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Author: Jason Michael Amundson Publisher: ISBN: Category : Glaciers Languages : en Pages : 186
Book Description
"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: Jason Michael Amundson Publisher: ISBN: Category : Glaciers Languages : en Pages : 186
Book Description
"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: Heather Stewart Publisher: ISBN: Category : Languages : en Pages : 94
Book Description
The Greenland Ice Sheet's (GIS) magnitude of change has been of the utmost importance in understanding cryospheric contributions to the earth's climate change. Of particular interest is the long-term record of Jakobshavn Isbræ, one of the largest outlet glaciers draining an estimated 6.5% of the GIS. Its recent rapid thinning, associated with nearly doubled velocities, indicates that Greenland's outlet glaciers are likely to make faster contributions to sea-level rise than previously believed. To evaluate whether ongoing observed changes are climatically significant, changes must be determined over longer time frames. Although the 35 km retreat of its calving front since the LIA (1850) is well documented, it cannot be used to accurately reconstruct the glacier's history; in particular, since much of its recent retreat, the terminus was likely floating and thus susceptible to small and short-lived climate perturbations.^Here, we combine a chronology of the LIA readvance and subsequent retreat determined from ice sheet threshold lake sediments, along with a 3D reconstruction of ice marginal retreat, measured from stereo imagery to investigate the evolution of the floating ice tongue and land-based margins in the Jakobshavn drainage basin. For this study, we constrain Jakobshavn Isbræ's longer-term context with proglacial threshold lake sediments. Four AMS radiocarbon dates from macrofossils immediately below the LIA sediments from three lake basins to the north of the fjord reveal that Jakobshavn Isbrae reached its LIA maximum extent between 530"10 and 370"60 cal yr BP (1400-1640 AD). Two AMS radiocarbon dates from a lake south of the fjord state that Jakobshavn reached its LIA maximum between 2250"70 and 2420"60 cal yr BP.^Furthermore, the continuous nature of the LIA-sediment units in all sites indicates that Jakobshavn remained at or near its LIA maximum position between 1400-1640 AD and into the 20th century. Using stereoscopic pairs of aerial images taken in 1985, and SPOT satellite images acquired in 2007, vegetation trimlines marking the LIA ice extent and 1985 and 2007 ice sheet margins were mapped in 3D by using a soft-copy workstation. Maximum retreat and thinning rates were measured at Jakobshavn Isbræ, where the calving front retreated at an average rate of 0.178 km yr-1 between the LIA and 1985. Retreat rates increased to 0.545 km yr-1 between 1985 and 2007. Land based margins in the Jakobshavn area record average retreat rates from the LIA to 1985 at .007 km yr-1 and increasing from 1985 to 2007 at 0.030 km yr-1.^However, an outlet glacier just 30 km south of Jakobshavn Isbræ, Alanngorliup Sermia, is at or just above its LIA margin, and has only retreated at a rate of 0.017 km yr-1 since 1985. Thinning rates had a similar trend of increasing at the calving front at a rate of -2.15 m yr-1 from the LIA to 1985 and increased to -4.48 m yr-1 between 1985 and 2007. Land based margins in the Jakobshavn Isbræ area averaged -0.67 m yr-1 from the LIA to 1985 and increased to -1.34 m yr-1 thinning rate between 1985 and 2007. Alanngorliup Sermia has no thinning rate recorded between the LIA and 1985 because of its position at the LIA trimline and has thinned at a rate of -0.31 m yr-1 between 1985 and 2007. These results suggest the greatest retreat and thinning occurred between 1985 and 2007. They also suggest different termini environments respond differently to the same climatic changes.^Varied patterns of retreat and elevation indicate dynamic controls of the Jakobshavn study area. These data suggest that although climate may be the greater driving force of the Jakobshavn margin, ice dynamics play a key role in the marginal evolution since the LIA. The net loss of ice from the GIS plays an important role in global sea-level rise, and therefore more detailed investigations of the causes for marked changes of margins are needed to assess ongoing future changes.
Author: Luke Copland Publisher: Springer ISBN: 9402411011 Category : Science Languages : en Pages : 426
Book Description
This book provides an overview of the current state of knowledge of Arctic ice shelves, ice islands and related features. Ice shelves are permanent areas of ice which float on the ocean surface while attached to the coast, and typically occur in very cold environments where perennial sea ice builds up to great thickness, and/or where glaciers flow off the land and are preserved on the ocean surface. These landscape features are relatively poorly studied in the Arctic, yet they are potentially highly sensitive indicators of climate change because they respond to changes in atmospheric, oceanic and glaciological conditions. Recent fracturing and breakup events of ice shelves in the Canadian High Arctic have attracted significant scientific and public attention, and produced large ice islands which may pose a risk to Arctic shipping and offshore infrastructure. Much has been published about Antarctic ice shelves, but to date there has not been a dedicated book about Arctic ice shelves or ice islands. This book fills that gap.
Author: Kira Olsen Publisher: ISBN: Category : Languages : en Pages :
Book Description
I confirm the presence of a correlation between iceberg volume and glacial-earthquake size, which moves us closer to having the ability to use remotely recorded seismic signals to quantify mass loss at Greenland glaciers. This work presents testable hypotheses for future model development.
Author: W. S. B. Paterson Publisher: Elsevier ISBN: 1483287254 Category : Science Languages : en Pages : 491
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: Jason Michael Amundson
Author: Jason Michael Amundson
Author: Charles Raymond Warren
Author: Heather Stewart
Author: Anker Weidick
Author: Charles Raymond Warren
Author: Iain Wheel
Author: Paul R. Prescott
Author: Luke Copland
Author: Kira Olsen
Author: W. S. B. Paterson