On the structure and origin of major glaciation cycles 2. The 100,000‐year cycle

Abstract

Climate over the past million years has been dominated by glaciation cycles with periods near 23,000, 41,000, and 100,000 years. In a linear version of the Milankovitch theory, the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity. But the 100,000-year radiation cycle (arising from eccentricity variation) is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing. We present phase observations showing that the geographic progression of local responses over the 100,000-year cycle is similar to the progression in the other two cycles, implying that a similar set of internal climatic mechanisms operates in all three. But the phase sequence in the 100,000-year cycle requires a source of climatic inertia having a time constant (--15,000 years) much larger than the other cycles (--5,000 years). Our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source. When these ice sheets, forced by precession and obliquity, exceed a critical size, they cease responding as linear Milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses. In our model, the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity-driven modulations in the 23,000-year sea level cycle. During an interval when sea level is forced upward from a major low stand by a Milankovitch response acting either alone or in combination with an internally driven, higher-frequency process, ice sheets grounded on continental shelves become unstable, mass wasting accelerates, and the resulting deglaciation sets the phase of one wave in the train of 100,000-year oscillations.Whether a glacier or ice sheet influences the climate depends very much on the scale .... The interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger, thereby gradually increasing its radius of influence. Johannes Oerlemans [1991, p. 155] 1. BACKGROUND AND PURPOSE Climate over the past half-million years has been dominated by glacial cycles with periods near 23, 41, and 100 kyr [Hays 14 DSDP607 A•5•3C index of ventilation 3427

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

“…According to modelling experiments, insolation impulse during Termination V was somewhat weak to drive glacial climate quickly towards full-interglacial conditions (Imbrie et al, 1993;Li et al, 1998). Additionally, European ice-sheet expansion was very large during MIS 12 (Donner, 1995), a fact which might help to explain not only the exceptional length of Termination V (Oppo et al, 1998;Bauch et al, 2000;Billups et al, 2004;Healey and Thunell, 2004;de Abreu et al, 2005) but also the difference in SST dynamics between polar and middle/low latitudes as revealed by us for the early interglacial phase.…”

Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary

“…In this age model, the 4-m-thick reversed polarity interval of diamictite and sandstone at the base of sequence 9 is inferred to represent a short-duration geomagnetic excursion within C6Cn.3n, and the LO of D. bisectus in CRP-2/2A is correlated with C6Cn.2r in the earliest Miocene. This alternative age model has been considered unlikely 28 because: (1) the polarity signal is robust for the interval of CRP core, (2) the MPTS 31 (3) the age of the LO of D. bisectus would be inconsistent with Southern Ocean records 30 .…”

“…Key for ice margin proximity is shown in Fig. 2 31 . In summary, the pattern of ice-volume change that is indicated by the deep ocean record (Fig.…”

“…Durations for intervals between biostratigraphic datums were estimated from inferred ,40-kyr frequencies in magnetic susceptibility records. The second age model is based on a new astronomically calibrated timescale 34 established by tuning the 40-kyr cycles in magnetic susceptibility records to orbital target solutions for obliquity and precession 31 . The astronomical chronology has subsequently been used to recalibrate the MPTS in the vicinity of the Oligocene/Miocene boundary 36 , and indicates that this boundary is ,900 kyr younger than that reported in ref.…”

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…Second, temporal development of ice-age cycles provides critical information about the nature of long-term climate cooling over the past few million years, in response to CO 2 reduction and interactions among ice, land cover, and climate (e.g., Clark et al, 2006;K€ ohler and Bintanja, 2008;de Boer et al, 2010de Boer et al, , 2012Hansen et al, 2013). Third, variable amplitude of individual ice ages helps to determine the relationship between climate change, astronomical climate forcing cycles, and climate feedbacks on timescales of 10se100s of kiloyears (e.g., Oglesby, 1990;Imbrie et al, 1993;Raymo et al, 2006;Colleoni et al, 2011Colleoni et al, , 2016Ganopolski and Calov, 2011;Carlson and Winsor, 2012;Abe-Ouchi et al, 2013;Hatfield et al, 2016;Liakka et al, 2016). Fourth, the size and spatial distribution of land ice during past glacials determines crustal rebound processes when ice masses melt, which in turn affects sea-level reconstructions for subsequent interglacials.…”