Biogeography in the Sub-Arctic. Группа авторов

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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

During the past decades it has become clear that the Greenland Ice Sheet was much larger than at present during the last glacial maximum, at ~21 ka BP. In the north‐west, the Greenland ice sheet coalesced with the Innuitian Ice Sheet that covered the Canadian Arctic Archipelago (Blake et al. 1992; Kelly and Bennike 1992; Bennike and Björck 2002). Studies of sediment cores and detailed bathymetrical surveys show that the margin of the Greenland Ice Sheet reached the edge of the continental shelf both in South‐East Greenland (Mienert et al. 1992), in central West Greenland (Ó Cofaigh et al. 2013), in North‐West Greenland (Dowdeswell et al. 2014; Slabon et al. 2016) and probably also in East Greenland (Winkelmann et al. 2010; Arndt et al. 2017; Laberg et al. 2017; Arndt 2018). In South Greenland, geophysical modelling implies that the margin of the ice sheet reached the shelf edge and even the highest mountains were glaciated (Bennike et al. 2002b). Jameson Land in central East Greenland is characterized by deep weathering and little glacial scouring, and Funder (1979) suggested that this area was ice free during the last glacial maximum. On the basis of surface exposure dating of glacial erratics, Håkansson et al. (2009) questioned this restricted extent, but Funder et al. (2011) maintained that Jameson Land was ice free. New surface exposure dating of bedrock surfaces in Jameson Land indicates that the area was ice‐covered during the last glacial maximum, but it was deglaciated already at ~18–21 ka (Håkansson et al. 2011). A major expansion of the Greenland ice sheet during the last glacial maximum is in accordance with results from ice core studies (Vinther et al. 2009; Simonsen et al. 2019). The temperature minimum during the last ice age is dated to ~25 ka BP in Greenland, at which time the mean annual temperature was ~23° lower than today (Dahl‐Jensen et al. 1998).

      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).

Among insects, head capsules of chironomid larvae are found in late glacial deposits (Bennike and Björck 2000) and remains of the caddis fly Apatania zonella are found in Early Holocene deposits (Bennike et al. 2000). Remains of the seed bug N. groenlandicus have been found in a fairly large number of deposits, and the species was an early immigrant to Greenland (Bennike et al. 2000; Böcher et al. 2012), although it has not been recorded from earliest Holocene deposits. Remains of water beetles are quite common in lake deposits and Colymbetes dolabratus remains have been recovered from Early Holocene deposits in both West and East Greenland. The ground beetle Bembidion grapii is widespread in southern Greenland and remains of it have been found in Early Holocene deposits in both East and West Greenland (Böcher and Bennike 1996; Böcher et al. 2012). The pill beetle S. metallica has also been found in Early Holocene deposits in West Greenland. A find dated to ~9920 years BP is the oldest record of a terrestrial beetle from Holocene Greenland (Böcher et al. 2012). From Mid‐Holocene deposits specimens of Rutidosoma globulus have recently been recorded; this is a species that is extremely rare in nowadays Greenland (Böcher et al. 2012). Finds in East Greenland of the leaf beetle Phratora cf. polaris in deposits dated to between 8700 and 7900 years BP are most surprising. This species, which is unknown in present day Greenland, is probably extinct СКАЧАТЬ