Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record

2009 ◽  
Vol 28 (27-28) ◽  
pp. 3085-3100 ◽  
Author(s):  
Sarah L. Greenwood ◽  
Chris D. Clark
Keyword(s):  
Ice Sheet ◽  
Flow Dynamics ◽  
Ice Flow ◽  
Glacial Landform

scholarly journals Ice flow dynamics of the Greenland Ice Sheet from SAR interferometry

1995 ◽  
Vol 22 (5) ◽  
pp. 575-578 ◽  
Author(s):  
E. Rignot ◽  
K. C. Jezek ◽  
H. G. Sohn
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Flow Dynamics ◽  
Sar Interferometry ◽  
Ice Flow

scholarly journals A rapidly converging spin-up method for the present-day Greenland ice sheet using the GRISLI ice-sheet model

2018 ◽  
Author(s):  
Sébastien Le clec'h ◽  
Aurélien Quiquet ◽  
Sylvie Charbit ◽  
Christophe Dumas ◽  
Masa Kageyama ◽  
...  
Keyword(s):  
Sea Level ◽  
Initial Conditions ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Flow Dynamics ◽  
Ice Thickness ◽  
Rapid Convergence ◽  
Ice Flow ◽  
Ice Volume ◽  
Basal Shear

Abstract. Providing reliable projections of the ice-sheet contribution to future sea-level rise has become one of the main challenges of the ice-sheet modelling community. To increase confidence in future projections, a good knowledge of the present-day state of the ice flow dynamics, which is critically dependent on basal conditions, is strongly needed. The main difficulty is tied to the scarcity of observations at the ice-bed interface at the scale of the whole ice sheet, resulting in poorly constrained parameterisations in ice-sheet models. To circumvent this drawback, inverse modelling approaches can be developed and validated against available data to infer reliable initial conditions of the ice sheet. Here, we present a spin-up method for the Greenland ice sheet using the thermo-mechanical hybrid GRISLI ice-sheet model. Our approach is based on the adjustment of the basal drag coefficient that relates the sliding velocities at the ice-bed interface to basal shear stress in unfrozen bed areas. This method relies on an iterative process in which the basal drag is periodically adjusted in such as way that the simulated ice thickness matches the observed one. The process depends on three parameters controlling the duration and the number of iterations. The best spin-up parameters are chosen according to two criteria to minimize errors in sea-level projections: the final difference between the simulated and the observed Greenland ice volume as well as the final ice volume trend which must both be as low as possible. To increase confidence in the inferred parameters, we also make sure that the final ice thickness root mean square error from the observations is not greater than a few tens of meters. Our best results are obtained after only 420 years of simulation, highlighting a rapid convergence and demonstrating that our method can be used for computationally expensive ice sheet models.

scholarly journals Ice-sheet scale distribution and morphometry of triangular-shaped hummocks (murtoos): a subglacial landform produced during rapid retreat of the Scandinavian Ice Sheet

2019 ◽  
Vol 60 (80) ◽  
pp. 115-126 ◽  
Author(s):  
Antti E. K. Ojala ◽  
Gustaf Peterson ◽  
Joni Mäkinen ◽  
Mark D. Johnson ◽  
Kari Kajuutti ◽  
...  
Keyword(s):  
Hydraulic System ◽  
Flow Direction ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Light Detection And Ranging ◽  
Ice Flow ◽  
Digital Elevation ◽  
Scandinavian Ice Sheet ◽  
Glacial Landform ◽  
Oriented Parallel

AbstractHigh-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, ‘murtoo’). Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.

scholarly journals Overestimation and Adjustment of Antarctic Ice Flow Velocity Fields Reconstructed from Historical Satellite Imagery

2021 ◽  
Author(s):  
Rongxing Li ◽  
Yuan Cheng ◽  
Haotian Cui ◽  
Menglian Xia ◽  
Xiaohan Yuan ◽  
...  
Keyword(s):  
Satellite Image ◽  
Ice Sheet ◽  
Image Data ◽  
Ground Truth ◽  
Flow Dynamics ◽  
Landsat 8 ◽  
Sea Level Changes ◽  
Velocity Mapping ◽  
Ice Flow

Abstract. Antarctic ice velocity maps describe the ice flow dynamics of the ice sheet and are one of the primary components used to estimate the Antarctic mass balance and contribution to global sea level changes. In comparison to velocity maps covering monthly to weekly time spans derived from the images of optical imaging satellites taken in recent decades, historical maps, from before the 1990s, generally cover longer time spans, e.g., over 10 years, due to the scarce spatial and temporal coverage of earlier satellite image data. We found velocity overestimations in such long-term maps that can reach from ~69 m a−1 (7-year span) in Totten Glacier, East Antarctica, up to ~930 m a−1 (10-year span) in Pine Island, West Antarctica. We propose an innovative Lagrangian velocity-based method for overestimation correction without the use of field observations or additional image data. The method is validated by using a set of “ground truth” velocity maps for Totten Glacier which are produced from high-quality Landsat 8 images from 2013 to 2020. Subsequently, the validated method is applied to a historical velocity map of the David Glacier region from images from 1972–1989 acquired during Landsat 1, 4 and 5 satellite missions. It is demonstrated that velocity overestimations of up to 39 m a−1 for David Glacier and 69 m a−1 for Totten Glacier can be effectively corrected. Furthermore, temporal acceleration information, e.g., on calving events, is preserved in the corrected velocity maps and can be used for long-term ice flow dynamics analysis. We recommend that overestimations of more than the velocity mapping uncertainty (1σ) be corrected. This velocity overestimation correction method can be applied to the production of regional and ice sheet-wide historical velocity maps from long-term satellite images.

scholarly journals Subglacial controls on the flow of Institute Ice Stream, West Antarctica

2016 ◽  
Vol 57 (73) ◽  
pp. 19-24 ◽  
Author(s):  
Martin J. Siegert ◽  
Neil Ross ◽  
Jilu Li ◽  
Dustin M. Schroeder ◽  
David Rippin ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Flow Dynamics ◽  
West Antarctica ◽  
Sharp Transition ◽  
Ice Flow ◽  
Subglacial Lake ◽  
Ice Stream ◽  
Grounding Line ◽  
Sloping Bed ◽  
Basal Melting

ABSTRACTThe Institute Ice Stream (IIS) rests on a reverse-sloping bed, extending >150 km upstream into the ~1.8 km deep Robin Subglacial Basin, placing it at the threshold of marine ice-sheet instability. Understanding IIS vulnerability has focused on the effect of grounding-line melting, which is forecast to increase significantly this century. Changes to ice-flow dynamics are also important to IIS stability, yet little is known about them. Here we reveal that the trunk of the IIS occurs downstream of the intersection of three discrete subglacial features; a large ‘active’ subglacial lake, a newly-discovered sharp transition to a zone of weak basal sediments and a major tectonic rift. The border of IIS trunk flow is confined by the sediment on one side, and by a transition between basal melting and freezing at the border with the Bungenstock Ice Rise. By showing how basal sediment and water dictate present-day flow of IIS, we reveal that ice-sheet stability here is dependent on this unusual arrangement.

scholarly journals Site information and initial results from deep ice drilling on Law Dome, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 3-10 ◽  
Author(s):  
V.I. Morgan ◽  
C.W. Wookey ◽  
J. Li ◽  
T.D. van Ommen ◽  
W. Skinner ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
High Accumulation ◽  
Ice Flow ◽  
Ice Cap ◽  
Basal Ice ◽  
Inland Ice ◽  
The Last Glacial Maximum ◽  
Initial Results ◽  
The Last Glacial

AbstractThe aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

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