[PDF] Changes In West Antarctic Ice Stream Velocities eBook

Author : C.J. van der Veen
Publisher : Springer Science & Business Media
Page : 376 pages
File Size : 48,23 MB
Release : 2012-12-06
Category : Science
ISBN : 9400937458

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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 : David A. Lilien
Publisher :
Page : 140 pages
File Size : 48,11 MB
Release : 2019
Category :
ISBN :

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Ice streams are the primary pathway by which Antarctic ice is evacuated to the ocean. Because the Antarctic ice sheets lose mass primarily through oceanic melt and calving, ice-stream dynamics exert a primary control on the mass balance of the ice sheets. Thus, changes in melt rates at the ice-sheet margins, or in accumulation in the ice-sheet interiors, affect ice-sheet mass balance on timescales modulated by the response time of the ice streams. Even abrupt changes in melt at the margins can cause ice-stream speedup and resultant thinning lasting millennia, so understanding the upstream propagation of marginally forced changes across timescales is key for understanding the ice sheets’ ongoing contribution to sea-level rise. This dissertation is comprised of three studies that use observations and models to understand changes to Antarctic ice-stream dynamics on timescales from decades to millennia. The first chapter synthesizes remotely sensed observations of Smith, Pope, and Kohler glaciers in West Antarctica to investigate the causes and extent of their retreat. These glaciers have displayed some of the largest measured grounding-line retreat, most rapid thinning, and largest speedup amongst Antarctic ice streams. This retreat has drawn interest in their stability both in its own right and as a harbinger of future changes to larger neighboring ice streams. In this study, recent melt rates were determined using flux divergence estimates derived from observations of ice thickness and surface velocity. Out-of-balance melt at the beginning of the study period indicates that the imbalance of this system predates the beginning of satellite velocity observations in 1996. Throughout much of 1996-2010, there was both greater melt over the ice shelves than flux across the grounding line, implying loss of floating ice and elevated melt forcing, and greater grounding-line flux than accumulation, implying adjustment of the grounded ice in response to the ongoing imbalance. The grounding line position of Kohler glacier, and a large melt channel that is unlikely to be a steady-state feature, suggest that the perturbation to this system began on Kohler glacier sometime around the 1970s. Viscosity of the ice shelves, inferred using a numerical model, indicates that weakening of the Crosson ice shelf was necessary to allow the observed speedup, though it is unable to determine whether the weakening was a cause or effect of the ongoing retreat. The second chapter uses a suite of numerical model simulations to determine the dominant drivers of the recent retreat of Smith, Pope, and Kohler glaciers, and extends those simulations that best match observations to evaluate likely future retreat. Similar to the findings of previous studies, the distribution of sub-shelf melt is found to be the primary control on the rate of grounding-line retreat, while the shelf-averaged melt rate exerts a secondary control. The model simulations indicate that, despite ongoing imbalance, the grounding-line position in 1996 was not inherently unstable, but rather elevated melt at the grounding line was required to cause the observed retreat. A weakening of the ice-shelf margins was found to hasten the onset of grounding-line retreat and led to greater speedup. However, without increases in melt beyond 1996 levels, marginal weakening was insufficient to initiate grounding-line retreat. All simulations that capture the observed retreat continue to lose mass until at least 2100, suggesting that ice in this basin may contribute over 8 mm to global mean sea level by 2100. The magnitude of thinning deep in the catchment suggests that the retreat of Kohler and Smith glacier may hasten the destabilization of the neighboring Thwaites glacier catchment. The third chapter uses the timescale of the recently drilled South Pole Ice Core (SPICEcore) and nearby geophysical observations to infer the history of ice flow near the South Pole during the last 10,000 years. The South Pole is located 180 km from the nearest ice divide and drains from the East Antarctic plateau through Academy glacier/Foundation ice stream. As a result, ice flow near the South Pole is potentially affected by the dynamics of these ice streams, and so the history of ice flow in this region has the potential to inform understanding of how marginally forced changes affect the ice-sheet interior. Because the South Pole is far from an ice divide, the accumulation record in SPICEcore incorporates both spatial variations in accumulation upstream and temporal variations in regional accumulation. Comparison between the SPICEcore accumulation record, derived by correcting measured layer thicknesses for thinning, with an accumulation record derived from new GPS and radar measurements upstream, yields insight into past ice flow and accumulation. When ice speeds are modeled as increasing by 15% since 10 ka, the upstream accumulation explains 77% of the variance in the SPICEcore-derived accumulation (vs. 22% without speedup). This correlation is only expected if the ice-flow direction and spatial pattern of accumulation were stable throughout the Holocene. The 15% speedup in turn suggests a slight (3-4%) steepening or thickening of the ice-sheet interior and provides a new constraint on the evolution of the East Antarctic Ice Sheet following the glacial termination.

Author : Narelle Paula Marie Baker
Publisher :
Page : pages
File Size : 27,51 MB
Release : 2012
Category :
ISBN :

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Subglacial hydrology is known to influence the flow of ice. However, difficulty in accessing the base of large ice sheets has made determining the interaction between ice streams, basal sediment and water difficult to discern. The aim of this thesis is to determine the influence of subglacial hydrology on the flow of the West Antarctic ice streams. This is achieved through development of a numerical flowline model, the Hydrology, Ice and Till (HIT) model. Ice thermodynamics are coupled to a till layer of Coulomb plastic rheology. The porosity of the till changes with basal melt and freeze and can be augmented by water transported through a subglacial conduit system. Water availability strongly affects ice flow, as till porosity influences the till failure strength and thereby the basal resistance of the ice. The model was developed in four stages and a number of sensitivity tests were performed. It was then applied to Kamb Ice Stream (Ice Stream C) and Whillians Ice Stream (Ice Stream B), West Antarctica. Results confirm that ice streams are capable of oscillating between fast and slow velocity states. Cycles are generated at the grounding line of an ice stream and the speed of the transition from slow to fast flow is governed by water availability. The period of oscillation of the cycles for the West Antarctic ice streams was found to be several hundred years, which is in line with observations of stagnation and reactivation of these ice streams. This shows that subglacial hydrology has a role in modulating the flow variability of ice streams and that rather large changes in the flow of the West Antarctic ice streams are likely to occur this century.

Author : Roger LeB. Hooke
Publisher : Cambridge University Press
Page : 537 pages
File Size : 23,31 MB
Release : 2019-12-05
Category : Business & Economics
ISBN : 1108427340

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The principles of glacier physics are developed from basic laws in this up-to-date third edition for advanced students and researchers.

Author : Jonathan L. Bamber
Publisher : Cambridge University Press
Page : 672 pages
File Size : 38,2 MB
Release : 2004-02-12
Category : Science
ISBN : 9780521808958

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A detailed and comprehensive overview of observational and modelling techniques for all climate change, environmental science and glaciology researchers.