HR: 1340h
AN: PP33B-0947    [Abstracts]
TI: The Spectral Evolution of Plio-Pleistocene $\delta^{18}$O
AU: * Lisiecki, L E
EM: Lorraine\_Lisiecki@brown.edu
AF: Brown University, 324 Brook St Box 1846, Providence, RI 02912
AB: Using a new stack of 57 benthic $\delta^{18}$O records, the evolution of $\delta^{18}$O over the last 5.3 Myr is described in terms of mean, variance, spectral density, and the shape of glacial cycles. The variance of $\delta^{18}$O exhibits an exponential increase with time and a strong response to long-term modulations in orbital forcing. From 5.3--1.7 Ma, the detrended variance of $\delta^{18}$O in the 41-kyr band has a correlation of 0.94 with obliquity modulation. The precession components of $\delta^{18}$O are also sensitive to orbital modulations, with the effects of modulation in the 23-kyr band increasing after 1.5 Ma. However, variance in the 100-kyr band of $\delta^{18}$O is anticorrelated with modulation of the 100-kyr eccentricity cycle and is not unique to the late Pleistocene. The dominance of the 100-kyr cycle in the late Pleistocene might represent the extension of trends which began before the onset of northern hemisphere glaciation (NHG), namely a steady increase in the 100-kyr variance and its sensitivity to 100-kyr power in eccentricity. Neither the onset of NHG nor the mid-Pleistocene revolution is associated with unique or abrupt transitions in the spectral response of $\delta^{18}$O relative to insolative forcing. However, a climate transition at 1.6 Ma results in a sudden change in the shape of glacial cycles, a trend toward warmer interglacials, changes in the climate's sensitivity to modulations of obliquity and precession, and a greater lag in the precession response of benthic $\delta^{18}$O. The initiation or strengthening of a climate feedback sensitive to precession may have triggered this transition.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting