The role of sub-Milankovitch climatic forcing in the initiation of the Northern Hemisphere glaciation

Mechanisms responsible for the initiation of major glaciation in the Northe rn Hemisphere at about 2.75 million years ago are poorly understood. A Lami nated terrestrial sequence from Pula maar, Hungary, containing about 320,00 0 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 transiti on. An analysis of the record implies that climatic variations at sub-Milan kovitch 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 provid ing the final trigger for the amplification of Northern Hemisphere ice shee ts.