Evaluation of Iceberg Calving Models Against Observations from Greenland Outlet Glaciers PDF Download
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Author: Tristan O. Amaral
Publisher:
ISBN: 9781085569576
Category : Glaciers
Languages : en
Pages : 104
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Book Description
The retreat and advance of marine-terminating outlet glaciers in Greenland plays a critical role in modulating ice sheet mass balance. However, the frontal ablation processes that regulate glacier terminus position are challenging to observe and thus difficult to represent in numerical ice flow models. Current models of the Greenland Ice Sheet rely upon simple iceberg calving and submarine melt parameterization to prescribe either a stable terminus position or iceberg calving rate, yet the relative accuracies and uncertainties of these criteria remain largely unknown at the ice sheet scale. Here, we evaluate six iceberg calving models from the literature against spatially and temporally diverse observations and model output from 50 marine-terminating outlet glaciers in Greenland. Five of six calving models successfully reproduce observed May/June terminus conditions with zero median model bias and low ice-sheet-wide uncertainty using fixed, spatially-optimized parameter values. However, when evaluated against time series observations from select glaciers, we find that calving models that predict a calving rate struggle to reproduce variations in observed terminus dynamics over seasonal and inter-annual time scales with single, optimized model parameters. Comparatively, calving models that prescribe a terminus position, rather than a calving rate, more accurately account for observed changes in terminus dynamics through time and are therefore less likely to generate glacier length and/or ice flux errors when employed in predictive ice flow models. Overall, our results indicate that the crevasse depth calving model reproduces observed terminus dynamics with high fidelity and should be considered a leading candidate for use in models of the Greenland Ice Sheet.
Author: Tristan O. Amaral
Publisher:
ISBN: 9781085569576
Category : Glaciers
Languages : en
Pages : 104
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Book Description
The retreat and advance of marine-terminating outlet glaciers in Greenland plays a critical role in modulating ice sheet mass balance. However, the frontal ablation processes that regulate glacier terminus position are challenging to observe and thus difficult to represent in numerical ice flow models. Current models of the Greenland Ice Sheet rely upon simple iceberg calving and submarine melt parameterization to prescribe either a stable terminus position or iceberg calving rate, yet the relative accuracies and uncertainties of these criteria remain largely unknown at the ice sheet scale. Here, we evaluate six iceberg calving models from the literature against spatially and temporally diverse observations and model output from 50 marine-terminating outlet glaciers in Greenland. Five of six calving models successfully reproduce observed May/June terminus conditions with zero median model bias and low ice-sheet-wide uncertainty using fixed, spatially-optimized parameter values. However, when evaluated against time series observations from select glaciers, we find that calving models that predict a calving rate struggle to reproduce variations in observed terminus dynamics over seasonal and inter-annual time scales with single, optimized model parameters. Comparatively, calving models that prescribe a terminus position, rather than a calving rate, more accurately account for observed changes in terminus dynamics through time and are therefore less likely to generate glacier length and/or ice flux errors when employed in predictive ice flow models. Overall, our results indicate that the crevasse depth calving model reproduces observed terminus dynamics with high fidelity and should be considered a leading candidate for use in models of the Greenland Ice Sheet.
Author: Cornelis J. Veen
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 4
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Book Description
The objective of this project was to develop simple yet realistic models of Greenland outlet glaciers to better understand ongoing changes and to identify possible causes for these changes. Several approaches can be taken to evaluate the interaction between climate forcing and ice dynamics, and the consequent ice-sheet response, which may involve changes in flow style. To evaluate the ice sheet response to mass-balance forcing, Van der Veen (Journal of Geophysical Research, in press) makes the assumption that this response can be considered a perturbation on the reference state and may be evaluated separately from how this reference state evolves over time. Mass-balance forcing has an immediate effect on the ice sheet. Initially, the rate of thickness change as compared to the reference state equals the perturbation in snowfall or ablation. If the forcing persists, the ice sheet responds dynamically, adjusting the rate at which ice is evacuated from the interior to the margins, to achieve a new equilibrium. For large ice sheets, this dynamic adjustment may last for thousands of years, with the magnitude of change decreasing steadily over time as a new equilibrium is approached. This response can be described using kinematic wave theory. This theory, modified to pertain to Greenland drainage basins, was used to evaluate possible ice-sheet responses to perturbations in surface mass balance. The reference state is defined based on measurements along the central flowline of Petermann Glacier in north-west Greenland, and perturbations on this state considered. The advantage of this approach is that the particulars of the dynamical flow regime need not be explicitly known but are incorporated through the parameterization of the reference ice flux or longitudinal velocity profile. The results of the kinematic wave model indicate that significant rates of thickness change can occur immediately after the prescribed change in surface mass balance but adjustments in flow rapidly diminish these rates to a few cm/yr at most. The time scale for adjustment is of the order of a thousand years or so.
Author: Jason Michael Amundson
Publisher:
ISBN:
Category : Glaciers
Languages : en
Pages : 186
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"Jakobshavn Isbræ, a fast-flowing outlet glacier in West Greenland, began a rapid retreat in the late 1990's. The glacier has since retreated over 15 km, thinned by tens of meters, and doubled its discharge into the ocean. The glacier's retreat and associated dynamic adjustment are driven by poorly-understood processes occurring at the glacier-ocean interface. These processes were investigated by synthesizing a suite of field data collected in 2007-2008, including timelapse imagery, seismic and audio recordings, iceberg and glacier motion surveys, and ocean wave measurements, with simple theoretical considerations. Observations indicate that the glacier's mass loss from calving occurs primarily in summer and is dominated by the semi-weekly calving of full-glacier-thickness icebergs, which can only occur when the terminus is at or near flotation. The calving icebergs produce long-lasting and far-reaching ocean waves and seismic signals, including 'glacial earthquakes'. Due to changes in the glacier stress field associated with calving, the lower glacier instantaneously accelerates by ~3% but does not episodically slip, thus contradicting the originally proposed glacial earthquake mechanism. We furthermore showed that the pre-dominance of calving during summer can be attributed to variations in the strength of the proglacial ice mélange (dense pack of sea ice and icebergs). Sea ice growth in winter stiffens the mélange and prevents calving; each summer the mélange weakens and calving resumes. Previously proposed calving models are unable to explain the terminus dynamics of Jakobshavn Isbræ (and many other calving glaciers). Using our field observations as a basis, we developed a general framework for iceberg calving models that can be applied to any calving margin. The framework is based on mass continuity, the assumption that calving rate and terminus velocity are not independent, and the simple idea that terminus thickness following a calving event is larger than terminus thickness at the event onset. Although the calving framework does not constitute a complete calving model, it provides a guide for future attempts to define a universal calving law"--Leaf iii.
Author: Robert M Krimmel
Publisher:
ISBN:
Category : Columbia Glacier (Alaska)
Languages : en
Pages : 4
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Author: W. S. B. Paterson
Publisher: Elsevier
ISBN: 1483287254
Category : Science
Languages : en
Pages : 491
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Book Description
This updated and expanded version of the second edition explains the physical principles underlying the behaviour of glaciers and ice sheets. The text has been revised in order to keep pace with the extensive developments which have occurred since 1981. A new chapter, of major interest, concentrates on the deformation of subglacial till. The book concludes with a chapter on information regarding past climate and atmospheric composition obtainable from ice cores.
Author: Anker Weidick
Publisher:
ISBN:
Category : Glaciers
Languages : en
Pages : 88
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Author: C.J. van der Veen
Publisher: Springer Science & Business Media
ISBN: 9400937458
Category : Science
Languages : en
Pages : 376
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Book Description
Few scientists doubt the prediction that the antropogenic release of carbon dioxide in the atmosphere will lead to some warming of the earth's climate. So there is good reason to investigate the possible effects of such a warming, in dependence of geographical and social economic setting. Many bodies, governmental or not, have organized meetings and issued reports in which the carbon dioxide problem is defined, reviewed, and possible threats assessed. The rate at which such reports are produced still increases. However, while more and more people are getting involved in the 'carbon dioxide business', the number of investigators working on the basic problems grows, in our view, too slowly. Many fundamental questions are still not answered in a satisfactory way, and the carbon dioxide building rests on a few thin pillars. One such fundamental question concerns the change in sea level associated with a climatic warming of a few degrees. A number of processes can be listed that could all lead to changes of the order of tens of centimeters (e. g. thermal expansion, change in mass balance of glaciers and ice sheets). But the picture of the carbon dioxide problem has frequently be made more dramatic by suggesting that the West Antarctic Ice Sheet is unstable, implying a certain probability of a 5 m higher sea-level stand within a few centuries.
Author: H. Jay Zwally
Publisher:
ISBN:
Category : Artificial satellites in earth sciences
Languages : en
Pages : 22
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Author: Joseph K. Landauer
Publisher:
ISBN:
Category : Glaciers
Languages : en
Pages : 16
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Author:
Publisher:
ISBN:
Category : Arctic regions
Languages : en
Pages : 616
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