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

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isbn: 9781118561355

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СКАЧАТЬ and fauna was found and a radiocarbon age determination of stems of the bryophyte S. scorpioides gave an age > 52 ka (Kusch et al. 2019). We suggest that the remains from Skallingen are of last interglacial age.

      Kap København, Peary Land. A fragment of a strongly weathered reindeer Rangifer tarandus antler found at the ground near Kap København gave a non‐finite age, and a last interglacial age has been proposed (Meldgaard and Bennike 1989).

      Zackenberg. A fragment of a mesosternum of A. alpina from an Early Holocene delta deposit at Zackenberg must have been reworked from interglacial, possibly Eemian, sediments (Christiansen et al. 2002).

      Early Weichselian Interstadial Deposits

      In addition to interglacial deposits, glacial and non‐glacial deposits that are referred to marine isotope stages 5d to 5a are also found along the coast of Jameson Land in East Greenland (Funder et al. 1998). The Hugin Sø Interstadial, which is correlated with marine isotope stade 5c, represents an ice‐free period during the early part of the Weichselian. The vegetation appears to have consisted of herbs and bryophytes only. Remains of S. oppositifolia are common, and seeds of Papaver sect. Scapiflora also occur (Bennike and Böcher 1994). These species are found all over Greenland, but play an increasingly larger role towards the north, and none of them have been found in deposits from the last interglacial. The only beetle species found is A. alpina, one of the most cold‐adapted ground beetles on Earth. It has been proposed that the mean temperature for the warmest month of the year was 3–4 °C lower than at present (Bennike and Böcher 1994), which is in accordance with the marine mollusc fauna that shows similarities to modern faunas from North Greenland (Funder et al. 1998). In contrast, the fossil bryophyte flora from the Hugin Sø Interstadial comprises several warmth‐demanding species such as Amphidium mougeotii and Polytrichastrum longisetum, which indicate a slightly warmer climate than at present (Hedenäs 1994). However, it is possible that some of the bryophyte material is reworked from Eemian deposits.

      The Last Glacial Maximum in Greenland

      Chronology of the Last Deglaciation

      A lot of data has been acquired that throw light on the chronology of the deglaciation of the ice‐free land parts of Greenland and a chronology for the last recession of the Inland Ice was proposed by Bennike and Björck et al. (2002). Their chronology was mainly based on radiocarbon dated shells from raised marine deposits. In addition to shell dates, the ages of algae, basal peat, basal gyttja, remains of land plants and drift wood were used. Most of the ice‐free parts of Greenland were deglaciated in the Early Holocene, between 11.5 and 8 ka BP, but in the far south some small areas became ice free during the late glacial period. During the past years, a number of studies have used surface exposure dating, which has improved our understanding of the patterns of ice retreat (e.g. Kelley et al. 2015; Sinclair et al. 2016), but the chronology suggested by Bennike and Björck et al. (2002) is still valid.

      Another surprising result of surface exposure dating is that Greenland was apparently nearly ice free for extended periods during the Quaternary (Schaefer et al. 2016).

      Late Glacial and Early to Mid‐Holocene Flora and Fauna

      Late glacial sediments from a locality in southernmost Greenland have been analysed for pollen (Björck et al. 2002). Not surprisingly, the concentration of pollen is extremely low and a large proportion of the pollen grains must be regarded as being long‐distance transported. Pollen of Poaceae, Sagina type, Saxifraga caespitosa type and Saxifraga stellaris type presumably come from the local vegetation, and the same apply to a few seeds of Minuartia sp. and Saxifraga cf. oppositifolia. The vegetation probably consisted of mosses and scattered pioneer herbs.

      Deposits from the earlier Holocene from West and East Greenland also contain remains of bryophytes and herbs only, and the herbs represented are species that can tolerate low summer temperatures and unstable soils (Fredskild 1985; Bennike et al. 1999; Bennike 2000a; Wagner et al. 2010; Bennike and Wagner 2012; Wagner and Bennike 2012). The first woody plant that appears to have immigrated to Greenland is E. nigrum, which was present from ~11 000 years BP. It was soon followed by S. herbacea, known from 10 800 years BP, and V. uliginosum, known from 10 500 years BP. Betula nana arrived in Greenland at ~8800 years BP, S. glauca at ~8700 years BP and Juniperus communis at ~8400 years BP.

      Chydorus arcticus is the most common and widespread cladoceran in Greenland, and the first species to immigrate after the last deglaciation, with the oldest remains dated to ~13 800 years BP. The species lived in South Greenland during the Younger Dryas. Daphnia arrived in South Greenland ~12 500 years ago. Acroperus harpae was also an early immigrant to South Greenland, but it disappeared during the Younger Dryas, and reappeared in the Early Holocene (Bennike and Björck 2000).