The history of the Antarctic climates over 'geologic' time-scales

Timing of the long-term tectonic effect on climate evolution has been random over the last 109 years, and has operated by altering the latitudinal distribution of land and sea, by affecting the loci of the sea and the importance of ocean currents, and by contributing to orographic and continentality effects. Among the detected cycles in climate, the longest appears to have a period of about 105 years. This has been a major cycle over the last 106 years but It is not recognised definitely in older rocks. Because only short geologic records have been studied, the prominent and important 10' year cycle cannot be correlated certainly with the Milankmitch parameters (particularly not with eccentricity of the orbit). The 4 x 104 year obliquity cycle appears to be the most significant among recognised cycles, owing to its simultaneous effects in both hemispheres and to its known Influence on Ice grouch through effects on high-latitude summer temperatures. Precession cycles of 2 x 104 years are clearly recognised in the geologic record. The cause of the 105 year cycle presently is unknown and causes are being sought in geophysical models of upper mantle stressing and relaxation in response to ice loading and melting.