Detection of significant climatic precession variability in early Pleistocene glacial cycles

Abstract

Despite having a large influence on summer insolation, climatic precession is thought to account for little variance in early Pleistocene proxies of ice volume and deep-water temperature. Various mechanisms have been suggested to account for the dearth of precession variability, including meridional insolation gradients, interhemispheric cancellation of ice-volume changes, and antiphasing between the duration and intensity of summer insolation. We employ a method termed Empirical Nonlinear Orbital Fitting (ENOF) to estimate the amplitudes of obliquity and precession forcing in early Pleistocene proxies and their respective leads or lags relative to the timing of orbital variations. Analysis of a high-resolution North Atlantic benthic δ 18 O record, comprising data from IODP sites U1308 and U1313, indicates a significantly larger precession contribution than previously recognized, with an average precession-to-obliquity amplitude ratio of 0.51 (0.30-0.76 95% confidence interval) in the rate-of-change of δ 18 O between 3 and 1 Ma. Averaged when eccentricity exceeds 0.05, this ratio rises to an average of 1.18 (0.84-1.53). Additional support for precession's importance in the early Pleistocene comes from its estimated amplitude covarying with eccentricity, analyses of other benthic δ 18 O records yielding similar orbital amplitude ratios, and use of an orbitally-independent timescale also showing significant precession. Precession in phase with Northern Hemisphere summer intensity steadily intensifies throughout the Pleistocene, in agreement with its more common identification during the late Pleistocene. A Northern Hemisphere ice sheet and energy balance model run over the early Pleistocene predicts orbital amplitudes consistent with observations when a cooling commensurate with North Atlantic sea surface temperatures is imposed. These results provide strong evidence that glaciation is influenced by climatic precession during the late Pliocene and early Pleistocene, and are consistent with hypotheses that glaciation is controlled by Northern Hemisphere summer insolation.

New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio-Pleistocene

“…Benthic δ 18 O is a key parameter in paleoceanography for understanding global climate evolution and is often used to study Plio-Pleistocene ice sheet response to orbital forcing through the amplitude evolution of its orbital frequencies (e.g., Liautaud et al, 2020;Lisiecki & Raymo, 2007) and as a constraint for ice sheet evolution models (de Boer et al, 2014;Pollard & DeConto, 2009). Three main features of Plio-Pleistocene benthic δ 18 O records are as follows: (1) obliquity frequency amplitude modulation (1/41 kyr −1 ) that matches the amplitude modulation of the orbital forcing prior to 1.4 Ma, (2) amplitude evolution of the precession frequencies (1/19-1/23 kyr −1 ) that is similar to the amplitude modulation of the orbital forcing but increases exponentially during the Pleistocene, and (3) an increase in ∼1/100 kyr −1 eccentricity frequency amplitude after 1.4 Ma that does not match orbital forcing (Lisiecki & Raymo, 2007).…”

James Croll and geological archives: testing astronomical theories of ice ages

“…If anti-phased precessional variations in ice volume did occur in the earliest Pleistocene in the mode of Raymo et al (2006), then the gradual increase in the amplitude of precession might reflect the expansion of northern hemisphere icesheets and a growing imbalance in northern and southern contributions to sea level, such that they would no longer cancel each other in the benthic δ 18 O record (Liautaud et al 2020). Alternatively, the steady intensification of the precession signal through the Quaternary simply reflects the gradual southward extension of northern hemisphere ice-sheet margins to lower latitudes, where the influence of precessional insolation changes is stronger (Liautaud et al 2020).…”

Observationally Constrained Cloud Phase Unmasks Orbitally Driven Climate Feedbacks

“…interhemispheric cancellation of ice-volume changes ( Raymo et al, 2006), summer duration and intensity being anti-phased (Huybers, 2006) and meridional insolation gradients (Raymo & Nisancioglu, 2003). A recent study using statistical methods argues that precession has a stronger contribution than previously recognized in the early Pleistocene and increases through this epoch (Liautaud et al, 2020).…”

“…These proxies show that Pleistocene glacial climates initially varied Confidential manuscript submitted to Geophysical Research Letters with a periodicity of around 40 kyr switching to 100 kyr around million years ago. The precession signal is modulated by eccentricity, and is weaker in the early Pleistocene and stronger in late Pleistocene records (Huybers, 2011;Liautaud et al, 2020). Numerous hypotheses have been proposed to explain the weak precession signal in the early Pleistocene proxies, e.g.…”