Weichselian glaciation

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Europe during the Weichselian and Würm cold periods

The last glacial period and its associated glaciation is known in Northern Europe as the Weichselian glaciation, Weichselian ice age (German: Weichsel-Eiszeit), Vistulian glaciation, Weichsel[1] or, less commonly, the Weichsel glaciation, Weichselian cold period (Weichsel-Kaltzeit), Weichselian glacial (Weichsel-Glazial), Weichselian Stage or, rarely, the Weichselian complex (Weichsel-Komplex). In the Alpine region it corresponds to the Würm glaciation. It was characterized by a large ice sheet that spread out from the Scandinavian Mountains[2] and extended as far as the east coast of Schleswig-Holstein, the March of Brandenburg and Northwest Russia.

In Northern Europe it was the youngest of the glacials of the Pleistocene ice age. The preceding warm period in this region was the Eemian interglacial. The last cold period began about 115,000 years ago and ended 11,700 years ago.[3] Its end corresponds with the end of the Pleistocene epoch and start of the Holocene.

Evolution of the Baltic Sea
Pleistocene
Eemian Sea (130,000–115,000 BC)
Ice sheets and seas (115,000–12,600 BC)
Holocene
Baltic Ice Lake (12,600–10,300 BC)
Yoldia Sea (10,300–9,500 BC)
Ancylus Lake (9,500–8,000 BC)
Mastogloia Sea (8,000–7,500 BC)
Littorina Sea (7,500–4,000 BC)
Modern Baltic Sea (4,000 BC–present)

Naming in other parts of the world

In other regions the glaciations of the last glacial period are given other names: for example that in the Alpine region is called the Würm glaciation, in the British Isles it is the Devensian glaciation and in North America, the Wisconsin glaciation.[4][5]

Development of the glaciation

The Fennoscandian Ice Sheet of the Weichselian glaciation most likely grew out of a mountain glaciation of small ice fields and ice caps in the Scandinavian Mountains. The initial glaciation of the Scandinavian Mountains would have been enabled by moisture coming from the Atlantic Ocean and the mountains high altitude. Perhaps the best modern analogues to this early glaciation are the ice fields of Andean Patagonia.[2] The growth of the ice sheet was accompained by an eastward migration of the ice divide from the Scandinavian Mountains eastwards into Sweden and the Baltic Sea.[6] As the ice sheets in northern Europe grew prior to the Last Glacial Maximum the Fennoscandian Ice sheet coalesced with the ice sheet that was growing in Barents Sea 24 ka BP (kiloannus or one thousand years Before Present) and with the ice sheet of the British Islands a about thousand years later. At this point the Fennoscandian Ice Sheet formed part of a larger Eurasian ice sheet complex —a contiguous glacial ice mass which spanned an area from Ireland to Novaya Zemlya.[6]

The central parts of the Weichsel ice sheet had cold-based conditions during the times of maximum extent. This mean that in areas like north-east Sweden and northern Finland pre-existing landforms and deposits escaped glacier erosion and are particularly well preserved at present.[7]

Last Glacial Maximum to Younger Dryas

  Maximum extent of the ice (Brandenburg Stage) during the Weichselian in North Germany (red line).
  Greatest extent of the older Saalian glaciation (yellow line).
Note that the coastlines are modern; coastlines during the Weichselian were different as sea level was lower.

The Last Glacial Maximum extent was first reached 22 ka BP in the southern boundary of the ice sheet in Denmark, Germany and Western Poland. In Eastern Poland, Lithuania, Belorussia and Pskov Oblast in Russia the ice sheet reached its maximum extent about 19 ka BP. In the remaining of northwestern Russia the largest glacier advance occurred 17 ka BP.[8] As the ice margin started to recede 22-17 ka BP Denmark (except Bornholm), Germany, Poland and Belorussia were ice-free 16 ka BP. The ice margin then retreated until the Younger Dryas when the ice sheet stabilized. At this point most of Götaland, Gotland, all of the Baltic states and the southeastern coast of Finland had added to the ice-free regions. In Russia lake Ladoga and Onega and the bulk of Kola Peninsula and the White Sea were free from ice during the Younger Dryas. Before the Younger Dryas deglaciation had not been uniform and small ice sheet re-advances had occurred forming a series of end-moraine systems, notably those in Götaland.[8]

Final deglaciation

When ice margin retreat resumed the ice sheet became increasingly concentrated in the Scandinavian Mountains (it had left Russia 10.6 ka BP and Finland 10.1 ka BP). Further retreat of the ice margin led the ice sheet to concentrate in two parts of the Scandinavian Mountains, one part in Southern Norway and another in Northern Sweden and Norway. These two centres were for a time linked. The linkage constituted a major drainage barrier that formed various large and ephemeral ice-dammed lakes. About 10.1 ka BP the linkage had disappeared and so did the Southern Norway centre of the ice sheet about thousand years later. The northern centre remained a few hundred years more so that by 9.7 ka BP the eastern Sarek Mountains hosted the last remnant of the Fennoscandian Ice Sheet.[8] As the ice sheet retreated to the Scandinavian Mountains this was not a return to its former mountain centred glaciation from which the ice sheet grew out, it was dissimilar in that the ice divide lagged behind as the ice mass concentrated in the west.[2]

Isostatic adjustment

Map of the Littorina Sea around 7000 years BP. Note the reduced area of Finland due to higher sea levels levels.

Isostatic adjustment bought by deglaciation is reflected in the shoreline changes of the Baltic Sea and other nearby bodies of water. In the Baltic Sea uplift has been greatest at the High Coast in the western Bothnian Sea. Within the High Coast the relict shoreline at 286 m in Skuleberget is at present the highest known point on Earth to have been uplifted by postglacial isostatic rebound.[9] North of the High Coast at Furuögrund off the coast of Skellefteå lies the area with the highest uplift rates at present with values of about 9 mm/yr.[9][10][11] Ongoing post-glacial rebound is thought to result in splitting of the Gulf of Bothnia into a southern gulf and a northern lake across Norra Kvarken no earlier than in about 2,000 years.[12]

Since deglaciation the rate of post-glacial rebound in the Kandalaksha Gulf has varied. Since the White Sea connected to the World's oceans uplift along southern coast of the gulf has totaled 90 m. In the interval 9,500–5,000 years ago uplift rate was of 9–13 mm/yr. Prior to the Atlantic period uplift rate had decreased to 5–5.5 mm/yr, to then rise briefly before arriving at the present uplift rate is of 4 mm/yr.[13]

Sequence and subdivisions of the Weichselian

Depiction of the Earth at the last glacial maximum. Illustration based on: Ice age terrestrial carbon changes revisited by Thomas J. Crowley (Global Biogeochemical Cycles, Vol. 9, 1995, pp. 377-389).

About 115,000 years ago[3] average temperatures dropped markedly and warmth-loving woodland species were displaced. This significant turning point in average temperatures marked the end of the Eemian interglacial and start of the Weichselian glacial stage. It is divided into three sections, based on the temperature variation: the Weichselian Early Glacial,[14][15] the Weichselian High Glacial[14] (also Weichselian Pleniglacial[15]) and the Weichselian Late Glacial.[15] During the Weichselian, there were frequent major variations in climate in the northern hemisphere, the so-called Dansgaard-Oeschger events.

The Weichsel Early Glacial (115,000 - 60,000 BC) is in turn divided into four stages:

  • Odderade Interstadial (WF IV). The pollen spectra indicate a boreal forest. It starts with a tree birch phase, which rapidly transitions to pine forest. Also apparent are larches and spruce as well as low numbers of alder.
  • Rederstall Stadial (also WF III). In North Germany the pollen spectra indicate a grassy tundra followed later by shrubby tundra.
  • the Brörup Interstadial (also WF II). Several profiles show a short period of cooling shortly after the start of the Brörup Interstadial, but this does not appear in all profiles. This led some authors to distinguish the first warm period as the Amersfoort Interstadial. However, since then, this first warm period and cooling phase has been included in the Brörup Interstadial. Northern Central Europe was populated by birch and pine woods. The Brörup Interstadial is identified with marine isotope stage 5c.
  • the Herning Stadial (also called WF I) was the first cold phase, in which northwestern Europe was largely treeless. It corresponds to marine isotope stage 5d.

In the Weichselian High Glacial (57,000 - c. 15,000 BC) the ice sheet advanced into North Germany. In this period, however, several interstadials have been documented.

  • Glaciation and ice sheet advances to North Germany (Brandenburg Phase, Frankfurt Phase, Pomeranian Phase, Mecklenburg Phase).
  • Denekamp Interstadial. The pollen spectra indicates a shrubby tundra landscape.
  • Hengelo Interstadial. The pollen show sedges (Cyperaceae) and temporarily a high number of dwarf birches (Betula nana).
  • Moershoofd Interstadial. The pollen spectra show a treeless tundra vegetation with a high proportion of sedges (Cyperaceae).
  • Glinde Interstadial (WP IV). The pollen diagrams indicate a treeless, shrubby tundra.
  • Ebersdorf Stadial (WP III). In North Germany this period is characterised by pollen-free sands.
  • Oerel Interstadial (WP II). The pollen diagrams point to a treeless, shrubby tundra in North Germany.
  • Schalkholz Stadial (WP I). The first ice advance may have already reached the southern Baltic Sea coast. At the type lokality of Schalkholz (county of Dithmarschen) pollen-free, sands indicate a largely vegetation-free landscape.

The short "Weichselian Late Glacial" (12,500 - c. 10,000 BC) was the period of slow warming after the Weichselian High Glacial. It was however again interrupted by some colder episodes.

Following the last of these cold periods, the Younger Dryas, the Weichselian Glacial ended with an abrupt climb in temperature around 9,660 ± 40 BC.[16] This was the start of our present interglacial, the Holocene.

In addition to the above subdivisions the depositions of the Weichselian Late Glacial following the retreat of the ice sheet are divided into four stages: the Germanic Glacial (Germaniglazial) (Germany becomes ice-free), the Danish Glacial (Daniglazial) (Denmark becomes ice-free), The Gotland Glacial (Gotiglazial) (Gotland becomes ice-free) and the Finnish Glacial (Finiglazial) (Finland and Norway become ice-free).[17]

See also

References

  1. ^ Whittow, John (1984). Dictionary of Physical Geography. London: Penguin, 1984, p. 580. ISBN 0-14-051094-X.
  2. ^ a b c Fredin, Ola (2002). "Glacial inception and Quaternary mountain glaciations in Fennoscandia". Quaternary International. 95–96: 99–112.
  3. ^ a b Litt et al. (2007: pp.45ff)
  4. ^ F.J. Monkhouse Principles of Physical Geography, London: University of London Press, 1970 (7th edn.), p. 254. SBN 340 09022 7
  5. ^ Whittow, John (1984). Dictionary of Physical Geography. London: Penguin, 1984, p. 265. ISBN 0-14-051094-X.
  6. ^ a b Patton, Henry; Hubbard, Alun; Andreasen, Karin; Auriac, Amandine; Whitehouse, Pippa L.; Stroeven, Arjen P.; Shackleton, Calvin; Winsborrow, Monica; Heyman, Jakob; Hall, Adrian M. (2017). "Deglaciation of the Eurasian ice sheet complex". Quaternary Science Reviews. 169: 148–172.
  7. ^ Sarala, Pertti (2005). "Weichselian stratigraphy, geomorphology and glacial dynamics in southern Finnish Lapland" (PDF). Bulletin of the Geological Society of Finland. 77: 71–104. Retrieved December 11, 2017.
  8. ^ a b c Stroeven, Arjen P.; Hättestrand, Clas; Kleman, Johan; Heyman, Jakob; Fabel, Derek; Fredin, Ola; Goodfellow, Bradley W.; Harbor, Jonathan M.; Jansen, John D.; Olsen, Lars; Caffee, Marc W.; Fink, David; Lundqvist, Jan; Rosqvist, Gunhild C.; Strömberg, Bo; Jansson, Krister N. (2016). "Deglaciation of Fennoscandia". Quaternary Science Reviews. 147: 91–121.
  9. ^ a b Berglund, M. (2012). "The highest postglacial shore levels and glacio-isostatic uplift pattern in northern Sweden". Geografiska Annaler: Series A, Physical Geography. doi:10.1111/j.1468-0459.2011.00443.x. {{cite journal}}: |access-date= requires |url= (help)
  10. ^ Ågren, J. and Svensson, R., 2006. Land uplift model and system definitions used for the RH 2000 adjustment of the Baltic levelling ring. The 15th General Meeting of the Nordic Geodetic Commission, Copenhagen, 29 May–2 June 2006, 1–9
  11. ^ Davis, J.L.; Mitrovica, J.X.; Scherneck, H.-G.; Fan, H. (1999). "Investigations of Fennoscandian glacial isostatic adjustment using modern sealevel records". Journal of Geophysical Research. 104 (B2): 2733–2747.
  12. ^ Tikkanen, Matti; Oksanen, Juha (2002). "Late Weichselian and Holocene shore displacement history of the Baltic Sea in Finland". Fennia. 180 (1–2). Retrieved December 22, 2017.
  13. ^ Romanenko, F.A.; Shilova, O.S. (2011). "The Postglacial Uplift of the Karelian Coast of the White Sea according to Radiocarbon and Diatom Analyses of LacustrineBoggy Deposits of Kindo Peninsula". Doklady Earth Sciences. 442 (2): 544–548. doi:10.1134/S1028334X12020079. {{cite journal}}: |access-date= requires |url= (help)
  14. ^ a b Wolfgang Schirmer, Quaternary field trips in central Europe, Volume 1, Pfeil, 1995, p. 375. ISBN 978-39-238-7191-9
  15. ^ a b c John Dodson (ed.), Earth Systems and Society, New York, London, etc., Springer, 2010 p. 173. ISBN 978-90-481-8716-4
  16. ^ Friedrich M, Kromer B, Spurk M, Hofmann J, Kaiser KF.(1999): Paleo-environment and radiocarbon calibration as derived from Late Glacial/Early Holocene tree-ring chronologies. In: Quaternary International 61:27–39.
  17. ^ Karl N. Thome (1998), Einführung in das Quartär. Das Zeitalter der Gletscher (in German), Berlin: Springer-Verlag, pp. 72 {{citation}}: Unknown parameter |publicationplace= ignored (|publication-place= suggested) (help)

Literature

  • Thomas Litt; Karl-Ernst Behre; Klaus-Dieter Meyer; Hans-Jürgen Stephan; Stefan Wansa (2007), T. Litt im Auftrag der Deutschen Stratigraphischen Kommission (ed.), "Stratigraphische Begriffe für das Quartär des norddeutschen Vereisungsgebietes", Stratigraphie von Deutschland - Quartär. Special issue. Eiszeitalter und Gegenwart/Quaternary Science Journal (in German), vol. 56, No. 1/2, Stuttgart: E. Schweizerbart’sche Verlagsbuchhandlung (Nägele und Obermiller), pp. 7–65, doi:10.3285/eg.56.1-2.02 (inactive 2017-01-20), ISSN 0424-7116 {{citation}}: Unknown parameter |publicationplace= ignored (|publication-place= suggested) (help)CS1 maint: DOI inactive as of January 2017 (link) CS1 maint: unflagged free DOI (link)
  • H. Liedtke & J. Marcinek: Physische Geographie Deutschlands, Justus Perthes Verlag, Gotha, 1995 ISBN 3-623-00840-0
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