248
Andrew CLARKE
Fig. 8.5. Suggested routes of dispersal of lower latitude bivalve molluscs into the Arctic Ocean. 1, Migration from the European Atlantic
shelf; 2, migration from the American Atlantic shelf; 3, migration from the Pacific shelf. These patterns are broadly similar to those proposed
by Zenkevitch (1963) for the fauna in general. Redrawn from Fedyakov and Naumov (1989).
ice-free Arctic Ocean, and it is likely that colonization
is continuing today.
The present-day Arctic shallow-water fauna is thus
the result of colonization by both Pacific and Atlantic
taxa (Fig. 8.5), but also reflects the impact of processes associated with repeated Pleistocene glaciations.
Reconstructions of the height of glaciation suggest
a substantial drop in sea-level, exposing vast areas
of continental shelf. During the many glacial cycles
during the Pleistocene, it now appears certain that Arctic continental-shelf faunal assemblages were almost
completely eradicated (Golikov and Scarlato, 1989;
Dunton, 1992). The current assemblages were formed
by survivors from refugia in unglaciated shelf areas of
the East Siberian and Beaufort Seas, or deeper (abyssal
or bathyal) waters of the Eurasian sector. Nesis (1984)
suggested that differences in the bathymetric ranges of
the fauna of the Pacific Arctic (typically stenobathic
1 )
and that of Atlantic Arctic (typically eurybathic
1 ) can
be explained by the different impacts of glaciation
in the two regions. In the Pacific Arctic much of
the continental shelf was exposed and unglaciated,
suggesting that shallow-water refugia may have been
available. In the Atlantic area, the continental shelves
were covered by ice shelves which may have descended
deep into the ocean. This suggests that abyssal waters
may have played an important biogeographic and
evolutionary role during the Pleistocene glaciation of
1 See Glossary, p. 477.
Andrew CLARKE
Fig. 8.5. Suggested routes of dispersal of lower latitude bivalve molluscs into the Arctic Ocean. 1, Migration from the European Atlantic
shelf; 2, migration from the American Atlantic shelf; 3, migration from the Pacific shelf. These patterns are broadly similar to those proposed
by Zenkevitch (1963) for the fauna in general. Redrawn from Fedyakov and Naumov (1989).
ice-free Arctic Ocean, and it is likely that colonization
is continuing today.
The present-day Arctic shallow-water fauna is thus
the result of colonization by both Pacific and Atlantic
taxa (Fig. 8.5), but also reflects the impact of processes associated with repeated Pleistocene glaciations.
Reconstructions of the height of glaciation suggest
a substantial drop in sea-level, exposing vast areas
of continental shelf. During the many glacial cycles
during the Pleistocene, it now appears certain that Arctic continental-shelf faunal assemblages were almost
completely eradicated (Golikov and Scarlato, 1989;
Dunton, 1992). The current assemblages were formed
by survivors from refugia in unglaciated shelf areas of
the East Siberian and Beaufort Seas, or deeper (abyssal
or bathyal) waters of the Eurasian sector. Nesis (1984)
suggested that differences in the bathymetric ranges of
the fauna of the Pacific Arctic (typically stenobathic
1 )
and that of Atlantic Arctic (typically eurybathic
1 ) can
be explained by the different impacts of glaciation
in the two regions. In the Pacific Arctic much of
the continental shelf was exposed and unglaciated,
suggesting that shallow-water refugia may have been
available. In the Atlantic area, the continental shelves
were covered by ice shelves which may have descended
deep into the ocean. This suggests that abyssal waters
may have played an important biogeographic and
evolutionary role during the Pleistocene glaciation of
1 See Glossary, p. 477.