scholarly journals Evolution of the early Antarctic ice ages

2017 ◽  
Vol 114 (15) ◽  
pp. 3867-3872 ◽  
Author(s):  
Diederik Liebrand ◽  
Anouk T. M. de Bakker ◽  
Helen M. Beddow ◽  
Paul A. Wilson ◽  
Steven M. Bohaty ◽  
...  
Keyword(s):  
Deep Sea ◽  
High Amplitude ◽  
Early Miocene ◽  
Glacial Cycles ◽  
Sea Temperature ◽  
Ice Volume ◽  
Ice Cap ◽  
Geological Past ◽  
Proxy Reconstructions ◽  
The Stability

Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene−Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial−interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.

scholarly journals A theory of glacial cycles: resolving Pleistocene puzzles

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.

scholarly journals Dynamics of ~100-kyr glacial cycles during the early Miocene

2010 ◽  
Vol 6 (6) ◽  
pp. 2741-2766
Author(s):  
D. Liebrand ◽  
L. J. Lourens ◽  
D. A. Hodell ◽  
B. de Boer ◽  
R. S. W. van de Wal
Keyword(s):  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Early Miocene ◽  
Glacial Cycles ◽  
Threshold Response ◽  
Ice Cap ◽  
Eastern Atlantic Ocean ◽  
Oxygen Isotope Record ◽  
Isotope Record

Abstract. Here, we present high-resolution stable isotope records from ODP Site 1264 in the South-Eastern Atlantic Ocean, which resolve the latest Oligocene to early Miocene (23.7–18.9 Ma) climate changes. Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded during distinct episodes (e.g., Mi zones) of low short-term (~100-kyr) eccentricity forcing, which occur two to four long-term (400-kyr) eccentricity cycles apart. We argue that a~non-linear mechanism, such as the merging of (several) large East Antarctic ice sheets, caused the build-up of a larger ice sheet. During the termination phases of these larger ice sheets, on the contrary, we find a more linear response of ice-sheet variability to orbital forcing and climate became highly sensitive to the ~100-kyr eccentricity cycle. At the Oligocene-Miocene transition the model output indicates a decrease in Northern Hemisphere temperatures such that a small ice cap could develop on Greenland. This Supports the hypothesis of a threshold response for the development of Northern Hemisphere land ice to decreasing pCO2.

scholarly journals Orbital climate variability on the northeastern Tibetan Plateau across the Eocene–Oligocene transition

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Hong Ao ◽  
Guillaume Dupont-Nivet ◽  
Eelco J. Rohling ◽  
Peng Zhang ◽  
Jean-Baptiste Ladant ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Climate Variability ◽  
Deep Sea ◽  
Sea Temperature ◽  
Temperature Variations ◽  
Continental Scale ◽  
Ice Volume ◽  
Global Ice Volume ◽  
Northeastern Tibetan Plateau ◽  
Environmental Responses

Abstract The first major build-up of Antarctic glaciation occurred in two consecutive stages across the Eocene–Oligocene transition (EOT): the EOT-1 cooling event at ~34.1–33.9 Ma and the Oi-1 glaciation event at ~33.8–33.6 Ma. Detailed orbital-scale terrestrial environmental responses to these events remain poorly known. Here we present magnetic and geochemical climate records from the northeastern Tibetan Plateau margin that are dated precisely from ~35.5 to 31 Ma by combined magneto- and astro-chronology. These records suggest a hydroclimate transition at ~33.7 Ma from eccentricity dominated cycles to oscillations paced by a combination of eccentricity, obliquity, and precession, and confirm that major Asian aridification and cooling occurred at Oi-1. We conclude that this terrestrial orbital response transition coincided with a similar transition in the marine benthic δ18O record for global ice volume and deep-sea temperature variations. The dramatic reorganization of the Asian climate system coincident with Oi-1 was, thus, a response to coeval atmospheric CO2 decline and continental-scale Antarctic glaciation.

Constraints on late Miocene ice volume variability from a global benthic δ18O compilation (8.0-5.0 Ma)

2020 ◽  
Author(s):  
Anna Joy Drury ◽  
Thomas Westerhold ◽  
David Hodell ◽  
Sarah White ◽  
Ana Christina Ravelo ◽  
...  
Keyword(s):  
Late Miocene ◽  
Deep Sea ◽  
Climate System ◽  
Sea Temperature ◽  
Ice Volume ◽  
Global Ice Volume ◽  
Pleistocene Climate ◽  
Geomagnetic Polarity ◽  
Low Amplitude ◽  
Geomagnetic Polarity Time Scale

<p>Accurate stable isotope stratigraphies are essential for understanding how past climates are influenced by orbital forcing. Deep-sea benthic foraminiferal δ<sup>18</sup>O and δ<sup>13</sup>C stratigraphies can provide precise astronomical age control and record changes in past deep-sea ocean temperatures, global ice volume and the carbon cycle. Our understanding of Plio-Pleistocene climate dynamics has improved through the development of global (LR04; Lisiecki & Raymo, 2005) and regional stacks (Ceara Rise; Wilkens et al., 2017). However, the late Miocene climate system remains poorly understood, in part because the late Miocene benthic foraminiferal δ<sup>18</sup>O stratigraphy is notoriously low amplitude.</p><p>Here, we present the first global late Miocene global benthic foraminiferal δ<sup>18</sup>O compilation spanning 8.00-5.33 Ma. We formed a “Base Stack” using six continuous benthic stratigraphies from the Atlantic (ODP Sites 982 (N), 926 (E) and 1264 (S)) and Pacific Oceans (IODP Sites U1337 and U1338 (E), ODP Site 1146 (W)). To avoid misidentification of individual excursions between sites, we verified existing splices, generated isotope data where necessary and established independent astrochronologies. To accompany the “Base Stack”, we compiled a “Comprehensive Stack”, which incorporates single-hole benthic δ<sup>18</sup>O stratigraphies to optimise global coverage.</p><p>The new global late Miocene benthic foraminiferal δ<sup>18</sup>O stack represents a stratigraphic reference section back to 8.00 Ma. The stack is accurately tied to the Geomagnetic Polarity Time Scale between Chrons C3r and C4n.2n using the magnetostratigraphy from IODP Site U1337. We recognise 68 new δ<sup>18</sup>O Marine Isotope Stages (MIS) between 7.7 and 6.5 Ma. An exceptional global response is imprinted on the dispersed sites between 7.7-6.9 & 6.4-5.4 Ma, when a strong 40 kyr heartbeat dominates the climate system. The origin of these cycles remains unclear. The influence of deep-sea temperature on the benthic δ<sup>18</sup>O stack is explored at IODP Site U1337 using Mg/Ca data. The dominant 40-kyr δ<sup>18</sup>O cycles are asymmetric, suggesting at least a partial ice volume imprint and raising the possibility that these cycles relate to early signs of northern hemisphere glaciation.</p>

scholarly journals The response of a simple Antarctic ice-flow model to temperature and sea-level fluctuations over the Cenozoic era

2007 ◽  
Vol 46 ◽  
pp. 69-77 ◽  
Author(s):  
C.I. Van Tuyll ◽  
R.S.W. Van De Wal ◽  
J. Oerlemans
Keyword(s):  
Sea Level ◽  
Deep Sea ◽  
Flow Model ◽  
Ice Sheet ◽  
Temperature Record ◽  
Ice Flow ◽  
Antarctic Ice Sheet ◽  
Sea Temperature ◽  
Ice Volume ◽  
The Antarctic

AbstractAn ice-flow model is used to simulate the Antarctic ice-sheet volume and deep-sea temperature record during Cenozoic times. We used a vertically integrated axisymmetric ice-sheet model, including bedrock adjustment. In order to overcome strong numerical hysteresis effects during climate change, the model is solved on a stretching grid. The Cenozoic reconstruction of the Antarctic ice sheet is accomplished by splitting the global oxygen isotope record derived from benthic foraminifera into an ice-volume and a deep-sea temperature component. The model is tuned to reconstruct the initiation of a large ice sheet of continental size at 34 Ma. The resulting ice volume curve shows that small ice caps (<107 km3) could have existed during Paleocene and Eocene times. Fluctuations during the Miocene are large, indicating a retreat back from the coast and a vanishing ice flux across the grounding line, but with ice volumes still up to 60% of the present-day volume. The resulting deep-sea temperature curve shows similarities with the paleotemperature curve derived from Mg/Ca in benthic calcite from 25 Ma till the present, which supports the idea that the ice volume is well reproduced for this period. Before 34 Ma, the reproduced deep-sea temperature is slightly higher than is generally assumed. Global sea-level change turns out to be of minor importance when considering the Cenozoic evolution of the ice sheet until 5 Ma.

scholarly journals Sea level and deep-sea temperature reconstructions suggest quasi-stable states and critical transitions over the past 40 million years

2021 ◽  
Vol 7 (26) ◽  
pp. eabf5326
Author(s):  
Eelco J. Rohling ◽  
Jimin Yu ◽  
David Heslop ◽  
Gavin L. Foster ◽  
Bradley Opdyke ◽  
...  
Keyword(s):  
Sea Level ◽  
Deep Sea ◽  
Dynamical Behavior ◽  
Linear Scaling ◽  
Sea Level Changes ◽  
Stable States ◽  
Sea Temperature ◽  
Ice Volume ◽  
The Past ◽  
Critical Transitions

Sea level and deep-sea temperature variations are key indicators of global climate changes. For continuous records over millions of years, deep-sea carbonate microfossil–based δ18O (δc) records are indispensable because they reflect changes in both deep-sea temperature and seawater δ18O (δw); the latter are related to ice volume and, thus, to sea level changes. Deep-sea temperature is usually resolved using elemental ratios in the same benthic microfossil shells used for δc, with linear scaling of residual δw to sea level changes. Uncertainties are large and the linear-scaling assumption remains untested. Here, we present a new process-based approach to assess relationships between changes in sea level, mean ice sheet δ18O, and both deep-sea δw and temperature and find distinct nonlinearity between sea level and δw changes. Application to δc records over the past 40 million years suggests that Earth’s climate system has complex dynamical behavior, with threshold-like adjustments (critical transitions) that separate quasi-stable deep-sea temperature and ice-volume states.

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