(poleward of the polar front) and a Wa¨ region
(equatorward of the polar front).
Deep-reaching mixing processes are present
in these regions. The associated high-nutrient
concentrations provide an opportunity for plankton to develop abundantly. Plankton provides
nutrition for great numbers of commercial fish,
especially on the continental shelves. The
shelves provide other sources of nutrition and
also serve as spawning grounds. For this reason,
the Grand Banks, the banks west of Greenland,
around Iceland, and the Faroes as well as the
shelf of Europe have become the main grounds
of high-sea fishing. Oceanic islands in these
regions, such as the Crozet Islands in the South
Indian Ocean, have Antarctic birds and mammals
which exist because of food chains that start in
these seas (Fig. 3.3).
3.2.2 630 Subtropical Division
Between the region of the trade wind currents, P
in the Dietrich system, and the region of the
westerlies, lies a region of transition designated
by the symbol, R. In this region, weak currents of
variable direction exist. This region is associated
with the subtropical high, which is associated
with weak winds—called the horse latitudes at
about 25
–30
north and south of the equator.
The horse latitudes are said to be so called from
the throwing overboard of horses in transport
from Europe to North America if the ship’s passage were delayed by calms.
Trade winds and westerlies flow around the
interior region of the horse latitudes. This causes
an accumulation of light surface water in the
center of the eddy. A deep, homogeneous,
warm, top layer is established, which is also
very saline because of the excess of evaporation
over precipitation (see Fig. 2.5, p. 13). No other
regions in the world ocean have higher temperature and salinity.
The R regions are also characterized by an
extremely low nutrient content since planktons
have consumed the nutrients. Therefore, the biomass assumes its smallest value in the surface
waters, such as in the Sargasso Sea in the central
R region of the North Atlantic Ocean. In contrast,
the absolute maximum of organic production in
the ocean has been found in the region of upwelling off Southwest Africa (see Fig. 2.4, p. 12).
As a consequence of very low plankton content, these regions are distinguished by extremely
clear, transparent water, which shows a deep
cobalt blue color. They are generally smooth
seas because storms rarely touched them.
3.2.3 640 High-Salinity Subtropical
Division
The high-salinity regions are not designated as
a separate variety by Dietrich, which Elliott
(1954) designates as type H. They have been
incorporated into the system presented in this
book. These regions are represented by the Mediterranean Sea, the Red Sea, and the Black Sea.
Continental influences are extremely strong
because the individual units are almost landlocked and water exchange with the oceans is
very slow. Each unit shows a strong individuality, but nevertheless certain characteristics permit grouping them into one major type. These
common characteristics are: almost landlocked
position, extremely strong continental influence,
wide range and variation of temperatures, wide
range of salinities, wide variation of air
Fig. 3.3 Elephant seals and penguins on the Crozet
Islands, South Indian Ocean. Photograph by Douglas
Mawson; from the American Geographical Society
Library, University of Wisconsin-Milwaukee Libraries
20
3 Ecoregions of the Oceans
(equatorward of the polar front).
Deep-reaching mixing processes are present
in these regions. The associated high-nutrient
concentrations provide an opportunity for plankton to develop abundantly. Plankton provides
nutrition for great numbers of commercial fish,
especially on the continental shelves. The
shelves provide other sources of nutrition and
also serve as spawning grounds. For this reason,
the Grand Banks, the banks west of Greenland,
around Iceland, and the Faroes as well as the
shelf of Europe have become the main grounds
of high-sea fishing. Oceanic islands in these
regions, such as the Crozet Islands in the South
Indian Ocean, have Antarctic birds and mammals
which exist because of food chains that start in
these seas (Fig. 3.3).
3.2.2 630 Subtropical Division
Between the region of the trade wind currents, P
in the Dietrich system, and the region of the
westerlies, lies a region of transition designated
by the symbol, R. In this region, weak currents of
variable direction exist. This region is associated
with the subtropical high, which is associated
with weak winds—called the horse latitudes at
about 25
–30
north and south of the equator.
The horse latitudes are said to be so called from
the throwing overboard of horses in transport
from Europe to North America if the ship’s passage were delayed by calms.
Trade winds and westerlies flow around the
interior region of the horse latitudes. This causes
an accumulation of light surface water in the
center of the eddy. A deep, homogeneous,
warm, top layer is established, which is also
very saline because of the excess of evaporation
over precipitation (see Fig. 2.5, p. 13). No other
regions in the world ocean have higher temperature and salinity.
The R regions are also characterized by an
extremely low nutrient content since planktons
have consumed the nutrients. Therefore, the biomass assumes its smallest value in the surface
waters, such as in the Sargasso Sea in the central
R region of the North Atlantic Ocean. In contrast,
the absolute maximum of organic production in
the ocean has been found in the region of upwelling off Southwest Africa (see Fig. 2.4, p. 12).
As a consequence of very low plankton content, these regions are distinguished by extremely
clear, transparent water, which shows a deep
cobalt blue color. They are generally smooth
seas because storms rarely touched them.
3.2.3 640 High-Salinity Subtropical
Division
The high-salinity regions are not designated as
a separate variety by Dietrich, which Elliott
(1954) designates as type H. They have been
incorporated into the system presented in this
book. These regions are represented by the Mediterranean Sea, the Red Sea, and the Black Sea.
Continental influences are extremely strong
because the individual units are almost landlocked and water exchange with the oceans is
very slow. Each unit shows a strong individuality, but nevertheless certain characteristics permit grouping them into one major type. These
common characteristics are: almost landlocked
position, extremely strong continental influence,
wide range and variation of temperatures, wide
range of salinities, wide variation of air
Fig. 3.3 Elephant seals and penguins on the Crozet
Islands, South Indian Ocean. Photograph by Douglas
Mawson; from the American Geographical Society
Library, University of Wisconsin-Milwaukee Libraries
20
3 Ecoregions of the Oceans