This article was researched and written by a student at Texas Tech University participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors, and by independent experts on each topic.
The Arctic region surrounds the Earth's North Pole, but its geographic limits have been variously described according to climatological, biological, cryospheric, cultural, and political criteria. Perhaps the most common (and technical) definition refers to that area North of latitude 66 degrees, 33 minutes North (the Arctic Circle). Within this region, there is at least one day each year in which the sun does not rise (polar night) and one in which it does not set (midnight sun).
The Arctic is almost equal in size to North America. It includes the Arctic Ocean and portions of Canada, Greenland, Russia, the United States of America, Iceland, Norway, Sweden and Finland. According to the Oxford English Dictionary, "Arctic" is derived from the Greek word 'arktikos' which means 'of the bear', or 'northern' (from the Greek 'arktos', a bear), referring to the constellation Ursa Major ('Great Bear') an important constellation seen in the Northern Hemisphere which was observed never to disappear, i.e. set, within the realms of the Arctic.
There are two main climate classifications in the Arctic: polar maritime climates, which include coastlines and islands near the Atlantic and Pacific Oceans, and polar continental climates (Arctic tundra), including areas in Alaska, Canada, and Siberia.
Polar continental areas experience winter weather from August or September through to March. During this time, temperatures range from about -35° F (-37° C) on average to lows of -65° F (-54° C). Most of the Arctic sees periods during the winter where the sun does not rise for many days. Conversely, in the summer, there are many days when the sun never sets. Polar continental climates are extreme in terms of temperature, but there is relatively little snowfall in most places. Precipitation is heaviest during the summer months for continental areas.
Polar maritime climates are relatively mild in comparison in terms of temperature and tend to involve a large amount of snowfall. The winter months are stormy and windy, and the temperature generally hovers around 20° F (-7° C). Summer temperatures range from as low as 20° F (-7° C) to as high as 80° F (27° C) across the Arctic, but the pleasant, warmer weather can quickly turn stormy.
Smaller sub-categories of climate zones include “ice” climates, the polar basin climate, and subarctic climates.
Much of the Arctic Circle is covered with permafrost, which is defined as any rock or soil that maintains a below-freezing temperature for at least two years. permafrost may or may not actually contain any ice. The upper layer of the frozen ground (the top 30-100 cm) is called the “active layer,” as it goes through annual periods of thawing and freezing due to seasonal temperature fluctuations. There is a thickness and coldness gradient going from the southern boundaries of the Arctic to the northernmost areas, based on climate. Areas can be categorized as having sporadic, discontinuous, or continuous permafrost. In some “continuous” permafrost areas, the ground may have been frozen for thousands of years. Permafrost poses many problems to the environment and its inhabitants. Ecological systems and human residential areas and infrastructure can be negatively affected by melting ice and landslides prompted by the thawing ground.
Arctic plants are well adapted to their unforgiving environment, which exposes them to extremely cold winters, harsh winds, blowing snow, and conditions of permafrost. Most of the plants have expedited life cycles adapted to short growing seasons, especially in the northern parts of the Arctic.
Just as there are two main climate classifications in the Arctic, there are also two main vegetation zones: the subarctic to the south and the tundra to the north. The bottom of the tundra zone is typically marked as the top of the boreal forest tree-line. Despite the presence of permafrost and lack of extensive precipitation, the tundra sustains many types of shallow-rooted plants. The sub-arctic forest is somewhat warmer in climate and is home to an even greater diversity of plants.
Vegetation in the subarctic zone, south of the treeline, can consist of spruce (Picea spp.), fir (Abies spp.), larch (Larix spp.), mountain ash (Sorbus americana), birch (Betula spp.), and many other distinctive plants. The types of trees in this zone vary from location to location. Although the boreal forest “treeline” is generally used as a marker for the transition from subarctic to tundra zones, some small shrub-like trees can be found in the lower parts of the tundra.
The tundra can be sub-categorized into the Low Arctic Tundra, the High Arctic Tundra, and Middle Arctic Tundra. Each of these ecoregions is characterized by a unique vegetation pattern. The Low Arctic Tundra has continuous permafrost with active layers that melt during the summer. This region is dominated by shrubby vegetation, including black spruce, white spruce, dwarf birch, and willow, in addition to herbs and lichens. The Low Arctic Tundra is a transition zone between the subarctic and tundra zones. The Middle Arctic tTundra is characterized by a decreasing occurrence of shrubs towards its northern boundary, which is caused by unfavourable weather conditions for such plant growth requirements. However, there is fairly uniform herb and lichen coverage. The coastal areas of this ecoregion generally have more vegetation due to comparatively milder weather conditions. The High Arctic Tundra region has the harshest climate and growing conditions of the three tundra ecoregions. Despite this, many plants and fungi are able to grow in certain areas. Moss, lichen, sedge, and cottongrass grow in the North. Southern areas include such herbs as the Arctic poppies (Papaver spp.), wood rush (Luzula spp.), wire rush (Juncus arcticus), and moss.
The Arctic zone has less wildlife diversity than many other ecosystems, but there are a number of animals that are specially adapted to its harsh environment. Many of these animals can be found across much of the Arctic at some point during each year.
A few of the more prominent Arctic land mammals include Arctic foxes (Alopex lagopus), caribou (Rangifer tarandus), lemmings (Dicrostonyx & Lemmus), muskoxen (Ovibos moschatus), and polar bears (Ursus maritimus). The Arctic fox preys on small birds and mammals and has a camouflaging coat that is grey in summer and white in winter. Caribou are large deer that migrate throughout the Arctic. Caribou are renowned for their great swimming abilities and are well adapted to the tundra environment. Lemmings are small vole-like mammals that burrow into the ground and live in the tundra. Muskoxen are large herding bison-like animals more closely related to sheep than they are to cattle. Their thick wool-like fur and large feet are among the many adaptations that they have for life in the Arctic. The Arctic wolf (Canis lupus arctos) is the main predator of the Muskoxen as well as the Caribou. The most familiar land-based predator, however, must be the Polar bear. Unique among Arctic land mammals, these giant bears spend most of their time near water hunting for fish and seal, traveling deep into pack-ice regions to find their prey.
Among the birds, snowy owls (Bubo scandiaca) live primarily in Arctic regions. They are unusual in that they do not 'migrate' south during the winter, but they do undergo 'irruptive dispersal', that is moving out of their breeding areas when their main prey, the lemming, suffers a declining population. At these times they can be found much further South. Unlike most other owls, Snowy owls are daytime hunters. The birds are also unusual within the Owls (Strigiformes) in being sexually dimorphic in coloration, with the male being almost pure white, the female being heavily barred. Ptarmigans (Lagopus spp.) are also characteristic birds of the tundra, remaining in the same area all year round. Like the snowy owls, major plumage differences exist, although while they do show sexual dimorphism, it is their seasonal variation in coloration that is most notable. These birds tend to have grey and brown plumage in summer, thus blending in with the lichens, vegetation and bare ground exposed during this period, and white in winter, when snow and ice predominate. The tundra is also home to several species of migratory birds, including shorebirds (Charadriiformes).
The Arctic Ocean
With an area of only 14.056 million sq km, the Artic Ocean is the smallest of the world’s oceans. A few of the more prominent areas of the Arctic Ocean include Baffin Bay, Beaufort Sea, Chukchi Sea, East Siberian Sea, Greenland Sea, Hudson Bay, Hudson Strait, Laptev Sea, and the Northwest Passage. Much of the central section of the Ocean is covered by a persistent icepack that expands in size during the winter and shrinks during the summer. Icebergs, glaciers, and ice islands make navigation potentially dangerous in many areas. Some Arctic sea mammals include the beluga whale, orca whale, sea otter, seal, and walrus.
Currently, the major environmental concern for the Arctic is global climate change. On the whole, the warming of Arctic temperatures is beginning to seriously impact the region. Huge areas of permafrost and ice sheets are melting, with a consequent increased occurrence of landslides and erosion, while the coastal landscape is beginning to change noticeably. Even the subartic tree flora is on the move North, invading pristine areas of tundra. Although there is much dispute in the scientific community about the ultimate outcome of this warming trend, there is no doubt that the Arctic is undergoing massive changes. Some scientists even believe that all of the ice in the Arctic will melt within the next fifty years.
One specific example of the negative ramifications of global warming is the case of polar bears, which are facing an increasing threat of imminent extinction. These giant white bears spend most of their time out on ice-covered sections of the Arctic Ocean hunting for seals and fish. They also use ice for migration routes and a place to raise their young. Changes in ice coverage could alter their normal living patterns, reduce their ability to hunt efficiently and thus reduce their chances of survival, which in turn affects the population biology of the species with more animals dying than normal. This has knock-on effects as it reduces their ability to recover from population crashes, further hindered by their naturally low reproductive rates, and leading to increasingly lower numbers of individuals and an already erratic distribution for the species as a whole.
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