- Arctic Ocean
- Peoples of the Arctic
- The fauna and the flora
The name of the Arctic comes from the Great Bear constellation, located to the north (arctos = bear (Greek)). This region takes in the Arctic Ocean, a large part of which is permanent ice (sea-ice) and the north of the continents which surround it: including the Scandinavian Peninsula, the north of Russia and Siberia, of Alaska, Canada, Greenland and Spitsbergen. The geopolitical situation of the Arctic is very different from that of the Antarctic. In fact, the territories concerned are all possessions of the countries encircling the Arctic Ocean (Norway, Russia , Canada, and so on).
Spitsbergen, and the whole of the Svalbard Islands, is dependent on Norway. However, the archipelago is governed by the 1920 Treaty of Paris signed by 14 countries, subsequently ratified by more than 40 nations. In 1925, Svalbard became an integral part of the kingdom of Norway. However, the terms of the treaty, give the citizens of several different countries the right to exploit the natural resources “on absolutely equal terms”. It also declares the complete demilitarization of the islands, but permits the establishment of scientific research stations. For this reason a considerable international community of scientists is based at Ny Ålesund, the location of the French bases Jean Corbel and Charles Rabot.
If the limits of the Arctic Ocean (13 000 000 km² and more than 4000 m depth) are perfectly defined, how can the border of the Arctic regions on land be fixed? By the Arctic Circle, the treeline or by the limit of the land that is constantly frozen at depth, the permafrost? The most commonly recognized answer is the line within which the air temperature never exceeds 10°C during the warmest months (July). This isotherm, called the Köppen line, coincides quite well with the transition from boreal forest (taiga) to tundra. According to this, the Arctic would stretch over an area of about 24 million km², including 17 million of ocean, a little more than 3 million of continent and nearly 4 million of scattered islands, from the Aleutians to Labrador, with its maximum diameter exceeding 7000 km.
The North Magnetic Pole Drift
The North Magnetic Pole is defined as the point on the Earth’s surface where the direction of the magnetic field runs exactly vertically downwards. At the North Magnetic Pole, the magnetic dip (the angle between the direction of the field and the horizontal) is 90° and the magnetic declination or variation (the angle between the direction of the field and the geographic North Pole) is not definite. In the same way there is a magnetic South Pole where the magnetic field is exactly vertical upwards.
Care should be taken not to confuse the magnetic poles (North and South) and geomagnetic poles. The latter are defined as the intersection points on the Earth’s surface where the axis of the magnetic dipole passing through the Earth’s centre gives the best first-order approximation of the global magnetic field. Inevitably therefore the geomagnetic North and South poles are antipodal, in contrast with the magnetic poles. The difference between the two types of pole stems from the fact that the Earth’s magnetic field is not exactly dipolar at the scale of the whole globe. This is why, even though all the magnetic meridians converge at the North Magnetic Pole, they do not arrive radially: compasses lead to the North Magnetic Pole without ever pointing in that direction!
James Ross was the first to fix an exact location for the North Magnetic Pole, in 1831. Amundsen followed in 1904. At that time the pole was situated at the Boothia Peninsula in the Far North of Canada. The pole moves around owing to the geomagnetic secular variation, itself induced by convection movements of liquid iron in the Earth’s core. For this reason expeditions were run regularly in the 20th Century to update the position of the pole on the magnetic maps.
The latest in situ determination of the position of the pole was performed by a Franco-Canadian team (L.R.Newitt, A.Chulliat and J.-J.Orgeval, Poly-Arctic project) in April 2007, using several measurements taken in a radius of about 100 km around the pole. The position obtained was 83.95°N, 121.02°W, effectively around 800 km to the north-west of Ellesmere Island. These field observations have been more and more difficult owing to increasing distances and global warming. For several years they have been complemented by satellite measurements.
The North Magnetic Pole drifted quite slowly (less than 10 km/year) towards Siberia from 1834 to 1980. From the mid 1980s, the speed of the drift has been increasing to reach the present-day 55 km/year (still towards Siberia). This speed appears to have stabilized since the beginning of the 2000s. If it continues at the same rate, the North Magnetic Pole will reach Siberia in around 2040.
This quite abrupt acceleration has yet to find a full explanation. It could be linked to an increase in the magnetic field flux in the polar area North of the Earth’s core. This increase could be caused by the expulsion of the lines of the magnetic field from the core, in a mechanism rather like the processes that induce sun spots.
The landscapes in the Arctic are extremely diversified. They include sea-ice, strongly carved coastlines, coastal plains, hills and mountains reaching beyond 6000 metres above sea level (Mount McKinley at 6194 m, in Denali Park in Alaska). Rivers and lakes abound, also tundra, and the region supports the world’s most extensive forests (Russian Taiga).
Sources Digital chart of the world; Institut Géographique National français (IGN). AMAP, 1997. Arctic Pollution Issues: A State of the Arctic Environment Report.
The original Russian term tundra denotes the circumpolar plant community which takes over from the taiga (which supports trees) towards the north. This community grows on soil that is permanently frozen, at least at depth, the permafrost. From south to north, the first type encountered is shrubby tundra with shrub-scattered moorland consisting of a range of species of dwarf willow, open moorland then grasslands (herbaceous tundra), followed by zones where mosses and lichens are the only representatives of vegetation (some of them are eaten by reindeer). All these plants have their growth slowed down by the climatic conditions (freezing, wind, etc.), the alternation between a long winter night and a long summer day and the poverty of the soil. The soil infertility is due to lower bacterial activity: there is very little decomposition of the organic matter that accumulates and gives rise to peat. The short vegetative period is however sufficient to attract a host of migratory birds (eider, black geese (Branta), snow goose, etc.) and make it a zone of intense animal life and reproduction.
This is a mass accumulation of floating ice, formed by freezing of sea water, also known as pack ice. Sea-ice consists of the year’s ice which forms at the beginning of winter (ice-jam) and thaws in spring (break-up) along with older polar ice. It is subjected to tidal movements and drifting driven by marine currents and winds.
The permafrost is a horizon of the subsurface which does not undergo thawing for at least 2 years running. It holds a record of the negative heat balance over a long period (103 years) with an accumulation of ice lenses, especially in the first 10 m of soil.
Its upper horizon thaws each year: this is the active layer where cryoturbation occurs in the form of stones circles. At present the permafrost stretches at low altitude between 57°N on the eastern sides of the continent and 70°N on the western margins. Its thickness varies from 20 m in the South reaching 300 m in the zones not overlain by ice 10 000 years BP and more than 600 m in the non-iced hyper-continental zones of the Quaternary (Siberia). The record depth is held by the Verkhoyansk Range in eastern Siberia where depth exceeds 1000 m. The permafrost can be continuous to the North (> 80% of the surface area), discontinuous (between 30 and 80%) and sporadic to the South (Iceland, Lapland, Quebec).
In the warmest times of the Holocene, 8000 years ago, the permafrost was restricted to the area included within the Arctic Circle. Since then it has again advanced towards the South. Following the fall in summer solar radiation during the Holocene, the current southward spread of the permafrost reaches about 1/3 of the extent it had at the Last Glacial Maximum.
The Russian authors consider the Arctic permafrost to be ancient (7-5 million years). Its thermal mass gave it deep resistance, both to the warming of the Lower Pliocene (4.2 million years BP, when there were palm trees in the Netherlands!) and to the warmest interglacial periods of the recent Quaternary, the Eemian (132-110 000 years BP, with Portuguese fish reaching Denmark !). A large amount of ice formed in the top layer of permafrost during warm humid episodes, for example 8000 years BP. The most recent permafrost is less rich in ice. When this accumulated ice melts the ground collapses: thermokarst or thaw lakes then form. This occurred already in the early Holocene and before the Little Ice Age.
When the permafrost cools down again, it can incorporate peat, blocking the annual production of methane, particularly in the continental subarctic climate zone. Deep down, around 200 m, large quantities of gas hydrates (methane) can build up; these accumulations do not form at shallower depths.
The current climate change
The permafrost is at present undergoing warming, moderated by the buffering effect of its ice mass. It is in particular the winter periods that are warmer. In Spitsbergen, all conditions being equal, the average freezing depth of continuous permafrost is 40 cm compared with the 1980s (ITEX, modelling, CRYOCLYM). In Alaska, Iceland and Spitsbergen, the discontinuous or sporadic forms of permafrost are deteriorating and disappearing. Strong warming of the climate would lead to retraction of permafrost back to its limits of 8000 years BP, although not to its complete disappearance. Most of the permafrost regions are seeing human-activity induced disturbances that favour melting. The case in Siberia or the North of Quebec (deforestation, movement of humans and goods, artificial lakes). The ongoing increase in summer rainfall accelerates this process, as it does for glaciers. Methane generation is currently resuming in thawed-out peat bogs, but the risk of degassing of permafrost-related methane hydrates is practically zero. Coastal areas are being subjected to a rise in sea level, strengthening violence of storms and seeing a lower sea-water freezing point. Factors leading to very rapid degradation of coastal permafrost, even without any particular rise in temperatures.
Brigitte Van Vliet-Lanoe UMR 8110 CNRS Processus et Bilans des Domaines Sédimentaires SN5, Université Sciences et Technologies de Lille 59655 VILLENEUVE D’ASCQ Cédex, FRANCE