The Arctic is not an easily definable geographic entity similar to, for example, Iceland, Lake Baykal, or even the Antarctic. Therefore, until recently, it has not been possible to arrive at any single definition of the area. Since the 1870s a large number of researchers representing different disciplines such as geography, climatology, and botany have tried to establish a widely acccpted criterion to delimit the Arctic boundary (Figure 1.1). In almost all the geographical monographs and other books dealing with Arctic or Polar regions one can find a variety of attempted definitions (e.g. Bruce 1911; Brown 1927; Nordenskjold and Mecking 1928; Baird 1964; Sater 1969; Sater et al. 1971; Baskakov 1971; Petrov 1971; Barry and Ives 1974; Weiss 1975; Sugden 1982; Young 1989; Boggs 1990; Stonehouse 1990; Barry 1995; Bernes 1996; Przybylak 1996a; Niedzwiedz 1997; Mills and Speak 1998). However, the most comprehensive reviews have been given by Petrov (1971) and Baskakov (1971). The oldest conception of the Arctic is one which considers it to be a region of the Northern Hemisphere tying north of the Arctic Circle (<p = 66°33'N). The majority of the above authors agree that this astronomically distinguished line of latitude cannot be considered to be the real Arctic boundary. This fact was noted as early as 1892 by Bruce (Bruce 1911) and later in 1927 by Brown, who wrote, "The Arctic and Antarctic circles merely mark the equatorial limits of the zones in which the sun is never more than 23°30' above the horizon. [...] The circles are astronomical lines without climatic significance." The careful reader will note that here Brown gives the wrong value of the height of the sun. The correct value is 47° and can be ascertained using the formula h = 90° - <p + 5 where <p is the geographical latitude and 8 is the declination of the sun.
A more meaningful and more frequently used definition of the Arctic is a climatological one. Among the many known climatic criteria, the most popu lar is still the older proposition given by Supan (1879, 1884), i.e. the 10°C mean isotherm of the warmest month. This criterion was later modified, first by Vahl (1911) and then by Nordenskjoid (1928). Vahl did not determine the precise borders of the Polar regions, but, as he seems to have let it coincide with the tree line, he regarded the equation V < 9.5° - 1/30 K to be the most favourable for the determination of the position of this boundary. In this formula V and K denote the mean temperature of the wannest and coldest months, respectively. Nordenskjoid (1928) found that the role of the coldest month in determining the Arctic boundary should be greater than was assumed Vahl (1911). Therefore, he proposed a new formula: V<9°-0.1 K. In addition, he also extended it to the seawater areas (see Figure 1.1). According to this criterion the Arctic includes regions in which the temperature of the warmest month ranges from 9°C (when the temperature of the coldest month is 0°C) to 13°C (when the temperature of the coldest month is -40°C).
The boundary of the Arctic can also be drawn using the criterion proposed by Gavrilova (1963) and Vowinckel and Orvig (1970). According to them, all areas where the net radiation balance is lower than 62.7 kJ/cm2 /year (15 kcal/ cm2 /year) may be considered to belong to the Arctic (Figure 1.1).
The authors of the Atlas Arktiki ( 1985) have recently presented a new, very good, proposition. The southern Arctic boundary has been delimited using mean long-term values of almost all meteorological elements. Thus, the concept of climatic régionalisation is employed. The Arctic perimeter on the continents lies mostly between the boundaries of the 10°C mean isotherm of the wannest month and the so-called Nordenskjold line (Figure 1.1). In addition, the authors of the Atlas have also distinguished seven climatic regions within the Arctic (Figure 1.2). These facts have persuaded me to adopt their definition of the Arctic for the purposes of this monograph.
The third criterion quite often used (aside from astronomical and climatológica! criteria) is a (geo)botanical one. The southern boundary of the tundra or the northern boundary of the tree line is considered to be the natural boundary of the Arctic. Supan (1879, 1884), in his classification of climates, was probably the first to distinguish the Arctic area using both climatological and gcobotanical criteria. The areas distinguished show a good corrélation and most other later analyses confirm Supan's finding. Sugden ( 1982) presents several advantages of using the tree line to delimit the southern land boundary of the Arctic. He writes, "Not only does it represent a fundamentally important vegetation boundary, but it is also important in terms of animal distributions. It coincides approximately with a mean July temperature isotherm of 10°C and thus is also of climatic significance." However, one must be aware that there arc also some disadvantages of this criterion. For example, as many as three possibilities to define the boundary of the Arctic can be used: a northern limit of continuous forest, a northern limit of erect trees, or a northern limit of species. For more details see Hare (1951) and references therein.
Almost all the above-presented criteria should be used exclusively with reference to land Arctic regions. However, in the present analysis wc also need to establish boundaries over sea areas. A number of researchers, mainly oceanographers, have suggested replacing the boundary at sea delimited using the above criteria with a boundary delimited using more appropriate criteria for a water environment. For example, Baskakov (1971) suggests that the boundary of the Arctic in the sea areas should be drawn according to oceanological characteristics, i.e. hydrological, ice, and géomorphologie. He has provided us with the most comprehensive definition of the oceanic Arctic region and I cite here only the most important fragment: "Those water areas may be considered part of the oceanic Arctic region which, during the cold period of the year, are generally (average outflow over a several year period) covered by sea ice of various ages including perennial ice, and in which the upper layer of water under the ice (of a depth of not less than 30 m) has negative temperature and low salinity (less than 34.5%o)." Simply speaking, as a sea boundary of the Arctic one can accept the southernmost extent normally reached by the Arctic Waters.
At the end of this section one should also mention the opinion of some researchers (Armstrong et al. 1978; Sugden 1982; Stonehouse 1990) who are convinced that it is practically impossible to achieve a delimiting of the précisé boundary of the Arctic which will gain the acceptance of scientists from different disciplines. Sugden (1982) has written, "...the boundaries should remain flexible. Some boundaries seem appropriate for some purposes and other boundaries for others." To a certain extent it is possible to agree with this view. However, I think that an Arctic boundary should be at least agreed on among scientists of the same discipline, e.g. among climatologists. In an era of global warming, this is becoming more and more urgently needed. Otherwise, our estimations of mean Arctic climatic trends may be equivocal (see Prcybylak 1996a, Przybylak 2000a, 2002a).
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