Climate
Science:
Investigating Climatic and Environmental Processes
Millennial Scale
Millennial scale
oscillations, often referred to as Dansgaard- Oeschger cycles in honor
of Willi Dangsgaard and Hans Oeschger, vary widely in amplitude and
in occurrence through the paleo record. They do not appear to be true
cycles despite their repetitive nature. (Ruddiman,
2001 ). During the 1990s a great deal of research focused on detecting
and dating millennial oscillations in regions of the world other than
the North Atlantic, such as the Santa Barbara Basin (Hendy,
1996 ) and even as far away as Antarctica (Steig,
1998 ).
The North Atlantic has been the focus of much of the research due to
the ice-rafted debris found in marine sediments. According to Ruddiman
(2001), during smaller ice-rafting events, debris include volcanic
rocks on Iceland and red sandstone from coastal areas. During larger
events, materials from eastern North America, such as limestone fragments
from Hudson Bay, are found. See map image below.
Gerard C. Bond, a researcher at the Lamont Doherty
Earth Observatory has suggested that the ~1,500 year cycle of ice-buildup
in the North Atlantic is related to solar cycles; when the sun is at
its most energetic, the Earths magnetic field is strengthened,
blocking more cosmic rays, which are a type of radiation coming in from
deep space. Certain isotopes, such as carbon-14, are formed when cosmic
rays hit plants and can be measured in ancient tree rings because they
cause the formation of carbon-14 that can be measured in ancient tree
rings. High levels of carbon-14 suggests an inactive sun. In his research
Bond noted that increases in icebergs and drift ice occurred at the
same times as the increase in carbon-14, indicating the sun was weaker
at such times. (Bond, 2001).
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