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4.2.8. Discussions about the cause of glacial cycles

When decomposed into periodic components, Milankovich forcing has large power in the periods around twenty thousand years and around forty thousand years, but not around a hundred thousand years. In order to explain the Quaternary glacial cycles, especially those of the recent 500 thousand years during which 100 thousand year cycle is apparent, we need to consider some non-linear system (i.e. a system whose output is not proportional to its input) whether we consider the cycles to be a response to Milankovitch forcing or to be internally generated oscillations. The likely candidate of the source of nonlinearity is continental ice sheets.

Various processes are involved in the variation of ice sheets (Abe-Ouchi and Masuda, 1993). Among those, the following processes seem to be important in order to explain the large variation of ice sheets and its large power at a period where the external forcing does not have such a large power.

(See Masuda and Abe-Ouchi, 1996, for some more details).

By the way, the speed of slip at the bottom of ice sheet is very different whether or not liquid water exist at the bottom. The speed of ice due to its plastic deformation is also strongly dependent on temperature. Due to these properties, ice sheets, which grew for thousands or ten thousands of years may collapse within one thousand years. This kind of events may cause global-scale climatic variation, either through the change of surface topography affecting the atmospheric circulation, or through the flood of melt water affecting the ocean circulation.


next up previous
Next: References Up: Factors of climatic variations Previous: Variation of clouds and

2003-09-10, 2004-05-10