Edited by Rachel Duncan 4th Edition ISBN 0-907649-91-2 London ...

The Polar Environment 7
except for powerful icebreakers. The tidal zone is lifeless. Vegetation is much reduced and
consists of rock desert, there being no real heaths, shrubs or willow copse.
The Low Arctic has a much greater snowfall and winters are not so cold or long,
often showing periods of thaw and refreeze. For this reason, the periglacial
geomorphologist will find much to study. Summertime is more extended and milder with a
July mean of 5–10°C. The coasts are ice-free for varying but longer periods. Protected
bays and fjords are ice covered even into the beginning of summer, but open coasts may be
ice-free all year. The tidal zone is inhabited by a considerable number of animals and the
vegetation very often forms a continuous mat of dwarf bush heath mixed with copses of
willow and shrub.
There are four boundaries commonly held to define the Antarctic: the most widely
accepted is the Antarctic convergence: a belt of water, in places only a few kilometres
wide, separating Antarctic surface water from slightly warmer and more saline sub-
Antarctic surface water. It is detectable at the surface by a sudden sharp gradient in sea
temperature; the other boundaries include the 10°C July isotherm, the northern limit of the
pack ice and the Antarctic Circle, which is defined in the Antarctic Treaty as 60°S. The
Antarctic covers a great deal more than the continent its self, including the sub-Antarctic
islands; e.g. the South Orkney, South Shetland and South Sandwich islands.
1.2 Special aspects of the polar regions
1.2.1 Magnetic poles
The magnetic poles lie some distance from the true poles. They do not align with the poles
of rotation because the electric currents that cause the magnetism are affected by magnetic
rocks in the Earth’s crust. The magnetic poles wander and the North Magnetic Pole has
drifted more than 750km since its discovery by James Clark Ross in 1831. The notional
‘geomagnetic’ poles are artificially calculated points based on where the magnetic poles
would be if they lay at either end of a straight bar magnet. The positions of these affect the
positions of the Aurora.
1.2.2 Aurora Borealis and Aurora Australis
The Aurora Borealis/Australis (Northern and Southern Lights) are caused by electrically
charged particles streaming from the sun and hitting the upper atmosphere and diverting
towards an oval ring centred on the geomagnetic pole (hence their appearance in polar
regions). They are at their best in the vicinity of this ring which tends to be nearer the polar
circle. See Pielou (1994) for more coverage.
1.2.3 Day length
Over the year, due to the tilt of the earth’s axis, the period of daylight varies far more in
polar than in temperate regions and even at 60° latitude there is almost twenty-four hour
daylight for the month spanning mid-summer; at higher latitudes continuous daylight lasts
even longer. Conversely, at either end of the summer season, short daylight can
considerably constrain travel. Twenty-four hour daylight sounds attractive but you must
still schedule sensible work and rest periods. Poor travelling surfaces can also result from
long summer days and many expeditions prefer "night" travel when the sun is lower,
resulting in cooler air temperatures and snow surfaces more likely to be frozen.