Short history of the Arctic environment
Last Ice Age and its importance for recent biodiversity patterns
A large portion of the arctic landmasses were covered by ice during the Last Glacial Maximum (LGM). The extent and timing of the ice sheets during the LGM varied among regions, and therefore, static maps of the LGM ice sheet extension are often misleading when identifying possible glacial refugia.
For those areas that remained ice free, the environment is believed to have been too extreme to support complex ecosystems. For example, no soil fauna is believed to have survived in situ throughout the last glacial episode (Brochmann et al. 2003). Consequently, most of the high Arctic, if not all, must have been colonized from southern populations surviving in unglaciated areas outside of the large ice shield. Recolonization began when the ice started to retreat.
The ice shield reached its maximum extend about 26 000-15 000 years before present (YBP), depending on region. The last areas were deglaciated about 10 000 YBP. This is essential to understand the forces shaping current biodiversity patterns and dynamics of arctic terrestrial ecosystems.
Small ice free areas during LGM are often difficult to infer based on physical parameters; however, they can occasionally be inferred through biological evidence. For example, the number of taxa persisting in situ throughout the Quaternary glaciations have been used to infer the large extension of ice-free ground in the Beringia land bridge area (Fedorov & Stenseth 2002, Abbott & Brochmann 2003, Cook et al. 2005, Weider & Hobæk 2000).
Characteristics of arctic ecosystems during the past 50,000 years
Recent research, based on ancient DNA conserved in permafrost, provided a unique clear picture of arctic ecosystems throughout the late Quaternary (past 50,000 years; Willerslev et al., 2014). For most of this period, dry steppe-tundra dominated by forbs was the characteristic arctic ecosystem. However, diversity declined steeply throughout the Arctic during the LGM. Dry steppe-tundra and mesic climate continued to dominate throughout the LGM in western Beringia and the interior regions of eastern Beringia (Elias & Croker, 2008). Wet tundra did not appear until the end of the glacial period, approximately 10,000 YBP, which is associated with the extinction of the charismatic mammoth (Willerslev et al, 2014).
In most of the eastern Palaearctic, large mammal fossil records remain as an imprinted signature of periglacial ecosystems throughout the Quaternary (Iacumin et al. 2000). On the western end of the Arctic, large areas of north western Greenland and the Canadian Arctic archipelago glacial refugia based on plant community assemblages (Eric Hultén, 1937), and invertebrate assemblages (Avila-Jimenez & Coulson 2011). Most of those areas are supported as LGM glacial refugia by molecular methods (Fedorov & Stenseth 2002, Abbott & Brochmann 2003, Cook et al. 2005, Weider & Hobæk 2000, Skrede et al. 2006, Alsos et al. 2007).
The Barents Sea Archipelagoes since the Last Glacial Maximum
Svalbard and Frans Josef Land were largely covered by ice during the LGM (Gataullin et al., 2001) and were exposed progressively as the ice began to retreat approximately 10,000 YBP. It is likely that few, if any, plants survived in situ during the LGM (Alsos et al., 2007), although a number of recent studies, both biological and glaciological, have hinted at the possible existence of refugia (Landvik et al., 2003; Westergaard et al., 2011). The south island of Novaya Zemlya remained ice free with shrub vegetation (Serebryanny et al., 1998; Velichko, 2002). The relatively short period since deglaciation, combined with the arctic climate and continuing periglacial soil processes, have strongly influenced habitats and ecosystems.