Biogeography in the Sub-Arctic. Группа авторов
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Название: Biogeography in the Sub-Arctic
Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Жанр: География
isbn: 9781118561355
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During MIS 7, the penultimate interglacial period, sea‐surface temperatures off southern Greenland were lower than those of MIS 13, and the pollen and spore content of sediment remained lower. The pollen assemblages are dominated by herb taxa, notably Poaceae and Cyperaceae, suggesting the development of tundra in southern Greenland (de Vernal and Hillaire‐Marcel 2008).
Marine Oxygen Isotope Stage 5e, the Last Interglacial
Southern Greenland. Pollen concentrations in samples from MIS 5e from core ODP 646 are five times higher than in Holocene samples, and the concentrations of fern spores are also higher. The assemblages are characterized by dominant Alnus and abundant spores of Osmunda. In samples from sediment core HU‐90‐013‐013 collected near ODP 646, more detailed analyses of MIS 5e document the pollen succession. A rapid increase of Alnus occurred during an early phase of MIS 5e, which suggests rapid development of shrub tundra after ice retreat. A subsequent increase of Osmunda represents a unique event in the last million years. It suggests the development of dense fern vegetation over southern Greenland under climatic conditions not unlike those of the modern boreal forest. Towards the end of MIS 5e, pollen and spore influxes decreased and at the same time herb percentages increased, indicating a change to herb tundra resulting from regional cooling at the onset of ice growth (de Vernal and Hillaire‐Marcel 2008).
Jameson Land. Deposits from the last interglacial are found along the south and west coast of Jameson Land in central East Greenland (Figures 1 and 5c and d). Most widespread are sandy, silty and clayey sediments, which were deposited in shallow marine water along the coast, partly in connection with deltas, in the coastal zone and in rivers. The deposits often contain shells of marine molluscs, and the fauna includes M. edulis, a warmth‐demanding southern extralimital species (Vosgerau et al. 1994). At many sites layers and lenses rich in organic detritus are found. The detritus consists mainly of washed together remains of plants that grew in the catchment area, but it also contains remains of insects and other invertebrates. The plant and animal remains give a regional picture of the non‐marine biotas.
Figure 10 Scanning electron microscope photographs of plant remains from last interglacial deposits in Jameson Land, East Greenland. (a) Catkin scale of Alnus cf. crispa. (b) Leaf of Dryas octopetala. (c) Leaf of Vaccinium uliginosum. (d) Endocarp of Arctostaphylos alpina. (e) Leaf of Phyllodoce coerulea. Scale bars: 1 mm.
Source: From Bennike and Böcher (1994).
The fossil flora includes many species of dwarf shrubs and other woody plants (Figure 10). Most noteworthy are common remains of Betula pubescens, which probably formed shrub or low forest on sheltered sites. At present, B. pubescens is confined to southernmost Greenland, whereas B. nana, today common in Jameson Land, has not been found in interglacial deposits in East Greenland. Samples from many localities contain remains of Alnus cf. crispa, which grows in south‐western Greenland and North America at present. Another woody plant that grows in southernmost Greenland at present is Cornus canadensis, fruits of which are rare in the fossil assemblages. Dwarf shrubs are represented by no less than 11 species, of which the majority is ericaceous. Remains of E. nigrum, V. uliginosum, Arctostaphylos alpina and D. octopetala are particularly common, whereas remains of Cassiope tetragona and Harrimanella hypnoides are rarer. Leaves of S. herbacea are common; this tiny woody plant is characteristic of snow beds. Herbaceous plants are represented by, for example, Melandrium apetalum and O. digyna, which are typical arctic plants that are common in the region today.
The fossil interglacial flora from Jameson Land is also rich in remains of bryophytes. The bryophyte flora is diverse with more than 60 identified taxa and it includes some southern extralimital species such as Climacium dendroides and Sphagnum warnstorfii (Hedenäs 1994). Abundant remains of Polytrichaceae and Racomitrium show that unstable soil with sparse vascular plant cover was important.
The fossil interglacial fauna of Coleoptera comprises almost 25 taxa of beetles, which is highly surprising considering that Jameson Land's present beetle fauna only comprises three species. In contrast to the flora of vascular plants, the beetle fauna comprised several species that are absent from the modern fauna of Greenland. On the other hand, many of Greenland's extant species are not represented as fossils in the interglacial fauna. The fauna comprises A. alpina (see below) and Otiorhynchus nodosus (Figure 11). The latter is a typical example of a Palaearctic species (Figure 12, see Plate section) that lived in Greenland during the last interglacial and the Holocene. The same applies to, for example, B. fasciatus and Simplocaria metallica.
Figure 11 Scanning electron microscope photographs of beetle remains from last interglacial deposits at Narsaarssuk near Thule air base, North‐West Greenland (a, b) and Jameson Land in East Greenland (c). (a) Elytron of Isochnus arcticus. (b) Half pronotum of Amara alpina. (c) Head of Otiorhynchus nodosus. Scale bars: 1 mm.
Source: From Böcher (1989) and Bennike and Böcher (1992).
All beetle species recorded live in the sub‐arctic bioclimatic zone (Bennike and Böcher 1994; Böcher 2012). The difference between the interglacial and the Holocene fauna indicates that chance dispersal plays a large role in determining which species colonized Greenland during the last and the present interglacial period. Half of the species are Palaearctic, and hence they must have immigrated to Greenland from Europe.
At a single site head capsules of midges were found. Some of these head capsules come from species that live in rivers – a biotope that is otherwise unrepresented in the palaeoecological data (Bennike et al. 2000). Furthermore, it may be mentioned that the fauna includes the freshwater bryozoan C. mucedo, which probably lives in south‐west Greenland at present (Fredskild 1983).
Figure 12 Maps of the northern part of the Earth, showing the present‐day range of the ground beetle Amara alpina and the weevil Otiorhynchus nodosus. The dots show fossil finds in Greenland, assumed to come from the last interglacial. Modern distributions according to Böcher (1989) and Bennike and Böcher (1994).
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