scholarly journals Constraints on holocene ice-thickness changes in central Greenland from the GISP2 ice-core data

1995 ◽  
Vol 21 ◽  
pp. 33-39 ◽  
Author(s):  
J. F. Bolzan ◽  
E. D. Waddington ◽  
R.B. Alley ◽  
D.A. Meese
Keyword(s):  
Inverse Method ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Thickness ◽  
The Core ◽  
Ice Sheet Modeling ◽  
Age Relation ◽  
Changes Over Time ◽  
Over Time

The depth–age relation observed in the GISP2 ice core is the result of the integrated effects of ice-sheet changes over time, as well as the accumulation-rate history. Here, we construct a forward model to compute ages at various depths in the core. In the model, these ages are functions of parameters that describe the ice thickness as a function of time. Using the maximum-likelihood inverse method, these parameters are iteratively adjusted until measured and computed ages agree satisfactorily. The results suggest that the thickness along the flowline connecting the GISP2 and GRIP drill sites has not changed significantly since the onset of the Holocene. We also derive bounds on the likely thickness changes. Because these bounds are independent of assumptions concerning the processes driving the ice-sheet evolution, they can provide useful constraints for other ice-sheet modeling efforts.

scholarly journals Constraints on holocene ice-thickness changes in central Greenland from the GISP2 ice-core data

1995 ◽  
Vol 21 ◽  
pp. 33-39 ◽  
Author(s):  
J. F. Bolzan ◽  
E. D. Waddington ◽  
R.B. Alley ◽  
D.A. Meese
Keyword(s):  
Inverse Method ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Thickness ◽  
The Core ◽  
Ice Sheet Modeling ◽  
Age Relation ◽  
Changes Over Time ◽  
Over Time

The depth–age relation observed in the GISP2 ice core is the result of the integrated effects of ice-sheet changes over time, as well as the accumulation-rate history. Here, we construct a forward model to compute ages at various depths in the core. In the model, these ages are functions of parameters that describe the ice thickness as a function of time. Using the maximum-likelihood inverse method, these parameters are iteratively adjusted until measured and computed ages agree satisfactorily. The results suggest that the thickness along the flowline connecting the GISP2 and GRIP drill sites has not changed significantly since the onset of the Holocene. We also derive bounds on the likely thickness changes. Because these bounds are independent of assumptions concerning the processes driving the ice-sheet evolution, they can provide useful constraints for other ice-sheet modeling efforts.

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 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

Abstract Studies 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.

Equality and Equity in Chinese Higher Education in the Post-massification Era: An Analysis Based on Chinese Scholarly Literature

2021 ◽  
pp. 1-22
Author(s):  
Qiang Zha
Keyword(s):  
Higher Education ◽  
Literature Review ◽  
Bibliometric Analysis ◽  
Chinese Higher Education ◽  
Scholarly Literature ◽  
The Core ◽  
Research Questions ◽  
Changes Over Time ◽  
Core Issues ◽  
Over Time

Abstract This paper examines several research questions relating to equality and equity in Chinese higher education via an extended literature review, which in turn sheds light on evolving scholarly explorations into this theme. First, in the post-massification era, has the Chinese situation of equality and equity in higher education improved or deteriorated since the late 1990s? Second, what are the core issues with respect to equality and equity in Chinese higher education? Third, how have those core issues evolved or changed over time and what does the evolution indicate and entail? Methodologically, this paper uses a bibliometric analysis to detect the topical hotspots in scholarly literature and their changes over time. The study then investigates each of those topical terrains against their temporal contexts in order to gain insights into the core issues.

scholarly journals The Age-Depth Profile in the Upper Part of a Steady-State Ice Sheet

1989 ◽  
Vol 35 (121) ◽  
pp. 406-417 ◽  
Author(s):  
Niels Reeh
Keyword(s):  
Steady State ◽  
Layer Thickness ◽  
Flow Line ◽  
Numerical Models ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Thickness ◽  
Western Slope ◽  
Simple Models

AbstractSimple analytical models are developed in order to study how up-stream variations in accumulation rate and ice thickness, and horizontal convergence/ divergence of the flow influence the age and annual layer-thickness profiles in a steady-state ice sheet. Generally, a decrease/increase of the accumulation rate and an increase/decrease of the ice thickness in the up-stream direction (i.e. opposite to the flow direction) results in older/younger ice at a given depth in the ice sheet than would result if the up-stream accumulation rate and ice thickness were constant along the flow line.Convergence/divergence of the up-stream flow will decrease/increase the effect of the accumulation-rate and ice-thickness gradients, whereas convergence/divergence has no influence at all on the age and layer-thickness profiles if the up-stream accumulation rate and ice thickness are constant along the flow line.A modified column-flow model, i.e. a model for which the strain-rate profile (or, equivalently, the horizontal velocity profile) is constant down to the depth corresponding to the Holocene/Wisconsinan transition 10 750 year BP., seems to work well for dating the ice back to 10 000–11 000 year B P. at sites in the slope regions of the Greenland ice sheet. For example, the model predicts the experimentally determined age profile at Dye 3 on the south Greenland ice sheet with a relative root-mean-square error of only 3% back to c. 10 700 year B.P. As illustrated by the Milcent location on the western slope of the central Greenland ice sheet, neglecting up-stream accumulation-rate and ice-thickness gradients, may lead to dating errors as large as 3000–000 years for c. 10 000 year old ice.However, even if these gradients are taken into account, the simple model fails to give acceptable ages for 10 000 year old ice at locations on slightly sloping ice ridges with strongly divergent flow, as for example the Camp Century location. The main reason for this failure is that the site of origin of the ice cannot be determined accurately enough by the simple models, if the flow is strongly divergent.With this exception, the simple models are well suited for dating the ice at locations where the available data or the required accuracy do not justify application of elaborate numerical models. The formulae derived for the age-depth profiles can easily be worked out on a pocket calculator, and in many cases will be a sensible alternative to using numerical flow models.

scholarly journals Identification of damage development in the core of steel cord belts with the diagnostic system

2021 ◽  
Author(s):  
Ryszard Blazej ◽  
Leszek Jurdziak ◽  
Agata Kirjanow-Blazej ◽  
Tomasz Kozłowski
Keyword(s):  
Diagnostic System ◽  
Water Migration ◽  
Damage Development ◽  
Copper Ore ◽  
The Core ◽  
Single Defect ◽  
Steel Cord ◽  
Belt Conveyors ◽  
Changes Over Time ◽  
Over Time

Abstract Belt conveyors are used for transporting bulk materials over distances. The core of the belt, by transferring the longitudinal stresses and ensuring proper frictional coupling of the belt, enables belt movement and transportation of materials on its surface. As the belt cover and edges are used, the belt becomes abraded, and the core is subject to fatigue. The result is the development of cracks in rubber covers across the belt, which leads to the development of damage not only along the cables (the natural direction of water migration and corrosion) but also in the direction transverse to the belt axis. Conducting a series of scans of the St-type belt operating in one of the underground copper ore mines in Poland allowed identifying the number of failures as well as their size and changes over time. These data were in turn used to determine the measures defining the condition of the belt such as the density of defects (the number of defects per 1 m of the belt), the density of the area of damage (the area of damage per 1 m of the belt) and the change in the average area of a single defect over time. By determining the regression of these measures in time and the rate of damage development in both directions (along the axis of the belt and across the belt), it was possible to forecast future states of the belt, as well as to evaluate the costs of different belt replacement strategies and the economic rationalization of the decision to replace them. This research has become possible owing to the development of the DiagBelt system for two-dimensional imaging of the damage to the core of steel-cord belts with resolution sufficiently high to allow tracking the development of single core defects.

scholarly journals The Debris-Laden Ice at the Bottom of the Greenland Ice Sheet

1979 ◽  
Vol 23 (89) ◽  
pp. 193-207 ◽  
Author(s):  
Susan Herron ◽  
Hoar ◽  
Chester C. Langway
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Deformation ◽  
Fine Grained ◽  
Free Zone ◽  
The Core ◽  
Oxidation Of Methane ◽  
Particle Aggregates ◽  
Glacier Ice

AbstractThe Camp Century, Greenland, ice core was recovered from a bore hole which extended 1 375 m from the surface of the Greenland ice sheet to the ice/sub-ice interface. The bottom 15.7 m of the core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 μm in diameter to particle aggregates which are a maximum of 3 cm in diameter: the average debris concentration is 0.24ºº by weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. The total gas concentration averages 51 ml/kg ice compared to the average of 101 ml/kg ice for the top 1 340 m. The gas composition of debris-bearing ice has apparently been modified by the oxidation of methane as reflected by traces of methane, high CO2 levels, and low O2 levels with respect to atmospheric air. Argon, which is not affected by the oxidation, shows an enrichment in samples with lower gas concentrations. Both the low gas concentrations in the debris-laden zone and the argon enrichment may be explained by the downward diffusion of gases from bubbly glacier ice into an originally bubble-free zone of refrozen debris-laden ice. Ice texture and ice-fabric analyses reveal extremely fine-grained ice and highly preferred crystal orientation in the lowermost 10 m of the core, indicating a zone of high deformation.

scholarly journals Mass Balance of the Greenland Ice Sheet at Dye 3

1985 ◽  
Vol 31 (108) ◽  
pp. 198-200 ◽  
Author(s):  
Niels Reeh ◽  
Niels S. Gundestrup
Keyword(s):  
Mass Balance ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Bottom Layer ◽  
Surface Strain ◽  
Ice Thickness ◽  
Strain Rates ◽  
Confidence Limits ◽  
Rate Of Increase

AbstractThe mass balance of the Greenland ice sheet at Dye 3 is estimated on the basis of observations of ice thickness, accumulation rate, surface velocities, and surface strain-rates. The calculations indicate a rate of increase of surface elevation of 3 cm/year, with 95% confidence limits of −3 cm/year and +9 cm/year. Previous estimates of the mass balance of the Greenland ice sheet by the same method reported large imbalances; these are most probably due to lack of precise data and the use of quantities measured at the surface as representative of depth-averaged quantities. The most reliable observations indicate that the interior regions of the Greenland ice sheet are at present thickening at a rate of a few centimetres per year; a contributing cause for this may be the slow thinning of a bottom layer of relatively soft Wisconsin ice.

scholarly journals Modelling binge–purge oscillations of the Laurentide ice sheet using a plastic ice sheet

2008 ◽  
Vol 48 ◽  
pp. 177-182 ◽  
Author(s):  
H.C. Steen-Larsen ◽  
D. Dahl-Jensen
Keyword(s):  
Melting Point ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Climate Feedbacks ◽  
Heinrich Events ◽  
Basal Sliding ◽  
Pressure Melting ◽  
Temperature Records

AbstractA simple combined heat and ice-sheet model has been used to calculate temperatures at the base of the Laurentide ice sheet. We let the ice sheet surge when the basal temperature reaches the pressure-melting temperature. Driving the system with the observed accumulation and temperature records from the GRIP ice core, Greenland, produces surges corresponding to the observed Heinrich events. This suggests that the mechanism of basal sliding, initiated when the basal temperature reaches the melting point, can explain the surges of the Laurentide ice sheet. This study highlights the importance of the surface temperature and accumulation rate as a means of forcing the timing and strength of the Heinrich events, thus implying important ice-sheet climate feedbacks.

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.

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