scholarly journals Numerical age computation of the antarctic ice sheet for dating deep ice cores

2007 ◽  
pp. 307-318 ◽  
Author(s):  
Bernd Mügge ◽  
Alexey Savvin ◽  
Reinhard Calov ◽  
Ralf Greve
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Antarctic Ice Sheet ◽  
The Antarctic

scholarly journals The Relationship of Ultrasonic Velocities to c-axis Fabrics and Relaxation Characteristics of Ice Cores from Byrd Station, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 147-153 ◽  
Author(s):  
A. J. Gow ◽  
H. Kohnen
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Vertical Axis ◽  
P Wave ◽  
Ultrasonic Technique ◽  
Antarctic Ice Sheet ◽  
Axis Orientation ◽  
Crystal Anisotropy ◽  
The Antarctic ◽  
Relaxation Characteristics

Abstract Deep cores from Byrd Station were used to calibrate an ultrasonic technique of evaluating crystal anisotropy in the Antarctic ice sheet. Velocities measured parallel (V p ↓) and perpendicular (V p →) to the vertical axis of the cores yielded data in excellent agreement with the observed c-axis fabric profile and with the in-situ P-wave velocity profile measured parallel to the bore-hole axis by Bentley. Velocity differences ΔV (ΔV = V p ↓ – V p→) in excess of 140 m s−1 for cores from below 1300 m attest to the tight clustering of c-axes of crystals about the vertical, especially in the zone 1 300-1800 m. A small but significant decline in V p ↓ with ageing of the core, as deduced from Bentley’s down-hole data, is attributed to the formation of oriented cracks that occur in the ice cores as they relax from environmental stresses. This investigation of cores from the 2164 m thick ice sheet at Byrd Station establishes the ultrasonic technique as a viable method of monitoring relaxation characteristics of drilled cores and for determining the gross trends of c-axis orientation in ice sheets. The Byrd Station data, in conjunction with Barkov’s investigation of deep cores from Vostok, East Antarctica, also indicate that crystal anisotropy in the Antarctic ice sheet is dominated by a clustering of c-axes about a vertical symmetry axis.

scholarly journals On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet

1979 ◽  
Vol 23 (89) ◽  
pp. 185-192 ◽  
Author(s):  
A. J. Gow ◽  
S. Epstein ◽  
W. Sheehy
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Gas Content ◽  
Antarctic Ice Sheet ◽  
Glacial Ice ◽  
Major Mechanism ◽  
Basal Ice ◽  
Polar Ice Sheets ◽  
Rock Interface ◽  
The Antarctic

Abstract Cores from the bottom 4.83 m of the Antarctic ice sheet at Byrd Station contain abundant stratified debris ranging from silt-sized particles to cobbles. The nature and disposition of the debris, together with measurements of the physical properties of the inclosing ice, indicate that this zone of dirt-laden ice originated by “freezing-in” at the base of the ice sheet. The transition from air-rich glacial ice to ice practically devoid of air coincided precisely with the first appearance of debris in the ice at 4.83 m above the bed. Stable-isotope studies made in conjunction with gas-content measurements also confirm the idea of incorporation of basal debris by adfreezing of melt water at the ice―rock interface. It is suggested that the absence of air from basal ice may well constitute the most diagnostic test for discriminating between debris incorporated in a melt―refreeze process and debris entrapped by purely mechanical means, e.g. shearing. We conclude from our observations on bottom cores from Byrd Station that “freezing-in” of basal debris is the major mechanism by which sediment is incorporated into polar ice sheets.

scholarly journals Unravelling the History of Climate Change

1998 ◽  
Vol 10 (3) ◽  
pp. 223-223
Author(s):  
Ian D. Goodwin
Keyword(s):  
Time Series ◽  
Spatial Configuration ◽  
Ice Sheet ◽  
Ice Cores ◽  
Antarctic Ice Sheet ◽  
Ice Volume ◽  
Sheet Surface ◽  
Evolutionary Response ◽  
Climate Records ◽  
The Antarctic

The spatial configuration of the Antarctic ice sheet has fluctuated widely during the Late Quaternary, primarily in response to climate and sea-level forcings. Ice core time-series have long been used as proxy climate records for the Antarctic ice sheet surface and polar atmosphere, and there has been a major multinational effort to drill ice cores on or near the summit of ice domes to retrieve the longest possible records. The annual layering of ice accumulation has afforded high resolution proxy climate records on annual to decadal intervals, spanning a few hundred to hundreds of thousands of years. These time-series have also detailed the changes in the ice sheet surface elevation and dynamics, particularly since the transition from glacial to Holocene climate. However, ice sheet sensitivity to external forcings and the associated fluctuations in ice volume are probably best researched around the ice sheet's margins. The sedimentary record in these circumAntarctic margins holds the key to our unravelling of past and future responses of the Antarctic ice sheet and circumpolar oceans to climate and environmental change, including: fluctuations in ice volume; the distribution of ice shelves; the production of Antarctic bottom water; the variability in the fast ice and pack ice characteristics; biogeochemical cycling and marine productivity; and the evolutionary response of marine and terrestrial species and ecosystems.

scholarly journals A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane Mountains

2021 ◽  
Vol 7 (14) ◽  
pp. eabc1008
Author(s):  
M. Van Ginneken ◽  
S. Goderis ◽  
N. Artemieva ◽  
V. Debaille ◽  
S. Decrée ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Numerical Models ◽  
Ice Sheet ◽  
Ice Cores ◽  
Antarctic Ice Sheet ◽  
Geological Record ◽  
Asteroid Impact ◽  
The Antarctic ◽  
The Impact ◽  
Impact Events

Large airbursts, the most frequent hazardous impact events, are estimated to occur orders of magnitude more frequently than crater-forming impacts. However, finding traces of these events is impeded by the difficulty of identifying them in the recent geological record. Here, we describe condensation spherules found on top of Walnumfjellet in the Sør Rondane Mountains, Antarctica. Affinities with similar spherules found in EPICA Dome C and Dome Fuji ice cores suggest that these particles were produced during a single-asteroid impact ca. 430 thousand years (ka) ago. The lack of a confirmed crater on the Antarctic ice sheet and geochemical and 18O-poor oxygen isotope signatures allow us to hypothesize that the impact particles result from a touchdown event, in which a projectile vapor jet interacts with the Antarctic ice sheet. Numerical models support a touchdown scenario. This study has implications for the identification and inventory of large cosmic events on Earth.

scholarly journals On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet

1979 ◽  
Vol 23 (89) ◽  
pp. 185-192 ◽  
Author(s):  
A. J. Gow ◽  
S. Epstein ◽  
W. Sheehy
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Gas Content ◽  
Antarctic Ice Sheet ◽  
Glacial Ice ◽  
Major Mechanism ◽  
Basal Ice ◽  
Polar Ice Sheets ◽  
Rock Interface ◽  
The Antarctic

AbstractCores from the bottom 4.83 m of the Antarctic ice sheet at Byrd Station contain abundant stratified debris ranging from silt-sized particles to cobbles. The nature and disposition of the debris, together with measurements of the physical properties of the inclosing ice, indicate that this zone of dirt-laden ice originated by “freezing-in” at the base of the ice sheet. The transition from air-rich glacial ice to ice practically devoid of air coincided precisely with the first appearance of debris in the ice at 4.83 m above the bed. Stable-isotope studies made in conjunction with gas-content measurements also confirm the idea of incorporation of basal debris by adfreezing of melt water at the ice―rock interface. It is suggested that the absence of air from basal ice may well constitute the most diagnostic test for discriminating between debris incorporated in a melt―refreeze process and debris entrapped by purely mechanical means, e.g. shearing. We conclude from our observations on bottom cores from Byrd Station that “freezing-in” of basal debris is the major mechanism by which sediment is incorporated into polar ice sheets.

Dome Fuji Station in East Antarctica and the Japanese Antarctic Research Expedition

2012 ◽  
Vol 8 (S288) ◽  
pp. 161-168 ◽  
Author(s):  
Kazuyuki Shiraishi
Keyword(s):  
General Scheme ◽  
Ice Sheet ◽  
Ice Cores ◽  
Climatic Conditions ◽  
East Antarctica ◽  
Potential Candidate ◽  
Syowa Station ◽  
Antarctic Ice Sheet ◽  
Antarctic Research ◽  
The Antarctic

AbstractJapanese Antarctic Research Expedition (JARE) commenced on the occasion of International Geophysical Year in 1957–1958. Syowa Station, the primary station for JARE operations, is located along the northeastern coastal region of Lützow-Holm Bay, East Antarctica (69° 00′S, 39° 35′E), and was opened on 29 January 1957. Since then, JARE have been carrying out research in various fields of earth and planetary sciences and life science. Astronomical science, however, has not been popular in Antarctica. In 1995, JARE established a new inland station, Dome Fuji Station (77° 19′S, 39° 42′E), which, at 3,810 m a.s.l., is located on one of major domes of the Antarctic ice sheet, some 1,000 km south of Syowa. The climatic conditions at Dome Fuji are harsh, with an annual average air temperature of −54°C, and a recorded minimum of −79°C. In 2007, JARE completed scientific drilling to obtain ice core samples of the Antarctic ice sheet reaching 3,050 m in depth. These ice cores record environmental conditions of the earth extending back some 720,000 B.P. In recent years, it is widely known that the high-altitude environment of inland Antarctica is suitable for astronomical observations and the Japanese astronomy community identified Dome Fuji Station as a potential candidate for a future astronomical observatory. In this article, the history of Japanese Antarctic activities are described in terms of access to the inland plateau of the Antarctic continent. The general scheme and future plans of science objectives and logistics of JARE will also be introduced.

scholarly journals The Relationship of Ultrasonic Velocities to c-axis Fabrics and Relaxation Characteristics of Ice Cores from Byrd Station, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 147-153
Author(s):  
A. J. Gow ◽  
H. Kohnen
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Vertical Axis ◽  
P Wave ◽  
Ultrasonic Technique ◽  
Antarctic Ice Sheet ◽  
Axis Orientation ◽  
Crystal Anisotropy ◽  
The Antarctic ◽  
Relaxation Characteristics

AbstractDeep cores from Byrd Station were used to calibrate an ultrasonic technique of evaluating crystal anisotropy in the Antarctic ice sheet. Velocities measured parallel (Vp ↓) and perpendicular (Vp →) to the vertical axis of the cores yielded data in excellent agreement with the observed c-axis fabric profile and with the in-situ P-wave velocity profile measured parallel to the bore-hole axis by Bentley. Velocity differences ΔV (ΔV = Vp ↓ – Vp→) in excess of 140 m s−1 for cores from below 1300 m attest to the tight clustering of c-axes of crystals about the vertical, especially in the zone 1 300-1800 m. A small but significant decline in Vp ↓ with ageing of the core, as deduced from Bentley’s down-hole data, is attributed to the formation of oriented cracks that occur in the ice cores as they relax from environmental stresses. This investigation of cores from the 2164 m thick ice sheet at Byrd Station establishes the ultrasonic technique as a viable method of monitoring relaxation characteristics of drilled cores and for determining the gross trends of c-axis orientation in ice sheets. The Byrd Station data, in conjunction with Barkov’s investigation of deep cores from Vostok, East Antarctica, also indicate that crystal anisotropy in the Antarctic ice sheet is dominated by a clustering of c-axes about a vertical symmetry axis.

scholarly journals The AntSMB dataset: a comprehensive compilation of surface mass balance field observations over the Antarctic Ice Sheet

2021 ◽  
Author(s):  
Yetang Wang ◽  
Minghu Ding ◽  
Carleen H. Reijmer ◽  
Paul C. J. P. Smeets ◽  
Shugui Hou ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Ice Cores ◽  
Field Measurements ◽  
Surface Mass Balance ◽  
Antarctic Ice Sheet ◽  
Surface Mass ◽  
Ground Penetrating ◽  
The Antarctic ◽  
Comprehensive Compilation

Abstract. A comprehensive compilation of observed records is needed for accurate quantification of surface mass balance (SMB) over Antarctica, which is a key challenge for calculation of Antarctic contribution to global sea level change. Here, we present the AntSMB dataset: a new quality-controlled dataset of a variety of published field measurements of the Antarctic Ice Sheet SMB by means of stakes, snow pits, ice cores, ultrasonic sounders and ground-penetrating radars. The dataset collects 268 913 individual multi-year averaged observations, 687 annual resolved time series from 675 sites extending back the past 1000 years, and 78 968 records at daily resolution from 32 sites across the whole ice sheet. These records are derived from ice core, snow pits, stakes/stake farms, ultrasonic sounders and ground-penetrating radar measurements. This is the first ice-sheet-scale compilation of SMB records at different temporal (daily, annual and multi-year) resolutions from multiple types of measurements, which is available at: https://doi.org/10.11888/Glacio.tpdc.271148 (Wang et al., 2021). The database has potentially wide applications such as the investigation of temporal and spatial variability in SMB, model validation, assessment of remote sensing retrievals and data assimilation.

On the origin, nature and uses of Antarctic ice-sheet radio-echo layering

1999 ◽  
Vol 23 (2) ◽  
pp. 159-179 ◽  
Author(s):  
Martin J. Siegert
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Cores ◽  
Internal Layers ◽  
Antarctic Ice Sheet ◽  
Ice Surface ◽  
Geological Features ◽  
Radio Echo Sounding ◽  
The Antarctic

Airborne radio-echo sounding (RES) data display layering within the Antarctic ice sheet. At ice depths below 1000m these layers are caused by horizons of ice with relatively high acidity which were originally deposited on the ice surface after large volcanic events. Layering which is less than 1000 m from the ice surface can also be due to variation in ice density. Theoretically, therefore, internal RES layering below 1000 m should represent isochronous planes. This theory is upheld under examination of existing RES data where internal layers have been observed to follow the rules of superposition. For example, RES layers are deposited as discrete bands, fold and fault in a manner analogous to geological features, never cross over each other and, in an undisturbed deposit, have a depth-age relationship which means that the oldest layers are located at the lowest level. Moreover, the location of internal layering is independent of radiowave receiver altitude, the frequency of the radiowave does not affect layer depth, and the pulse width of the e/m wave does not affect identification of layers. Thus, RES reflects actual dielectric layering within the ice sheet. Glaciologists use RES layering for a number of reasons, including: (1) correlating ice cores; (2) as boundary conditions for numerical models to help determine the direction of ice flow; and (3) as a means of identifying the three-dimensional ice-sheet geometry and architecture.

Antarctic Uncertainty: Learning more about past ice sheet shapes with Bayesian methods

2020 ◽  
Author(s):  
Fiona Turner ◽  
Richard Wilkinson ◽  
Caitlin Buck ◽  
Julie M. Jones ◽  
Louise Sime
Keyword(s):  
Bayesian Methods ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Paired Data ◽  
Antarctic Ice Sheet ◽  
The Antarctic ◽  
The Relationship ◽  
Water Isotope

<p>Understanding the effect warming has on ice sheets is vital for accurate projections of climate change. A better understanding of how the Antarctic ice sheets have changed size and shape in the past would allow us to improve our predictions of how they may adapt in the future; this is of particular relevance in predicting future global sea level changes. This research makes use of previous reconstructions of the ice sheets, ice core data and Bayesian methods to create a model of the Antarctic ice sheet at the Last Glacial Maximum (LGM). We do this by finding the relationship between the ice sheet shape and water isotope values. </p><p>We developed a prior model which describes the variation between a set of ice sheet reconstructions at the LGM. A set of ice sheet shapes formed using this model was determined by a consultation with experts and run through the general circulation model HadCM3, providing us with paired data sets of ice sheet shapes and water isotope estimates. The relationship between ice sheet shape and water isotopes is explored using a Gaussian process emulator of HadCM3, building a statistical distribution describing the shape of the ice sheets given the isotope values outputted by the climate model. We then use MCMC to sample from the posterior distribution of the ice sheet shape and attempt to find a shape that creates isotopic values matching as closely as possible to the observations collected from ice cores. This allows us to quantify the uncertainty in the shape and incorporate expert beliefs about the Antarctic ice sheet during this time period. Our results suggests that there may have been a thicker West Antarctic ice sheet at the LGM than previously estimated.</p>

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