scholarly journals Basal melting at the Ekström Ice Shelf, Antarctica, estimated from mass flux divergence

2012 ◽  
Vol 53 (60) ◽  
pp. 294-302 ◽  
Author(s):  
Niklas Neckel ◽  
Reinhard Drews ◽  
Wolfgang Rack ◽  
Daniel Steinhage
Keyword(s):  
Steady State ◽  
Mass Flux ◽  
Large Scale ◽  
Snow Accumulation ◽  
Ice Thickness ◽  
Flux Divergence ◽  
Ice Shelf ◽  
Mass Fluxes ◽  
Radio Echo Sounding ◽  
Basal Melting

AbstractWe characterize the basal mass balance of the Ekström Ice Shelf, Dronning Maud Land, Antarctica, using interferometrically derived surface velocities and ice thickness measurements from radio-echo sounding (RES). The surface velocities are based on data from European Remote-sensing Satellites-1 and -2 (ERS-1/2) during 1994–97. The ice thickness grid consists of 136 RES profiles acquired between 1996 and 2006. Mass fluxes are calculated along selected RES profiles where possible, to reduce uncertainties from ice thickness interpolation. Elsewhere large-scale mass fluxes are calculated using interpolated ice thickness data. Themass flux into the Ekström Ice Shelf from the main grounded drainage basins is estimated to be 3.19±0.4Gt a–1. The mass flux near the ice shelf front is 2.67±0.3Gt a–1. Assuming steady state, and based on the equation of continuity, we interpret the residual mass flux as a combined effect of snow accumulation and subglacial melting/refreezing. Using net snow accumulation rates from previous studies, we link the mass flux divergence in irregular-shaped polygons to processes beneath the ice shelf. The highest subglacial melt rates of ~1.1ma–1 are found near the grounding zone of two main inflow glaciers, and around the German station Neumayer III. The detection of unlikely refreezing in a small area ~15 km west of Neumayer III is attributed to both dataset inaccuracies and a (possibly past) violation of the steady-state assumption. In general, the method and input data allow mapping of the spatial distribution of basal melting and the results are in good agreement with several previous studies.

scholarly journals Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 201
Author(s):  
A. Jenkins ◽  
C.S.M. Doake
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Flow Line ◽  
Average Rate ◽  
Ice Shelf ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
State Models ◽  
Basal Melting ◽  
Echo Sounding

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.

scholarly journals Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica

1988 ◽  
Vol 11 ◽  
pp. 165-172 ◽  
Author(s):  
R. H. Thomas ◽  
S. N. Stephenson ◽  
R. A. Bindschadler ◽  
S. Shabtaie ◽  
C. R. Bentley
Keyword(s):  
Snow Accumulation ◽  
Gravity Potential ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Major Activity ◽  
Ice Stream ◽  
Grounding Line ◽  
Ice Stream B ◽  
Basal Melting

Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker.There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.

scholarly journals Basal Mass Balance Along a Flow Line on Ronne Ice Shelf, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 201-201
Author(s):  
A. Jenkins ◽  
C.S.M. Doake
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Flow Line ◽  
Average Rate ◽  
Ice Shelf ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
State Models ◽  
Basal Melting ◽  
Echo Sounding

Recent glaciological work on Ronne Ice Shelf has focused on an assumed flow line which extends from Rutford Ice Stream grounding line to the ice front. Results from doppler satellite surveying and radio echo-sounding are used in kinematic calculations to determine the basal mass balance, assuming the flow line to be in a steady state. Models suggest that basal melting dominates over most of the flow line and is most pronounced at the extremities. In the region within 300 km of the grounding line and over the final 45 km before the ice front, at least 1 m/a on average must melt away to maintain the observed velocity and thickness profile. More gentle melting occurs over about half the remaining distance, but in a region between 130 and 300 km in from the ice front, basal freezing must occur at an average rate of about 0.1 m/a to maintain a steady state. The existence of a thin layer of saline ice underlying the ice shelf, which persists for a further 80 km down-stream before being melted away entirely, is consistent with the weak returns observed during both airborne and ground-based radio echo-sounding in this region.

scholarly journals Investigations of the mass balance of the southeastern Ronne Ice Shelf, Antarctica

1999 ◽  
Vol 29 ◽  
pp. 250-254 ◽  
Author(s):  
A. Lambrecht ◽  
C. Mayer ◽  
H. Oerter ◽  
U. Nixdorf
Keyword(s):  
Mass Balance ◽  
Mass Flux ◽  
Ice Sheet ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Southeastern Part ◽  
Ice Stream ◽  
Grounding Line ◽  
Radio Echo Sounding ◽  
Stream Transport

AbstractData from the Filchner V Campaign were used to investigate the mass-balance conditions in the southeastern Ronne Ice Shelf (RIS), Antarctica. Radio-echo sounding and seismic measurements over this area show a maximum ice thickness of >2000 m close to the grounding line of Foundation Ice Stream. The measurements also revealed that the position of this grounding line is 40 km further south than previously thought. New mass-flux calculations result in an estimate of 51 km3 a−1 for the ice-stream transport from the ice sheet into the eastern ice shelf. The Mollereisstrom (MES), west of Foundation Ice Stream, shows a maximum ice thickness of 1100-1200 m in the grounding-line area and a mass flux of 23 km3 a−1.Assuming steady-state conditions, mass-balance calculations based on the new data result in a mean melt rate of about 1 ma−1 at the ice-shelf base for the entire southeastern part of the RIS. The melt rate in the grounding-line area of Foundation Ice Stream exceeds 9 m a−1. In contrast, other ice streams draining into the Filchner-Ronne Ice Shelf show maximum melt rates from 1-2 ma-1. (MES) to 4 ma−1 (Rutford Ice Stream). Our calculations indicate that nearly all of the ice deposited in the drainage area of the eastern RIS on the ice sheet does not reach the ice-shelf front as original meteoric ice, but is melted at the ice-shelf base.

scholarly journals Thinning and Grounding-Line Retreat on Ross Ice Shelf, Antarctica

1988 ◽  
Vol 11 ◽  
pp. 165-172 ◽  
Author(s):  
R. H. Thomas ◽  
S. N. Stephenson ◽  
R. A. Bindschadler ◽  
S. Shabtaie ◽  
C. R. Bentley
Keyword(s):  
Snow Accumulation ◽  
Gravity Potential ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Major Activity ◽  
Ice Stream ◽  
Grounding Line ◽  
Ice Stream B ◽  
Basal Melting

Detailed measurements of surface topography, ice motion, snow accumulation, and ice thickness were made in January 1974 and again in December 1984, along an 8 km stake network extending from the ice sheet, across the grounding line, and on to floating ice shelf in the mouth of slow-moving Ice Stream C, which flows into the eastern side of Ross Ice Shelf, Antarctica. During the 11 years between surveys, the grounding line retreated by approximately 300 m. This was caused by net thinning of the ice shelf, which we believe to be a response to the comparatively recent, major decrease in ice discharge from Ice Stream C. Farther inland, snow accumulation is not balanced by ice discharge, and the ice stream is growing progressively thicker. There is evidence that the adjacent Ice Stream B has slowed significantly over the last decade, and this may be an early indication that this fast-moving ice stream is about to enter a period of stagnation similar to that of Ice Stream C. Indeed, these large ice streams flowing from West Antarctica into Ross Ice Shelf may oscillate between periods of relative stagnation and major activity. During active periods, large areas of ice shelf thicken and run aground on seabed to form extensive “ice plains” in the mouth of the ice stream. Ultimately, these become too large to be pushed seaward by the ice stream, which then slows down and enters a period of stagnation. During this period, the grounding line of the ice plain retreats, as we observe today in the mouth of Ice Stream C, because nearby ice shelf, no longer compressed by ice-stream motion, progressively thins. At the same time, water within the deformable till beneath the ice starts to freeze on to the base of the ice stream, and snow accumulation progressively increases the ice thickness. A new phase of activity would be initiated when the increasing gravity potential of the ice stream exceeds the total resistance of the shrinking ice plain and the thinning layer of deformable till at the bed. This could occur rapidly if the effects of the shrinking ice plain outweigh those of the thinning (and therefore stiffening) till. Otherwise, the till layer would finally become completely frozen, and the ice stream would have to thicken sufficiently to initiate significant heating by internal deformation, followed by basal melting and finally saturation of an adequate thickness of till; this could take some thousands of years.

scholarly journals Antarctic ice shelf thickness change from multimission lidar mapping

2019 ◽  
Vol 13 (7) ◽  
pp. 1801-1817 ◽  
Author(s):  
Tyler C. Sutterley ◽  
Thorsten Markus ◽  
Thomas A. Neumann ◽  
Michiel van den Broeke ◽  
J. Melchior van Wessem ◽  
...  
Keyword(s):  
High Resolution ◽  
Climate Models ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Flux Divergence ◽  
Ice Shelf ◽  
Thickness Change ◽  
Ice Shelves

Abstract. We calculate rates of ice thickness change and bottom melt for ice shelves in West Antarctica and the Antarctic Peninsula from a combination of elevation measurements from NASA–CECS Antarctic ice mapping campaigns and NASA Operation IceBridge corrected for oceanic processes from measurements and models, surface velocity measurements from synthetic aperture radar, and high-resolution outputs from regional climate models. The ice thickness change rates are calculated in a Lagrangian reference frame to reduce the effects from advection of sharp vertical features, such as cracks and crevasses, that can saturate Eulerian-derived estimates. We use our method over different ice shelves in Antarctica, which vary in terms of size, repeat coverage from airborne altimetry, and dominant processes governing their recent changes. We find that the Larsen-C Ice Shelf is close to steady state over our observation period with spatial variations in ice thickness largely due to the flux divergence of the shelf. Firn and surface processes are responsible for some short-term variability in ice thickness of the Larsen-C Ice Shelf over the time period. The Wilkins Ice Shelf is sensitive to short-timescale coastal and upper-ocean processes, and basal melt is the dominant contributor to the ice thickness change over the period. At the Pine Island Ice Shelf in the critical region near the grounding zone, we find that ice shelf thickness change rates exceed 40 m yr−1, with the change dominated by strong submarine melting. Regions near the grounding zones of the Dotson and Crosson ice shelves are decreasing in thickness at rates greater than 40 m yr−1, also due to intense basal melt. NASA–CECS Antarctic ice mapping and NASA Operation IceBridge campaigns provide validation datasets for floating ice shelves at moderately high resolution when coregistered using Lagrangian methods.

scholarly journals Ice-shelf basal channels in a coupled ice/ocean model

2012 ◽  
Vol 58 (212) ◽  
pp. 1227-1244 ◽  
Author(s):  
Carl V. Gladish ◽  
David M. Holland ◽  
Paul R. Holland ◽  
Stephen F. Price
Keyword(s):  
Ocean Circulation ◽  
Coupled System ◽  
Ocean Model ◽  
Subsurface Water ◽  
Ice Thickness ◽  
Ice Shelf ◽  
First Approximation ◽  
Grounding Line ◽  
History Of ◽  
Basal Melting

AbstractA numerical model for an interacting ice shelf and ocean is presented in which the ice- shelf base exhibits a channelized morphology similar to that observed beneath Petermann Gletscher’s (Greenland) floating ice shelf. Channels are initiated by irregularities in the ice along the grounding line and then enlarged by ocean melting. To a first approximation, spatially variable basal melting seaward of the grounding line acts as a steel-rule die or a stencil, imparting a channelized form to the ice base as it passes by. Ocean circulation in the region of high melt is inertial in the along-channel direction and geostrophically balanced in the transverse direction. Melt rates depend on the wavelength of imposed variations in ice thickness where it enters the shelf, with shorter wavelengths reducing overall melting. Petermann Gletscher’s narrow basal channels may therefore act to preserve the ice shelf against excessive melting. Overall melting in the model increases for a warming of the subsurface water. The same sensitivity holds for very slight cooling, but for cooling of a few tenths of a degree a reorganization of the spatial pattern of melting leads, surprisingly, to catastrophic thinning of the ice shelf 12 km from the grounding line. Subglacial discharge of fresh water along the grounding line increases overall melting. The eventual steady state depends on when discharge is initiated in the transient history of the ice, showing that multiple steady states of the coupled system exist in general.

Contributions of Convective and Orographic Gravity Waves to the Brewer–Dobson Circulation Estimated from NCEP CFSR

2020 ◽  
Vol 77 (3) ◽  
pp. 981-1000
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Byeong-Gwon Song
Keyword(s):  
Gravity Waves ◽  
Mass Flux ◽  
Convective Heating ◽  
Flux Divergence ◽  
Mass Fluxes ◽  
Time Period ◽  
Physically Based ◽  
Total Mass Flux ◽  
Convective Gravity Waves

Abstract Contributions of convective gravity waves (CGWs) and orographic gravity waves (OGWs) to the Brewer–Dobson circulation (BDC) are examined and compared to those from resolved waves. OGW drag (OGWD) is provided by NCEP Climate Forecast System Reanalysis (CFSR), while CGW drag (CGWD) is obtained from an offline calculation of a physically based CGW parameterization with convective heating and background data provided by CFSR. CGWD contributes to the shallow branch of the BDC regardless of the season, while OGWD contributes to both the shallow and deep branches except for the summertime, when OGWs hardly propagate into the stratosphere. At 70 hPa, the annual-mean tropical upward mass fluxes from Eliassen–Palm flux divergence (EPD), OGWD, and CGWD are 68%, 7%, and 4% of the total mass flux, respectively. The tropical upward mass flux at 70 hPa shows an increasing trend during the time period from 1979 to 1998, with 28%, 18%, and 6% of the trend driven by EPD, OGWD, and CGWD, respectively. The width of the turnaround latitudes tends to narrow for the streamfunctions induced by OGWD and CGWD but tends to widen for that induced by EPD. The contributions of GWD from MERRA (MERRA-2) to the climatology and long-term trend of the BDC are 7% (7%) and 13% (4%), respectively, somewhat smaller than the contributions of CGWD plus OGWD, which are estimated from CFSR to be 12% and 20%, respectively.

scholarly journals Large-scale rheology of the Ross Ice Shelf, Antarctica, computed by a control method

1997 ◽  
Vol 24 ◽  
pp. 43-48 ◽  
Author(s):  
Vincent Rommelaere ◽  
Douglas R. MacAyeal
Keyword(s):  
Large Scale ◽  
Control Method ◽  
Equilibrium Equations ◽  
Ice Shelf ◽  
The West ◽  
Ross Ice Shelf ◽  
Stress Equilibrium ◽  
West Antarctic ◽  
Flow Law ◽  
Basal Melting

Measurements made during the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS, 1973–78) are used to determine the large-scale rheological conditions of the Ross Ice Shelf, Antarctica. Our method includes a numerical ice-shelf model based on the stress-equilibrium equations and control theory. We additionally perform a few tests on simplified geometries to investigate the precision of our method. Our results consist of a map of the depth-averaged viscosity of the central part of the Ross Ice Shelf to within an uncertainty of 20%. We find that the viscosity variations are consistent with Glen’s flow law. Application of a more realistic flow law in our study provides little enhancement of ice-shelf model accuracy until uncertainties associated with basal melting conditions and with temperature profiles at inflow boundaries are addressed. Finally, our results suggest a strong viscosity anomaly in the west-central part of the ice shelf, which is interpreted to be associated with changes in the dynamics of Ice Stream A or B at least 1000 years ago. This feature conforms to the prevailing notion that the West Antarctic ice streams are unsteady.

scholarly journals Liquid Brine in Ice Shelves

1975 ◽  
Vol 14 (70) ◽  
pp. 125-136 ◽  
Author(s):  
R. H. Thomas
Keyword(s):  
Steady State ◽  
Heat Transport ◽  
Thermal Equilibrium ◽  
Transport Model ◽  
Percolation Model ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Brine Layer ◽  
Good Agreement

Holes drilled into thin areas of the Brunt Ice Shelf encounter a layer of liquid brine less than 1 m thick approximately at sea-level. Assuming the brine to be moving horizontally, analysis of its effects on thermal equilibrium gives an estimate of steady-state annual brine flow that is in good agreement with the value deduced from a percolation model. The effect of firn density on percolation rates is such that the slope of an active brine layer increases rapidly as ice thickness increases. However, the heat transport model predicts that brine layers are unlikely to be active in both very thick and very thin ice shelves.

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