The spectral evolution of Plio-Pleistocene d¹⁸O

Lorraine Lisiecki (AGU Poster, 2004)

Using a new stack of 57 benthic d18O records, the evolution of d¹⁸O over the last 5.3 Myr is described in terms of mean, variance, spectral density, and the shape of glacial cycles. The variance of d¹⁸O 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 d¹⁸O in the 41-kyr band has a correlation of 0.94 with obliquity modulation. The precession components of d¹⁸O are strongly correlated with precession modulation for the entire Plio-Pleistocene. However, variance in the 100-kyr band of d¹⁸O 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 transition is associated with unique or abrupt transitions in the spectral response of d¹⁸O 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, reduced sensitivity to obliquity modulations, and a greater lag in the precession response of benthic d¹⁸O.