THE POLAR DEEP SEAS
249
the Arctic Ocean. Vinogradova (1997) has concluded
that the deep-sea fauna of the central Arctic basins
is essentially Pleistocene in age, having been formed
primarily as the consequence of repeated descent
into deep water of shelf fauna driven by changes in
temperature, glaciation and sea-level.
Relatively little is known of the biogeographical
affinities of the Arctic abyssal fauna, although the
isopod fauna contains a majority of genera with close
affinity to cosmopolitan abyssal genera. Of the rest,
25% of the genera are found only in the North
Atlantic, and 10% are found only in North Pacific
(Menzies et al., 1973). The isopod fauna shows the
expected bathymetric zonation, the deeper fauna being
dominated by Asellota.
In summary, the Arctic abyssal fauna appears to
contain elements that reveal ancient connections to the
deep-sea faunas of both the Pacific and Atlantic. The
Arctic abyssal fauna has, however, long been isolated
from the Pacific, and although there remains a deepwater connection to the Norwegian Basin, there is no
contiguity to the abyssal North Atlantic. The species
richness appears to be low. Although the Arctic deep
sea probably acted as an important refugium during
glacial maxima it would appear that the Pleistocene
glaciation was the cause of considerable extinction
within the abyssal fauna as well as on the continental
shelf.
THE ANTARCTIC DEEP SEA
The Antarctic is a large land-mass surrounded by a
deep ocean. It thus forms almost a mirror image of
the Arctic basin. The Southern Ocean surrounding
Antarctica is defined oceanographically as those waters
south of the Antarctic Polar Front (Fig. 8.6). Referred
to as the Antarctic Convergence in the earlier literature,
this marks the northernmost limit of cold surface
waters.
The Antarctic Polar Front is a particularly wellmarked oceanographic feature, and one which defines
the geographical range of many Southern Ocean
zooplankton (Hardy and Gunther, 1935; John, 1936;
Angel, 1997). It is, however, essentially a surface
feature which has less relevance to the distribution of
mesopelagic or benthic fauna. The mesopelagic fauna
of the Southern Ocean has been little studied, but it
contains species known to be widespread (Clarke and
Holmes, 1987). The benthic fauna of Antarctica also
contains species known from South America (Dell,
1972; Arntz et al., 1994).
From a benthic perspective, two features of Southern
Ocean topography are important. The first is the
unusually deep nature of the continental shelves around
Antarctica, and the second is the relationship of the
deep-sea floor to surrounding ocean basins.
The continental shelves around Antarctica are typically over 500 m deep and often reach >800 m at the
edge of the continental shelf. In many areas there are
deeper basins within the shelves, and in a few places
these may reach 1000 m. Two factors appear to have
been important in deepening the continental shelves
around Antarctica. The first is a general isostatic
depression caused by the enormous mass of continental
ice, and the second is scouring by ice-shelves as
they extend seawards at glacial maxima. The relative
importance of these two processes is still a matter
of some debate, but recent geophysical evidence has
shown clearly that previous extensions of the ice-sheet
have scoured vast quantities of sediment from the inner
continental shelves and deposited these at the edge and
on the continental slope (Anderson, 1990; Anderson
et al., 1991).
Deep-water topography
Even a casual glance at a bathymetric map of the
Southern Ocean will reveal vast areas of seabed at
abyssal depths (Fig. 8.7). These form effectively four
basins. The Atlantic–Indian basin lies to the north of
Dronning Maud Land, from the northernmost Weddell
Sea (roughly longitude 30ºW) to its easternmost
boundary at the Kerguelen Plateau (roughly 60ºE).
This basin is effectively the southernmost section of
the deep Atlantic Ocean, although the Atlantic–Indian
ridge separates it from the Agulhas Basin to the north.
Further to the east, running roughly from the
Kerguelen Plateau to longitude 150ºE, is the shallowest
of the four basins, the South Indian Basin. This
is separated from the main Indian Ocean basin by
the Southeast Indian Ridge. The southern Pacific
Ocean is more complex close to Antarctica in that
these are two deep basins, the Southeast Pacific and
Southwest Pacific Basins, separated by the Pacific–
Antarctic Ridge (Fig. 8.7).
This topography would suggest that the faunal
characteristics of each of these basins would contain
individual Indian, Pacific or Atlantic Ocean elements.
Superimposed on these would be features associated
249
the Arctic Ocean. Vinogradova (1997) has concluded
that the deep-sea fauna of the central Arctic basins
is essentially Pleistocene in age, having been formed
primarily as the consequence of repeated descent
into deep water of shelf fauna driven by changes in
temperature, glaciation and sea-level.
Relatively little is known of the biogeographical
affinities of the Arctic abyssal fauna, although the
isopod fauna contains a majority of genera with close
affinity to cosmopolitan abyssal genera. Of the rest,
25% of the genera are found only in the North
Atlantic, and 10% are found only in North Pacific
(Menzies et al., 1973). The isopod fauna shows the
expected bathymetric zonation, the deeper fauna being
dominated by Asellota.
In summary, the Arctic abyssal fauna appears to
contain elements that reveal ancient connections to the
deep-sea faunas of both the Pacific and Atlantic. The
Arctic abyssal fauna has, however, long been isolated
from the Pacific, and although there remains a deepwater connection to the Norwegian Basin, there is no
contiguity to the abyssal North Atlantic. The species
richness appears to be low. Although the Arctic deep
sea probably acted as an important refugium during
glacial maxima it would appear that the Pleistocene
glaciation was the cause of considerable extinction
within the abyssal fauna as well as on the continental
shelf.
THE ANTARCTIC DEEP SEA
The Antarctic is a large land-mass surrounded by a
deep ocean. It thus forms almost a mirror image of
the Arctic basin. The Southern Ocean surrounding
Antarctica is defined oceanographically as those waters
south of the Antarctic Polar Front (Fig. 8.6). Referred
to as the Antarctic Convergence in the earlier literature,
this marks the northernmost limit of cold surface
waters.
The Antarctic Polar Front is a particularly wellmarked oceanographic feature, and one which defines
the geographical range of many Southern Ocean
zooplankton (Hardy and Gunther, 1935; John, 1936;
Angel, 1997). It is, however, essentially a surface
feature which has less relevance to the distribution of
mesopelagic or benthic fauna. The mesopelagic fauna
of the Southern Ocean has been little studied, but it
contains species known to be widespread (Clarke and
Holmes, 1987). The benthic fauna of Antarctica also
contains species known from South America (Dell,
1972; Arntz et al., 1994).
From a benthic perspective, two features of Southern
Ocean topography are important. The first is the
unusually deep nature of the continental shelves around
Antarctica, and the second is the relationship of the
deep-sea floor to surrounding ocean basins.
The continental shelves around Antarctica are typically over 500 m deep and often reach >800 m at the
edge of the continental shelf. In many areas there are
deeper basins within the shelves, and in a few places
these may reach 1000 m. Two factors appear to have
been important in deepening the continental shelves
around Antarctica. The first is a general isostatic
depression caused by the enormous mass of continental
ice, and the second is scouring by ice-shelves as
they extend seawards at glacial maxima. The relative
importance of these two processes is still a matter
of some debate, but recent geophysical evidence has
shown clearly that previous extensions of the ice-sheet
have scoured vast quantities of sediment from the inner
continental shelves and deposited these at the edge and
on the continental slope (Anderson, 1990; Anderson
et al., 1991).
Deep-water topography
Even a casual glance at a bathymetric map of the
Southern Ocean will reveal vast areas of seabed at
abyssal depths (Fig. 8.7). These form effectively four
basins. The Atlantic–Indian basin lies to the north of
Dronning Maud Land, from the northernmost Weddell
Sea (roughly longitude 30ºW) to its easternmost
boundary at the Kerguelen Plateau (roughly 60ºE).
This basin is effectively the southernmost section of
the deep Atlantic Ocean, although the Atlantic–Indian
ridge separates it from the Agulhas Basin to the north.
Further to the east, running roughly from the
Kerguelen Plateau to longitude 150ºE, is the shallowest
of the four basins, the South Indian Basin. This
is separated from the main Indian Ocean basin by
the Southeast Indian Ridge. The southern Pacific
Ocean is more complex close to Antarctica in that
these are two deep basins, the Southeast Pacific and
Southwest Pacific Basins, separated by the Pacific–
Antarctic Ridge (Fig. 8.7).
This topography would suggest that the faunal
characteristics of each of these basins would contain
individual Indian, Pacific or Atlantic Ocean elements.
Superimposed on these would be features associated