HR: 16:05h
AN: PP14A-01 INVITED     [Abstracts]
TI: Emiliani Lecture: On Glaciations and their Causes
AU: * Raymo, M E
EM: raymo@bu.edu
AF: Boston University, Dept. of Earth Sciences, Boston, MA 02215 United States
AB: The glacial cycles observed in proxy records of the past 2.8 Ma, represent some of the largest and most significant changes in past climate. However, after more than 50 years of investigations, led notably by Emiliani, the physical mechanisms driving the ice age cycles are not well understood. Well-dated deep sea records appear to confirm the early work of Milankovitch [1930], namely that major fluctuations in global climate, associated with ice age cycles, are caused by variations in insolation at critical latitudes and seasons. Based mainly on climate proxy records from the last 0.5 Ma, a general scientific consensus emerged that variations in summer insolation at high northern latitudes are the dominant influence on climate over tens of thousands of years. Climate variance at precessional and obliquity frequencies appears to be linearly forced and coherent with northern summer insolation and only the 100 Ka cycle is left unexplained by this model [e.g., Imbrie et al. 1992; 1993]. Typically, the 100 Ka cycle is ascribed to nonlinear responses to Milankovitch forcing or due to internal variability at this time scale arising within the climate system itself. In the latter case, Milankovitch forcing may not be essential for sustaining the oscillations, although the precession and obliquity signal sets the timing of terminations and thus the phase of the oscillation [e.g., Saltzman and Verbitsky, 1994; Gildor and Tziperman, 2001]. In the late Pliocene/early Pleistocene, no significant variance at the 100 Ka period is observed in benthic d18O records and one might expect that global ice volume would have varied linearly and coherently with northern summer insolation, as it did more recently. However, while summer insolation is dominated, at nearly every latitude (or in any month or combination of months), by the 23 Ka precession period, this frequency is barely discernable in only a small stretch of the late Pliocene/early Pleistocene ice volume record and is absent over most of the 2.8-0.8 m.y. interval. This lecture will discuss possible physical mechanisms responsible for the 41 Ka cycles in late Pliocene and early Pleistocene climate records as well as reasons behind the transition to and development of the 23 Ka and 100 Ka cycles. I will present recent results highlighting our successes and failures in modeling the 41 Ka climate cycles as well as discuss constraints provided by data.
DE: 4934 Insolation forcing
DE: 4946 Milankovitch theory
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005