Dynamics of the Scharffenbergbotnen blue-ice area, Dronning Maud Land, Antarctica

AbstractGround-penetrating radar (GPR) surveys in Scharffenbergbotnen valley, Dronning Maud Land, Antarctica, complement earlier, relatively sparse data on the ice-flow dynamics and mass-balance distribution of the area. The negative net surface mass balance in the valley appears to be balanced by the inflow. The flow regime in Scharffenbergbotnen defines four separate mass-balance areas, and about 60 times more ice enters the valley from the northwestern entrance than via the narrow western gate. We formalize and compare three methods of determining both the surface age gradient of the blue ice and the dip angles of isochrones in the firn/blue-ice transition zone: observed and dated radar internal reflections, a geometrical model of isochrones, and output from a flowline model. The geometrical analysis provides generally applicable relationships between ice surface velocity and surface age gradient or isochrone dip angle.

Download Full-text

Present dynamics and future prognosis of a slowly surging glacier

The Cryosphere ◽

10.5194/tc-5-299-2011 ◽

2011 ◽

Vol 5 (1) ◽

pp. 299-313 ◽

Cited By ~ 49

Author(s):

G. E. Flowers ◽

N. Roux ◽

S. Pimentel ◽

C. G. Schoof

Keyword(s):

Mass Balance ◽

Force Balance ◽

Surface Velocity ◽

Internal Dynamic ◽

Ice Dynamics ◽

Surface Mass ◽

Ice Surface ◽

Glacier Ice ◽

Glacier Flow ◽

Negative Balance

Abstract. Glacier surges are a well-known example of an internal dynamic oscillation whose occurrence is not a direct response to the external climate forcing, but whose character (i.e. period, amplitude, mechanism) may depend on the glacier's environmental or climate setting. We examine the dynamics of a small (∼5 km2) valley glacier in Yukon, Canada, where two previous surges have been photographically documented and an unusually slow surge is currently underway. To characterize the dynamics of the present surge, and to speculate on the future of this glacier, we employ a higher-order flowband model of ice dynamics with a regularized Coulomb-friction sliding law in both diagnostic and prognostic simulations. Diagnostic (force balance) calculations capture the measured ice-surface velocity profile only when non-zero basal water pressures are prescribed over the central region of the glacier, coincident with where evidence of the surge has been identified. This leads to sliding accounting for 50–100% of the total surface motion in this region. Prognostic simulations, where the glacier geometry evolves in response to a prescribed surface mass balance, reveal a significant role played by a bedrock ridge beneath the current equilibrium line of the glacier. Ice thickening occurs above the ridge in our simulations, until the net mass balance reaches sufficiently negative values. We suggest that the bedrock ridge may contribute to the propensity for surges in this glacier by promoting the development of the reservoir area during quiescence, and may permit surges to occur under more negative balance conditions than would otherwise be possible. Collectively, these results corroborate our interpretation of the current glacier flow regime as indicative of a slow surge that has been ongoing for some time, and support a relationship between surge incidence or character and the net mass balance. Our results also highlight the importance of glacier bed topography in controlling ice dynamics, as observed in many other glacier systems.

Download Full-text

Present dynamics and future prognosis of a slowly surging glacier

The Cryosphere Discussions ◽

10.5194/tcd-4-1839-2010 ◽

2010 ◽

Vol 4 (4) ◽

pp. 1839-1876

Author(s):

G. E. Flowers ◽

N. Roux ◽

S. Pimentel

Keyword(s):

Mass Balance ◽

Surface Profile ◽

Yukon Territory ◽

Force Balance ◽

Surface Velocity ◽

Internal Dynamic ◽

Ice Dynamics ◽

Surface Mass ◽

Ice Surface ◽

Glacier Flow

Abstract. Glacier surges are a well-known example of an internal dynamic oscillation whose occurrence is not a direct response to the external climate forcing, but whose character (e.g. period, mechanism) may depend on the glacier's environmental or climate setting. We examine the dynamics of a small (~5 km2) valley glacier in the Yukon Territory of Canada, where two previous surges have been photographically documented and an unusually slow surge is currently underway. To characterize the dynamics of the present surge, and to speculate on the future of this glacier, we employ a higher-order flowband model of ice dynamics with a Coulomb-friction sliding law in both diagnostic and prognostic simulations. Diagnostic (force balance) calculations capture the measured ice-surface velocity profile only when high basal water pressures (55–90% of flotation) are prescribed over the central region of the glacier, consistent with where evidence of the surge has been identified. This leads to sliding accounting for 50–100% of the total surface motion. Prognostic simulations, where the glacier geometry evolves in response to a prescribed surface mass balance, reveal a significant role played by a large bedrock bump beneath the current equilibrium line of the glacier. This bump provides resistance to ice flow sufficient to cause the formation of a bulge in the ice-surface profile. We suggest that the bedrock bump contributes to the propensity for surges in this glacier, such that conditions suppressing ice-bulge formation over the bump may also inhibit surges. In our calculations such a situation arises for sufficiently negative values of mass balance. Collectively, these results corroborate our interpretation of the current glacier flow regime as indicative of a "slow surge", and confirm a relationship between surge incidence or character and the net mass balance. Our results also highlight the importance of glacier bed topography in controlling ice dynamics, as observed in many other glacier systems.

Download Full-text

Ice flow modelling to constrain the surface mass balance and ice discharge of San Rafael Glacier, Northern Patagonia Icefield

Journal of Glaciology ◽

10.1017/jog.2018.46 ◽

2018 ◽

Vol 64 (246) ◽

pp. 568-582 ◽

Cited By ~ 3

Author(s):

GABRIELA COLLAO-BARRIOS ◽

FABIEN GILLET-CHAULET ◽

VINCENT FAVIER ◽

GINO CASASSA ◽

ETIENNE BERTHIER ◽

...

Keyword(s):

Mass Balance ◽

Flow Model ◽

Surface Velocity ◽

Shear Stresses ◽

Surface Mass Balance ◽

Ice Dynamics ◽

Ice Flow ◽

Surface Mass ◽

Northern Patagonia ◽

San Rafael

ABSTRACTWe simulate the ice dynamics of the San Rafael Glacier (SRG) in the Northern Patagonia Icefield (46.7°S, 73.5°W), using glacier geometry obtained by airborne gravity measurements. The full-Stokes ice flow model (Elmer/Ice) is initialized using an inverse method to infer the basal friction coefficient from a satellite-derived surface velocity mosaic. The high surface velocities (7.6 km a−1) near the glacier front are explained by low basal shear stresses (<25 kPa). The modelling results suggest that 98% of the surface velocities are due to basal sliding in the fast-flowing glacier tongue (>1 km a−1). We force the model using different surface mass-balance scenarios taken or adapted from previous studies and geodetic elevation changes between 2000 and 2012. Our results suggest that previous estimates of average surface mass balance over the entire glacier (Ḃ) were likely too high, mainly due to an overestimation in the accumulation area. We propose that most of SRG imbalance is due to the large ice discharge (−0.83 ± 0.08 Gt a−1) and a slightly positiveḂ(0.08 ± 0.06 Gt a−1). The committed mass-loss estimate over the next century is −0.34 ± 0.03 Gt a−1. This study demonstrates that surface mass-balance estimates and glacier wastage projections can be improved using a physically based ice flow model.

Download Full-text

Ice flux of Plogbreen, a small ice stream in Dronning Maud Land, Antarctica

Annals of Glaciology ◽

10.3189/172756404781813844 ◽

2004 ◽

Vol 39 ◽

pp. 409-416

Author(s):

Jim Hedfors ◽

Veijo Allan Pohjola

Keyword(s):

Mass Balance ◽

Ice Core ◽

Austral Summer ◽

Snow Accumulation ◽

Surface Velocity ◽

Cross Sectional ◽

Ice Surface ◽

Dronning Maud Land ◽

Using Data

AbstractAs part of a long-term mass-balance program run by SWEDARP since 1988, a detailed study on Plogbreen, Dronning Maud Land, Antarctica, was undertaken during the austral summer of 2003 to investigate the long-term mass balance. We compare ice outflux, φout, through a cross-sectional gate with ice influx, φin, from the upstream catchment area. The φin is based on calculations of snow accumulation upstream of the gate using data available from published ice-core records. The φout is based on Glen’s flow law aided by thermodynamic modeling and force-budget calculations. Input data from the field consist of measurements of ice surface velocity and ice geometry. The ice surface velocity was measured using repeated differential global positioning system surveying of 40 stakes over a period of 25 days. The ice geometry was determined by 174 km of ground-penetrating radar profiling using ground-based 8MHz dipole antennas. This study presents the collected velocity and geometry data as well as the calculated ice flux of Plogbreen. The results show a negatively balanced system within the uncertainty limits; φout = 0.55 ± 0.05 km3 a–1 and φin = 0.4 ± 0.1 km3 a–1. We speculate that the negative balance can be explained by recent eustatic increase reducing resistive stresses and inducing accelerated flow.

Download Full-text

Ice-rise stratigraphy reveals changes in surface mass balance over the last millennia in Dronning Maud Land

Journal of Glaciology ◽

10.1017/jog.2018.81 ◽

2018 ◽

Vol 64 (248) ◽

pp. 932-942 ◽

Cited By ~ 1

Author(s):

VIKRAM GOEL ◽

CARLOS MARTÍN ◽

KENICHI MATSUOKA

Keyword(s):

Mass Balance ◽

Surface Mass Balance ◽

Synoptic Scale ◽

Ice Flow ◽

Glacial Retreat ◽

Surface Mass ◽

The Past ◽

Dronning Maud Land ◽

Atmospheric Changes ◽

Ice Model

ABSTRACTWe use ice flow modelling to simulate the englacial stratigraphy of Blåskimen Island, an ice rise in Dronning Maud Land and elucidate the evolution of this data-sparse region. We apply a thermo-mechanically coupled Elmer/Ice model to a profile along flowlines and through the ice-rise summit, where surface mass balance (SMB), flow velocity and ice stratigraphy were recently measured. We conclude that: (i) the ice rise is presently thickening at a rate of 0.5~0.6 m ice equivalent per year (mieq a−1), which is twice an earlier estimate using the field data and the input–output method; (ii) present thickening started 20–40 years in the past, before which the ice rise was in a steady state; (iii) SMB contrast between the upwind and downwind slopes was stronger than the present value by ~23% (or 0.15 mieq a−1) prior to ~1100 years ago. Since then, this contrast has been decreasing overall. We surmise that these SMB changes are likely a result of synoptic-scale atmospheric changes, rather than local atmospheric changes controlled by local ice topography. Our technique effectively assimilates geophysical data, avoiding the complexity of ice flow beneath the ice divide. Thus, it could be applied to other ice rises to elucidate the recent glacial retreat.

Download Full-text

Volume and velocity changes at Mittivakkat Gletscher, southeast Greenland

Journal of Glaciology ◽

10.3189/2013jog13j017 ◽

2013 ◽

Vol 59 (216) ◽

pp. 660-670 ◽

Cited By ~ 15

Author(s):

Sebastian H. Mernild ◽

Niels T. Knudsen ◽

Matthew J. Hoffman ◽

Jacob C. Yde ◽

Edward Hanna ◽

...

Keyword(s):

Mass Balance ◽

Peak Velocity ◽

Dynamic Effect ◽

Snow Accumulation ◽

Surface Velocity ◽

Surface Mass ◽

Ice Surface ◽

Winter Snow ◽

Summer Warming ◽

Velocity Changes

AbstractWe document changes for Mittivakkat Gletscher, the peripheral glacier in Greenland with the longest field-based observed mass-balance and surface velocity time series. Between 1986 and 2011, this glacier changed by −15% in mean ice thickness and −30% in volume. We attribute these changes to summer warming and lower winter snow accumulation. Vertical strain compensated for ∼60% of the elevation change due to surface mass balance (SMB) in the lower part, and ∼25% in the upper part. The annual mean ice surface velocity changed by −30%, which can be fully explained by the dynamic effect of ice thinning, within uncertainty. Mittivakkat Gletscher summer surface velocities were on average 50–60% above winter background values, and up to 160% higher during peak velocity events. Peak velocity events were accompanied by uplift of a few centimeters.

Download Full-text

Nivlisen, an Antarctic ice shelf in Dronning Maud Land: geodetic–glaciological results from a combined analysis of ice thickness, ice surface height and ice-flow observations

Journal of Glaciology ◽

10.3189/172756506781828953 ◽

2006 ◽

Vol 52 (176) ◽

pp. 17-30 ◽

Cited By ~ 14

Author(s):

Martin Horwath ◽

Reinhard Dietrich ◽

Michael Baessler ◽

Uwe Nixdorf ◽

Daniel Steinhage ◽

...

Keyword(s):

Mass Balance ◽

Atlantic Coast ◽

Sar Interferometry ◽

Ice Thickness ◽

Ice Shelf ◽

Equilibrium Relation ◽

Ice Flow ◽

Near Surface ◽

Ice Surface ◽

Ground Penetrating

AbstractExtensive observations on Nivlisen, an ice shelf on Antarctica’s Atlantic coast, are analyzed and combined to obtain a new description of its complex glaciological regime. We generate models of ice thickness (primarily from ground-penetrating radar), ellipsoidal ice surface height (primarily from ERS-1 satellite altimetry), freeboard height (by utilizing precise sea surface information) and ice-flow velocity (from ERS-1/-2 SAR interferometry and GPS measurements). Accuracy assessments are included. Exploiting the hydrostatic equilibrium relation, we infer the ‘apparent air layer thickness’ as a useful measure for a glacier’s density deviation from a pure ice body. This parameter exhibits a distinct spatial variation (ranging from ≈2 to ≈16m) which we attribute to the transition from an ablation area to an accumulation area. We compute mass-flux and mass-balance parameters on a local and areally integrated scale. The combined effect of bottom mass balance and temporal change averaged over an essential part of Nivlisen is –654 ± 170 kg m–2 a–1, which suggests bottom melting processes dominate. We discuss our results in view of temporal ice-mass changes (including remarks on historical observations), basal processes, near-surface processes and ice-flow dynamical features. The question of temporal changes remains open from the data at hand, and we recommend further observations and analyses for its solution.

Download Full-text

Thinning and slowdown of Greenland's Mittivakkat Gletscher

The Cryosphere Discussions ◽

10.5194/tcd-6-4387-2012 ◽

2012 ◽

Vol 6 (5) ◽

pp. 4387-4415

Author(s):

S. H. Mernild ◽

N. T. Knudsen ◽

M. J. Hoffman ◽

J. C. Yde ◽

W. H. Lipscomb ◽

...

Keyword(s):

Mass Balance ◽

Peak Velocity ◽

Greenland Ice Sheet ◽

Dynamic Effect ◽

Surface Velocity ◽

Ice Thickness ◽

Elevation Change ◽

Surface Mass ◽

Ice Surface ◽

Summer Warming

Abstract. Here, we document changes for the Mittivakkat Gletscher, the glacier in Greenland (disconnected to the Greenland Ice Sheet, GrIS) having the longest observed mass balance and surface velocity time series (since 1995). Between 1986 and 2011, this glacier decreased by 15% in mean ice thickness and 30% in volume. We attribute these changes to summer warming and less winter snowfall. The vertical strain was able to compensate about 60% of the elevation change due to surface mass balance (SMB) in the lower part, and about 25% in the upper part. The annual mean ice surface velocity decreased by 30%, likely as a dynamic effect of ice thinning. Mittivakkat Gletscher summer surface velocities were on average 50–60% above winter background values, and up to 160% higher during peak velocity events.

Download Full-text

Radar-detected englacial stratigraphy in the Pensacola Mountains, Antarctica: implications for recent changes in ice flow and accumulation

Annals of Glaciology ◽

10.3189/2013aog63a371 ◽

2013 ◽

Vol 54 (63) ◽

pp. 91-100 ◽

Cited By ~ 8

Author(s):

Seth Campbell ◽

Greg Balco ◽

Claire Todd ◽

Howard Conway ◽

Kathleen Huybers ◽

...

Keyword(s):

Mass Balance ◽

Surface Elevation ◽

Ice Flow ◽

Ice Surface ◽

Valley Glacier ◽

Glacier Ice ◽

Elevation Changes ◽

Ice Sheet Dynamics ◽

Surface Ice ◽

Ground Penetrating

AbstractWe used measurements of radar-detected stratigraphy, surface ice-flow velocities and accumulation rates to investigate relationships between local valley-glacier and regional ice-sheet dynamics in and around the Schmidt Hills, Pensacola Mountains, Antarctica. Ground-penetrating radar profiles were collected perpendicular to the long axis of the Schmidt Hills and the margin of Foundation Ice Stream (FIS). Within the valley confines, the glacier consists of blue ice, and profiles show internal stratigraphy dipping steeply toward the nunataks and truncated at the present-day ablation surface. Below the valley confines, the blue ice is overlain by firn. Data show that upward-progressing overlap of actively accumulating firn onto valley-glacier ice is slightly less than ice flow out of the valleys over the past ∼1200 years. The apparent slightly negative mass balance (-0.25 cm a-1) suggests that ice-margin elevations in the Schmidt Hills may have lowered over this time period, even without a change in the surface elevation of FIS. Results suggest that (1) mass-balance gradients between local valley glaciers and regional ice sheets should be considered when using local information to estimate regional ice surface elevation changes; and (2) interpretation of shallow ice structures imaged with radar can provide information about local ice elevation changes and stability.

Download Full-text