scholarly journals Dielectric Permittivity of Glacier Ice Measured In Situ by Radar Wide-Angle Reflection

1978 ◽  
Vol 21 (85) ◽  
pp. 315-329 ◽  
Author(s):  
Kenneth C. Jezek ◽  
John W. Clough ◽  
Charles R. Bentley ◽  
Sion Shabtaie
Keyword(s):  
Physical Phenomenon ◽  
Ice Core ◽  
Wide Angle ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Satisfactory Model ◽  
Glacier Ice ◽  
Path Geometry ◽  
Ray Path

AbstractValues of relative permittivity measured by the wide-angle reflection technique on the Ross ice Shelf show substantial variations between sites, from 3.09 to 2.89, with estimated errors of ±0.03. The largest values, closest to those normally measured in the laboratory, are found nearest to the grounded ice sheet; values decrease generally in the direction of thinner ice that has been longer on the ice shelf. We believe the variation reflects some real physical phenomenon in the ice shelf, either a true variation in the permittivity of the ice or a complication of the ray-path geometry, but are not able to offer a satisfactory model at present. We hope an explanation will be forthcoming when actual ice core samples from the deep shelf ice are available for examination.

scholarly journals Dielectric Permittivity of Glacier Ice Measured In Situ by Radar Wide-Angle Reflection

1978 ◽  
Vol 21 (85) ◽  
pp. 315-329 ◽  
Author(s):  
Kenneth C. Jezek ◽  
John W. Clough ◽  
Charles R. Bentley ◽  
Sion Shabtaie
Keyword(s):  
Physical Phenomenon ◽  
Ice Core ◽  
Wide Angle ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Satisfactory Model ◽  
Glacier Ice ◽  
Path Geometry ◽  
Ray Path

Abstract Values of relative permittivity measured by the wide-angle reflection technique on the Ross ice Shelf show substantial variations between sites, from 3.09 to 2.89, with estimated errors of ±0.03. The largest values, closest to those normally measured in the laboratory, are found nearest to the grounded ice sheet; values decrease generally in the direction of thinner ice that has been longer on the ice shelf. We believe the variation reflects some real physical phenomenon in the ice shelf, either a true variation in the permittivity of the ice or a complication of the ray-path geometry, but are not able to offer a satisfactory model at present. We hope an explanation will be forthcoming when actual ice core samples from the deep shelf ice are available for examination.

New determinations of tides on the north-western Ross Ice Shelf

2020 ◽  
pp. 1-14
Author(s):  
Richard D. Ray ◽  
Kristine M. Larson ◽  
Bruce J. Haines
Keyword(s):  
Time Series ◽  
Tide Gauge ◽  
High Rate ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Global Positioning ◽  
North Western

Abstract New determinations of ocean tides are extracted from high-rate Global Positioning System (GPS) solutions at nine stations sitting on the Ross Ice Shelf. Five are multi-year time series. Three older time series are only 2–3 weeks long. These are not ideal, but they are still useful because they provide the only in situ tide observations in that sector of the ice shelf. The long tide-gauge observations from Scott Base and Cape Roberts are also reanalysed. They allow determination of some previously neglected tidal phenomena in this region, such as third-degree tides, and they provide context for analysis of the shorter datasets. The semidiurnal tides are small at all sites, yet M2 undergoes a clear seasonal cycle, which was first noted by Sir George Darwin while studying measurements from the Discovery expedition. Darwin saw a much larger modulation than we observe, and we consider possible explanations - instrumental or climatic - for this difference.

scholarly journals Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Masahiro Minowa ◽  
Shin Sugiyama ◽  
Masato Ito ◽  
Shiori Yamane ◽  
Shigeru Aoki
Keyword(s):  
Freezing Point ◽  
East Antarctica ◽  
Ice Shelf ◽  
Rate Estimate ◽  
Ice Shelves ◽  
Plume Water ◽  
Warm Deep Water ◽  
Glacier Ice ◽  
Basal Melting

AbstractBasal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302–12 m-thick ocean cavity beneath 234–412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65–0.95°C, leading to a mean basal melt rate estimate of 1.42 m a−1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

scholarly journals The SUBGLACIOR drilling probe: concept and design

2014 ◽  
Vol 55 (68) ◽  
pp. 233-242 ◽  
Author(s):  
O. Alemany ◽  
J. Chappellaz ◽  
J. Triest ◽  
M. Calzas ◽  
O. Cattani ◽  
...  
Keyword(s):  
Methane Concentration ◽  
Ice Core ◽  
Ice Sheet ◽  
General Concept ◽  
International Partnerships ◽  
Trapped Gases ◽  
Glacier Ice ◽  
Suitable Site ◽  
The Antarctic

AbstractIn response to the ‘oldest ice’ challenge initiated by the International Partnerships in Ice Core Sciences (IPICS), new rapid-access drilling technologies through glacier ice need to be developed. These will provide the information needed to qualify potential sites on the Antarctic ice sheet where the deepest section could include ice that is >1Ma old and still in good stratigraphic order. Identifying a suitable site will be a prerequisite for deploying a multi-year deep ice-core drilling operation to elucidate the cause and mechanisms of the mid-Pleistocene transition from 40 ka glacial–interglacial cycles to 100 ka cycles. As part of the ICE&LASERS/SUBGLACIOR projects, we have designed an innovative probe, SUBGLACIOR, with the aim of perforating the ice sheet down to the bedrock in a single season and continuously measuring in situ the isotopic composition of the melted water and the methane concentration in trapped gases. Here we present the general concept of the probe, as well as the various technological solutions that we have favored so far to reach this goal.

scholarly journals Chemical Profile of the Ross Ice Shelf at Little America V, Antarctica

1974 ◽  
Vol 13 (69) ◽  
pp. 431-435 ◽  
Author(s):  
C. C. Langway ◽  
M. Herron ◽  
J. H. Cragin
Keyword(s):  
Ice Core ◽  
Chemical Profile ◽  
Ice Shelf ◽  
Ross Ice Shelf

Measurements of the concentrations of Na+K+, Mg2+, and Ca2+were made on 28 samples from the 255 m deep ice core from Little America V. All concentrations decrease sharply with depth from the firn–ice transition at 52 m to somewhere between 125 m and 150 m. From 150 m to 250 m the cationic concentrations are relatively constant. This is interpreted to indicate that the ice above 125 m fell as snow on the Ross Ice Shelf and that ice below 150 m originated inland on Marie Byrd Land.

scholarly journals Ice Core Studies of Ward Hunt Ice Shelf, 1960

1964 ◽  
Vol 5 (37) ◽  
pp. 39-59 ◽  
Author(s):  
R. H. Ragle ◽  
R. G. Blair ◽  
L. E. Persson
Keyword(s):  
Ice Core ◽  
Polarized Light ◽  
Ice Cores ◽  
Laboratory Analysis ◽  
Dartmouth College ◽  
The Arctic ◽  
Ice Shelf ◽  
Glacier Ice ◽  
Initial Work ◽  
Physical And Chemical

AbstractA four-man party representing the Arctic Institute of North America and the Department of Geology, Dartmouth College, went to the Ward Hunt Ice Shelf in 1960 to obtain ice cores for subsequent laboratory analysis. The overall objective of the project was to study the structural and stratigraphic history of the shelf and its relationship to the environment through laboratory analysis of the cores, using stratigraphic. petrologic, chemical, and physical methods.The four cores obtained were logged, packed, and shipped to Dartmouth College for detailed study. The stratigraphy and structure of the ice were studied under natural and plane polarized light conditions. The results of this initial work showed that the cores were composed of four ice types: glacier ice, lake ice, sea ice, and transition ice. Chlorinity, sulfate, and density profiles complemented megascopic studies and were most useful criteria for plotting stratigraphie changes in ice type.Results of the investigations thus far have yielded new information about the gross structure and stratigraphy of the ice shelf and re-entrant. They have also shown that the physical and chemical techniques employed will be useful in future ice-core analysis.

scholarly journals Ice Core Studies of Ward Hunt Ice Shelf, 1960

1964 ◽  
Vol 5 (37) ◽  
pp. 39-59 ◽  
Author(s):  
R. H. Ragle ◽  
R. G. Blair ◽  
L. E. Persson
Keyword(s):  
Ice Core ◽  
Polarized Light ◽  
Ice Cores ◽  
Laboratory Analysis ◽  
Dartmouth College ◽  
The Arctic ◽  
Ice Shelf ◽  
Glacier Ice ◽  
Initial Work ◽  
Physical And Chemical

Abstract A four-man party representing the Arctic Institute of North America and the Department of Geology, Dartmouth College, went to the Ward Hunt Ice Shelf in 1960 to obtain ice cores for subsequent laboratory analysis. The overall objective of the project was to study the structural and stratigraphic history of the shelf and its relationship to the environment through laboratory analysis of the cores, using stratigraphic. petrologic, chemical, and physical methods. The four cores obtained were logged, packed, and shipped to Dartmouth College for detailed study. The stratigraphy and structure of the ice were studied under natural and plane polarized light conditions. The results of this initial work showed that the cores were composed of four ice types: glacier ice, lake ice, sea ice, and transition ice. Chlorinity, sulfate, and density profiles complemented megascopic studies and were most useful criteria for plotting stratigraphie changes in ice type. Results of the investigations thus far have yielded new information about the gross structure and stratigraphy of the ice shelf and re-entrant. They have also shown that the physical and chemical techniques employed will be useful in future ice-core analysis.

scholarly journals Snow on the Ross Ice Shelf: comparison of reanalyses and observations from automatic weather stations

2013 ◽  
Vol 7 (5) ◽  
pp. 1399-1410 ◽  
Author(s):  
L. Cohen ◽  
S. Dean
Keyword(s):  
Statistical Evaluation ◽  
Snow Accumulation ◽  
High Temporal Resolution ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
In Situ Observations ◽  
Weather Stations ◽  
Event Based ◽  
Precipitation Events

Abstract. Snow accumulation measurements from automatic weather stations (AWS) around the Ross Ice Shelf (RIS), Antarctica, are used to provide a new set of ground-based observations which are compared to precipitation from the ECMWF ERA-Interim and NCEP/NCAR Reanalysis-2 datasets. The high temporal resolution of the AWS snow accumulation measurements allow for an event-based comparison of reanalyses precipitation to the in situ observations. Snow accumulation records from nine AWS provide multiple years of accumulation data between 2008 and 2012 over a relatively large, homogeneous region of Antarctica, and also provide the basis for a statistical evaluation of accumulation and precipitation events. The complex effects of wind on snow accumulation (which can both limit and enhance accumulation) complicate the use of the accumulation measurements, but this analysis shows that they can provide a valuable source of ground-based observations for comparisons to modelled precipitation on synoptic timescales. The analysis shows that ERA-Interim reproduces more precipitation events than NCEP-2, and these events correspond to an average 8.2% more precipitation. Significant correlations between reanalyses and AWS event sizes are seen at several stations and show that ERA-Interim consistently produces larger precipitation events than NCEP-2.

scholarly journals The grounding zone of the Ross Ice Shelf, West Antarctica, from ice-penetrating radar

2011 ◽  
Vol 57 (205) ◽  
pp. 917-928 ◽  
Author(s):  
Joseph A. MacGregor ◽  
Sridhar Anandakrishnan ◽  
Ginny A. Catania ◽  
Dale P. Winebrenner
Keyword(s):  
Satellite Altimetry ◽  
In Situ Measurements ◽  
Airborne Radar ◽  
Ice Accretion ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Persistent Layer

AbstractAs ice streams flow into the Ross Ice Shelf, West Antarctica, their bed coupling transitions from weak to transient to zero as the ice goes afloat. Here we explore the nature of the bed across these crucial grounding zones using ice-penetrating radar. We collected several ground-based 2 MHz radar transects across the grounding zones of Whillans and Kamb Ice Streams and inferred bed-reflectivity changes from in situ measurements of depth-averaged dielectric attenuation, made possible by the observation of both primary and multiple bed echoes. We find no significant change in the bed reflectivity across either grounding zone. Combined with reflectivity modeling, this observation suggests that a persistent layer of subglacial water (>∼0.2 m) is widespread several kilometers upstream of the grounding zone. Our results are consistent with previous inferences of gradual grounding zones across this sector of the Ross Ice Shelf from airborne radar and satellite altimetry. Separately, the only clear bed-reflectivity change that we observed occurs ∼40 km downstream of the Kamb Ice Stream grounding zone, which we attribute to the onset of marine ice accretion onto the base of the ice shelf. This onset is much nearer to the grounding zone than previously predicted.

scholarly journals Holocene Climatic Records From Antarctic Ice

1990 ◽  
Vol 14 ◽  
pp. 354-354
Author(s):  
J.R Petit ◽  
N.I. Barkov ◽  
J.P. Benoist ◽  
J. Jouzel ◽  
Y.S. Korotkevich ◽  
...  
Keyword(s):  
Ice Core ◽  
Detailed Comparison ◽  
East Antarctica ◽  
Polar Regions ◽  
Ice Shelf ◽  
Temperature Changes ◽  
The Holocene ◽  
Ross Ice Shelf ◽  
Climatic Record ◽  
Isotopic Records

The climate of the Holocene is, for continental regions from middle and low latitudes, relatively well documented from pollen studies and other sources. To obtain a global picture, these data must be supplemented by climatic series from polar regions. Such information may be extracted from δD or δ18O ice-core profiles but the interpretation of these isotopic records suffers some limitations, (1) because, expected temperature changes being small, they can be obscured by noise effects in the isotope-temperature relationship, and (2) because they can be influenced, especially in coastal regions, by changes in origin of the ice.With this in mind, we focus our presentation on Dome C and Vostok cores drilled on the East Antarctica Plateau and essentially undisturbed by ice-flow conditions. The detailed comparison between these continuous isotopic records makes it possible to know which part of the isotopic signal is climatically significant. Spectral properties of these two records are also examined over the Holocene period. In addition, we present isotopic results obtained on a 950 m ice core drilled at Komsomolskaia (also on the East Antarctica Plateau) by the Soviet Antarctic Expedition. This core fully covers the Holocene and, although discontinuous, the new data help us to document the East Antarctica isotopic record.From these data, an average climatic record is constructed which shows that the East Antarctica climate was fairly stable during the Holocene, marginally warmest around 10 kyear B.P. and coldest in periods around 1.5 and 6 kyear B P. These features are discussed in relation with other Antarctic data (Byrd, Law Dome, Ross Ice Shelf) and with climate records from both southern and northern hemispheres

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