Thermal control of ice-stream margins

The thermal balance at the base of an ice sheet near an ice-stream margin was investigated theoretically. Specifically, conditions such that the base of the ice sheet would be frozen in the absence of heat generated by the ice motion were investigated. The base of the ice stream is maintained at mel...

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Main Author: Raymond, Charles F.
Format: Other/Unknown Material
Language:unknown
Published: 1993
Subjects:
46
Online Access:http://ntrs.nasa.gov/search.jsp?R=19930022708
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record_format openpolar
spelling ftnasantrs:oai:casi.ntrs.nasa.gov:19930022708 2023-05-15T16:40:52+02:00 Thermal control of ice-stream margins Raymond, Charles F. Unclassified, Unlimited, Publicly available Jul 1, 1993 http://ntrs.nasa.gov/search.jsp?R=19930022708 unknown http://ntrs.nasa.gov/search.jsp?R=19930022708 Accession ID: 93N31897 No Copyright Other Sources 46 NASA. Goddard Space Flight Center, The First Annual West Antarctic Ice Sheet (WAIS) Science Workshop; p 34 1993 ftnasantrs 2012-02-15T19:56:21Z The thermal balance at the base of an ice sheet near an ice-stream margin was investigated theoretically. Specifically, conditions such that the base of the ice sheet would be frozen in the absence of heat generated by the ice motion were investigated. The base of the ice stream is maintained at melting as a result of high dissipation of heat at the base associated with its fast motion over the bed. Heat dissipation in the inter-ice-stream ridge ice is presumed to be too small to maintain melting conditions on the bed there. Two opposing effects can be identified near the shear margin separating the fast and slow motions. Because the velocity of an ice stream falls off toward its margin, there is a near margin heat deficit zone where the heat generated at the bed is not, by itself, sufficient to maintain melting conditions. Without some counteracting process, the base could freeze inward toward the ice stream and cause it to narrow. The marginal shearing generates heat within the ice above the bed. This heat produces a thermal shielding effect that tends to warm the bed on both sides of the boundary between the fast and slow motion. This shielding effect, if strong enough, could produce a thawed zone beyond the fast/slow boundary. If melting at the bed by itself allows fast motion, then the ice stream would be free to widen. A coupled mass and heat flow model is being developed to examine these competing processes. Preliminary calculations using available information for boundary conditions appropriate for Ice Stream B predict that the shielding effect is most important. This tentative result suggests that thermal conditions are such that the ice stream could widen unstably. Other constraints would be required to stabilize the width. Possible factors could be bed morphology beneath ridges that does not allow fast motion even in thawed conditions, or inward advection of cold ice from the ridges across the margin and into the ice stream, which suppresses the shielding effect. The unknown geothermal heat flow beneath ice streams and inter ice-stream ridges is a major uncertainty in doing these calculations. Other/Unknown Material Ice Sheet Ice Stream B NASA Technical Reports Server (NTRS)
institution Open Polar
collection NASA Technical Reports Server (NTRS)
op_collection_id ftnasantrs
language unknown
topic 46
spellingShingle 46
Raymond, Charles F.
Thermal control of ice-stream margins
topic_facet 46
description The thermal balance at the base of an ice sheet near an ice-stream margin was investigated theoretically. Specifically, conditions such that the base of the ice sheet would be frozen in the absence of heat generated by the ice motion were investigated. The base of the ice stream is maintained at melting as a result of high dissipation of heat at the base associated with its fast motion over the bed. Heat dissipation in the inter-ice-stream ridge ice is presumed to be too small to maintain melting conditions on the bed there. Two opposing effects can be identified near the shear margin separating the fast and slow motions. Because the velocity of an ice stream falls off toward its margin, there is a near margin heat deficit zone where the heat generated at the bed is not, by itself, sufficient to maintain melting conditions. Without some counteracting process, the base could freeze inward toward the ice stream and cause it to narrow. The marginal shearing generates heat within the ice above the bed. This heat produces a thermal shielding effect that tends to warm the bed on both sides of the boundary between the fast and slow motion. This shielding effect, if strong enough, could produce a thawed zone beyond the fast/slow boundary. If melting at the bed by itself allows fast motion, then the ice stream would be free to widen. A coupled mass and heat flow model is being developed to examine these competing processes. Preliminary calculations using available information for boundary conditions appropriate for Ice Stream B predict that the shielding effect is most important. This tentative result suggests that thermal conditions are such that the ice stream could widen unstably. Other constraints would be required to stabilize the width. Possible factors could be bed morphology beneath ridges that does not allow fast motion even in thawed conditions, or inward advection of cold ice from the ridges across the margin and into the ice stream, which suppresses the shielding effect. The unknown geothermal heat flow beneath ice streams and inter ice-stream ridges is a major uncertainty in doing these calculations.
format Other/Unknown Material
author Raymond, Charles F.
author_facet Raymond, Charles F.
author_sort Raymond, Charles F.
title Thermal control of ice-stream margins
title_short Thermal control of ice-stream margins
title_full Thermal control of ice-stream margins
title_fullStr Thermal control of ice-stream margins
title_full_unstemmed Thermal control of ice-stream margins
title_sort thermal control of ice-stream margins
publishDate 1993
url http://ntrs.nasa.gov/search.jsp?R=19930022708
op_coverage Unclassified, Unlimited, Publicly available
genre Ice Sheet
Ice Stream B
genre_facet Ice Sheet
Ice Stream B
op_source Other Sources
op_relation http://ntrs.nasa.gov/search.jsp?R=19930022708
Accession ID: 93N31897
op_rights No Copyright
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