scholarly journals A Reconsideration of the Mass Balance of a Portion of the Ross Ice Shelf, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 381-384 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Small Region ◽  
Volume Element ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Velocity ◽  
Flow Band ◽  
Input Gate ◽  
North Western

AbstractThe identification of a small region of grounded ice in the north-western sector of the Ross Ice Shelf has forced a re-evaluation of the mass-balance calculations carried out by Thomas and Bentley (1978). Those authors concluded that the Ross Ice Shelf up-stream of Crary Ice Rise was thickening, but they did not take into account the effects on the velocity field of grounded ice (of which they were unaware), which is located near the input gate to their volume element. Reasonable estimates of the degree to which the ice velocity just up-stream of the grounded ice is diminished indicate that it is no longer possible to conclude that the ice shelf is thickening using Thomas and Bentley’s original flow band. Therefore, a new flow band was chosen which was grid east of Thomas and Bentley’s band and unaffected by any nearby grounded areas. The mass balance in this flow band was found to be zero within experimental error; a difference exceeding about 0.2 m a−1in magnitude between the thickening and bottom freeze-on rates is unlikely.

scholarly journals A Reconsideration of the Mass Balance of a Portion of the Ross Ice Shelf, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 381-384 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Small Region ◽  
Volume Element ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Velocity ◽  
Flow Band ◽  
Input Gate ◽  
North Western

AbstractThe identification of a small region of grounded ice in the north-western sector of the Ross Ice Shelf has forced a re-evaluation of the mass-balance calculations carried out by Thomas and Bentley (1978). Those authors concluded that the Ross Ice Shelf up-stream of Crary Ice Rise was thickening, but they did not take into account the effects on the velocity field of grounded ice (of which they were unaware), which is located near the input gate to their volume element. Reasonable estimates of the degree to which the ice velocity just up-stream of the grounded ice is diminished indicate that it is no longer possible to conclude that the ice shelf is thickening using Thomas and Bentley’s original flow band. Therefore, a new flow band was chosen which was grid east of Thomas and Bentley’s band and unaffected by any nearby grounded areas. The mass balance in this flow band was found to be zero within experimental error; a difference exceeding about 0.2 m a−1 in magnitude between the thickening and bottom freeze-on rates is unlikely.

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 Glaciological settings and recent mass balance of Blåskimen Island in Dronning Maud Land, Antarctica

2017 ◽  
Vol 11 (6) ◽  
pp. 2883-2896 ◽  
Author(s):  
Vikram Goel ◽  
Joel Brown ◽  
Kenichi Matsuoka
Keyword(s):  
Mass Balance ◽  
Field Measurements ◽  
The South ◽  
Ice Shelf ◽  
Surface Mass ◽  
The Past ◽  
The North ◽  
Dronning Maud Land ◽  
North Western ◽  
Method Show

Abstract. The ice-shelf-fringed coast of Dronning Maud Land in East Antarctica contains numerous ice rises that influence the dynamics and mass balance of the region. However, only a few of these ice rises have been investigated in detail. Here, we present field measurements of Blåskimen Island, an isle-type ice rise adjacent to Fimbul Ice Shelf. This ice rise is largely dome shaped, with a pronounced ridge extending to the south-west from its summit (410 m a.s.l.). Its bed is mostly flat and about 100 m below the current sea level. Shallow radar-detected isochrones dated with a firn core reveal that the surface mass balance is higher on the south-eastern (upwind) slope than on the north-western (downwind) slope by ∼ 37 %, and this pattern has persisted for at least the past decade. Moreover, arches in radar stratigraphy suggest that the summit of the ice rise has been stable for ∼ 600 years. Ensemble estimates of the mass balance using the input–output method show that this ice rise has thickened by 0.12–0.37 m ice equivalent per year over the past decade.

scholarly journals Tabular Icebergs: Implication from Geophysical Studies of Ice Shelves

1980 ◽  
Vol 1 ◽  
pp. 55-55
Author(s):  
Sion Shabtaie ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Sea Water ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Frictional Drag ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Rift Zones ◽  
Different Characteristics ◽  
Ice Water

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridges and troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration of the berg in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice-shelf barrier at four sites in flow bands of very different characteristics are shown. In some places rifting upstream from the barrier shows regular spacings, suggesting a periodic calving. Differential bottom melting near the barrier causes the icebergs to have an uneven surface and bottom (i.e. dome-shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass-balance rates of tabular icebergs.

scholarly journals Tabular Icebergs: Implications from Geophysical Studies of Ice Shelves

1982 ◽  
Vol 28 (100) ◽  
pp. 413-430 ◽  
Author(s):  
Sion Shabtaie ◽  
Charles R. Bentley
Keyword(s):  
Mass Balance ◽  
Sea Water ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Frictional Drag ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Rift Zones ◽  
Different Characteristics ◽  
Ice Water

AbstractRecent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridge/troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration in the course of transport.The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.Radar profiles of the ice shelf front at four sites in flow bands of very different characteristics are shown. In some places rifting up-stream from the front shows regular spacings, suggesting a periodic calving. Differential bottom melting near the front causes the icebergs to have an uneven surface and bottom (i.e. dome shaped).Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass balance rates of tabular icebergs.

scholarly journals Geodetic Results of the Ross Ice Shelf Survey Expeditions, 1962–63 and 1965–66

1969 ◽  
Vol 8 (52) ◽  
pp. 67-90 ◽  
Author(s):  
Egon Dorrer ◽  
Walther Hofmann ◽  
Wilfried Seufert
Keyword(s):  
Maximum Velocity ◽  
Careful Study ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
The North ◽  
Parallel Movement ◽  
Time Reduction ◽  
Observation Method ◽  
East West

By means of modern geodetic observation techniques the ice movement along an east-west and a north-south profile across the Ross Ice Shelf, Antarctica, was measured during the two Antarctic summers, 1962–63 and 1965–66. 103 markers were placed on the 910 km long traverse. Distances were measured by tellurometer, and traverse angles by a precision theodolite between all consecutive markers, normally 8 to 9 km apart. For this type of observation method, six men distributed into three groups of two men each were necessary.The main part of the paper deals with data processing and with the computation of the ice movement. As the ice moves, the geometrical configuration of the traverse changes during the epoch of observation. For this “reduction to epoch” problem two methods are described in detail: (1) time reduction of observations, and (2) time reduction of positions. Between the two field journeys, only linear ice movement can be assumed. It is possible, however, to determine acceleration and curvature of the ice flow at all traverse points where the traverse angles differ considerably from 180°.The result of all computations is the field of velocity vectors along the traverse. Obvious characteristics are the rapid increase of velocity between the McMurdo Ice Shelf and Ross Ice Shelf, the uniform and nearly parallel movement in the middle of the ice shelf (maximum velocity 935 m year−1), the decrease of velocity along the north-south profile, and the systematic increase of divergence of the flow lines towards the ice margins. Careful study of the velocity vector field shows some deviations from an entirely uniform distribution.

scholarly journals The Equilibrium State of the Eastern Half of the Ross Ice Shelf

1978 ◽  
Vol 20 (84) ◽  
pp. 509-518 ◽  
Author(s):  
Robert H. Thomas ◽  
Charles R. Bentley
Keyword(s):  
Indirect Evidence ◽  
Melting Rate ◽  
Snow Accumulation ◽  
Surface Strain ◽  
The South ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Average Value ◽  
West Antarctic ◽  
Flow Band

AbstractMeasurements of ice thickness, velocity, snow accumulation rates, and surface strain-rates are used to examine the state of equilibrium of three flow bands of the Ross Ice Shelf. The analysis gives the rate of thickening of the ice shelf in terms of the basal freezing rate, which is unknown. However, indirect evidence suggests that the basal flux ranges from a small value of freezing in the south to a melting rate of about one meter of ice per year at the ice front. If these values are correct then the flow band in the south-east corner of the ice shelf appears to be thickening at an average value of (34 ± 15) cm of ice per year. Persistent thickening at this rate must lead to grounding of large areas of the ice shelf. This would restrict drainage from West Antarctic ice streams which feed this part of the ice shelf and these would tend to thicken and advance their grounding lines into the ice shelf. Further north, near the RISP bore-hole site, the ice shelf is probably in equilibrium. The largest flow band is to the south and east of Roosevelt Island, and this also may be in equilibrium if there is significant bottom melting from ice shelf that is more than 100 km from the ice front.

scholarly journals Pattern of Ice Surface Lowering for Rennick Glacier, Northern Victoria Land, Antarctica

1979 ◽  
Vol 22 (86) ◽  
pp. 53-65 ◽  
Author(s):  
Paul A. Mayewski ◽  
John W. Attig ◽  
David J. Drewry
Keyword(s):  
Mass Balance ◽  
Sea Level ◽  
Current Fluctuations ◽  
Ice Shelf ◽  
Surface Cover ◽  
Ross Ice Shelf ◽  
Ice Surface ◽  
Victoria Land ◽  
Grounding Line ◽  
And Sea Level

AbstractRennick Glacier is one of the major ice drainages in northern Victoria Land. Unlike glaciers farther south along the Transantarctic Mountains, Rennick Glacier does not drain into the Ross Ice Shelf but flows directly into a seasonally ice-covered ocean. Therefore, current fluctuations of this glacier are unhampered by the dampening effects of the Ross Ice Shelf. The primary controls on the activity of this glacier and others in this region are mass balance and sea-level.Two major glacial events are recorded in the upper Rennick Glacier region. The location of erratics and glacially scoured features suggest that during the oldest or Evans glaciation ice covered all but the highest peaks in the region. Following this glaciation a re-advance produced the Rennick glaciation. Drift produced during this glaciation has a surface cover of unweathered clasts and is commonly found in the form of recessional moraines with associated ice-marginal lakes. Rennick Glacier is currently in a recessional phase of the Rennick glaciation. The phase is characterized by physical re-adjustments of local ice masses including progressive inland migration of the Rennick Glacier grounding line. To date the grounding line has migrated up to the mid-point of the glacier. This trend may be expected to continue.

Modelling the ocean circulation beneath the Ross Ice Shelf

2003 ◽  
Vol 15 (1) ◽  
pp. 13-23 ◽  
Author(s):  
DAVID M. HOLLAND ◽  
STANLEY S. JACOBS ◽  
ADRIAN JENKINS
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ross Sea ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Shelf Water ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Shelf Water

We applied a modified version of the Miami isopycnic coordinate ocean general circulation model (MICOM) to the ocean cavity beneath the Ross Ice Shelf to investigate the circulation of ocean waters in the sub-ice shelf cavity, along with the melting and freezing regimes at the base of the ice shelf. Model passive tracers are utilized to highlight the pathways of waters entering and exiting the cavity, and output is compared with data taken in the cavity and along the ice shelf front. High Salinity Shelf Water on the western Ross Sea continental shelf flows into the cavity along the sea floor and is transformed into Ice Shelf Water upon contact with the ice shelf base. Ice Shelf Water flows out of the cavity mainly around 180°, but also further east and on the western side of McMurdo Sound, as observed. Active ventilation of the region near the ice shelf front is forced by seasonal variations in the density structure of the water column to the north, driving rapid melting. Circulation in the more isolated interior is weaker, leading to melting at deeper ice and refreezing beneath shallower ice. Net melting over the whole ice shelf base is lower than other estimates, but is likely to increase as additional forcings are added to the model.

scholarly journals The Unsteady State of The Ross Ice Shelf (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 339
Author(s):  
Charles R. Bentley
Keyword(s):  
Ice Cores ◽  
Secular Change ◽  
Supporting Evidence ◽  
Ice Shelf ◽  
Outlet Glacier ◽  
Thickness Change ◽  
Ross Ice Shelf ◽  
Input Flux ◽  
Entire Flow ◽  
Flow Band

According to our present picture, the Ross Ice Shelf is subject to relatively rapid changes, perhaps constantly out of steady state, but not undergoing a long-term secular change. Recent supporting evidence comes from a flow band of ice extending from the edges of Beardmore Glacier as far as Nimrod Glacier. The boundaries of that band and of ice stemming from several individual glaciers within it have been traced on airborne radar records. Using measurements made as part of the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) program, mass-flux variations along the bands have been calculated. The band from Nimrod Glacier, a major outlet glacier from the East Antarctic inland ice sheet, shows no significant deviations from zero for the sum of thence thickness change rate ∂H/∂t and bottom melt rate. ḃH. We interpret this to mean that ∂H/∂t and ḃH are separately small. Significant flux variations in the entire flow band are then attributed to relatively large variations in input flux from the alpine glaciers of the Transantarctic Mountains, and from zones between the glaciers. Although flux variations are not coherent between individual glacier bands, the average strengths of internal reflections (from bottom crevasses and/or included moraine), exhibit a semi-coherent variation with a period of 400 a that correlates with 180 variations in ice cores from Dome C and Byrd station.

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