Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 46

The North Atlantic Islands comprise from south to north, the Faroe Islands, Iceland and Greenland (Figure 1, see Plate section). They span almost 30° of latitude from temperate to high arctic climates, from North‐West Europe to North America. The Faroe Islands are a group of small islands with an area of 1400 km², whereas Greenland is the largest island on Earth, covering an area of 2 166 086 km², of which 410 449 km² are ice free. Iceland with an area of 103 100 km² is intermediate in size.

Large parts of the North Atlantic islands are mountainous, with the highest peak at 3693 m found in East Greenland. In addition to the Inland Ice, numerous local ice caps and other types of glaciers are found in Greenland and Iceland, whereas the Faroe Islands are unglaciated. Fjords and straits are common.

The mean temperature for the warmest month shows a fall from 10 to 12 °C in the Faroe Islands, Iceland and southern‐most Greenland to 2 °C in the far north and the mean temperature for the coldest month shows a fall from 4 to –34 °C. The precipitation also falls towards the north, from ~4000 mm/year locally on the Faroe Islands and on ice caps in south‐western Iceland to below 200 mm/year in some areas of northern Greenland. The Faroe Islands, Iceland and south‐west Greenland are influenced by northward flowing relatively warm ocean currents, whereas North and East Greenland as well as northern Iceland are influenced by cold, southward flowing currents. The sea off northern Greenland is covered by ice all year round, whereas sea ice is not found in the Faroe Islands, which are characterized by a strongly maritime climate.

The number of native vascular plants is ~520 in Greenland, ~ 460 in Iceland and ~ 250 in the Faroe Islands, which reflects the different areas of ice‐free land. Scrubs, heaths, grasslands, and mires are the main vegetation types, but in the Faroe Islands, Iceland and southernmost Greenland forested areas are also found. In these areas farming is also widespread. Farthest to the north, at 83°N, areas of polar desert, where no woody plants can survive, are found. Fell fields with scattered plants are found on windy places where the snow is blown away during the winter. The number of indigenous beetles is ~36 in Greenland, ~ 150 in Iceland and ~ 160 in the Faroe Islands.

Figure 1 Map of the North Atlantic region showing the location of place names used in the text.

The famous, deep ice cores from the Greenland ice sheet have provided a wealth of detailed information about regional climate history during the past 123 000 years. However, the ice cores have only provided little information about past plant and animal life. The only exception is the basal ice from DYE3 which contains ancient DNA. Most information on interglacial biotas in the North Atlantic Islands comes from open geological sections formed by river erosion or coastal erosion. In contrast, interglacial sediments have been discovered in a number of lakes on Baffin Island in eastern arctic Canada (e.g. Miller et al. 1999). Most of these lake records are confined to the last interglacial stage, but in one lake succession, sediments from several interglacial stages are found (Briner et al. 2007).

The North Atlantic Islands were repeatedly glaciated during the Quaternary glacial stages and only glimpses of the pre‐Holocene history are available. Nevertheless, the scattered occurrences of interglacial deposits give a fairly detailed picture of plant and animal life as well as climatic changes. Holocene deposits are much more widespread than pre‐Holocene deposits, and detailed studies of changes of climate, vegetation history as well as flora and fauna history have been conducted. Late glacial lake deposits have been found in northern Iceland and in southernmost Greenland.

Figure 2 Stratigraphical overview of the Quaternary (the last 2.6 Ma) showing ages of interglacial deposits from the North Atlantic islands. Fm: formation.

This review focuses on non‐marine biotas. We present data for the Quaternary, the last 2.6 million years (Ma), and cover the Faroe Islands, Iceland and Greenland. In a geological sense the postglacial, or Holocene, is also an interglacial stage, and we include some notes on Early and Middle Holocene biotas. We focus on vascular plants and beetles but also summarize data on other taxa where available. Pollen, spores, plant macro‐fossils and animal fossils have been studied. Figure 1 shows the location of place names used in the text and Figure 2 provides a chronological overview. When discussing radiocarbon ages we use ages calibrated to calendar years BP.

Marine interglacial deposits in the North Atlantic Islands were first described in the 1800s, but description of non‐marine deposits followed later. In the Faroe Islands only a single interglacial deposit has been located, which was studied by Rasmussen (1972), Jóhansen (1985), Wastegård et al. (2005) and recently by Bennike et al. (2018). Data on the Early to Mid‐Holocene biotic history were presented by Jóhansen (1985), Bennike et al. (1998) and Hannon et al. (2003, 2010). So far, no late glacial deposits have been recovered in the Faroe Islands.

In Iceland, plant fossils from interglacial deposits were first described in the 1930s (Áskelsson 1938; Líndal 1939) and a review of the palaeobotany of Pleistocene deposits in Iceland was recently provided by Grímsson (2011). The oldest interglacial plant‐bearing deposits are from the Early Quaternary, and the youngest interglacial deposits with plant and invertebrate remains probably date from the last interglacial period. Pollen analyses and macro‐fossil analyses of late glacial and Early Holocene deposits in Iceland were conducted by Rundgren (1995, 1998) and Rundgren and Ingólfsson (1999). Studies of the Early to Mid‐Holocene vegetation history of Iceland have been published by, for example, Caseldine (2001), Wastl et al. (2001), Hallsdóttir (1995), Hallsdóttir and Caseldine (2005) and Caseldine et al. (2006).

In Greenland non‐marine interglacial biotas were not documented until 1979, when the Kap København Formation was discovered (Funder and Hjort 1980; Funder et al. 1984, 1985, 2001; Bennike 1990; Böcher 1995). The first description of Late Quaternary interglacial biotas in Greenland was published by Meldgaard and Bennike (1989). Later on, near‐shore marine deposits with washed‐out remains of plants and invertebrates were discovered in North‐West and East Greenland in the 1990s (Funder 1990; Bennike and Böcher 1992, 1994; Funder et al. 1994, 1998; Hedenäs 1994; Hedenäs and Bennike 2003; Böcher 2012). Remains of southern extra‐limital plants and beetles have been discovered at several sites. Southern extra‐limital species are species that only occur south of the fossil locality at present. Interglacial deposits in Greenland with non‐marine biotas are mainly dated to the Early Quaternary and to the last interglacial stage, the Eemian. Analyses of Holocene non‐marine floras and faunas were initiated by Iversen (1954) and followed up by Fredskild, Funder and Bennike (e.g. Fredskild 1973, 1983, 1985; Funder 1978, 1979; Bennike et al. 1999, 2008a,b; Bennike 2000a; Wagner et al. 2008; Bennike and Wagner 2012; Wagner and Bennike 2012). In addition to pollen, plant macro‐fossils and insect remains have been studied. Arthropod remains from Early to Mid‐Holocene deposits have been reported by, for example, Fredskild et al. (1975), Böcher and Fredskild (1993), Böcher and Bennike (1996), Bennike et al. (2000, 2004) and Böcher et al. (2012).