scholarly journals Rock debris in an Antarctic ice shelf

2012 ◽  
Vol 53 (60) ◽  
pp. 235-240 ◽  
Author(s):  
K.W. Nicholls ◽  
H.F.J. Corr ◽  
K. Makinson ◽  
C.J. Pudsey
Keyword(s):  
Sea Water ◽  
Ice Sheet ◽  
Radar Data ◽  
Coarse Sand ◽  
Potential Mechanism ◽  
Ice Shelf ◽  
Ice Streams ◽  
History Of ◽  
Seaward Edge

AbstractWe have discovered a band of stones and coarse sand in the Ronne Ice Shelf, Antarctica, some 60 m above the ice shelf’s base, 40 km from its seaward edge and 420 km from the point where the ice originally went afloat. A study of ice-sounding radar data from across the Ronne Ice Shelf has revealed other areas likely to contain debris in significant quantities. It appears that basal debris at the margins of ice streams feeding the ice shelf can be buried in the ice shelf by sea water freezing-on at the ice-shelf base. These findings are evidence for a mechanism active in a present-day ice-sheet/shelf system, which enables icebergs to transport large volumes of ice-rafted debris, and which also provides a potential mechanism for the formation of ice rises near ice fronts. We anticipate that a seismics study of debris melted from the ice shelf and deposited beneath will provide a valuable control on the history of ice-shelf–ocean interactions.

Relict flow stripes on the Ross Ice Shelf

1991 ◽  
Vol 15 ◽  
pp. 132-138 ◽  
Author(s):  
G. Casassa ◽  
K.C. Jezek ◽  
J. Turner ◽  
I.M. Whillans
Keyword(s):  
Ice Sheet ◽  
Radar Data ◽  
Present Position ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
Avhrr Data ◽  
Complex Patterns

Analysis of AVHRR data collected during the summer and winter over the Ross Ice Shelf reveals complex patterns of curvilinear stripes. In particular, a large, looping pattern of stripes is observed west of Crary Ice Rise in an area where conventional glaciological data collected with surface and airborne methods have been interpreted to suggest uncomplicated flow. On the basis of previous work using radar data to study ice flow downstream of Crary Ice Rise, we conclude that the stripes represent relict flowlines. The mechanism that produces these stripes is unclear, but we hypothesize that they are associated with subtle topography. Based solely on the patterns of stripes and their location in the outflow of major ice streams, we propose that they are related to an ice raft torn from the grounded ice sheet about 400 km upstream from its present position.

scholarly journals Technologies for retrieving sediment cores in Antarctic subglacial settings

2016 ◽  
Vol 374 (2059) ◽  
pp. 20150056 ◽  
Author(s):  
Dominic A. Hodgson ◽  
Michael J. Bentley ◽  
James A. Smith ◽  
Julian Klepacki ◽  
Keith Makinson ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Stream ◽  
Whillans Ice Stream ◽  
History Of ◽  
Subglacial Lakes ◽  
Physical And Chemical ◽  
The Antarctic

Accumulations of sediment beneath the Antarctic Ice Sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings. Retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies. This paper briefly reviews the history of sediment sampling in subglacial environments. It then outlines some of the technological challenges and constraints in developing the corers being used in sub-ice shelf settings (e.g. George VI Ice Shelf and Larsen Ice Shelf), under ice streams (e.g. Rutford Ice Stream), at or close to the grounding line (e.g. Whillans Ice Stream) and in subglacial lakes deep under the ice sheet (e.g. Lake Ellsworth). The key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures.

Relict flow stripes on the Ross Ice Shelf

1991 ◽  
Vol 15 ◽  
pp. 132-138 ◽  
Author(s):  
G. Casassa ◽  
K.C. Jezek ◽  
J. Turner ◽  
I.M. Whillans
Keyword(s):  
Ice Sheet ◽  
Radar Data ◽  
Present Position ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ross Ice Shelf ◽  
Avhrr Data ◽  
Complex Patterns

Analysis of AVHRR data collected during the summer and winter over the Ross Ice Shelf reveals complex patterns of curvilinear stripes. In particular, a large, looping pattern of stripes is observed west of Crary Ice Rise in an area where conventional glaciological data collected with surface and airborne methods have been interpreted to suggest uncomplicated flow. On the basis of previous work using radar data to study ice flow downstream of Crary Ice Rise, we conclude that the stripes represent relict flowlines. The mechanism that produces these stripes is unclear, but we hypothesize that they are associated with subtle topography. Based solely on the patterns of stripes and their location in the outflow of major ice streams, we propose that they are related to an ice raft torn from the grounded ice sheet about 400 km upstream from its present position.

scholarly journals Dynamical processes involved in the retreat of marine ice sheets

2001 ◽  
Vol 47 (157) ◽  
pp. 271-282 ◽  
Author(s):  
Richard C.A. Hindmarsh ◽  
E. Le Meur
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Grounding Line ◽  
Neutral Equilibrium ◽  
Generally True

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.

scholarly journals An improved bathymetry compilation for the Bellingshausen Sea, Antarctica, to inform ice-sheet and ocean models

2010 ◽  
Vol 4 (4) ◽  
pp. 2079-2101 ◽  
Author(s):  
A. G. C. Graham ◽  
F. O. Nitsche ◽  
R. D. Larter
Keyword(s):  
Ocean Circulation ◽  
Ice Sheet ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Sea Floor ◽  
Bellingshausen Sea ◽  
Warm Deep Water ◽  
Basal Melting

Abstract. The southern Bellingshausen Sea (SBS) is a rapidly-changing part of West Antarctica, where oceanic and atmospheric warming has led to the recent basal melting and break-up of the Wilkins ice shelf, the dynamic thinning of fringing glaciers, and sea-ice reduction. Accurate sea-floor morphology is vital for understanding the continued effects of each process upon changes within Antarctica's ice sheets. Here we present a new bathymetric grid for the SBS compiled from shipborne echo-sounder, spot-sounding and sub-ice measurements. The 1-km grid is the most detailed compilation for the SBS to-date, revealing large cross-shelf troughs, shallow banks, and deep inner-shelf basins that continue inland of coastal ice shelves. The troughs now serve as pathways which allow warm deep water to access the ice fronts in the SBS. Our dataset highlights areas still lacking bathymetric constraint, as well as regions for further investigation, including the likely routes of palaeo-ice streams. The new compilation is a major improvement upon previous grids and will be a key dataset for incorporating into simulations of ocean circulation, ice-sheet change and history. It will also serve forecasts of ice stability and future sea-level contributions from ice loss in West Antarctica, required for the next IPCC assessment report in 2013.

Constraining ice shelf basalt melting rates from isochrone data

2021 ◽  
Author(s):  
Vjeran Visnjevic ◽  
Reinhard Drews ◽  
Clemens Schannwell ◽  
Inka Koch
Keyword(s):  
Ocean Circulation ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Ice Shelves ◽  
Inverse Approach ◽  
History Of ◽  
Forward And Inverse Modeling ◽  
Basal Melting

<p>Ice shelves buttress ice flow from the continent towards the ocean, and their disintegration results in increased ice discharge.  Ice-shelf evolution and integrity is influenced by surface accumulation, basal melting, and ice dynamics. We find signals of all of these processes imprinted in the ice-shelf stratigraphy that can be mapped using isochrones imaged with radar.</p><p>Our aim is to develop an inverse approach to infer ice shelf basal melt rates using radar isochrones as observational constraints. Here, we investigate the influence of basalt melt rates on the shape of isochrones using combined insights from both forward and inverse modeling. We use the 3D full Stokes model Elmer/Ice in our forward simulations, aiming to reproduce isochrone patterns observed in our data. Moreover we develop an inverse approach based on the shallow shelf approximating, aiming to constrain basal melt rates using isochronal radar data and surface velocities. Insights obtained from our simulations can also guide the collection of new radar data (e.g., profile lines along vs. across-flow) in a way that ambiguities in interpreting the ice-shelf stratigraphy can be minimized. Eventually, combining these approaches will enable us to better constrain the magnitude and history of basal melting, which will give valuable input for ocean circulation and sea level rise projections.</p>

scholarly journals Multidecadal observations of the Antarctic ice sheet from restored analog radar records

2019 ◽  
Vol 116 (38) ◽  
pp. 18867-18873 ◽  
Author(s):  
Dustin M. Schroeder ◽  
Julian A. Dowdeswell ◽  
Martin J. Siegert ◽  
Robert G. Bingham ◽  
Winnie Chu ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Radar Data ◽  
West Antarctica ◽  
Ice Shelf ◽  
Topographic Features ◽  
Optical Film ◽  
Polar Ice Sheets ◽  
Scientific Potential ◽  
Radar Measurements ◽  
The Antarctic

Airborne radar sounding can measure conditions within and beneath polar ice sheets. In Antarctica, most digital radar-sounding data have been collected in the last 2 decades, limiting our ability to understand processes that govern longer-term ice-sheet behavior. Here, we demonstrate how analog radar data collected over 40 y ago in Antarctica can be combined with modern records to quantify multidecadal changes. Specifically, we digitize over 400,000 line kilometers of exploratory Antarctic radar data originally recorded on 35-mm optical film between 1971 and 1979. We leverage the increased geometric and radiometric resolution of our digitization process to show how these data can be used to identify and investigate hydrologic, geologic, and topographic features beneath and within the ice sheet. To highlight their scientific potential, we compare the digitized data with contemporary radar measurements to reveal that the remnant eastern ice shelf of Thwaites Glacier in West Antarctica had thinned between 10 and 33% between 1978 and 2009. We also release the collection of scanned radargrams in their entirety in a persistent public archive along with updated geolocation data for a subset of the data that reduces the mean positioning error from 5 to 2.5 km. Together, these data represent a unique and renewed extensive, multidecadal historical baseline, critical for observing and modeling ice-sheet change on societally relevant timescales.

scholarly journals Can Relict Crevasse Plumes on Antarctic Ice Shelves Reveal a History of Ice-Stream Fluctuation?

1988 ◽  
Vol 11 ◽  
pp. 77-82 ◽  
Author(s):  
D. R. MacAyeal ◽  
R. A. Bindschadler ◽  
K. C. Jezek ◽  
S. Shabtaie
Keyword(s):  
Numerical Model ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
Stream Discharge ◽  
Ice Stream ◽  
History Of

Configurations of relict surface-crevasse bands and medial moraines that emanate from the shear margins of ice streams are simulated, using a numerical model of an ideal rectangular ice shelf to determine their potential for recording a past ice-stream discharge chronology.

scholarly journals Isostatic Equilibrium Grounding Line Between The West Antarctic Ice Sheet And The Ross Ice Shelf

1979 ◽  
Vol 24 (90) ◽  
pp. 500 ◽  
Author(s):  
C. R. Bentley ◽  
L. Greischar
Keyword(s):  
Ice Sheet ◽  
Shelf Area ◽  
Ice Shelf ◽  
Ice Streams ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
Isostatic Rebound ◽  
West Antarctic ◽  
Grounding Line ◽  
Eastern Half

Abstract Taking various retreat-rates for the presumed grounded ice sheet in the Ross embayment during Wisconsin time, as calculated by Thomas (Thomas and Bentley, 1978), and assuming a time constant of 4400 years for isostatic rebound, a sea-floor uplift of 100±50 m still to be expected in the grid western part of the Ross Ice Shelf can be calculated. The expected uplift diminishes from grid west to grid east, and is probably negligible in the eastern half of the shelf area. There are extensive areas near the present grounding line where the water depth beneath the shelf is less than 100 m, so that uplift would lead to grounding. As grounding occurred, the neighboring ice shelf would thicken, causing grounding to advance farther. This process would probably extend the grounding line to a position running grid north-eastward across the shelf from the seaward end of Roosevelt Island, deeply indented by the extensions of the present ice streams. Floating ice would remain in the grid south-eastern half of the shelf.

scholarly journals Tidal influences on a future evolution of the Filchner–Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

2018 ◽  
Vol 12 (2) ◽  
pp. 453-476 ◽  
Author(s):  
Rachael D. Mueller ◽  
Tore Hattermann ◽  
Susan L. Howard ◽  
Laurie Padman
Keyword(s):  
Ocean Circulation ◽  
Three Dimensional ◽  
Ocean Model ◽  
Tidal Currents ◽  
Weddell Sea ◽  
Ice Shelf ◽  
Ice Streams ◽  
Future Evolution ◽  
History Of ◽  
Basal Melting

Abstract. Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner–Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

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