to the global sea level drop. Our reconstruction shows the ice sheet in the Russian Arctic was less than half the size of that in Grosswald s (1993, 1998) reconstruction. 2. The limit of the LGM Barents Kara Ice Sheet was located in the SE part of the Barents Sea (i.e. in the Pechora Sea) and the western Kara Sea. 3. During the LGM there was a cold and dry continental climate along the northern coast of mainland Russia, and major ice-dammed lakes did not exist in front of the Barents Kara Ice Sheet. Acknowledgements Eva Bjrseth made the drawings. Brian Robins corrected the English language. The journals reviewers Steve L. Forman and Leonid Polyak provided many useful comments. 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