Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response
Subglacial bed roughness is one of the main factors controlling the rate of future Antarctic ice-sheet retreat and also one of the most uncertain. A common technique to constrain the bed roughness using ice-sheet models is basal inversion, tuning the roughness to reproduce the observed present-day i...
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ftcopernicus:oai:publications.copernicus.org:tc103456 2023-06-06T11:46:49+02:00 Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response Berends, Constantijn J. Wal, Roderik S. W. Akker, Tim Lipscomb, William H. 2023-04-12 application/pdf https://doi.org/10.5194/tc-17-1585-2023 https://tc.copernicus.org/articles/17/1585/2023/ eng eng doi:10.5194/tc-17-1585-2023 https://tc.copernicus.org/articles/17/1585/2023/ eISSN: 1994-0424 Text 2023 ftcopernicus https://doi.org/10.5194/tc-17-1585-2023 2023-04-17T16:23:11Z Subglacial bed roughness is one of the main factors controlling the rate of future Antarctic ice-sheet retreat and also one of the most uncertain. A common technique to constrain the bed roughness using ice-sheet models is basal inversion, tuning the roughness to reproduce the observed present-day ice-sheet geometry and/or surface velocity. However, many other factors affecting ice-sheet evolution, such as the englacial temperature and viscosity, the surface and basal mass balance, and the subglacial topography, also contain substantial uncertainties. Using a basal inversion technique intrinsically causes any errors in these other quantities to lead to compensating errors in the inverted bed roughness. Using a set of idealised-geometry experiments, we quantify these compensating errors and investigate their effect on the dynamic response of the ice sheet to a prescribed forcing. We find that relatively small errors in ice viscosity and subglacial topography require substantial compensating errors in the bed roughness in order to produce the same steady-state ice sheet, obscuring the realistic spatial variability in the bed roughness. When subjected to a retreat-inducing forcing, we find that these different parameter combinations, which per definition of the inversion procedure result in the same steady-state geometry, lead to a rate of ice volume loss that can differ by as much as a factor of 2. This implies that ice-sheet models that use basal inversion to initialise their model state can still display a substantial model bias despite having an initial state which is close to the observations. Text Antarc* Antarctic Ice Sheet Copernicus Publications: E-Journals Antarctic The Cryosphere 17 4 1585 1600 |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
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English |
description |
Subglacial bed roughness is one of the main factors controlling the rate of future Antarctic ice-sheet retreat and also one of the most uncertain. A common technique to constrain the bed roughness using ice-sheet models is basal inversion, tuning the roughness to reproduce the observed present-day ice-sheet geometry and/or surface velocity. However, many other factors affecting ice-sheet evolution, such as the englacial temperature and viscosity, the surface and basal mass balance, and the subglacial topography, also contain substantial uncertainties. Using a basal inversion technique intrinsically causes any errors in these other quantities to lead to compensating errors in the inverted bed roughness. Using a set of idealised-geometry experiments, we quantify these compensating errors and investigate their effect on the dynamic response of the ice sheet to a prescribed forcing. We find that relatively small errors in ice viscosity and subglacial topography require substantial compensating errors in the bed roughness in order to produce the same steady-state ice sheet, obscuring the realistic spatial variability in the bed roughness. When subjected to a retreat-inducing forcing, we find that these different parameter combinations, which per definition of the inversion procedure result in the same steady-state geometry, lead to a rate of ice volume loss that can differ by as much as a factor of 2. This implies that ice-sheet models that use basal inversion to initialise their model state can still display a substantial model bias despite having an initial state which is close to the observations. |
format |
Text |
author |
Berends, Constantijn J. Wal, Roderik S. W. Akker, Tim Lipscomb, William H. |
spellingShingle |
Berends, Constantijn J. Wal, Roderik S. W. Akker, Tim Lipscomb, William H. Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
author_facet |
Berends, Constantijn J. Wal, Roderik S. W. Akker, Tim Lipscomb, William H. |
author_sort |
Berends, Constantijn J. |
title |
Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
title_short |
Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
title_full |
Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
title_fullStr |
Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
title_full_unstemmed |
Compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
title_sort |
compensating errors in inversions for subglacial bed roughness: same steady state, different dynamic response |
publishDate |
2023 |
url |
https://doi.org/10.5194/tc-17-1585-2023 https://tc.copernicus.org/articles/17/1585/2023/ |
geographic |
Antarctic |
geographic_facet |
Antarctic |
genre |
Antarc* Antarctic Ice Sheet |
genre_facet |
Antarc* Antarctic Ice Sheet |
op_source |
eISSN: 1994-0424 |
op_relation |
doi:10.5194/tc-17-1585-2023 https://tc.copernicus.org/articles/17/1585/2023/ |
op_doi |
https://doi.org/10.5194/tc-17-1585-2023 |
container_title |
The Cryosphere |
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17 |
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4 |
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1585 |
op_container_end_page |
1600 |
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1767952278211264512 |