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Figure 2.40. Arctic freezing induced by increased flow of tropical waters to the north (adapted
from Uriarte, 2009).
current, already fairly dense and salty, became even denser as it cooled on its way
north, and so sunk before reaching the Arctic Ocean.''
The decreased penetration of tropical waters to the north resulted in cooling
and eventual glaciation of the north. Uriarte prepared a diagram of this theory as
shown in Figure 2.38b .
2.5
ICE AGES IN THE RECENT GEOLOGICAL PAST
As we shall demonstrate in the sections of this topic that follow, there is evidence
that the climate of the Earth has undergone significant sharp oscillations over the
past 3 million years, superimposed on a downward long-term trend (Zachos et al.,
2001). The Earth has vacillated between two end points.
At one end point the climate of the Earth is not unlike that prevailing today,
give or take a few degrees. Under these conditions, there are residual ice sheets
covering Antarctica and Greenland, and the poles are covered with snow and ice
the year around. However, the climate of the Earth at moderate latitudes is quite
benign. This is commonly called an interglacial period, and the current interglacial
period is known as the ''Holocene''. There is evidence that there may have been
significant temperature fluctuations during past interglacials, and the Holocene
appears to be unique in its duration and stability. Furthermore, there is some
evidence that the previous two interglacials reached higher temperatures than we
have experienced in the Holocene.
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