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.

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 A new ice-core record from Lomonosovfonna, Svalbard: viewing the 1920–97 data in relation to present climate and environmental conditions

2001 ◽  
Vol 47 (157) ◽  
pp. 335-345 ◽  
Author(s):  
Elisabeth Isaksson ◽  
Veijo Pohjola ◽  
Tauno Jauhiainen ◽  
John Moore ◽  
Jean Francis Pinglot ◽  
...  
Keyword(s):  
Barents Sea ◽  
Major Ions ◽  
Accumulation Rate ◽  
Pure Shear ◽  
Ice Core ◽  
Climatic Conditions ◽  
Temperature Record ◽  
The Core ◽  
Ice Core Record ◽  
Ice Field

AbstractIn 1997 a 121 m ice core was retrieved from Lomonosovfonna, the highest ice field in Spitsbergen, Svalbard (1250 m a.s.l.). Radar measurements indicate an ice depth of 126.5 m, and borehole temperature measurements show that the ice is below the melting point. High-resolution sampling of major ions, oxygen isotopes and deuterium has been performed on the core, and the results from the uppermost 36 m suggest that quasi-annual signals are preserved. The 1963 radioactive layer is situated at 18.5–18.95 m, giving a mean annual accumulation of 0.36 m w.e. for the period 1963–96. The upper 36 m of the ice core was dated back to 1920 by counting layers provided by the seasonal variations of the ions in addition to using a constant accumulation rate, with thinning by pure shear according to Nye (1963). The stratigraphy does not seem to have been obliterated by meltwater percolation, in contrast to most previous core sites on Svalbard. The anthropogenic influence on the Svalbard environment is illustrated by increased levels of sulphate, nitrate and acidity. Both nitrate and sulphate levels started to increase in the late 1940s, remained high until the late 1980s and have decreased during the last 15 years. The records of δ18O, MSA (methane-sulphonic acid), and melt features along the core agree with the temperature record from Longyearbyen and the sea-ice record from the Barents Sea at a multi-year resolution, suggesting that this ice core reflects local climatic conditions.

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.

A Paleoclimate Model of Northern Hemisphere Ice Sheets

1981 ◽  
Vol 15 (2) ◽  
pp. 126-142 ◽  
Author(s):  
G.E. Birchfield ◽  
Johannes Weertman ◽  
Albert T. Lunde
Keyword(s):  
Accumulation Rate ◽  
Heuristic Method ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Power Spectra ◽  
Ablation Rate ◽  
Noise Spectrum ◽  
Ice Volume ◽  
Ice Load

AbstractA model for predicting the growth and decay of ice sheets based on the astronomical theory of climate change is presented. The purpose of the study in part is to isolate the role of the ice-sheet physics and earth response under varying ice load by simplifying to the extreme the role of the hydrosphere-atmosphere. Ice sheet physics and the response of the lithosphere-asthenosphere under the ice load are modeled explicitly. Insolation anomalies (taken at a fixed latitude) directly force latitudinal displacement of the snow line. Accumulation rate a, and ablation rate a′ evaluated at mean sea level are specificed as external constants; a,a′ decrease linearly with ice sheet elevation. Rough tuning of the model to the general shape of the ice-volume record of the last two major glacials determines the external constants. Model predictions of the ages of several events in the last major glaciation compare well with the radiological ages. The six glacial terminatios (I–VI) over the last 600,000 yr are identified and the predicted ages compare reasonably well with the δ18O record for two deep-sea cores. A direct comparison of model power spectra of ice volume as a function of period with spectra of the δ18O record shows apparent underprediction of power near 100,000 yr. When a quantitative but heuristic method for taking into account the “red noise” spectrum evident in the geological records is used, a much more favorable comparison is possible. The model prediction lends support to the hypothesis that the nonlinearity of the ice-sheet physics is responsible for the 100,000-yr periodicity in the geological record of the late Pleistocene.

Antarctic ice volume for the last 740 ka calculated with a simple ice sheet model

2005 ◽  
Vol 17 (2) ◽  
pp. 281-287 ◽  
Author(s):  
J. OERLEMANS
Keyword(s):  
Sea Level ◽  
Deep Sea ◽  
Relative Phase ◽  
Ice Sheet ◽  
Ice Cores ◽  
Temperature History ◽  
Glacial Cycle ◽  
Ice Volume ◽  
The Antarctic ◽  
And Sea Level

Fluctuations in the volume of the Antarctic ice sheet for the last 740 ka are calculated by forcing a simple ice sheet model with a sea-level history (from a composite deep sea δ18O record) and a temperature history (from the Dome C deuterium record). Antarctic ice volume reaches maximum values of about 30 × 1015 m3, 3 to 8 ka after glacial maxima [defined as maximum values of the deep sea δ18O record]. Minimum values of ice volume reached in the course of interglacial periods are about 26 × 1015 m3. Most of the time the temperature forcing (larger accumulation) and sea-level forcing (grounding-line retreat) tend to have competing effects. However, towards the end of a glacial cycle, when temperature rises and sea-level is still relatively low, the ice volume reaches a peak. The peak value is very sensitive to the relative phase of the sea-level forcing with respect to the temperature forcing. This is further studied by looking at the response of the model to purely periodic forcings with different relative phase. The large sensitivity of ice sheet size to the phase of the forcings may have some implications for dating of deep ice cores. Care has to be taken by using anchor points from the deep sea record.

Uranium-Series Age Estimates and Paleoclimatic Significance of Pleistocene Tufas from the Lahontan Basin, California and Nevada

1988 ◽  
Vol 30 (2) ◽  
pp. 165-176 ◽  
Author(s):  
Yong Lao ◽  
Larry Benson
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Climatic Conditions ◽  
Lake Levels ◽  
Threshold Size ◽  
Ice Volume ◽  
Uranium Series ◽  
Global Ice Volume ◽  
Paleoclimatic Significance ◽  
Age Estimates

An extended chronology of Lahontan basin lake levels based on uranium-series age estimates correlates with the global ice-volume record. Lake highstands occur at or shortly after times of maximum ice-sheet size. Moderate size lakes occur when the global ice volume is about 80% of its maximum. The data indicate that lake levels rise and fall relative to the proximity of the mean position of the jetstream. When the continental ice sheet is above some threshold size or shape, it appears that the large-scale circulation and climatic conditions are right for producing lakes of moderate to large size within the Lahontan basin.

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.

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