Bispectra of climate cycles show how ice ages are fuelled

Abstract. The increasingly nonlinear response of the climate–cryosphere system to insolation forcing during the Pliocene and Pleistocene, as recorded in benthic foraminiferal stable oxygen isotope ratios (δ18O), is marked by a distinct evolution in ice-age cycle frequency, amplitude, phase, and geometry. To date, very few studies have thoroughly investigated the non-sinusoidal shape of these climate cycles, leaving precious information unused to further unravel the complex dynamics of the Earth's system. Here, we present higher-order spectral analyses of the LR04 δ18O stack that describe coupling and energy exchanges among astronomically paced climate cycles. These advanced bispectral computations show how energy is passed from precession-paced to obliquity-paced climate cycles during the Early Pleistocene (from ∼2500 to ∼750 ka) and ultimately to eccentricity-paced climate cycles during the Middle and Late Pleistocene (from ∼750 ka onward). They also show how energy is transferred among many periodicities that have no primary astronomical origin. We hypothesise that the change of obliquity-paced climate cycles during the mid-Pleistocene transition (from ∼1200 to ∼600 ka), from being a net sink into a net source of energy, is indicative of the passing of a land-ice mass loading threshold in the Northern Hemisphere (NH), after which cycles of crustal depression and rebound started to resonate with the ∼110 kyr eccentricity modulation of precession. However, precession-paced climate cycles remain persistent energy providers throughout the Late Pliocene and Pleistocene, which is supportive of a dominant and continuous fuelling of the NH ice ages by insolation in the (sub)tropical zones, and the control it exerts on meridional heat and moisture transport through atmospheric and oceanic circulation.

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Bispectra of climate cycles show how ice ages are fuelled

10.5194/cp-2019-43 ◽

2019 ◽

Author(s):

Diederik Liebrand ◽

Anouk T. M. de Bakker

Keyword(s):

Complex Dynamics ◽

Ice Age ◽

Early Pleistocene ◽

Oceanic Circulation ◽

Ice Ages ◽

Cycle Frequency ◽

Climate Cycles ◽

Middle And Late Pleistocene ◽

Heat And Moisture ◽

Earth’S System

Abstract. The increasingly nonlinear response of the climate-cryosphere system to insolation forcing during the Pliocene and Pleistocene, as recorded in benthic foraminiferal stable oxygen isotope ratios (δ18O), is marked by a distinct evolution in ice-age cycle frequency, amplitude, phase, and geometry. To date, very few studies have thoroughly investigated the nonsinusoidal shape of these climate cycles, leaving precious information unused to further unravel the complex dynamics of the Earth's system. Here, we present higher-order spectral analyses of the LR04 δ18O stack that describe coupling and energy exchanges among astronomically-paced climate cycles during the Pliocene and Pleistocene. These advanced bispectral computations show how energy is passed from precession-paced to obliquity-paced climate cycles during the Early Pleistocene (~ 2,500–~ 750 ka), and ultimately to eccentricity-paced climate cycles during the Middle and Late Pleistocene (from ~ 750 ka onward). They also show how energy is transferred among many cycles that have no primary astronomical origin. We hypothesize that the change of obliquity-paced climate cycles during the mid-Pleistocene transition (~ 1,200–~ 600 ka), from being a net sink into a net source of energy, is indicative of the passing of a land-ice mass-loading threshold in the Northern Hemisphere (NH), after which cycles of crustal depression and rebound started to resonate with the ~ 110-kyr eccentricity modulation of precession. However, precession-paced climate cycles remain persistent energy providers throughout the Late Pliocene and entire Pleistocene, which is supportive of a dominant and continuous fuelling of the NH ice ages by insolation in the (sub-) tropical zones, and the control it exerts on meridional heat and moisture transport through atmospheric and oceanic circulation.

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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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The origin of the 1500-year climate cycles in Holocene North-Atlantic records

Climate of the Past Discussions ◽

10.5194/cpd-3-679-2007 ◽

2007 ◽

Vol 3 (2) ◽

pp. 679-692 ◽

Cited By ~ 18

Author(s):

M. Debret ◽

V. Bout-Roumazeilles ◽

F. Grousset ◽

M. Desmet ◽

J. F. McManus ◽

...

Keyword(s):

Ocean Circulation ◽

Ice Core ◽

Ice Age ◽

Data Series ◽

Oceanic Circulation ◽

Solar Forcing ◽

The Holocene ◽

Relative Contribution ◽

Climate Cycles ◽

Wavelets Analysis

Abstract. Since the first suggestion of 1500-year cycles in the advance and retreat of glaciers (Denton and Karlen, 1973), many studies have uncovered evidence of repeated climate oscillations of 2500, 1500, and 1000 years. During last glacial period, natural climate cycles of 1500 years appear to be persistent (Bond and Lotti, 1995) and remarkably regular (Mayewski et al., 1997; Rahmstorf, 2003), yet the origin of this pacing during the Holocene remains a mystery (Rahmstorf, 2003), making it one of the outstanding puzzles of climate variability. Solar variability is often considered likely to be responsible for such cyclicities, but the evidence for solar forcing is difficult to evaluate within available data series due to the shortcomings of conventional time-series analyses. However, the wavelets analysis method is appropriate when considering non-stationary variability. Here we show by the use of wavelets analysis that it is possible to distinguish solar forcing of 1000- and 2500- year oscillations from oceanic forcing of 1500-year cycles. Using this method, the relative contribution of solar-related and ocean-related climate influences can be distinguished throughout the 10 000 Holocene intervals since the last ice age. These results reveal that the mysteriously regular 1,500-year climate cycles are linked with the oceanic circulation and not with variations in solar output as previously argued (Bond et al., 2001). In this light, previously studied marine sediment (Bianchi and McCave, 1999; Giraudeau et al., 2000), ice core (O'Brien et al., 1995) and dust records (Jackson et al., 2005) can be seen to contain the evidence of combined forcing mechanisms, whose relative influences varied during the course of the Holocene. Circum-Atlantic climate records cannot be explained by solar forcing, but require changes in ocean circulation, as suggested previously (Broecker et al., 2001; McManus et al., 1999).

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Changes in the Poleward Energy Flux by the Atmosphere and Ocean as a Possible Cause for Ice Ages

Quaternary Research ◽

10.1016/0033-5894(74)90001-5 ◽

1974 ◽

Vol 4 (2) ◽

pp. 117-127 ◽

Cited By ~ 77

Author(s):

Reginald E. Newell

Keyword(s):

Energy Flux ◽

Energy Budget ◽

General Circulation ◽

Ice Age ◽

Polar Regions ◽

Oceanic Circulation ◽

Ice Ages ◽

Ocean Energy ◽

The Past ◽

Speculative Hypothesis

It is proposed that the two preferred modes of temperature and circulation of the atmosphere which occurred over the past 100,000 yr correspond to two modes of partitioning of the poleward energy flux between the atmosphere and ocean. At present the ocean carries an appreciable fraction of the transport, for example about three-eighths at 30°N. In the cold mode it is suggested that the ocean carries less, and the atmosphere more, than at present. During the formation of the ice, at 50,000 BP, for example, the overall flux is expected to be slightly lower than at present and during melting, at 16,000 BP, slightly higher. The transition between the modes is seen as a natural imbalance in the atmosphere-ocean energy budget with a gradual warming of the ocean during an Ice Age eventually cluminating in its termination. At the present the imbalance is thought to correspond to a natural cooling of the ocean, which will lead to the next Ice Age.The magnitude of temperature changes in the polar regions differ between the hemispheres in the same way as present seasonal changes, being larger in the northern than in the southern hemisphere.Overall the atmospheric energy cycle was more intense during the Ice Ages than now.Observational tests are proposed by which predictions from the present arguments may be compared with deductions about the environment of the past.Data used for the present state of the atmospheric general circulation are the latest global data available and contain no known major uncertainties. However, data for the oceanic circulation and energy budget are less well known for the present and almost unknown for the past. Hence the proposed imbalances must be treated as part of a speculative hypothesis, but one which eventually may be subject to observational test as no solar variability is invoked.

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The origin of the 1500-year climate cycles in Holocene North-Atlantic records

Climate of the Past ◽

10.5194/cp-3-569-2007 ◽

2007 ◽

Vol 3 (4) ◽

pp. 569-575 ◽

Cited By ~ 104

Author(s):

M. Debret ◽

V. Bout-Roumazeilles ◽

F. Grousset ◽

M. Desmet ◽

J. F. McManus ◽

...

Keyword(s):

Ocean Circulation ◽

Ice Core ◽

Ice Age ◽

Data Series ◽

Oceanic Circulation ◽

Solar Forcing ◽

The Holocene ◽

Relative Contribution ◽

Climate Cycles ◽

Wavelets Analysis

Abstract. Since the first suggestion of 1500-year cycles in the advance and retreat of glaciers (Denton and Karlen, 1973), many studies have uncovered evidence of repeated climate oscillations of 2500, 1500, and 1000 years. During last glacial period, natural climate cycles of 1500 years appear to be persistent (Bond and Lotti, 1995) and remarkably regular (Mayewski et al., 1997; Rahmstorf, 2003), yet the origin of this pacing during the Holocene remains a mystery (Rahmstorf, 2003), making it one of the outstanding puzzles of climate variability. Solar variability is often considered likely to be responsible for such cyclicities, but the evidence for solar forcing is difficult to evaluate within available data series due to the shortcomings of conventional time-series analyses. However, the wavelets analysis method is appropriate when considering non-stationary variability. Here we show by the use of wavelets analysis that it is possible to distinguish solar forcing of 1000- and 2500- year oscillations from oceanic forcing of 1500-year cycles. Using this method, the relative contribution of solar-related and ocean-related climate influences can be distinguished throughout the 10 000 yr Holocene intervals since the last ice age. These results reveal that the 1500-year climate cycles are linked with the oceanic circulation and not with variations in solar output as previously argued (Bond et al., 2001). In this light, previously studied marine sediment (Bianchi and McCave, 1999; Chapman and Shackleton, 2000; Giraudeau et al., 2000), ice core (O'Brien et al., 1995; Vonmoos et al., 2006) and dust records (Jackson et al., 2005) can be seen to contain the evidence of combined forcing mechanisms, whose relative influences varied during the course of the Holocene. Circum-Atlantic climate records cannot be explained exclusively by solar forcing, but require changes in ocean circulation, as suggested previously (Broecker et al., 2001; McManus et al., 1999).

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Emergence of critical climate states during the Pleistocene

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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4DVAR HF radar assimilation South of Africa

10.21203/rs.3.rs-90821/v1 ◽

2020 ◽

Author(s):

Xavier Couvelard ◽

Christophe Messager ◽

Pierrick Penven ◽

Phillipe Lattes

Keyword(s):

Complex Dynamics ◽

Surface Current ◽

Hf Radar ◽

Detailed Knowledge ◽

Oceanic Circulation ◽

Geostrophic Currents ◽

Area Of Interest ◽

Covered Area ◽

The One ◽

Gas Fields

Abstract The oceanic circulation south of Africa is characterized by a complex dynamics with a strong variability due to the presence of the Agulhas current and numerous eddies. The area of interest of this paper, is also the location of several natural gas fields under seafloor which are targeted for drilling and exploitation.The complex and powerful ocean currents induce significant issues for ship operations at the surface as well as under the surface for deep sea operations. Therefore, the knowledge of the state of the currents and the ability to forecast them in a realistic manner could greatly enforce the safety of various marine operation. Following this objective an array of HF radar systems was deployed to allow a detailed knowledge of the Agulhas currents and its associated eddy activity. It is shown in this study that 4DVAR assimilation of HF radar allow to represent the surface circulation more realistically. Two kind of experiments have been performed, a one-month analysis and two days forecast. The one-month 4DVAR experiment have been compared to geostrophic currents issued from altimeters and highlight an important improvement of the geostrophic currents. Furthermore, despite the restricted size of the area covered with HF radar, we show that the solution is improved almost in the whole domain, mainly upstream and downstream of the HF radar's covered area. We also show that while benefits of the assimilation on the surface current intensity is significantly reduced in the first 6 hours of the forecast, the correction in direction persists after 48 hours.

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The residence time of Southern Ocean surface waters and the 100,000-year ice age cycle

Science ◽

10.1126/science.aat7067 ◽

2019 ◽

Vol 363 (6431) ◽

pp. 1080-1084 ◽

Cited By ~ 16

Author(s):

Adam P. Hasenfratz ◽

Samuel L. Jaccard ◽

Alfredo Martínez-García ◽

Daniel M. Sigman ◽

David A. Hodell ◽

...

Keyword(s):

Southern Ocean ◽

Residence Time ◽

Surface Waters ◽

High Amplitude ◽

Ice Age ◽

Ice Ages ◽

Glacial Cycle ◽

Surface Circulation ◽

Carbon Dioxide Release ◽

The Antarctic

From 1.25 million to 700,000 years ago, the ice age cycle deepened and lengthened from 41,000- to 100,000-year periodicity, a transition that remains unexplained. Using surface- and bottom-dwelling foraminifera from the Antarctic Zone of the Southern Ocean to reconstruct the deep-to-surface supply of water during the ice ages of the past 1.5 million years, we found that a reduction in deep water supply and a concomitant freshening of the surface ocean coincided with the emergence of the high-amplitude 100,000-year glacial cycle. We propose that this slowing of deep-to-surface circulation (i.e., a longer residence time for Antarctic surface waters) prolonged ice ages by allowing the Antarctic halocline to strengthen, which increased the resistance of the Antarctic upper water column to orbitally paced drivers of carbon dioxide release.

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GEOMORPHOLOGY, NEOTECHONICS AND PALEOGEOGRAPHY OF THE NATURAL GEOLOGICAL MONUMENTSON "STARUNIA" TERRITORY

Visnyk of Taras Shevchenko National University of Kyiv Geology ◽

10.17721/1728-2713.86.01 ◽

2019 ◽

pp. 6-12

Author(s):

T. Kalynii ◽

V. Omelchenko

Keyword(s):

Economic Status ◽

Ice Age ◽

Coarse Grained ◽

Early Pleistocene ◽

The Carpathians ◽

Dwarf Birch ◽

Geomorphological Map ◽

Tourist Center ◽

Pleistocene Mammals ◽

River Valleys

A survey of geomorphological and neotectonic features around "The Starunia paleontological site" allows to produce a complete description of paleogeographic conditions and geological age of the Pleistocene mammals. The floodplain terraces I and II and a redevelopment valley have been distinguished on the geomorphological map and a sketch of cross-section of the Velyky Lukavets River valley. The location of fossil fauna (mammoth and rhinoceroses) has been indicated. The prospect of finding new extinct Pleistocene mammals preserved in bitumen and salt has been substantiated. In the late Pliocene, the northeast macro-slope of the Carpathians was dissected by many parallel river valleys transverse to the main Carpathian direction of structures and longitudinal valleys. The rivers took down coarse-grained material from the mountains that formed the high terraces and debris cones (inland delta) of the ancient Dniester valley. The latter was formed at the foot of the Carpathians, in the area of the modern village of Loyeva and the Dniester, then gradually retreated 30–40 km to the northeast and took its present location on the longitude of the town of Halych. Its block mass alluvium formed two ancient terrace plains – Krasna and Loyeva. The climate was subtropical, the type of the present Mediterranean, as evidenced by the red-brown color of the clayey cement of coarse-grained alluvium and cover clays with active migration of iron and manganese. In the early Pleistocene, in the wide swampy valley of the river Lukavets Velykyi, the winding beds of the last stage of river valleys development were quietly meandered. Monotonous dark gray to black marsh accumulations, silt clays, biogenic silts with numerous plant remains accumulated. Landscapes – tundra with dwarf birch, alder, willow etc. The climate was severe, consistent with Wurm (Valdai) glaciation (59–13 thousand years ago). Perhaps just then herds of mammoths and rhinos grazed in the valleys of the Starunia territory and our ancestors Cro-Magnons lived here. The extremely important practical value of Starunia is that further expansion of research and creation of an international ecological-tourist center – the Geopark of the Ice Age will significantly improve the socio-economic status of the village of Starunia, provide the population with new jobs and raise the level of tourism in the Ivano-Frankivsk region. The authors hope that the unique phenomenon of Starunia will be preserved for future generations.

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