Scandinavian Ice Sheet

The Scandinavian Ice Sheet (SIS), the centre of which was situated in the Scandinavian mountain range, covered Finland and the NW Russian Plain several times during the Quaternary cold stages.

From: Developments in Quaternary Sciences , 2004

Quaternary Glaciations Extent and Chronology

Igor N. Demidov , ... Matti Saarnisto , in Developments in Quaternary Sciences, 2004

Conclusions

The Scandinavian ice sheet, the Barents-Kara Sea ice sheet and possibly a Timan ice sheet occupied different parts of the Arkhangelsk region during the Late, the Middle and the Early Valdaian glaciations. Their tills, with a characteristic pattern of directional properties and clast provenances, are separated by marine, fluvial and lacustrine sediments, which have been dated by radiocarbon and luminescence. This means that since the Mikulian interglacial, ice sheets developed independently in different parts of the European North. In the Late Valdaian, the maximum of the last Scandinavian glaciation was asynchronous in various regions of Russia. Possibly, this is controlled by the distance from the centre of glaciation in the Gulf of Bothnia, but less dependent on peculiarities in the topography beneath different ice flows and the regional palaeoclimate.

At present there are three major uncertainties on the Valdaian glacial history in the Arkhangelsk area. One deals with the configuration and glaciation centre of the so-called 'Timan ice sheet' from the Early Valdaian. Another question is the position of the western boundary of the Barents-Kara Sea glaciation during the Middle Valdaian and whether or not it was confluent with a Scandinavian Ice Sheet west of the Arkhangelsk region. A third option is to map the distribution of deposits belonging to the Late Valdaian Scandinavian glaciation in the Kuloi area and possibly trace these deposits northwards to the Kanin Peninsula.

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Quaternary Glaciations Extent and Chronology

Juha Pekka Lunkka , ... Olli Sallasmaa , in Developments in Quaternary Sciences, 2004

1.1 Pre-Weichselian cold stages

The Scandinavian Ice Sheet (SIS), the centre of which was situated in the Scandinavian mountain range, covered Finland and the NW Russian Plain several times during the Quaternary cold stages. It is not exactly known how many times Finland and adjacent areas were covered by ice during the Quaternary. This is because the area is situated close to the glaciation centre and each ice advance eroded most of the previously deposited interglacial and glacial sediments. In most cases therefore only the sediments deposited during the last cold stage (Weichselian) rest on the Pre-Cambrian bedrock. Except for some scattered remnants of Saalian-age esker ridges in the ice-divide zone of northern Finland (Finnish Lapland), there are no distinct geomorphological landforms related to pre-Weichselian glaciations. However, there are a number of sites where pre-Weichselian organic and glacial sediments have been preserved, particularly in central Lapland and western Finland. These sites provide the basis for the Quaternary stratigraphy of Finland.

According to the Finnish till stratigraphy, there are six, stratigraphically-significant till beds in Finnish Lapland. The uppermost three are thought to represent Weichselian tills (Till Beds I-III). The so-called Till Bed IV was laid down during the Saalian glaciation, and the two lowermost till beds, that underlie a Holsteinian peat stratum (Hirvas & Eriksson, 1988) may represent Elsterian or pre-Elsterian tills (cf. Hirvas & Nenonen, 1987, Hirvas, 1991). Although Elsterian or pre-Elsterian tills are preserved at scattered localities in northern Finland, there is no conclusive evidence for pre-Saalian tills in southern Finland. On the other hand, Saalian glacigenic sediments are well preserved in the Pohjanmaa (Ostrobothnia) area in southwestern Finland. In that area, Eemian interglacial deposits are underlain by Saalian till and glaciofluvial sediments at several sites (cf. Eriksson et al., 1980, Forsström et al., 1988, Hirvas & Niemelä, 1986, Aalto et al., 1989, Gibbard et al., 1989, Saarnisto & Salonen, 1995, Nenonen, 1995). There is only one site south of the Salpausselkä end moraine zone in Helsinki where three till beds have been encountered (Hirvas et al., 1995). The lowermost of these might have been laid down prior to the Weichselian Stage.

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Quaternary Glaciations - Extent and Chronology

Peter Johansson , ... Pertti Sarala , in Developments in Quaternary Sciences, 2011

9.1 Introduction

The Scandinavian ice sheet, the centre of which is situated in the Scandinavian mountain range, covered Finland and the northwestern Russian Plain several times during the Quaternary cold stages. It is not known precisely how many times Finland and adjacent areas were covered by ice during the Quaternary. This is because the area is situated close to the glaciation centre, and the ice-advances eroded and deformed most of previously deposited interglacial and glacial sediments during the cold stages. Therefore, it is common that only the pre-Quaternary weathered bedrock surface and the sediments deposited during the last cold stage (Weichselian) rest on the pre-Cambrian bedrock. Except for some scattered remnants of the Saalian esker ridges ( Kujansuu and Eriksson, 1995) in the ice-divide zone of northern Finland (Finnish Lapland) and in the major river valleys in the Pohjanmaa area, in western Finland (for location: Fig. 9.1), there are no distinct geomorphological landforms related to pre-Weichselian glaciations. However, there are a number of sites where Middle and Late Pleistocene organic and glacial sediments have been preserved, particularly in northern Finland and western Finland (cf. Hirvas, 1991; Nenonen, 1995). These sites provide the basis for the general Quaternary stratigraphy of Finland.

Figure 9.1. A deglaciation map of Finland showing the southern Lapland marginal formations and the main Late Weichselian end and interlobate moraines, ice lakes and ice limits. Key sites marked on the map are: 1, Veskoniemi; 2, Sokli; 3, Maaselkä; 4, Tepsankumpu; 5, Naakenavaara; 6, Rautuvaara; 7, Permantokoski; 8, Kauvonkangas; 9, Oulainen; 10, Hitura; 11, Ruunaa; 12, Pohjankangas; 13, Virtasalmi; 14, Vuosaari.

According to the Finnish till stratigraphy, there are six stratigraphically significant till beds in Finnish Lapland, and three till beds in southern Finland. In northern Finland, the key site for the till stratigraphy is the Rautuvaara area in western Finnish Lapland (Hirvas et al., 1977; Hirvas, 1991). The three uppermost till beds are thought to represent Weichselian-age tills (Till Beds I–III), two of these (Till Beds I and II) are thought to have been deposited during the Late Weichselian. The so-called Till Bed IV was laid down during the Saalian glaciation. The two lowermost till beds (Till Beds V and VI) that occur beneath the Holsteinian peat horizon may represent Elsterian or pre-Elsterian tills (cf. Hirvas and Nenonen, 1987; Hirvas, 1991). In the southern part of Finland, south of latitude 65°N, there are three stratigraphically important till beds interbedded with minerogenic sediments (mainly sand and silt) that form the basis of glaciation history of the area (see e.g. Nenonen, 1995; Saarnisto and Lunkka, 2004; Svendsen et al., 2004). At some localities, well-developed palaeosols and peat and gyttja layers are associated within or with these intertill sand and silt units indicating ice-free periods during the Late Pleistocene.

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Changes in the Heavy-Mineral Spectra on Their Way From Various Sources to Joint Sinks

A.J. (Tom) Van Loon , M. Pisarska-Jamroży , in Sediment Provenance, 2017

2 Geographical Setting

During the Pleistocene, the Scandinavian ice sheet drained huge amounts of sediment-laden meltwater (see Brodzikowski and Van Loon, 1992, for the various depositional processes and the resulting lithofacies). The sedimentary particles were deposited in front of the ice mainly on sandurs but partially also in the ice-marginal valleys of the central European lowlands (Fig. 4.1) that ran parallel to the ice-sheet margin and perpendicular to the prograding sandurs. The streams in the ice-marginal valleys flowed to the west because the area sloped to the north-northwest, and because the sandurs and the ice mass prevented a current direction to the north. The ice-marginal valleys were fed also by extraglacial rivers flowing northward from the more elevated areas in the south, as already found by, among others, Woldstedt (1950), Galon (1961), and Kozarski (1962).

Figure 4.1. Position of the study area (rectangle of Fig. 3) within the Central European Lowland.

The main ice-marginal valleys of Poland and Germany are the Wrocław-Magdeburg-Bremen, the Głogów-Baruth-Hamburg, the Vilnius-Warsaw-Poznań-Berlin and the Toruń-Eberswalde ice-marginal valleys (Fig. 4.2). The Toruń-Eberswalde ice-marginal valley, also referred to as the Noteć-Warta ice-marginal valley, is the longest one. It can be divided geographically into several basins and valleys, viz. the Toruń Basin, the Middle Noteć valley, the Gorzów Basin, and the Eberswalde valley. The part under study here is 300   km long and comprises the middle and western parts of the Toruń-Eberswalde ice-marginal valley, that is, the Middle Noteć valley and the Gorzów Basin. In the following, the abbreviation IMV will be used for this specific part of this specific ice-marginal valley.

Figure 4.2. Distribution of ice-marginal valleys in Europe, showing the study area (rectangle of Fig. 3) as the middle part of a much larger system. Modified after Pisarska-Jamroży (2015).

The sites from where the heavy-mineral composition was analyzed are three gravel pits on the Drawa and Gwda sandurs and five gravel pits in the Toruń-Eberswalde IMV (Fig. 4.3). At two sites in the IMV samples were taken from both terrace sediments and the Pleistocene substratum. Both sandurs and the IMV were fed by meltwater streams; the meltwater streams on the sandurs in turn fed the Toruń-Eberswalde IMV. As mentioned earlier, the IMV was fed also by extraglacial rivers running from the south, which slightly changed the proportion of some heavy minerals (Pisarska-Jamroży, 2015; Pisarska-Jamroży et al., 2015a). For this reason, the heavy minerals from three sites on terraces of the Pomeranian phase along these southern rivers were also analyzed. Obviously, the sediments at the study sites in the IMV were partly also derived from the catchment area of the IMV farther to the east. In addition, the proglacial and extraglacial areas in front of the ice formed a source of fine particles that were carried along by winds and that partly were deposited on the sandurs and in the IMV.

Figure 4.3. Regional setting of the Drawa and the Gwda sandurs and the Toruń-Eberswalde ice-marginal valley, with sampling sites.

Both the two sandurs and the terrace under study in the Toruń-Eberswalde IMV date from the Pomeranian phase of the Weichselian glaciation, when the Scandinavian Ice Sheet almost reached the area (16–17   ka; Marks, 2012). The Drawa and Gwda sandurs (Fig. 4.3) are large examples (80 and 110   km long, respectively), and the Toruń-Eberswalde IMV is the largest (>500   km long, 2–20   km wide) IMV of the European lowlands; it runs from eastern Poland to Germany.

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Quaternary Glaciations - Extent and Chronology

Michael Houmark-Nielsen , in Developments in Quaternary Sciences, 2011

5.5.4 The Kattegat Ice Stream

In southern Norway and south-west Sweden, the SIS transgressed the coast late in MIS 3. Glaciers filled the Norwegian channel and calved into the North Sea and Kattegat. At the same time, an incipient regression is recorded in northern Denmark. The marine conditions in the Skærumhede Group were replaced by deposition of lacustrine fines and fluvial sand with Arctic plant remains in a partly glacier-dammed Kattegat ice lake. In northern Denmark and south-western Sweden, deposits of the Kattegat ice lake were overridden by the Kattegat Ice Stream around 30–27   ka ago (Figs. 5.4 and 5.6). The latter reached its maximum across central Denmark and in northwest Skåne and deposited till of Norwegian provenance (Houmark-Nielsen, 2003; Larsen et al., 2009), while periglacial conditions with Arctic treeless vegetation were maintained in southern Denmark. Deglaciation caused the Kattegat ice lake to re-open, however, still dammed off from the Atlantic Ocean by glacier ice flowing out of the Norwegian Channel. The Kattegat Ice Stream apparently has left no recognisable morphological features, thus, its distribution is founded on stratigraphical evidence alone. Type sections for the Kattegat till comprise Hundested, North Samsø and Lønstrup (Fig. 5.1, sites 15, 16 and 17)

Figure 5.6. Palaeogeographical reconstruction of the Kattegat Ice Stream ca. 29–27   ka ago.

 From Houmark-Nielsen et al. (2005). For explanation of symbols, see Fig. 5.3.

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Quaternary Glaciations Extent and Chronology

Jan Mangerud , in Developments in Quaternary Sciences, 2004

Ice thickness – did nunataks exist in Norway?

The surface geometry, and thus the thickness, of the Scandinavian Ice Sheet are much more poorly known than its areal limits. The author will therefore discuss the problems at some length. For more than a hundred years there has been discussion as to whether mountain peaks in Norway protruded as nunataks above the ice surface during the Quaternary glaciations, especially during the Late Weichselian glacial maximum. Recent reviews of the discussion are given in Sollid & Sørbel (1979), Mangerud et al. (1979), Nesje et al. (1987, 1988) and Nesje & Dahl (1992). Earlier the main focus was whether plants had survived on nunataks or not, whereas here a three-dimensional reconstruction of the Scandinavian Ice Sheet is considered.

Nesje et al. (1987) and Nesje & Dahl (1992) argue that there were ice-free summits across much of southern Norway during the Late Weichselian glacial maximum, using the altitudinal distribution of autochthonous block fields as the main argument (Fig. 9). They plotted altitudes of summits with and without block fields and found a geographically consistent altitudinal boundary between the two types. They postulate that the block fields pre-date the Late Weichselian, and that the lower limit represents a glacial erosional boundary showing the maximum elevation of the Late Weichselian ice sheet surface (Fig. 9). They also maintain that their reconstruction is supported by the distribution of alpine pinnacle topography without indications of glacial moulding, and also by the distribution of 'refugiai plants'. In the Nordfjord area their interpretation has subsequently been supported by cosmogenic nuclide exposure ages giving 55 ka (10Be age) or 71 ka (26Al age) for bedrock surfaces in the block field, and 21 ka on bedrock below the limit of block fields (Brook et al., 1996). Another area with pinnacles that have traditionally been considered to have remained ice-free is western Andøya in northern Norway (Fig. 1). There this interpretation is supported by mapping of moraines and by the stratigraphy in lakes, as mentioned above (Vorren & Plassen, 2002).

The hypothesis of ice-free nunataks is attractive to explain the cited observations; it is difficult to envisage an eroding glacier overriding the block fields, and for the writer even more so for the tall and narrow pinnacles. Therefore these arguments have been used in favour of the nunatak theory for more than a century. The number of observations and the consistent pattern in the Nordfjord-Møre area in western Norway (Fig. 10) seem to favour that the interpretation might be correct in that area (Nesje et al., 1987; Sollid & Sørbel, 1979). In this area it is also glaciologically reasonable because the deep fjords would efficiently drain the ice flow. However, the interpretation becomes more difficult, or rather impossible, when the limit is extended further across southern Norway, which would imply a maximum ice thickness of less than 800 m, and a maximum altitude of the ice sheet of about 1600 m a.s.l. in the eastern ice divide areas (Nesje & Dahl, 1990; Nesje et al., 1988). A closer look at some of the arguments therefore seems necessary.

Fig. 10. The distribution of summits, with and without blockfields are plotted in a NW-SE cross section across inner Nordfjord The lower boundary of the blockfields is assumed to represent the Late Weichselian glacial limit. The Younger Dryas moraines are also shown.

 Taken from A. Nesje (written communication, 2000), updated from Brook et al. (1996). Copyright © 2000

Block fields are not unambiguous proof that ice has not overridden the site. On the contrary, it has been demonstrated that both block fields and other unconsolidated sediments have survived below the Scandinavian Ice Sheet and yet show little evidence of glacial overriding (Kleman, 1994; Kleman & Borgström, 1990; Kleman & Hättestrand, 1999; Lagerbäck & Robertsson, 1988). In fact, it is just as difficult to understand how sharp-ridged eskers have survived below glaciers (Lagerbäck & Robertsson, 1988), as it is the pinnacles discussed above. Meltwater channels from the last deglaciation cut through block fields at many localities in the Norwegian and Swedish mountains demonstrating that the ice-sheet surface was above the lower limit of block fields (Borgström, 1999; Sollid & Sørbel, 1994). All of the cited authors argue that the unconsolidated deposits, in most cases, survived beneath cold-based ice. In addition the summits with block fields would certainly have lain in the cold-based zone if they were covered by glacial ice. In reply to this Nesje & Dahl (1990) argue that the limit between cold and warm-based ice should not be parallel to the ice surface, and as mentioned above, this could be a valid argument for the Nordfjord-Møre area where this limit is very consistent. However, an alternative explanation could be that the block fields were covered by cold-based ice, and that the lower limit does not show the boundary to warm-based ice, but a later erosion limit formed at a younger and lower ice-surface.

The botanical argument, first presented around 1890, was in fact the one that started the discussion about ice-free nunataks (Birks, 1993; Mangerud, 1973). The main argument is that Some mountain plants, with particular emphasis on endemics and West-Arctic species, have a bi-centric distribution in Norway, which suggests that they survived the glaciation close to these centres. However, it has recently been demonstrated that this distribution pattern can be explained by other factors, and it has no weight as argument for ice-free nunataks (Birks, 1993).

Fjeldskaar (2000) has tested the thin ice sheet interpretation by isostatic modelling. Using the ice sheet of Nesje & Dahl (1990) he found that the predicted tilt of deglacial shorelines was less than 50% of the observed tilt, and he concluded that the results "seem to rule out the thin ice model as a viable option". Lambeck et al. (1998; 2000), on the other hand, obtain moderate ice thickness from reverse modelling based on observed sea level curves.

Most glaciological models (e.g. Boulton et al., 1985; Dowdeswell & Siegert, 1999; Holmlund & Fastook, 1993) predict considerably thicker ice than that reconstructed by Nesje & Dahl (1990; 1992), especially in central areas. However, the ice thickness in climate-driven models are very dependent on the amount of precipitation and the duration of ice build up, and both factors are partly dependent on assumptions in the models. All models are also so simple that they cannot be used to reconstruct the regional ice thickness in any detail. Certainly, they cannot be used as an argument against empirical reconstructions in the fjord areas, such as Nesje et al.' s reconstruction in Nordfjord.

The writer concludes that the lower limit of block fields is not an unique criterion that can be used to map the ice sheet surface during the Late Weichselian glacial maximum, although the interpretation presented for Nordfjord and some other coastal areas may, nevertheless be correct. The conflict with the results based on isostatic modelling has made this problem even more urgent to solve, because isostatic modelling, beside glaciological modelling, is the most used technique to determine past ice sheet thickness world wide (e.g. Dowdeswell & Siegelt, 1999; Lambeck et al., 2000; Peltier, 1994).

Here the writer supports and further develops an hypothesis proposed by Longva & Thorsnes (1997). For a century it has been accepted that the first Late Weichselian glacial advance to northern Denmark was from Norway (Sjørring, 1983), an interpretation supported by all recent studies (Houmark-Nielsen, 1999). This conclusion, mainly based upon numerous Norwegian erratics in the north Danish tills, was also supported by till fabric and glaciotectonic deformation features, which showed flow from the north. It is difficult to envisage an ice flow carrying erratics from Norway to Denmark if there was an active ice stream in the Norwegian Channel. In fact it appears impossible if that ice stream was developed as far upstream, as shown in Fig. 8, because flow from Norway would simply be 'cut off'′ and drain into the ice stream. Longva & Thorsnes (1997) described three generations of ice flow directions based on the sea-floor morphology in the outer part of Oslofjorden. Deep, diffuse furrows with a direction showing that the ice crossed the Norwegian Channel represent the oldest generation. It is interpreted to show the ice flow to the Late Weichselian ice limit in northern Denmark (Longva & Thorsnes, 1997). Deep furrows, with a more south-westerly direction represent the next generation. This change in direction was likely the result of ice culmination over Central Norway-Sweden moving eastwards. The youngest flutes show a very plastic ice flow along the Norwegian Channel, and are interpreted to represent an ice stream in the channel (Longva & Thorsnes, 1997).

The observations cited from Oslofjorden are compatible with a hypothesis that there first developed a thick Scandinavian ice sheet, for example as the one shown by Kleman & Hättestrand (1999). This ice sheet may have developed without peripheral ice streams, or at least without an ice stream in the Norwegian Channel. Ice from Norway could then move across the Norwegian Channel to Denmark and the North Sea. This ice sheet could have had a steeper surface slope, although it still moved on derformable beds in peripheral areas. In Denmark and the shallow part of the North Sea, there was probably permafrost during the advance, favouring a steeper ice surface (Clark et al., 1999), although that could not have been the case in the deep Norwegian Channel. All summits in Central Norway could in this early phase have been covered by frozen-bed ice. Subsequently the ice streams developed, probably from the shelf edge and propagating upstream. That would lead to a major drawdown of the ice-sheet surface, and possibly to a situation similar to that reconstructed by Nesje & Dahl (1990; 1992) (Fig. 9).

Cross-profiles across the Scandinavian Ice Sheet according to Svendsen & Mangerud (1987) are shown in Figure 11. The writer considers that the pattern of the profile of the minimum model for the Late Weichselian maximum probably is correct, showing low surface slopes on deformable beds across the shelf in the west and in eastern areas. However, it is assumed that ice thickness was closer to the maximum model over Scandinavia. The Younger Dryas ice surface profile was probably closer to the shown minimum model.

Fig. 11. A profile across Fennoscandia adapted from Svendsen and Mangerud (1987). Upper panel: Shore lines of different ages. Middle panel: Alternative ice-sheet profiles for the Late Weichselian maximum and the Younger Dryas. Full lines show maximum thickness, stippled lines minimum thickness. Lower panel: Present day uplift.

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Quaternary Glaciations Extent and Chronology

G.S. Boulton , ... M. Broadgate , in Developments in Quaternary Sciences, 2004

3.2.1 'Pre-varve' retreat

There is strong evidence that the maximum extent of the Late Weichselian Scandinavian ice sheet was time-transgressive. The earliest advance to the maximum for which evidence is available is in the southwest, where the ice sheet, flowing from a centre in southwest Norway, crossed the North Sea to become confluent with an ice sheet over the British Isles at about 28 ka ( Sejrup et al., 1994, 2000) (Fig. 8). There is evidence that during this phase, the Norwegian Channel, which extends from the Skagerrak and skirts the southern and southwestern coast of Norway as far as the continental shelf edge off southwest Norway, was the location of a major ice stream (King et al., 1996; Sejrup et al., 1996, 1997).

The connection between the European and British ice sheets was broken shortly after 23 ka, and the European ice sheet margin retreated to the vicinity of the coast of southwest Norway by about 20ka (Valen et al., 1996). Between 20 ka and 18 ka, the ice sheet readvanced from the vicinity of the Norwegian coast to reach a maximum just beyond the southwest margin of the Norwegian Channel (the Tampen advance; Sejrup et al., 1994). It seems most likely that the sharp re-entrant in the maximum extent of the Weichselian ice sheet margin in northern Jutland (Fig. 8) represents an overstepping by this advance of the margin of the older North Sea ice sheet, such that the maximum extent in much of Jutland and northwest Germany, is roughly contemporary with the Tampen advance. Furthermore, the distribution of moraines in northern Germany suggests that the eastward continuation of this advance, represented by the north-south Weichselian ice margin through Denmark, also oversteps the line of the older, Brandenburg moraines and continues into the Poznan Moraines (Fig. 8).

The configuration of moraines in northern Germany and Poland (Fig. 8) suggests that an early advance occurred in this sector to the glacial maximum along the Brandenburg-Lezno moraines, and that this was followed by a retreat and then a readvance which created the Poznan stage moraines (Kozarski, 1986, 1988).

Further to the east and west, the readvance formed the glacial maximum. It is possible that the early, Brandenburg-Lezno advance was a consequence of stronger ice sheet flow down the axis of the southern Baltic Sea. It may reflect the same phase of ice sheet growth which led to extension of ice from the southern Norwegian centre of ice sheet growth into the North Sea.)

The later, Pomeranian Moraines (Fig. 8), have been shown by Kozarski (1986) to cut across the earlier, post-Poznan Moraines in Poland, representing yet another major advance of the ice sheet margin in this sector. The Gardno Moraine in northernmost Poland (Kozarski, 1986) may represent a relatively small readvance, as there is no clear evidence of major cross-cutting relationships with the major moraines to the south.

There is very little independent evidence of the age of the glacial maximum or of ice-marginal positions in the southern (German-Polish) sector of the ice sheet. Prior to its maximum extent, the expanding ice sheet moved across the southern Norwegian and southwest Swedish coasts between 30 and 24 ka (Hillefors, 1974; Andersen, 1987) and crossed the Polish coast slightly before 22ka BP (Kozarski, 1988). The ice sheet is suggested to have advanced to the maximum extent in Poland shortly after 20 ka BP (TL yr -Ralska-Jasiewiczowa & Rzetkowska, 1987; Mojski, 1992). The time window for the glacial maximum in Poland is closed by an uncalibrated 14C date of 13,500 BP on the northern coast of Poland on the earliest organic deposits after deglaciation (Ralska-Jasiewiczowa & Rzetkowska, 1987). Adjusting this date using the correction of Bard et al. (1993), gives an age of 15,950 BP (from here on 14C ages are given as corrected ages unless otherwise stated). Although there is considerable uncertainty about the timing of the glacial maximum and of deglaciation of the area to the south of the Baltic Sea, the above estimates are not inconsistent with other records. The isotopic minimum in deep-ocean stratigraphy, thought to record the global ice volume maximum during the last glacial period, occurred at 22 ka (Imbrie et al., 1984), as did the period of maximum cooling in the Greenland ice-core record (Johnsen et al., 1992; Bond et al., 1993).

Support for the general distribution of retreat isochrons in the southeast sector of the ice sheet during the early stages of retreat is given by Sandgren et al. (1997), who have used palaeomagnetic correlations with varve-dated sites in southern Sweden and Karelia to suggest deglaciation of Lake Tamula in Estonia at 14,400 calendar years BP. It indicates that the proposed isochrons are consistent with the time of deglaciation of northern Poland and of southern Estonia (Fig. 8).

If the ice sheet readvances in the southern sector margin (Kozarski, 1988) are climatically driven rather than dynamic, it is tempting to suggest the following correlations with post-LGM cooling events in the GISP/GRIP records: Poznan Moraine – 18,500 BP; Pomeranian Moraine -16,500 BP; Gardno Moraine- 15,400 BP; compared with Kozarski's (1986) estimates of 20,400 for the Lezno, 18,400 for the Poznan, 15,200 for the Pommeranian and 13,300 BP for the Gardno moraines.

The trend of morainic features in the southeastern sector of the ice sheet suggests that the features which are co-linear with the Gardno Moraine ultimately converge, about 300 km south of Lake Ladoga, with the maximum extent of the Weichselian glaciation (Fig. 8), just as the Poznan and Pommeranian moraines appear to further west. If this is so, it suggests that whilst the southern and south western margins of the ice sheet were retreating by up to 300 km, the eastern and southeastern margins of the ice sheet were stationary or still advancing. This conclusion is supported by evidence that in the area to the southeast of the White Sea, the glacial maximum was not reached until after 17 ka and that retreat from the maximum position did not begin until about 15 ka (Larsen et al., 1999).

In the northern sector, the ice sheet appears to have reached a maximum in northern Norway between 19-18.5 ka BP (Vorren et al., 1988), whilst an ice sheet over the Barents Sea, believed to have been confluent with the European ice sheet, is thought to have reached its maximum extent and begun to collapse rapidly by 15 ka and had largely disappeared by 12 ka (Landvik et al., 1998).

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Quaternary Glaciations Extent and Chronology

Jürgen Ehlers , ... Stefan Wansa , in Developments in Quaternary Sciences, 2004

Introduction

Germany was affected by three different types of Pleistocene glaciation: the Fenno-Scandinavian ice sheets in the north, the Alpine glaciation in the south and a number of local glaciations in the upland areas. Recent overviews had been given by Benda (1995) and by Ehlers (1996).

In the Late Tertiary the sea withdrew from the Northwest European Basin, and fluvial deposition prevailed. The deposits of the resulting 'Baltic River Sytem' can be traced from the island of Sylt well into the Netherlands. They contain lydites from the southern Central German uplands as well as large blocks, which must have been transported by drift ice from the eastern Baltic region (Gripp,, 1964). The 'Loosener Kiese' of Mecklenburg are regarded as part of this river system (von Bülow, 1969). It remained active until the advance of the first Pleistocene ice sheets altered the drainage system both fundamentally and irreversably.

The basic subdivision of the north German Quaternary stratigraphy was established by the end of the last century. It was originally assumed that north Germany, like the Alps, had been affected by three glaciations (Penck 1879). The names Elsterian, Saalian, and Weichselian first appeared in 1910 on the 1:25,000 map sheets of the 'Könglich Preußische Geologische Landesanstalt'. The glacial limits in north Germany have been largely defined in the course of large-scale geological mapping of the individual till sheets. Only in exceptional cases were maximum glacial positions found to be marked by significant end moraines.

After it had been found out that the Alps had been glaciated (at least) four times instead of three (Penck & Brückner, 1909/11), there has been no lack of attempts to identify corresponding till units in North Germany. However, neither the proposed subdivision of the Saalian into two independent glaciations nor the assumed detection of an additional older (Elbe) glaciation (Van Werveke, 1927) could stand up to close inspection.

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ARCHAEOLOGICAL RECORDS | Postglacial Adaptations

G. Bailey , in Encyclopedia of Quaternary Science (Second Edition), 2013

World Overview

By archaeological convention, the Postglacial is defined as the period beginning with the final melting of the Scandinavian ice sheet at about 10 radiocarbon ka BP. This date also marks the conventional beginning of the Mesolithic period, seen as the continuation of a Paleolithic hunter-gatherer way of life adapted to the changed environmental conditions of the Postglacial – in particular, the change from the glacial steppe with its migrating herds of large mammals, to heavily forested environments with fewer resources. This is a view shaped by European data and intellectual history, in which the Mesolithic has traditionally been viewed as a period of cultural and demographic decline or stasis, marking time until Neolithic farmers from the Near East entered Europe, some 8 radiocarbon ka BP, replacing the hunter-gatherer way of life across the continent over the following three millennia.

Archaeological investigations now demonstrate that this notion of progressive evolution through uniform stages of development is greatly oversimplified. So far from being a period of cultural stagnation, these 'Mesolithic' millennia that preceded the development of full-scale village farming are now seen as representing a period of radical change and innovation, while Mesolithic achievements in their turn were built on developments, already well underway, in the closing millennia of the Last Glacial period (Mithen, 2003).

From an archaeological point of view, there are good reasons to extend the period of 'Postglacial' adaptations back to the beginning of the warming trend initiated at about 13 radiocarbon ka BP with the Late Glacial interstadials, and perhaps back to 16 radiocarbon ka BP, when sea levels began their sustained rise from the low point of the Last Glacial Maximum (see Last Glacial Maximum GCMs). As sea level rose to reach its present position about 6 radiocarbon ka BP, progressive inundation of the continental shelf removed extensive areas of lowland territory, breached intercontinental land connections, brought existing hinterlands within reach of milder 'oceanic' climates, and culminated in the creation of entirely new coastal landscapes. The impact of sea-level rise on paleoecology and paleogeography would have differed in different areas, but the effects would have been experienced worldwide. They were especially marked in regions with shallow continental shelves, such as northwest Europe, where large areas of hunting territory were lost, only to be replaced by the creation of shallow inshore waters, indented coastlines, and offshore islands and archipelagos, with more productive and more easily accessible supplies of fish, sea mammals, and intertidal mollusks.

It is during this Late Glacial period of changing environmental conditions, and especially between 13 and 12 radiocarbon ka BP, that we see the first stages of population expansion into new territory exposed by glacial retreat in northern Eurasia, the first unequivocal evidence for the expansion of human populations into the Americas (Dillehay, 2000), the extensive use of microblade technologies with miniature bladelets and points blunted along one edge to provide inserts for hafted hunting weapons throughout large areas of the inhabited world, and the development of pottery in China, the Russian Far East, and Japan (Habu, 2004, Kuzmin et al., 2004).

Regions strongly affected by glaciation saw the rapid spread of populations into deglaciated territory, and the development of coastal and inland economies with significant dependence on aquatic resources along the shorelines of newly created lakes and coastlines throughout the northerly regions of Eurasia and North America. In subsequent millennia, subsistence economies throughout the world diversified into new niches exploiting a wider range of animal and plant food resources, including the first evidence for sustained and intensive use of marine resources on many of the world's coastlines. In semiarid environments at lower latitudes, stands of seed-bearing plants began to expand as climatic conditions improved, creating the basis for intensive harvesting of plant foods. In the Near East, this process was underway from as early as 12 radiocarbon ka BP, ultimately leading to agriculture based on cereal cultivation and domestic animals.

In temperate latitudes, the same climatic trends favored the expansion of woodland cover and reimmigration of deciduous trees, resulting in a complex and rapidly shifting geographical mosaic of vegetation and faunal patterns, in which the large herds of steppe animals such as reindeer, horse, and bison were replaced by woodland species of deer and wild boar. At the same time, these changes in vegetation brought with them new opportunities for food – nut-bearing shrubs and trees such as hazel, oak, and chestnut, and edible roots, leafy greens, and fruits. Hunting parties found new opportunities for seeking out prey such as chamois and ibex on the higher slopes of mountains above the treeline made accessible by deglaciation. Other resources such as birds and small mammals played a larger role, facilitating greater residential stability, larger communities of people, and smaller territories.

High-latitude regions with sub-Arctic conditions were first occupied from at least 10 radiocarbon ka BP on the coastlines of Norway and Alaska, and the final retreat of the North American ice sheets and the opening up of tundra environments in northern Canada and Greenland was closely followed by the expansion of 'paleoeskimo' populations into the high Artic regions of North America between 5 and 4 radiocarbon ka BP. The occupation of this new niche was accompanied by exploitation of sea mammals alongside hunting of animals on land, and by dramatic and rapid expansions of human range. In Norway, 2,000   km of coastline was colonized in a matter of generations (Bjerck, 2008). In North America, 4,800   km of new territory from the Alaskan border to northeast Greenland was opened up in a few centuries (Fiedel, 1987).

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Evidence of Glacier and Ice Sheet Extent on Glaciated Landscapes☆

D.M. Mickelson , C. Winguth , in Reference Module in Earth Systems and Environmental Sciences, 2014

Examples for Controversial Areas of Vertical Ice Extent

Evidence for vertical ice sheet extent is often controversial. For example, ice thickness at the LGM of the Scandinavian Ice Sheet in the mountainous areas in southwestern Norway has long been debated. While ice-free regions in western and northern Norway have been postulated on the basis of biological findings (survival of endemic plant and animal species), geomorphic evidence (presence of steep-sided peaks, cirque topography, summit block fields), and cosmogenic dating, thick ice that covered all mountain peaks has been inferred from numerical modeling of glaciological processes, preconsolidation testing, isostatic response, till fabrics, and striation patterns.

A similar controversy has evolved around glacial extent in eastern Baffin Island, Arctic Canada. While some researchers inferred ice-free refugia and large outlets of Laurentide ice that were restricted to fjords and valleys, others suggested a complete ice cover of Baffin Island during the last glaciation (see overview in Miller et al., 2002).

As methods of dating improve and we gain a better understanding of how cold-based glaciers function and how to interpret the meager traces they leave behind, these controversies will likely be resolved.

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