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State and trends


Extreme climate events, such as winter thaws, happen more frequently and may accelerate shifts in ecological community structure and processes. As Arctic ecosystems are interdependent, changes in the frozen environment are altering physical, biophysical, and biological links. All of these climate-related effects are compounded by rapid socio- economic development in the North, creating additional challenges for northern communities and indigenous lifestyles that depend on Arctic ecosystem services (Vincent et al. 2011).


Regional consequences of Arctic warming include the alteration of watersheds by glacial melt and the loss of large ice sheets. This melting leads to the exposure of coastlines not previously subject to coastal erosion, which is compounded by a rise in sea levels and increased vulnerability to extreme weather conditions (NRC 2008). Combined with thawing permafrost, this affects the migration patterns of larger animals, changing or denying access to seasonal habitat and altering the local balance between predator and prey (NRC 2008).


2.7.7 Marine ecosystems


The melting of sea ice has created new expanses of open ocean, allowing large populations of phytoplankton to bloom and alter the marine food chain. On land, shrublands are expanding into the tundra and invasive insects are spreading across the forests. As Arctic summers warm and the ice-free season lengthens, more species from the south migrate northward. Competition from these species for food and other resources could potentially lead to major ecosystem reorganization and species extinction. Arctic ecologists are particularly concerned about tipping points: thresholds at which a small change in climate could precipitate abrupt, major, and irreversible ecological consequences (Schuur et al. 2015; Everett et al. 2014).


Vegetation in the high Arctic is affected by continuing summer land-temperature increases resulting from sea ice loss. Areas marginal to perennial sea ice and the margins of the large glaciers will see the most rapid changes as ice


vanishes (Bhatt et al. 2010). The decline of sea ice affects marine mammals throughout their key life history stages. Ice-obligate species–polar bears, walruses, and some seals– need sea ice as a platform for hunting, birthing, and rearing young. And, while some seal species are fully adapted to sea ice habitats, they sometimes reproduce and feed from shore, so are considered ice-associated species. The three endemic Arctic cetacean species are also ice associated, and at least five cetacean species migrate to and occupy Arctic habitats, primarily during the productive summer–autumn season (Bhatt et al. 2014; Figure 2.7.5).


2.7.8 Terrestrial ecosystems


The expected and partially observed increased primary productivity of Arctic tundra may increase the supply of food for Arctic ungulates. However, the overall quality of forage may decline during warming, for example, if the nitrogen content of key fodder species for ungulates dropped. At the same time, lichen biomass, an important winter fodder for reindeer, is decreasing over parts of the Arctic region (Joly et al. 2009; Turunen et al. 2009).


More frequent rain-on-snow icing events and thicker snow packs, caused by warmer winters and increased precipitation, may restrict access to vegetation and have profound negative influences on the population dynamics of Arctic ungulates (Hansen et al. 2011). Heavy mortality due to such conditions has been documented in some semi-domestic reindeer herds and musk oxen in recent years (Bartsch et al. 2010; Forbes et al. 2009; Grenfell and Putkonen 2008). Studies also document that these icing events affect the dynamics of a resident vertebrate community–including small mammals, reindeer, and Arctic fox–in Svalbard (Hansen et al. 2013). In contrast, Tyler et al. (2008) and Tyler (2010) suggested that generally warmer winters enhance reindeer populations.


Warming-induced mismatches between forage availability and quality, and timing of calving may have a role in the decline of circumpolar reindeer and caribou populations (Post et al. 2009a; b; Post and Forchhammer 2008), although


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