Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 47

At Borðoyarvík near Klaksvík in the north‐eastern part of the Faroe Islands, an interglacial deposit is exposed in a coastal cliff section (Rasmussen 1972; Wastegård et al. 2005). The deposit is ~1 m thick and dominated by clay with a content of total organic carbon that decreases from 6% in the lower part to 2% in the upper part. The diatom flora comprises some marine or brackish taxa, but the common presence of statoblasts of the freshwater bryozoan Cristatella mucedo, especially in the lower part of the unit, may contradict a brackish water environment, because the species usually does not occur in brackish water (but see Økland and Økland 2000).

Notes on the pollen flora are found in Rasmussen (1972; sample analysed by Johs. Iversen), in Jóhansen (1985, p. 12) and in Wastegård et al. (2005). Iversen reported a dominance of Empetrum and Poaceae, with some Betula and rare grains of Pinus and Corylus. Jóhansen reported pollen of Buxus, Betula, Lonicera, Plantago lanceolata, Nymphaea, Poaceae, Cyperaceae and Ericales. Wastegård et al. (2005) found Alnus, Betula, Carpinus, Picea, Pinus, Ericaceae, Apiaceae and Asteraceae. A more recent study (Bennike et al. 2018) indicates accumulation in a coastal lagoon in a landscape and climate similar to that of the Mid‐Holocene.

Plant macrofossils are represented by a few pieces of wood. One of them was identified to Pinus and another to Picea or Larix (Rasmussen 1972; Jóhansen 1985). However, it is possible that the wood is driftwood (Wastegård et al. 2005) and if so it may not provide information on the local flora. Betula remains were referred to as Betula sp. by Wastegård et al. (2005), but the remains come from tree birches (Betula sect. Albae, Bennike et al. 2018). Cristatella mucedo, Betula sect. Albae and Ajuga are fairly thermophilous and may indicate summer temperatures slightly higher than at present. The interglacial deposit at Borðoyarvík can be referred to the Eemian, based on tephrochronological studies (Wastegård et al. 2005).

The Faroe Islands were covered by a local ice cap during the last glacial stage (Jørgensen and Rasmussen 1986; Sejrup et al. 2005), and the oldest minimum dates for the deglaciation are ~11.3 ka (Jóhansen 1985; Hannon et al. 2010). The Early Holocene vegetation history of the Faroe Islands is best documented from a high‐resolution study of lake sediments from Lykkjuvøtn on Sandøy (Hannon et al. 2010). Some information is also available from sub‐marine lake deposits from Skálafjørður (Bennike et al. 1998; Tendal 2004; Bennike 2010). Plants documented by macrofossil finds from Early Holocene deposits include the shrubs Salix herbacea, Betula nana, Empetrum nigrum, the herbs Stellaria alsine, Oxyria digyna, Rumex acetosa, Ranunculus flammula, Ranunculus acris, Cardaminopsis petraea, Filipendula ulmaria, Viola palustris, Caltha palustris, the club moss Selaginella selaginoides and the water plants Isoetes lacustris, Potamogeton pusillus, Potamogeton filiformis, Myriophyllum alterniflorum and Sparganium angustifolium (Jóhansen 1985; Bennike et al. 1998; Hannon et al. 2010). The invertebrate fauna from Skálafjørður includes the sponge Racekiela ryderi, an amphi‐Atlantic species that probably arrived by long distance chance dispersal by birds. The same probably applies to the bryozoans Plumatella sp. and C. mucedo. The coleopteran fauna includes the ground beetle Nebria rufescens that is common and widespread in the islands today. The Early Holocene flora and fauna from the Faroe Islands indicate a climate similar to the present.