The Role of Sub-Milankovitch Climatic Forcing in the Initiation of the Northern Hemisphere Glaciation

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Science  23 Jul 1999:
Vol. 285, Issue 5427, pp. 568-571
DOI: 10.1126/science.285.5427.568

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Mechanisms responsible for the initiation of major glaciation in the Northern Hemisphere at about 2.75 million years ago are poorly understood. A laminated terrestrial sequence from Pula maar, Hungary, containing about 320,000 years in annual layers between 3.05 and 2.60 million years ago, provides a detailed record of rates of climatic change across this dramatic transition. An analysis of the record implies that climatic variations at sub-Milankovitch frequencies (less than or equal to 15,000 years) were an important driving force during this transitional interval and that, as the threshold was approached, these increased in frequency and amplitude, possibly providing the final trigger for the amplification of Northern Hemisphere ice sheets.

  • * Present address: School of Geography, University of Oxford, Oxford OX1 3TB, UK.

  • To whom correspondence should be addressed. E-mail: a.kleczkowski{at}

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