scholarly journals Rifting processes and ice-flow modulation observed on Mertz Glacier, East Antarctica

2015 ◽  
Vol 61 (230) ◽  
pp. 1183-1193 ◽  
Author(s):  
L. Lescarmontier ◽  
B. Legresy ◽  
N.W. Young ◽  
R. Coleman ◽  
L. Testut ◽  
...  
Keyword(s):  
East Antarctica ◽  
Sea Surface ◽  
Gps Data ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Flow Modulation ◽  
Tidal Circulation ◽  
Glacier System ◽  
Large Velocity ◽  
East West

AbstractWe investigated the evolution of two major rifts cutting across Mertz Glacier Tongue, East Antarctica, using a combination of satellite images and 60 day sets of GPS data from two stations deployed either side of the western rift in 2007. The eastern rift began to open in the early 1990s, and the western rift initiated in 2002 in conjunction with the collision of a large iceberg with the tongue. Velocity time series derived from the 2007 GPS data exhibited strong variations at tidal periods modulated by sea-surface height and sea-surface slope and reproduced here with a conceptually simple model. We found that opening of the western rift in 2002 leads to a dramatic change in behavior of the tongue as the large range in velocity (700–2400 m a−1) observed in 2000 was largely reduced (1075–1225 m a−1) in 2007. Opening of the western rift decoupled the glacier from the transverse loading on the tongue driven by east–west tidal circulation. This loading previously induced time-varying lateral drag, which caused the large velocity range. Our results suggest changes in the mechanical behavior of an ice tongue impact the dynamics of the outlet glacier system and should be considered in longer-term mass-balance evaluations.

scholarly journals Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, and the long-term speed-up of Holmes Glacier

2016 ◽  
Author(s):  
B. W. J. Miles ◽  
C. R. Stokes ◽  
S. S. R. Jamieson
Keyword(s):  
Sea Ice ◽  
East Antarctica ◽  
High Temporal Resolution ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Ice Shelves ◽  
Glacier Terminus ◽  
Wilkes Land ◽  
Speed Up

Abstract. The floating ice shelves and glacier tongues which fringe the Antarctic continent are important because they help buttress ice flow from the ice sheet interior. Dynamic feedbacks associated with glacier calving have the potential to reduce buttressing and subsequently increase ice flow into the ocean. However, there are few high temporal resolution studies on glacier calving, especially in East Antarctica. Here we use remote sensing to investigate monthly glacier terminus change across six marine-terminating outlet glaciers in Porpoise Bay (−76° S, 128° E), Wilkes Land (East Antarctica), between November 2002 and March 2012. This reveals a large simultaneous calving event in January 2007, resulting in a total of ~ 2900 km2 of ice being removed from glacier tongues. Our observations suggest that sea-ice must be removed from glacier termini for any form of calving to take place, and we link this major calving event to a rapid break-up of the multi-year sea-ice which usually occupies Porpoise Bay. Using sea-ice concentrations as a proxy for glacier calving, and by analysing available satellite imagery stretching back to 1963, we reconstruct the long-term calving activity of the largest glacier in Porpoise Bay: Holmes (West) Glacier. This reveals that its present-day velocity (~ 1450 m a−1) is approximately 50 % faster than between 1963 and 1973 (~ 900 m a−1). We also observed the start of a large calving event in Porpoise Bay in March 2016 that is consistent with our reconstructions of the periodicity of major calving events. These results highlight the importance of sea-ice in modulating outlet glacier calving and velocity in East Antarctica.

scholarly journals New velocity map and mass-balance estimate of Mertz Glacier, East Antarctica, derived from Landsat sequential imagery

2003 ◽  
Vol 49 (167) ◽  
pp. 503-511 ◽  
Author(s):  
Etienne Berthier ◽  
Bruce Raup ◽  
Ted Scambos
Keyword(s):  
Velocity Field ◽  
Drainage Basin ◽  
Flow Speed ◽  
East Antarctica ◽  
Landsat Images ◽  
Mean Velocity ◽  
Speed Increase ◽  
Glacier System ◽  
Show Evidence ◽  
Basal Melting

AbstractAutomatic feature tracking on two Landsat images (acquired inJanuary 2000 and December 2001) generates a complete and accurate velocity field of Mertz Glacier, East Antarctica. This velocity field shows two main tributaries to the ice stream. Between the tributaries, a likely obstruction feature in the bedrock results in a slow-down of the flow. A third Landsat image, acquired in 1989 and combined with the 2000 image, permits the determination of the glacier mean velocity during the 1990s. Although some parts of the Mertz Glacier system show evidence of slight speed increase, we conclude that the Mertz flow speed is constant within our uncertainty (35 m a−1). Using this complete velocity field, new estimates of the ice discharge flux, 17.8 km3 a−1 (16.4 Gt a−1), and of the basal melting of the tongue, 11 m a−1 of ice, are given. Our results lead to an apparent imbalance of the drainage basin (ice discharge 3.5 km3 a−1 lower than the accumulation). Considering previous studies in the Mertz Glacier area, we then discuss the uncertainty of this imbalance and the problems with accumulation mapping for this region.

scholarly journals Ice flow velocities over Vostok Subglacial Lake, East Antarctica, determined by 10 years of GNSS observations

2013 ◽  
Vol 59 (214) ◽  
pp. 315-326 ◽  
Author(s):  
A. Richter ◽  
D.V. Fedorov ◽  
M. Fritsche ◽  
S.V. Popov ◽  
V.Ya. Lipenkov ◽  
...  
Keyword(s):  
Flow Velocity ◽  
East Antarctica ◽  
Global Navigation Satellite Systems ◽  
Steady Increase ◽  
Lake Area ◽  
Ice Flow ◽  
Satellite Systems ◽  
Subglacial Lake ◽  
Gnss Observations ◽  
Flow Velocities

AbstractRepeated Global Navigation Satellite Systems (GNSS) observations were carried out at 50 surface markers in the Vostok Subglacial Lake (East Antarctica) region between 2001 and 2011. The horizontal ice flow velocity vectors were derived with accuracies of 1 cm a−1 and 0.5°, representing the first reliable information on ice flow kinematics in the northern part of the lake. Within the lake area, ice flow velocities do not exceed 2 m a−1. The ice flow azimuth is southeast in the southern part of the lake and turns gradually to east-northeast in the northern part. In the northern part, as the ice flow enters the lake at the western shore, the velocity decreases towards the central lake axis, then increases slightly past the central axis. In the southern part, a continued acceleration is observed from the central lake axis across the downstream grounding line. Based on the observed flow velocity vectors and ice thickness data, mean surface accumulation rates are inferred for four surface segments between Ridge B and Vostok Subglacial Lake and show a steady increase towards the north.

scholarly journals Sensitivity of Greenland Ice Sheet Projections to Model Formulations

2013 ◽  
Vol 59 (216) ◽  
pp. 733-749 ◽  
Author(s):  
H. Goelzer ◽  
P. Huybrechts ◽  
J.J. Fürst ◽  
F.M. Nick ◽  
M.L. Andersen ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Sea Level ◽  
Flow Model ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Glacier Dynamics

AbstractPhysically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6–18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14–31 % higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

scholarly journals Constraints on glacier flow from temperature-depth profiles in the ice. Application to EPICA Dome C.

2016 ◽  
Author(s):  
Ignacio Hermoso de Mendoza ◽  
Jean-Claude Mareschal ◽  
Hugo Beltrami
Keyword(s):  
Heat Flux ◽  
Velocity Profile ◽  
Boundary Conditions ◽  
Temperature Profile ◽  
East Antarctica ◽  
Surface Velocity ◽  
Function Parameter ◽  
Unknown Parameters ◽  
Conduction Model ◽  
Ice Flow

Abstract. A one-dimensional (1-D) ice flow and heat conduction model is used to calculate the temperature and heat flux profiles in the ice and to constrain the parameters characterizing the ice flow and the thermal boundary conditions at the Dome C drilling site in East Antarctica. We use the reconstructions of ice accumulation, glacier height and air surface temperature histories as boundary conditions to calculate the ice temperature profile. The temperature profile also depends on a set of poorly known parameters, the ice velocity profile and magnitude, basal heat flux, and air-ice surfaces temperature coupling. We use Monte Carlo methods to search the parameters' space of the model, compare the model output with the temperature data, and find probability distributions for the unknown parameters. We could not determine the sliding ratio because it has no effect on the thermal profile, but we could constrain the flux function parameter p that determines the velocity profile. We determined the basal heat flux qb = 49.0  ± 2.7 (2σ)m W m−2, almost equal to the apparent value. We found an ice surface velocity of vsur = 2.6 ± 1.9 (2σ)m y−1 and an air-ice temperature coupling of 0.8 ± 1.0(2σ)K. Our study confirms that the heat flux is low and does not destabilize the ice sheet in east Antarctica.

scholarly journals Glacier disequilibrium in the Convoy Range, Transantarctic Mountains, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 269-276 ◽  
Author(s):  
T.J. Chinn
Keyword(s):  
Field Work ◽  
Snow Accumulation ◽  
Low Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Regime Changes ◽  
Positive Balance ◽  
Geological Map ◽  
Glacier Flow ◽  
Surficial Deposits

Field work for a geological map of the Convoy Range included mapping glaciers, moraines and surficial deposits. A range of glaciological indicators, including supraglacial and other moraines and margin morphology, has been used to assess the present equilibrium of the glaciers. Fields of rafted supraglacial moraine have accumulated over long periods of time at specific low-gradient, low-velocity locations. As the glacier regime changes, the shape of the moraine field distorts, signalling a change in flow pattern. By reversing the ice flow vectors directed at the moraine field, the directions from whence the debris came are shown. Unsorting the contortions of supraglacial moraine fields reveals the nature of the changes in glacier regime. Moraine-field configurations all suggest that local glaciers are expanding in response to higher local precipitation, estimated to have occurred between 2000 and 8000 year BP, most likely coincident with the world-wide “climatic optimum” of about 6000 year BP.Ice-cliff morphology, fresh terminal moraines and boulder trains indicate that larger local glaciers are currently receding from a Holocene maximum, while the margin of the large Mackay Ice Sheet outlet glacier shows no evidence of recent recession and is probably close to its Holocene maximum. In contrast, areas of present snow cover are expanding, superimposing a recent positive balance (decades to hundreds of years), which has yet to reverse a general recession of mid- to high-altitude glaciers. Local hollows in some névé areas imply that glacier flow is not in equilibrium with snow accumulation.

scholarly journals Rhombus and Rhomboid Parallelogram Patterns on Glaciers: Natural Indicators of Strain

1979 ◽  
Vol 22 (87) ◽  
pp. 247-261 ◽  
Author(s):  
Charles J. Waag ◽  
Keith Echelmeyer
Keyword(s):  
Strain Rate ◽  
Flow Direction ◽  
Acute Angle ◽  
Principal Strain ◽  
Obtuse Angle ◽  
Strain Rates ◽  
Ice Flow ◽  
Glacier System ◽  
Glacier Ice

AbstractSubtle rhombus and rhomboid parallelogram patterns occur on Vaughan Lewis Glacier and the Gilkey Glacier System, Juneau Icefield, Alaska. The patterns are within the firn at the firn-ice interface, are formed by differential recrystallization within narrow preferred zones, and are apparently manifestations of stresses transferred upward from the glacier ice. On the glaciers of the Gilkey System the patterns occur where intense lateral shortening is indicated by abrupt convergence of medial moraines and an abundance of extension crevasses. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids are subparallel to the strike of extension crevasses, therefore to the axis of shortening. The long axes of the rhombi and the acute angle bisectors of the rhomboids are parallel to the foliation, and ice-flow direction. The angles of the parallelograms are variable locally, but average 105° and 75°; the variation seems to reflect intensity and duration of stress. Similar parallelograms occur within the troughs of wave bulges below the Vaughan Lewis Icefall. In the wave bulges, the foliation arcs parallel the wave. The long axes of the rhombi and acute angle bisectors of the rhomboids parallel the foliation around the foliation arc. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids parallel the strikes of radial crevasses, are perpendicular to the direction of extension, and form a fan divergent down-stream. The precise mechanisms and conditions of formation of the parallelograms are not yet understood. Preliminary strain-rate measurements suggest, however, that correlations exist between the orientations of the principal strain-rates and the axes of the patterns, and between the magnitude of the strain-rates and the axial lengths of the patterns.

scholarly journals Accumulation patterns around Dome C, East Antarctica, in the last 73 kyr

2018 ◽  
Vol 12 (4) ◽  
pp. 1401-1414 ◽  
Author(s):  
Marie G. P. Cavitte ◽  
Frédéric Parrenin ◽  
Catherine Ritz ◽  
Duncan A. Young ◽  
Brice Van Liefferinge ◽  
...  
Keyword(s):  
Large Scale ◽  
Flow Model ◽  
East Antarctica ◽  
Small Scale ◽  
Time Interval ◽  
Accumulation Rates ◽  
Ice Flow ◽  
Last Glacial ◽  
Prevailing Wind Direction ◽  
The Last Glacial

Abstract. We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, since the last glacial. We use a set of 18 isochrones spanning all observable depths of the ice column, interpreted from various ice-penetrating radar surveys and a 1-D ice flow model to invert for accumulation rates in the region. The shallowest four isochrones are then used to calculate paleoaccumulation rates between isochrone pairs using a 1-D assumption where horizontal advection is negligible in the time interval of each layer. We observe that the large-scale (100s km) surface accumulation gradient is spatially stable through the last 73 kyr, which reflects current modeled and observed precipitation gradients in the region. We also observe small-scale (10 s km) accumulation variations linked to snow redistribution at the surface, due to changes in its slope and curvature in the prevailing wind direction that remain spatially stationary since the last glacial.

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