124,000-year periodicity in terrestrial vegetation change during the late Pliocene epoch
Willis KJ., Kleczkowski A., Crowhurst SJ.
The late Pliocene (~3-2.6 million years ago) is an interval of exceptional interest for understanding the Earth's climate system. It was a time of progressive global cooling, resulting in the growth of large terrestrial ice sheets and the initiation of extensive Northern Hemisphere glaciation 1,2 . The build up of the ice sheets was cyclical and apparently paced by the orbitally driven oscillations in incoming solar radiation (Milankovitch cycles) at periods of approximately 41 kyr (obliquity) and 23- 19 kyr (precession). Here we present a high-resolution continental record of late Pliocene climate change, detailing the response of terrestrial vegetation to this interval of dramatic global environmental change. The annually laminated sequence of lake sediments from Pula maar, in Hungary, represents approximately 320 kyr of accumulation between ~ 3.0 and 2.6 million years ago. Spectral analyses of the record indicate terrestrial responses to incoming solar radiation at obliquity and precession periodicities, but the strongest response appears at a period of ~124kyr. Calculations indicate that variations in insolation forcing at this periodicity were negligible at this time. The Pula record thus demonstrates that internally driven nonlinear responses of the climate system, at a period of ~124kyr, were at least as important as external forcing at the orbital frequencies of precession and obliquity in driving late Pliocene large-scale environmental change.