scholarly journals Response to Comment on "Deep-Sea Temperature and Ice Volume Changes Across the Pliocene-Pleistocene Climate Transitions"

Science ◽  
2010 ◽  
Vol 328 (5985) ◽  
pp. 1480-1480 ◽  
Author(s):  
S. Sosdian ◽  
Y. Rosenthal
Keyword(s):  
Deep Sea ◽  
Volume Changes ◽  
Sea Temperature ◽  
Ice Volume ◽  
Pleistocene Climate ◽  
Climate Transitions

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 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 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.

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.

scholarly journals Antarctic ice volume and deep-sea temperature during the last 50 Myr: a model study

2004 ◽  
Vol 39 ◽  
pp. 13-19 ◽  
Author(s):  
Johannes Oerlemans
Keyword(s):  
Deep Sea ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Climatic Conditions ◽  
Algebraic Expression ◽  
Temperature Record ◽  
Sea Temperature ◽  
Ice Volume ◽  
Wide Range ◽  
Order Of Magnitude

AbstractA simple quasi-analytical model is used to study the sensitivity of the Antarctic ice sheet to climate change. The model is axisymmetrical and has a profile that only depends on the ice-sheet radius. The climatic conditions are represented by three parameters: the altitude of the runoff line, the accumulation rate above the runoff line, and the balance gradient below the runoff line. The ice sheet may extend into the sea. At the grounding line the ice velocity is assumed to be proportional to the water depth. For this set-up, an explicit algebraic expression for the total mass budget of the ice sheet can be derived. After calibration of the model with respect to the present-day ice sheet, equilibrium states are studied for a wide range of temperatures. The model predicts a maximum ice volume (+3.4%) for a temperature that is 2.5 K above the present value. For a temperature increase of 7 K, mass loss by runoff and calving are about the same. In this case the ice volume is about 82% of the current value. The ice-sheet model is used to correct the Cenozoic deep-sea temperature record (δ18O record from benthic foraminifera in ocean sediments) for Antarctic ice volume. The model is forced with the oxygen isotope record, which is then corrected for the calculated ice volume. Therefore, the resulting deep-sea temperature and Antarctic ice-volume curves are mutually consistent. It is concluded that for the last 35×106 years the δ18O record truly is a mixed temperature/ice-volume record, in which the contributions from these parameters have the same order of magnitude.

Assessing the Global Meltwater Spike

1982 ◽  
Vol 17 (2) ◽  
pp. 148-172 ◽  
Author(s):  
Glenn A. Jones ◽  
William F. Ruddiman
Keyword(s):  
Deep Sea ◽  
Planktonic Foraminifera ◽  
World Ocean ◽  
Equatorial Atlantic ◽  
Low Salinity ◽  
Ice Volume ◽  
Middle Latitudes ◽  
Mixing Intensity ◽  
Entire World ◽  
Isotopic Signal

AbstractL. V. Worthington (1968, Meteorological Monographs 8, 63–67) hypothesized that a low-salinity lid covered the entire world ocean. By deconvolving isotopic curves from the western equatorial Pacific and equatorial Atlantic, W. H. Berger, R. F. Johnson, and J. S. Killingley (1977), Nature (London) 269, 661–663) and W. H. Berger (1978, Deep-Sea Research 25, 473–480) reconstructed “meltwater spikes” similar to those actually observed in the Gulf of Mexico and thus apparently confirmed the Worthington hypothesis. It is shown that this conclusion is unwarranted. The primary flaw in the reconstructed meltwater spikes is that the mixing intensity used in the deconvolution operation is overestimated. As a result, structure recorded in the mixed isotopic record becomes exaggerated in the attempt to restore the original unmixed record. This structure can be attributed to variable ice-volume decay during deglaciation, effects of differential solution on planktonic foraminifera, temporal changes in abundance of the foraminifera carrying the isotopic signal, and analytical error. An alternative geographic view to the global low-salinity lid is offered: a map showing portions of the ocean potentially affected by increased deglacial meltwater at middle and high latitudes and by increased precipitation-induced runoff at low and middle latitudes.

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