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 ).

Millennial changes in the North Atlantic

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 Earth’s 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).


Sources and deposition of ice-rafted debris
Images from Ruddiman, 2001 used by permission of W. H. Freeman & Co.

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