124,000-year periodicity in terrestrial vegetation change during the late Pliocene epoch

The late Pliocene (similar to 3-2.6 million years ago) is an interval of ex ceptional interest for understanding the Earth's climate system. It was a t ime of progressive global cooling, resulting in the growth of large terrest rial ice sheets and the initiation of extensive Northern Hemisphere glaciat ion(1,2). The build up of the ice sheets was cyclical and apparently paced by the orbitally driven oscillations in incoming solar radiation (Milankovi tch cycles) at periods of approximately 41 kyr (obliquity) and 23-19 kyr (p recession). Here we present a high-resolution continental record of late Pl iocene climate change, detailing the response of terrestrial vegetation to this interval of dramatic global environmental change. The annually laminat ed sequence of lake sediments from Pula maar, in Hungary, represents approx imately 320 kyr of accumulation between similar to 3.0 and 2.6 million year s ago. Spectral analyses of the record indicate terrestrial responses to in coming solar radiation at obliquity and precession periodicities, but the s trongest response appears at a period of similar to 124 kyr. Calculations i ndicate that variations in insolation forcing at this periodicity were negl igible at this time. The Pula record thus demonstrates that internally driv en nonlinear responses of the climate system, at a period of similar to 124 kyr, were at least as important as external forcing at the orbital frequen cies of precession and obliquity in driving late Pliocene large-scale envir onmental change.