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.

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 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 Nonlinear response of the Antarctic Ice Sheet to late Quaternary sea level and climate forcing

2019 ◽  
Vol 13 (10) ◽  
pp. 2615-2631 ◽  
Author(s):  
Michelle Tigchelaar ◽  
Axel Timmermann ◽  
Tobias Friedrich ◽  
Malte Heinemann ◽  
David Pollard
Keyword(s):  
Sea Level ◽  
Late Quaternary ◽  
Ice Sheet ◽  
Volume Changes ◽  
Antarctic Ice Sheet ◽  
Glacial Ice ◽  
Ice Volume ◽  
Global Sea Level ◽  
The Individual ◽  
The Antarctic

Abstract. Antarctic ice volume has varied substantially during the late Quaternary, with reconstructions suggesting a glacial ice sheet extending to the continental shelf break and interglacial sea level highstands of several meters. Throughout this period, changes in the Antarctic Ice Sheet were driven by changes in atmospheric and oceanic conditions and global sea level; yet, so far modeling studies have not addressed which of these environmental forcings dominate and how they interact in the dynamical ice sheet response. Here, we force an Antarctic Ice Sheet model with global sea level reconstructions and transient, spatially explicit boundary conditions from a 408 ka climate model simulation, not only in concert with each other but, for the first time, also separately. We find that together these forcings drive glacial–interglacial ice volume changes of 12–14 ms.l.e., in line with reconstructions and previous modeling studies. None of the individual drivers – atmospheric temperature and precipitation, ocean temperatures, or sea level – single-handedly explains the full ice sheet response. In fact, the sum of the individual ice volume changes amounts to less than half of the full ice volume response, indicating the existence of strong nonlinearities and forcing synergy. Both sea level and atmospheric forcing are necessary to create full glacial ice sheet growth, whereas the contribution of ocean melt changes is found to be more a function of ice sheet geometry than climatic change. Our results highlight the importance of accurately representing the relative timing of forcings of past ice sheet simulations and underscore the need for developing coupled climate–ice sheet modeling frameworks that properly capture key feedbacks.

scholarly journals Nature of basal debris in the GISP2 and Byrd ice cores and its relevance to bed processes

1996 ◽  
Vol 22 ◽  
pp. 134-140 ◽  
Author(s):  
Anthony J. Gow ◽  
Debra A. Meese
Keyword(s):  
Stable Isotope ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Direct Interaction ◽  
Ice Cores ◽  
Glacial Meltwater ◽  
Core Drilling ◽  
Basal Ice ◽  
Rock Interface ◽  
Antarctic Ice Sheets

Successful core-drilling to bedrock of both the Greenland and Antarctic ice sheets offers unique opportunities for examining processes acting at the bed. At Byrd Station, Antarctica, penetration of the bed was accompanied by upwelling of glacial meltwater into the drillhole. The nature and disposition of sediment in the 4.83 m thick debris-rich basal ice, together with stable-isotope and gas analyses of the enclosing ice, confirm that incorporation of the debris occurred simultaneously with periodic “freeze-on” of basal meltwater. Currently, the presence of substantial meltwater at the ice/rock interface likely precludes any erosive activity at the bed. At GISP2, Greenland, basal silly ice, 13.1 m thick, is currently frozen to the bed at −9° C. Limited studies of the silty ice at GISP 2, together with results of more comprehensive investigations obtained by GRIP researchers on basal ice at a companion site at Summit indicate that the sediment-bearing basal ice likely formed in the absence of an ice sheet and was therefore unrelated to direct interaction of the present ice sheet with its bed. The fact that the basal ice at Summit is frozen to the bottom also precludes any likelihood of erosive activity at the bed.

scholarly journals Air Content Of The Byrd Core And Past Changes In The West Antarctic Ice Sheet

1982 ◽  
Vol 3 ◽  
pp. 269-273 ◽  
Author(s):  
D. Raynaud ◽  
I. M. Whillans
Keyword(s):  
Stable Isotope ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Isotope Ratios ◽  
Ice Age ◽  
Gas Content ◽  
Stable Isotope Ratios ◽  
Antarctic Ice Sheet

Analyses of ice cores taken from the Antarctic ice sheet can provide information on the environmental conditions under which the ice was formed. New results from measurements of gas content and stable isotope ratios in the Byrd station ice core are discussed and interpreted in terms of past iceflow changes.165 selected ice samples from 32 different depth levels along the core were processed for total gas content V and stable isotope ratios. This large dataset is used to discuss the variability and significance of the values of V at different depths. The short term variations of V are mainly explained by heterogeneities of the pore volume when the firn pores close off.The general trends in the values of V with depth are then used to investigate the possibility of past changes in the ice sheet. They suggest near-steady flow during the past few tens of thousands of years and that a thickening of about 200 to 250 m occurred in this area of the ice sheet at the end of the last ice age. This thickening could be due to a change in the accumulation rate.

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 The Chemical Stratigraphy of Polar Ice Sheets — A Method of Dating Ice Cores

1981 ◽  
Vol 27 (95) ◽  
pp. 3-9
Author(s):  
A. T. Wilson ◽  
C. H. Hendy
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Antarctic Ice Sheet ◽  
The Core ◽  
Similar Work ◽  
Polar Ice Sheets ◽  
Vostok Station ◽  
East Antarctic Ice Sheet

AbstractStudies of the chemical stratigraphy in the snow near Vostok station, which is near the centre of the East Antarctic ice sheet, show that sodium exhibits annual concentration differences of up to a factor of ten. Similar work on the 952 m Vostok ice core enabled accumulation rates along selected parts of the core to be determined. This in turn enables the core to be dated. The accumulation rate in this central region of the East Antarctic ice sheet for the last 50000 years has been determined and is presented. An interesting result is that the accumulation rate during the last glacial period is only half that in post-glacial times. Results from the bottom of the core provide some evidence of a past surge in the East Antarctic ice sheet.

scholarly journals Nature of basal debris in the GISP2 and Byrd ice cores and its relevance to bed processes

1996 ◽  
Vol 22 ◽  
pp. 134-140 ◽  
Author(s):  
Anthony J. Gow ◽  
Debra A. Meese
Keyword(s):  
Stable Isotope ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Direct Interaction ◽  
Ice Cores ◽  
Glacial Meltwater ◽  
Core Drilling ◽  
Basal Ice ◽  
Rock Interface ◽  
Antarctic Ice Sheets

Successful core-drilling to bedrock of both the Greenland and Antarctic ice sheets offers unique opportunities for examining processes acting at the bed. At Byrd Station, Antarctica, penetration of the bed was accompanied by upwelling of glacial meltwater into the drillhole. The nature and disposition of sediment in the 4.83 m thick debris-rich basal ice, together with stable-isotope and gas analyses of the enclosing ice, confirm that incorporation of the debris occurred simultaneously with periodic “freeze-on” of basal meltwater. Currently, the presence of substantial meltwater at the ice/rock interface likely precludes any erosive activity at the bed. At GISP2, Greenland, basal silly ice, 13.1 m thick, is currently frozen to the bed at −9° C. Limited studies of the silty ice at GISP 2, together with results of more comprehensive investigations obtained by GRIP researchers on basal ice at a companion site at Summit indicate that the sediment-bearing basal ice likely formed in the absence of an ice sheet and was therefore unrelated to direct interaction of the present ice sheet with its bed. The fact that the basal ice at Summit is frozen to the bottom also precludes any likelihood of erosive activity at the bed.

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.

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