scholarly journals A borehole camera system for imaging the deep interior of ice sheets

2002 ◽  
Vol 48 (163) ◽  
pp. 622-628 ◽  
Author(s):  
Frank Carsey ◽  
Alberto Behar ◽  
A. Lonne Lane ◽  
Vince Realmuto ◽  
Hermann Engelhardt
Keyword(s):  
Ice Sheets ◽  
Hot Water ◽  
Ice Streams ◽  
Camera System ◽  
West Antarctic ◽  
California Institute Of Technology ◽  
Deep Interior ◽  
Field Season ◽  
Institute Of Technology ◽  
Borehole Camera

AbstractThe design and first deployment is described for the Jet Propulsion Laboratory–California Institute of Technology ice borehole camera system for acquisition of down-looking and side-looking images in a borehole made by a hot-water drill. The objective of the system is to acquire images in support of studies of the basal dynamics and thermodynamics of West Antarctic ice streams. A few sample images, obtained during the 2000/01 Antarctic field season, are shown from the basal layers of Ice Stream C.

scholarly journals On the geometry of core-catcher holders for hot-water based ice coring of sediment-laden ice

2009 ◽  
Vol 55 (189) ◽  
pp. 188-190 ◽  
Author(s):  
S.W. Vogel
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Hot Water ◽  
Ice Streams ◽  
Water Ice ◽  
West Antarctic ◽  
California Institute Of Technology ◽  
Basal Ice ◽  
Core Catcher ◽  
Institute Of Technology

Analysis of sediment-laden ice accreted at the base of ice sheets provides useful information on subglacial conditions and processes that otherwise cannot be observed or are very difficult to observe. While sediment-laden accreted basal ice can be accessed directly at the terminus of alpine glaciers, the basal zone of ice sheets is only accessible by drilling. Small amounts of sediment in the ice have provided few or no problems for conventional ice-core drilling (Gow and others, 1979; Weis and others, 1997); however, the higher-sediment-content accreted ice beneath West Antarctic ice streams (Vogel and others, 2005) has not been recovered using the California Institute of Technology (Caltech) hot-water ice corer (Engelhardt and others, 2000).

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 The Dynamics of Marine Ice Sheets

1979 ◽  
Vol 24 (90) ◽  
pp. 167-177 ◽  
Author(s):  
Robert H. Thomas
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
The North ◽  
West Antarctic ◽  
Grounding Line ◽  
Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

scholarly journals The Dynamics of Marine Ice Sheets

1979 ◽  
Vol 24 (90) ◽  
pp. 167-177 ◽  
Author(s):  
Robert H. Thomas
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Shelves ◽  
The North ◽  
West Antarctic ◽  
Grounding Line ◽  
Ice Sheet Dynamics

AbstractMarine ice sheets rest on land that, for the most part, is below sea-level. Ice that flows across the grounding line, where the ice sheet becomes afloat, either calves into icebergs or forms a floating ice shelf joined to the ice sheet. At the grounding line there is a transition from ice-sheet dynamics to ice-shelf dynamics, and the creep-thinning rate in this region is very sensitive to sea depth; rising sea-level causes increased thinning-rates and grounding-line retreat, falling sea-level has the reverse effect. If the bedrock slopes down towards the centre of the ice sheet there may be only two stable modes: a freely-floating ice shelf or a marine ice sheet that extends to the edge of the continental shelf. Once started, collapse of such an ice sheet to form an ice shelf may take place extremely rapidly. Ice shelves which form in embayments of a marine ice sheet, or which are partially grounded, have a stabilizing influence since ice flowing across the grounding line has to push the ice shelf past its sides. Retreat of the grounding line tends to enlarge the ice shelf, which ultimately may become large enough to prevent excessive outflow from the ice sheet so that a new equilibrium grounding line is established; removal of the ice shelf would allow retreat to continue. During the late-Wisconsin glacial maximum there may have been marine ice sheets in the northern hemisphere but the only current example is the West Antarctic ice sheet. This is buttressed by the Ross and Ronne Ice Shelves, and if climatic warming were to prohibit the existence of these ice shelves then the ice sheet would collapse. Field observations suggest that, at present, the ice sheet may be advancing into parts of the Ross Ice Shelf. Such advance, however, would not ensure the security of the ice sheet since ice streams that drain to the north appear to flow directly into the sea with little or no ice shelf to buttress them. If these ice streams do not flow over a sufficiently high bedrock sill then they provide the most likely avenues for ice-sheet retreat.

scholarly journals The Uncertain Future of the West Antarctic Ice Sheet

Eos ◽  
2017 ◽  
Vol 98 ◽  
Author(s):  
Terence Hughes
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Ice Sheets ◽  
Ice Streams ◽  
The West ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
Ice Shelves ◽  
West Antarctic ◽  
Uncertain Future

A recent paper in Reviews of Geophysics discusses how climate change could affect ice streams, ice sheets, ice shelves, and sea ice in Antarctica.

Glacial geomorphology: Towards a convergence of glaciology and geomorphology

2010 ◽  
Vol 34 (3) ◽  
pp. 327-355 ◽  
Author(s):  
Robert G. Bingham ◽  
Edward C. King ◽  
Andrew M. Smith ◽  
Hamish D. Pritchard
Keyword(s):  
Remote Sensing ◽  
Numerical Modelling ◽  
Landscape Evolution ◽  
Ice Sheets ◽  
Ice Streams ◽  
Glacial Geomorphology ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Future Challenges ◽  
Glacial Landform

This review presents a perspective on recent trends in glacial geomorphological research, which has seen an increasing engagement with investigating glaciation over larger and longer timescales facilitated by advances in remote sensing and numerical modelling. Remote sensing has enabled the visualization of deglaciated landscapes and glacial landform assemblages across continental scales, from which hypotheses of millennial-scale glacial landscape evolution and associations of landforms with palaeo-ice streams have been developed. To test these ideas rigorously, the related goal of imaging comparable subglacial landscapes and landforms beneath contemporary ice masses is being addressed through the application of radar and seismic technologies. Focusing on the West Antarctic Ice Sheet, we review progress to date in achieving this goal, and the use of radar and seismic imaging to assess: (1) subglacial bed morphology and roughness; (2) subglacial bed reflectivity; and (3) subglacial sediment properties. Numerical modelling, now the primary modus operandi of ‘glaciologists’ investigating the dynamics of modern ice sheets, offers significant potential for testing ‘glacial geomorphological’ hypotheses of continental glacial landscape evolution and smaller-scale landform development, and some recent examples of such an approach are presented. We close by identifying some future challenges in glacial geomorphology, which include: (1) embracing numerical modelling as a framework for testing hypotheses of glacial landform and landscape development; (2) identifying analogues beneath modern ice sheets for landscapes and landforms observed across deglaciated terrains; (3) repeat-surveying dynamic subglacial landforms to assess scales of formation and evolution; and (4) applying glacial geomorphological expertise more fully to extraterrestrial cryospheres.

A kinematic formalism for tracking ice-ocean mass exchange on the Earth's surface and estimating sea-level change 

2021 ◽  
Author(s):  
Surendra Adhikari ◽  
Erik Ivins ◽  
Eric Larour ◽  
Lambert Caron ◽  
Helene Seroussi
Keyword(s):  
Solid Earth ◽  
Sea Level ◽  
Mass Exchange ◽  
Ice Sheets ◽  
Earth System ◽  
Generic Level ◽  
California Institute Of Technology ◽  
Ocean Mass ◽  
Institute Of Technology ◽  
And Sea Level

<p>Polar ice sheets are important components of the Earth System.  As the geometries of land, ocean, and ice sheets evolve, they must be consistently captured within the lexicon of geodesy.  Understanding the interplay between the processes such as ice-sheet dynamics, solid-Earth deformation, and sea-level adjustment requires both geodetically consistent and mass conserving descriptions of evolving land and ocean domains, grounded ice sheets and floating ice shelves, and their respective interfaces. Here we present mathematical descriptions of a generic level set that can be used to track both the grounding lines and coastlines, in light of ice-ocean mass exchange and complex feedbacks from the solid Earth and sea level. We next present a unified method to accurately compute the sea-level contribution of evolving ice sheets based on the change in ice thickness, bedrock elevation and mean sea level caused by any geophysical processes. Our formalism can be applied to arbitrary geometries and at all time scales. While it can be used for applications with modeling, observations and the combination of two, it is best suited for Earth System models, comprising ice sheets, solid Earth and sea level, that seek to conserve mass.</p><p>© 2020 California Institute of Technology. Government sponsorship is acknowledged.</p>

Automated mineral analysis in TASK8

1990 ◽  
Vol 48 (2) ◽  
pp. 212-213
Author(s):  
William F. Chambers ◽  
Arthur A. Chodos ◽  
Roland C. Hagan
Keyword(s):  
National Laboratory ◽  
Control Program ◽  
Mineral Analysis ◽  
Alamos National Laboratory ◽  
Mineral Phase ◽  
Los Alamos National Laboratory ◽  
California Institute Of Technology ◽  
Mineral Phases ◽  
Letter Code ◽  
Institute Of Technology

TASK8 was designed as an electron microprobe control program with maximum flexibility and versatility, lending itself to a wide variety of applications. While using TASKS in the microprobe laboratory of the Los Alamos National Laboratory, we decided to incorporate the capability of using subroutines which perform specific end-member calculations for nearly any type of mineral phase that might be analyzed in the laboratory. This procedure minimizes the need for post-processing of the data to perform such calculations as element ratios or end-member or formula proportions. It also allows real time assessment of each data point.The use of unique “mineral codes” to specify the list of elements to be measured and the type of calculation to perform on the results was first used in the microprobe laboratory at the California Institute of Technology to optimize the analysis of mineral phases. This approach was used to create a series of subroutines in TASK8 which are called by a three letter code.

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