Ecoregions of the Oceans
3
3.1
500 Polar Domain
At times, or during the winter, ice of the Arctic or
Antarctic Oceans covers these regions. They are
characterized, in general, by ocean water that is
greenish, low in temperature, low in salt content,
and rich in small, sometimes microscopic plant
and animal organisms, known as plankton. The
duration of ice provides a basis for division into
(a) an inner polar zone (division) covered by ice
for the entire year, and (b) an outer polar zone
(division) where, with a 50 % probability, ice is
encountered during winter and spring. Figure 3.1
shows the global locations of the polar
ecoregions of the oceans.
3.1.1 510 Inner Polar Division
In the Arctic region, the inner polar region
includes the deep Arctic basin and the northern
passages of the Canadian Archipelago; in the
Antarctic region it includes a narrow belt around
the Antarctic ice shelf. This is the region that
Dietrich (1963) designates as Bi. Although the
region is always covered with ice, the ice itself is
in continuous motion, clockwise around the
poles. In the Northern Hemisphere this area is
free of icebergs, because no glaciers touch this
region. Hummocked pack ice forms impenetrable ridges with intermittent leads and openings
here and there, due to severe ice pressure. In
contrast, the central parts of the inner polar
region are relatively flat, pack-ice fields.
The Arctic Ocean, which is surrounded by
landmasses, is normally covered by pack ice
throughout the year, although open leads are
numerous in the summer. The relatively warm
North Atlantic drift maintains an ice-free zone
off the northern Coast of Norway. The situation
is quite different in the Antarctic, where a vast,
open ocean bounds the sea ice zone on the equatorward margin. Because the ice flows can drift
freely north into warmer waters, the Antarctic ice
pack does not spread far beyond 60
S latitude in
the cold season.
Air temperatures are generally below freezing, and the annual variation of air temperature is
large. Because of the low air temperatures and
the resultant low capacity of the air to hold moisture, the annual amount of precipitation is very
small, but exceeds evaporation.
3.1.2 520 Outer Polar Division
Adjacent to the inner polar region lies the outer
polar region, which is regularly covered by pack
ice during winter in both hemispheres. It is classified as Ba¨ in the Dietrich system. Pack ice does
not originate within this region. It represents ice
carried into this region by oceanic currents from
the inner polar region, and forms fields of drifting
ice that will gradually melt. Oceanic currents
considerably influence the position of the
boundaries of this region. With the cold East
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_3, # Springer Science+Media, LLC 2014
17
3
3.1
500 Polar Domain
At times, or during the winter, ice of the Arctic or
Antarctic Oceans covers these regions. They are
characterized, in general, by ocean water that is
greenish, low in temperature, low in salt content,
and rich in small, sometimes microscopic plant
and animal organisms, known as plankton. The
duration of ice provides a basis for division into
(a) an inner polar zone (division) covered by ice
for the entire year, and (b) an outer polar zone
(division) where, with a 50 % probability, ice is
encountered during winter and spring. Figure 3.1
shows the global locations of the polar
ecoregions of the oceans.
3.1.1 510 Inner Polar Division
In the Arctic region, the inner polar region
includes the deep Arctic basin and the northern
passages of the Canadian Archipelago; in the
Antarctic region it includes a narrow belt around
the Antarctic ice shelf. This is the region that
Dietrich (1963) designates as Bi. Although the
region is always covered with ice, the ice itself is
in continuous motion, clockwise around the
poles. In the Northern Hemisphere this area is
free of icebergs, because no glaciers touch this
region. Hummocked pack ice forms impenetrable ridges with intermittent leads and openings
here and there, due to severe ice pressure. In
contrast, the central parts of the inner polar
region are relatively flat, pack-ice fields.
The Arctic Ocean, which is surrounded by
landmasses, is normally covered by pack ice
throughout the year, although open leads are
numerous in the summer. The relatively warm
North Atlantic drift maintains an ice-free zone
off the northern Coast of Norway. The situation
is quite different in the Antarctic, where a vast,
open ocean bounds the sea ice zone on the equatorward margin. Because the ice flows can drift
freely north into warmer waters, the Antarctic ice
pack does not spread far beyond 60
S latitude in
the cold season.
Air temperatures are generally below freezing, and the annual variation of air temperature is
large. Because of the low air temperatures and
the resultant low capacity of the air to hold moisture, the annual amount of precipitation is very
small, but exceeds evaporation.
3.1.2 520 Outer Polar Division
Adjacent to the inner polar region lies the outer
polar region, which is regularly covered by pack
ice during winter in both hemispheres. It is classified as Ba¨ in the Dietrich system. Pack ice does
not originate within this region. It represents ice
carried into this region by oceanic currents from
the inner polar region, and forms fields of drifting
ice that will gradually melt. Oceanic currents
considerably influence the position of the
boundaries of this region. With the cold East
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_3, # Springer Science+Media, LLC 2014
17