Glacial variability over the last two million years: an extended depth-derived agemodel, continuous obliquity pacing, and the Pleistocene progression

Abstract

The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters AbstractAn agemodel not relying upon orbital assumptions is estimated over the last 2 Ma using depth in marine sediment cores as a proxy for time. Agemodel uncertainty averages AE10 Ka in the early Pleistocene ($2-1 Ma) and AE7 Ka in the late Pleistocene ($1 Ma to the present). Twelve benthic and five planktic d18 O records are pinned to the agemodel and averaged together to provide a record of glacial variability. Major deglaciation features are identified over the last 2 Ma and a remarkable 33 out of 36 occur when Earth's obliquity is anomalously large. During the early Pleistocene deglaciations occur nearly every obliquity cycle giving a 40 Ka timescale, while late Pleistocene deglaciations more often skip one or two obliquity beats, corresponding to 80 or 120 Ka glacial cycles which, on average, give the $100 Ka variability. This continuous obliquity pacing indicates that the glacial theory can be simplified. An explanation for the $100 Ka glacial cycles only requires a change in the likelihood of skipping an obliquity cycle, rather than new sources of long-period variability. Furthermore, changes in glacial variability are not marked by any single transition so much as they exhibit a steady progression over the entire Pleistocene. The mean, variance, skewness, and timescale associated with the glacial cycles all exhibit an approximately linear trend over the last 2 Ma. A simple model having an obliquity modulated threshold and only three adjustable parameters is shown to reproduce the trends, timing, and spectral evolution associated with the Pleistocene glacial variability. r

Pleistocene sea-surface temperature evolution: Early cooling, delayed glacial intensification, and implications for the mid-Pleistocene climate transition

“…An evolving climate response to orbital variability has also been proposed, including an increasingly non-linear response to obliquity pacing (Huybers, 2007), which may relate to changing carbon cycle / Antarctic temperature / radiative forcing relationships (Masson-Delmotte et al, 2010).…”

Feedback between deglaciation, volcanism, and atmospheric CO2

“…It may be that the progression of Pleistocene climate towards larger and more asymmetric glacial cycles (e.g. Huybers, 2007) can, in part, be understood as the synchronization and attendant amplification of the feedback between volcanic systems and glacial variability.…”

Pleistocene glacial variability as a chaotic response to obliquity forcing

“…Absence of a longterm trend in CO 2 is observed for the late Pleistocene (Lüthi et al, 2008) and can be inferred for the middle Pleistocene (MedinaElizalde and Lea, 2005). Second is to illustrate how the appearance of 40 ky and ∼100 ky glacial variability over the course of the Pleistocene is consistent with a fundamental obliquity pacing of both styles of glaciation (Huybers and Wunsch, 2005;Huybers, 2007) (Fig. 1a, b).…”