Antarctic Climate Evolution
by Sandra Passchier, Montclair State University
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The Antarctic continent is an amazing place on Earth.
It is situated over the South Pole and it is covered by a thick layer of ice.
At its thickest point the ice is over 4000 m (12,000 ft) thick.
The Antarctic Continent has not always been covered by ice.
Many millions of years ago in a time called the Eocene,
Antarctica must have had a much warmer climate.
There may have already been ice on the continent,
but it was not as thick and widespread as it is today.
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Eocene erratic from Mount Discovery, McMurdo Sound, Antarctica. Note fossil shells.
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Drilling for Antarctica's climate history
Geologists think that the Antarctic ice sheet developed in the late Eocene
and that it has grown and melted periodically through time until the present. Since the 1970's a number of drilling projects have targeted glacial sediments on the Antarctic margin. Recently (1997- 2000) two Legs of ship drilling and drilling from a stable platform in the Ross Sea by the Cape Roberts Drilling Project yielded a wealth of new information. The central goal of the drilling projects was to penetrate Eocene and older strata to collect information about Antarctica's earliest ice sheet history and to gain more insight into the character of more recent Neogene ice sheet behavior. The newest drilling program targeting Neogene strata in McMurdo Sound is called the Antarctic Drilling Program (ANDRILL).
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An Antarctic active volcano
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Mount Erebus is an Antarctic active volcano.
In the McMurdo Sound region, where Mount Erebus is located,
volcanoes have been active for the past 25 million years.
Ash layers of ancient volcanoes have been found in the Cape Roberts and ANDRILL drillcores. These layers are important because radiometric dating of the ash provides a time framework for the events reconstructed from the sediment cores.
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Transantarctic Mountains
The Transantarctic Mountains are several thousands of kilometres long.
Valley glaciers draining the Antarctic ice sheet have eroded valleys with steep walls.
In these valley walls sandstones are exposed that are several hundreds of million years old.
They were mainly deposited by rivers in a time when Antarctica was part of the supercontinent Gondwana.
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In many places the sandstones are separated by chocolate brown layers of igneous rock.
These brown layers, called "sills", were once molten rock, which was squeezed inbetween the sandstone layers.
The emplacement of the sills happened about 180 million years ago in the Jurassic, in a time when dinosaurs were dominating terrestrial life. It marked the beginning of the break-up of Gondwana, which eventually culminated in the isolation of the icy continent Antarctica.
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