The fundamental source of Late Pleistocene 100-kyr glacial cycles is not well understood. Milankovitch theory posits that glacial cycles are driven by changes in Northern Hemisphere summer insolation at high latitudes (i.e., over northern ice sheets), as affected by orbital cycles in precession, obliquity, and eccentricity. However, Milankovitch theory cannot explain 100-kyr glacial cycles because insolation forcing lacks 100-kyr power. I will discuss several leading hypotheses about the orbital drivers of Late Pleistocene glacial cycles, which differ in attributing the fundamental source of these cycles to either 41-kyr obliquity cycles or amplitude modulation of the precession index by the 100-kyr eccentricity cycle. Improved age constraints for Late Pleistocene climate records demonstrate that both obliquity and precession play an important role in pacing 100-kyr glacial cycles and refute the “obliquity skipping” hypothesis proposed by Huybers and Wunsch (2005).
Lorraine Lisiecki is a Professor in the Department of Earth Science at the University of California, Santa Barbara, where she’s been a faculty member since 2008. Her academic training began with a bachelor’s degree from MIT with an emphasis in planetary science. She went on to earn a master’s degree from MIT in geosystems modeling and a PhD in paleoclimate from Brown University, where she studied Earth’s glacial cycles of the past 5 Myr. Her research focuses on compilation of ocean sediment core data, using statistics and stratigraphic analysis to better understand the causes of past climate change. In 2008, she received the Subaru Outstanding Woman in Science Award from the Geological Society of America.