10
J.T. Eastman and A. Clarke
separation of West Antarctica (the Antarctic Peninsula) from South
America. Although faunal evidence suggests some shallow water faunal
exchange, the deep water basins of the AtlanticlW eddellian Province and
the Pacific Ocean were still separated.
The area of West Antarctica contains many microplates, the detailed
movements of which have yet to be resolved. Nevertheless it is clear that
the Drake Passage between South America and the Antarctic Peninsula
first opened in the early Oligocene [45]. By this time Australia had already
moved north from East Antarctica, and the CircumAntarctic Current had
probably started by about 25 Ma BP.
The movement of West Antarctic microplates and the fragmentation of
the Scotia arc allowed a free exchange of fauna between the previously
isolated Pacific and Weddellian (ex-Tethys) Provinces. Coupled with the
oceanographic isolation of Antarctic by the inception of the
Circumantarctic Current and the formation of the Polar Front, this also
effectively reduced any exchange of shallow water faunal elements
between West Antarctica and South America. The scene was therefore set
for the continued evolution of the marine fauna of the Antarctic continental
shelf in effective isolation from nearby faunas.
Climatic History
It is widely recognized that the waters around Gondwana in the late
Cretaceous were mild, with bottom temperatures about 12 DC [46]. This
was followed by a distinct warming phase in the early Tertiary, during
which bottom temperatures may have reached 16 DC. After this warm
period, which lasted through much of the Eocene, there started the
sustained cooling which has dominated much (but by no means all) of the
remainder of the Tertiary.
The first evidence of widespread sea-ice and continental glaciation
appears in the late Eocene/early Oligocene [46]. This corresponds with a
sharp drop in bottom temperature; the seawater temperatures are, however,
cold rather than truly polar. The Oligocene appears to have been generally
cool or cold at high latitudes, and this matches the time when the physical
and oceanographic isolation of Antarctica became complete. This was
followed, however, by a period of global warming in the middle Miocene,
when Southern Ocean bottom temperatures may have reached 10 DC. High
latitude seawater temperatures then fell in the mid to late Miocene, perhaps
by as much as 4-5 degrees DC. This was accompanied by a switch from
predominantly equatorial to strongly meridional circulation patterns in the
large ocean basins, with major consequences for global heat transfer.
After brief periods of warming in the late Miocene and early Pliocene,
J.T. Eastman and A. Clarke
separation of West Antarctica (the Antarctic Peninsula) from South
America. Although faunal evidence suggests some shallow water faunal
exchange, the deep water basins of the AtlanticlW eddellian Province and
the Pacific Ocean were still separated.
The area of West Antarctica contains many microplates, the detailed
movements of which have yet to be resolved. Nevertheless it is clear that
the Drake Passage between South America and the Antarctic Peninsula
first opened in the early Oligocene [45]. By this time Australia had already
moved north from East Antarctica, and the CircumAntarctic Current had
probably started by about 25 Ma BP.
The movement of West Antarctic microplates and the fragmentation of
the Scotia arc allowed a free exchange of fauna between the previously
isolated Pacific and Weddellian (ex-Tethys) Provinces. Coupled with the
oceanographic isolation of Antarctic by the inception of the
Circumantarctic Current and the formation of the Polar Front, this also
effectively reduced any exchange of shallow water faunal elements
between West Antarctica and South America. The scene was therefore set
for the continued evolution of the marine fauna of the Antarctic continental
shelf in effective isolation from nearby faunas.
Climatic History
It is widely recognized that the waters around Gondwana in the late
Cretaceous were mild, with bottom temperatures about 12 DC [46]. This
was followed by a distinct warming phase in the early Tertiary, during
which bottom temperatures may have reached 16 DC. After this warm
period, which lasted through much of the Eocene, there started the
sustained cooling which has dominated much (but by no means all) of the
remainder of the Tertiary.
The first evidence of widespread sea-ice and continental glaciation
appears in the late Eocene/early Oligocene [46]. This corresponds with a
sharp drop in bottom temperature; the seawater temperatures are, however,
cold rather than truly polar. The Oligocene appears to have been generally
cool or cold at high latitudes, and this matches the time when the physical
and oceanographic isolation of Antarctica became complete. This was
followed, however, by a period of global warming in the middle Miocene,
when Southern Ocean bottom temperatures may have reached 10 DC. High
latitude seawater temperatures then fell in the mid to late Miocene, perhaps
by as much as 4-5 degrees DC. This was accompanied by a switch from
predominantly equatorial to strongly meridional circulation patterns in the
large ocean basins, with major consequences for global heat transfer.
After brief periods of warming in the late Miocene and early Pliocene,