Emergence of critical climate states during the Pleistocene

Mapping Intimacies ◽

10.5194/egusphere-egu21-3630 ◽

2021 ◽

Author(s):

Nicholas Golledge

Keyword(s):

Dynamical Systems ◽

Late Pleistocene ◽

Dominant Frequency ◽

Climate System ◽

Ice Age ◽

Early Pleistocene ◽

Glacial Cycles ◽

Pleistocene Climate ◽

System Nodes ◽

Systems Framework

During the Pleistocene (approximately 2.6 Ma to present) glacial to interglacial climate variability evolved from dominantly 40 kyr cyclicity (Early Pleistocene) to 100 kyr cyclicity (Late Pleistocene to present). Three aspects of this period remain poorly understood: Why did the dominant frequency of climate oscillation change, given that no major changes in orbital forcing occurred? Why are the longer glacial cycles of the Late Pleistocene characterised by a more asymmetric form with abrupt terminations? And how can the Late Pleistocene climate be controlled by 100 kyr cyclicity when astronomical forcings of this frequency are so much weaker than those operating on shorter periods? Here we show that the decreasing frequency and increasing asymmetry that characterise Late Pleistocene ice age cycles both emerge naturally in dynamical systems in response to increasing system complexity, with collapse events (terminations) occuring only once a critical state has been reached. Using insights from network theory we propose that evolution to a state of criticality involves progressive coupling between climate system 'nodes', which ultimately allows any component of the climate system to trigger a globally synchronous termination. We propose that the climate state is synchronised at the 100 kyr frequency, rather than at shorter periods, because eccentricity-driven insolation variability controls mean temperature change globally, whereas shorter-period astronomical forcings only affect the spatial pattern of thermal forcing and thus do not favour global synchronisation. This dynamical systems framework extends and complements existing theories by accomodating the differing mechanistic interpretations of previous studies without conflict.

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A theory of glacial cycles: resolving Pleistocene puzzles

10.5194/cp-2021-94 ◽

2021 ◽

Author(s):

Hsien-Wang Ou

Keyword(s):

Freezing Point ◽

Surface Air Temperature ◽

Climate System ◽

Ice Age ◽

Early Pleistocene ◽

Polar Ice ◽

Glacial Cycles ◽

Convective Flux ◽

Ice Volume ◽

Ice Cap

Abstract. Since the summer surface air temperature that regulates the ice margin is anchored on the sea surface temperature, we posit that the climate system constitutes the intermediary of the orbital forcing of the glacial cycles. As such, the relevant forcing is the annual solar flux absorbed by the ocean, which naturally filters out the precession effect in early Pleistocene but mimics the Milankovitch insolation in late Pleistocene. For a coupled climate system that is inherent turbulent, we show that the ocean may be bistable with a cold state defined by the freezing point subpolar water, which would translate to ice bistates between a polar ice cap and an ice sheet extending to mid-latitudes, enabling large ice-volume signal regardless the forcing amplitude so long as the bistable thresholds are crossed. Such thresholds are set by the global convective flux, which would be lowered during the Pleistocene cooling, whose interplay with the ice-albedo feedback leads to transitions of the ice signal from that dominated by obliquity to the emerging precession cycles to the ice-age cycles paced by eccentricity. Through a single dynamical framework, the theory thus may resolve many long-standing puzzles of the glacial cycles.

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On the astronomical forcing of simple conceptual ice age models

10.5194/egusphere-egu2020-10137 ◽

2020 ◽

Author(s):

Gaëlle Leloup ◽

Didier Paillard

Keyword(s):

Conceptual Model ◽

Climate Model ◽

Ice Age ◽

Early Pleistocene ◽

Model Parameters ◽

Ice Ages ◽

Glacial Cycles ◽

Orbital Parameters ◽

Ice Volume ◽

Astronomical Forcing

Variations of the Earth&#8217;s orbital parameters are known to pace the ice volume variations of the last million year [1], even if the precise mechanisms remain unknown. Several conceptual models have been used to try to better understand the connection between ice-sheet changes and the astronomical forcing. An often overlooked question is to decide which astronomical forcing can best explain the observed cycles.A rather traditional practice was to use the insolation at a some specific day of the year, for instance at mid-july [2] or at the june solstice [3]. But it was also suggested that the integrated forcing above some given threshold could be a better alternative [4]. In a more recent paper, Tzedakis et al. [5] have shown that simple rules, based on the original Milankovitch forcing or caloric seasons, could also be used to explain the timing of ice ages. Here we adapt and simplify the conceptual model of Parrenin and Paillard 2003 [6], to first reduce the set of parameters. Like in the original conceptual model from [6], this simplified conceptual model is based on climate oscillations between two states: glaciation and deglaciation. It switches to one another when crossing a defined threshold. While the triggering of glaciations is only triggered by orbital parameters, the triggering of deglaciations is triggered by a combination of orbital parameters and ice volume. Then, we apply the different possible forcings listed above and we try to adapt the model parameters to reproduce the ice volume record, at least in a qualitative way. This allows us to discuss which kind of astronomical forcing better explains the Quaternary ice ages, in the context of such simple threshold-based models.[1] Variations in the Earth's Orbit: Pacemaker of the Ice Ages, Hays et al., 1976, Science&#8232;[2] Modeling the Climatic Response to Orbital Variations, Imbrie and Imbrie, 1980, Science&#8232;[3] The timing of Pleistocene glaciations from a simple multiple-state climate model, Paillard, 1998, Nature[4] Early Pleistocene Glacial Cycles and the Integrated Summer Insolation Forcing, Huybers et al., 2006, Science[5] A simple rule to determine which insolation cycles lead to interglacials, Tzedakis et al., 2017, Nature[6] Amplitude and phase of glacial cycles from a conceptual model, Parrenin Paillard, 2003, EPSL.

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Oscillators and relaxation phenomena in Pleistocene climate theory

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2011.0315 ◽

2012 ◽

Vol 370 (1962) ◽

pp. 1140-1165 ◽

Cited By ~ 93

Author(s):

Michel Crucifix

Keyword(s):

Limit Cycle ◽

Relaxation Oscillator ◽

Homoclinic Orbits ◽

Ice Age ◽

Glacial Cycles ◽

Stochastic Dynamical Systems ◽

Pleistocene Climate ◽

Stochastic Fluctuations ◽

Earth’S Climate ◽

Almost All

Ice sheets appeared in the northern hemisphere around 3 Ma (million years) ago and glacial–interglacial cycles have paced Earth's climate since then. Superimposed on these long glacial cycles comes an intricate pattern of millennial and sub-millennial variability, including Dansgaard–Oeschger and Heinrich events. There are numerous theories about these oscillations. Here, we review a number of them in order to draw a parallel between climatic concepts and dynamical system concepts, including, in particular, the relaxation oscillator, excitability, slow–fast dynamics and homoclinic orbits. Namely, almost all theories of ice ages reviewed here feature a phenomenon of synchronization between internal climate dynamics and astronomical forcing. However, these theories differ in their bifurcation structure and this has an effect on the way the ice age phenomenon could grow 3 Ma ago. All theories on rapid events reviewed here rely on the concept of a limit cycle excited by changes in the surface freshwater balance of the ocean. The article also reviews basic effects of stochastic fluctuations on these models, including the phenomenon of phase dispersion, shortening of the limit cycle and stochastic resonance. It concludes with a more personal statement about the potential for inference with simple stochastic dynamical systems in palaeoclimate science.

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How can a glacial inception be predicted?

The Holocene ◽

10.1177/0959683610394883 ◽

2011 ◽

Vol 21 (5) ◽

pp. 831-842 ◽

Cited By ~ 22

Author(s):

Michel Crucifix

Keyword(s):

Greenhouse Gas ◽

Numerical Models ◽

Climate System ◽

Ice Age ◽

Glacial Cycles ◽

The Holocene ◽

Stochastic Dynamical System ◽

Northern Summer ◽

External Forcings ◽

Inference Network

The Early Anthropogenic Hypothesis considers that greenhouse gas concentrations should have declined during the Holocene in absence of humankind activity, leading to glacial inception around the present. It partly relies on the fact that present levels of northern summer incoming solar radiation are close to those that, in the past, preceded a glacial inception phenomenon, associated with declines in greenhouse gas concentrations. However, experiments with various numerical models of glacial cycles show that next glacial inception may still be delayed by several tens of thousands of years, even with the assumption of a decline in greenhouse gas concentrations during the Holocene. Furthermore, as we show here, conceptual models designed to capture the gross dynamics of the climate system as a whole suggest also that small disturbances may sometimes cause substantial delays in glacial events, causing a fair level of unpredictability on ice age dynamics. This suggests the need for a validated mathematical description of climate system dynamics that allows us to quantify uncertainties on predictions. Here, it is proposed to organise our knowledge about the physics and dynamics of glacial cycles through a Bayesian inference network. Constraints on the physics and dynamics of climate can be encapsulated into a stochastic dynamical system. These constraints include, in particular, estimates of the sensitivity of the components of climate to external forcings, inferred from plans of experiments with large simulators of the atmosphere, oceans and ice sheets. On the other hand, palaeoclimate observations are accounted for through a process of parameter calibration. We discuss promises and challenges raised by this programme.

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Changes in the extent of North American ice sheets during the late Cenozoic

Canadian Journal of Earth Sciences ◽

10.1139/e97-126 ◽

1998 ◽

Vol 35 (5) ◽

pp. 504-509 ◽

Cited By ~ 48

Author(s):

René W Barendregt ◽

Edward Irving

Keyword(s):

North America ◽

Late Pleistocene ◽

North American ◽

Ice Sheets ◽

Ice Age ◽

Early Pleistocene ◽

Pleistocene Glaciations ◽

Late Cenozoic ◽

Ice Volume

Magnetostratigraphy indicates that Early Pleistocene glaciations in North America, instead of forming one continuous ice mass from Atlantic to Pacific as they did in the Late Pleistocene, were characterized by eastern and western ice masses separated by a 2000 km wide north-south ice-free corridor down the centre of the continent. We argue, therefore, that the area covered by ice during periods of glaciation, and hence probably ice volume, in North America was considerably less in the first 2 Ma of the late Cenozoic than it was in the last 0.7 Ma. This is consistent with delta 18O records of ocean cores indicating the ice volumes were much less in the earlier than in the later part of the Cenozoic Ice Age.

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A Quantitative Descriptive Analysis of Students Motivation, Emotions, and Self-Regulation Processes Using Dynamical Systems Framework

PsycEXTRA Dataset ◽

10.1037/e629492011-042 ◽

2011 ◽

Author(s):

Jeannine Turner ◽

Ralph Waugh

Keyword(s):

Dynamical Systems ◽

Descriptive Analysis ◽

Self Regulation ◽

Quantitative Descriptive Analysis ◽

Quantitative Descriptive ◽

Systems Framework

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Palaeolithic Cave Art at Creswell Crags in European Context

10.1093/oso/9780199299171.001.0001 ◽

2007 ◽

Keyword(s):

Late Pleistocene ◽

Rock Art ◽

Ice Age ◽

Upper Palaeolithic ◽

Southern France ◽

European Context ◽

The World ◽

Cave Art ◽

Illustrated Book

Cave art is a subject of perennial interest among archaeologists. Until recently it was assumed that it was largely restricted to southern France and northern Iberia, although in recent years new discoveries have demonstrated that it originally had a much wider distribution. The discovery in 2003 of the UK's first examples of cave art, in two caves at Creswell Crags on the Derbyshire/Nottinghamshire border, was the most surprising illustration of this. The discoverers (the editors of the book) brought together in 2004 a number of Palaeolithic archaeologists and rock art specialists from across the world to study the Creswell art and debate its significance, and its similarities and contrasts with contemporary Late Pleistocene ("Ice Age") art on the Continent. This comprehensively illustrated book presents the Creswell art itself, the archaeology of the caves and the region, and the wider context of the Upper Palaeolithic era in Britain, as well as a number of up-to-date studies of Palaeolithic cave art in Spain, Portugal, France, and Italy which serve to contextualize the British examples.

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A Giant Ostrich from the Lower Pleistocene Nihewan Formation of North China, with a Review of the Fossil Ostriches of China

Diversity ◽

10.3390/d13020047 ◽

2021 ◽

Vol 13 (2) ◽

pp. 47

Author(s):

Eric Buffetaut ◽

Delphine Angst

Keyword(s):

Geographical Distribution ◽

Late Pleistocene ◽

North China ◽

Hebei Province ◽

Early Pleistocene ◽

Wide Geographical Distribution ◽

Lower Pleistocene ◽

The Crimea

A large incomplete ostrich femur from the Lower Pleistocene of North China, kept at the Muséum National d’Histoire Naturelle (Paris), is described. It was found by Father Emile Licent in 1925 in the Nihewan Formation (dated at about 1.8 Ma) of Hebei Province. On the basis of the minimum circumference of the shaft, a mass of 300 kg, twice that of a modern ostrich, was obtained. The bone is remarkably robust, more so than the femur of the more recent, Late Pleistocene, Struthio anderssoni from China, and resembles in that regard Pachystruthio Kretzoi, 1954, a genus known from the Lower Pleistocene of Hungary, Georgia and the Crimea, to which the Nihewan specimen is referred, as Pachystruthio indet. This find testifies to the wide geographical distribution of very massive ostriches in the Early Pleistocene of Eurasia. The giant ostrich from Nihewan was contemporaneous with the early hominins who inhabited that region in the Early Pleistocene.

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