Biogeography in the Sub-Arctic. Группа авторов
Чтение книги онлайн.

Читать онлайн книгу Biogeography in the Sub-Arctic - Группа авторов страница 36

Название: Biogeography in the Sub-Arctic

Автор: Группа авторов

Издательство: John Wiley & Sons Limited

Жанр: География

Серия:

isbn: 9781118561355

isbn:

СКАЧАТЬ are well known from a few investigations of midden layers in central West Greenland, with remarkably well‐preserved remains (Figures 5e and 14; Böcher and Fredskild 1993).

Photo depicts scanning electron microscope photographs of remains of insect remains from Mid-Holocene midden deposits from Qeqertasussuk, West Greenland. (a, b) Elytra of Hydroporus morio and S. metallica. (c, d) Heads of Micralymna brevilingue and Nysius groenlandicus.

      Source: From Böcher and Fredskild (1993).

      Among vertebrates, the known temporal range of the small fish Gasterosteus aculeatus extends back to ~10 ka, that of reindeer R. tarandus to ~9 ka, that of wolf Canis lupus to ~8 ka and that of musk‐ox Ovibos moschatus to ~5 ka (Meldgaard 1986; Bennike 1997, 2013; Bennike and Björck 2002; Campos et al. 2010).

      The debate is still very much alive. Among the botanists who in more recent times have advocated most warmly for survival is Tyge Böcher. Thus he wrote: ‘Is it a too daring assumption that the (tree) birch held its own … in the lowlands on sunny sides of the mountains during the last Glacial Age? If the Greenland birch (Betula pubescens coll.) demonstrably constitutes a special form cycle which is not identical with Icelandic or American races, this will highly strengthen such a survival hypothesis’ (Böcher 1956). Tree birch is one of the most warmth demanding plant species in Greenland, and is only found in the far south of Greenland. If it survived the last ice age in Greenland, this would mean that ice‐free areas were present and that the climate was not much different from the present. Tyge Böcher also proposed that the dwarf birch could be an ice age survivor. Even though dwarf birch is far less warmth demanding than tree birch, it also has a northern range limit in Greenland, and from a Greenland point of view it cannot be considered a cold adapted plant. Betula species are prolific pollen producers and their former arrival at a certain area in Greenland is usually marked by an abrupt increase in pollen values. It is now clear from palaeobotanical studies of lake deposits that all three Greenlandic birch species are Holocene immigrants (Fredskild 1991).

      Among zoologists that have advocated for survival on the North Atlantic Islands the Swedish entomologist Carl Lindroth must be mentioned. Originally Lindroth suggested that many beetle species had colonized the Faroe Islands, Iceland and Greenland over a land bridge, which he suggested had existed after the last ice age. When geological investigations in the North Atlantic showed that such a land bridge could not have existed this late, Lindroth proposed that the beetles had colonized the North Atlantic Islands in interglacial time and survived the last ice age (Lindroth 1957, 1973).

An illustration of a map depicting the Earth’s northern parts with arrows that show immigration routes to the North Atlantic islands.

      Source: From Bennike (1999).

      With respect to Iceland, Rundgren and Ingólfsson (1999) suggested that survival was supplemented by renewed immigration during each interglacial period. The interglacial floras and faunas show that rich biota existed in suitable biotopes on the North Atlantic islands during the Quaternary interglacials. However, the interglacial occurrences do not prove continuity, as pointed out by Buckland and Panagiotakopulu (2010). Anyway, it is clear that the old discussion about survival contra immigration is far from dead.

      1 Aalto, M., Eriksson, B., and Hirvas, H. (1992). Naakenavaara interglacial – a till covered peat deposit in western Finnish Lapland. Bulletin of the Geological Society of Finland 64: 169–181.

      2 Andrews, J.T., Hardarsdóttir, J., Helgadóttir, G. et al. (2000). The N and W Iceland shelf: insights into the Last Glacial Maximum ice extent and deglaciation based on acoustic stratigraphy and basal radiocarbon AMS dates. Quaternary Science Reviews 19: 619–631.

      3 Arndt, J.E. (2018). Marine geomorphological record of Ice Sheet development in East Greenland since the Last Glacial Maximum. Journal of Quaternary Science 33: 853–864.

      4 Arndt, J.E., Jokat, W., and Dorschel, B. (2017). The last glaciation and deglaciation of the Northeast Greenland continental shelf revealed by hydro‐acoustic data. Quaternary Science Reviews 160: 45–56.

      5 Áskelsson, J. (1938). Kvartärgeologischen Studien auf Island II. Interglaziale Pflanzenablagerungen. Meddelelser fra Dansk Geologisk Forening 9: 300–319.

      6 Bennike, O. (1989). Trichotropis bicarinata (Gastropoda) from the Plio‐Pleistocene Kap København Formation, new to the fossil fauna of Greenland. Mededelingen van de Werkgroep voor Tertiaire en Kwartaire Geologie 26: 137–143.

      7 Bennike, O. (1990). The Kap København Formation: stratigraphy and palaeobotany of a Plio‐Pleistocene sequence in Peary Land, North Greenland. Meddelelser om Grønland, Geoscience 23: 85.

      8 Bennike, СКАЧАТЬ