Dr. Lorraine Lisiecki (UCSB Earth Science Department)

Title: Trends and transitions in climate dynamics of the last 5 million years: Results from time series analysis

Abstract: Climate system dynamics translate cyclic changes in Earth's orbit into glacial responses. Therefore, the shape and amplitude of glacial cycles over the last 5.3 Myr can be used to characterize the dynamics of glacial responses and the changes in climate dynamics associated with the long-term cooling of the Plio-Pleistocene. The variance of ice volume (benthic d18O) displays an exponential increase with time, which when removed reveals strong, proportional responses to amplitude modulations in orbital forcing over most of the Plio?Pleistocene, demonstrating that ice volume changes are forced by orbital precession and obliquity. One exception is the nearly constant amplitude of 41-kyr glacial cycles after ~1.4 Myr ago, which suggests that these cycles may be self-sustained and/or paced by obliquity. Collectively, trends in the shape of glacial cycles and the sensitivity of d18O to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2.5 and 1.4 Myr ago but show no significant change associated with the appearance of strong 100-kyr cycles during the mid-Pleistocene transition. Additionally, I find that the time-dependent 100-kyr power of orbital eccentricity has been anticorrelated with that of climate since 5 Myr ago. This supports the hypothesis that internally driven climate feedbacks are the source of the 100-kyr climate cycles.