Fluctuations of a Greenlandic Tidewater Glacier from the Little Ice Age to Present PDF Download
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Author: James M. Lea
Publisher:
ISBN:
Category : Geological modeling
Languages : en
Pages : 0
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Significant uncertainty surrounds the influence of atmospheric and oceanic forcing on the fluctuations of tidewater glacier outlets of the Greenland ice sheet (GrIS), with the majority of studies focussing on dynamics over the last two decades. Although numerical model based projections exist anticipating the future dynamics of major GrIS outlets, these have been made using temporally limited model calibration periods (5 years) compared to the centennial timescales that they seek to predict over. The ability of these numerical models to simulate the centennial timescale dynamics of GrIS tidewater glaciers has therefore not been explicitly tested. This thesis seeks to calibrate a well-established one-dimensional tidewater glacier numerical model against post-Little Ice Age maximum (LIAmax) observations of a major tidewater glacier outlet of GrIS. The study site chosen is Kangiata Nunaata Sermia (KNS); the largest tidewater outlet in SW Greenland south of Jakobshavn Isbræ. This glacier is known to have undergone retreat of20 km since its LIAmax, though the timing of this retreat and response to climate forcing is currently poorly constrained. Utilising a range of source material, it is demonstrated that KNS is likely to have achieved its LIAmax by 1761, experiencing either one, or two multi-kilometre retreats by 1859, and retreats of a similar scale between 1921-1968, and 1997-2012. Terminus fluctuations of KNS were in phase with climate anomalies, where data were available for comparison (1871-2012). To allow accurate comparison to numerical model output, the accuracy of different methods of quantifying glacier terminus change was also evaluated. Two new methods were devised so observations could be matched with greater accuracy than existing methods allowed. Glacier sensitivity to climate forcing was evaluated using the numerical model.
Author: James M. Lea
Publisher:
ISBN:
Category : Geological modeling
Languages : en
Pages : 0
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Book Description
Significant uncertainty surrounds the influence of atmospheric and oceanic forcing on the fluctuations of tidewater glacier outlets of the Greenland ice sheet (GrIS), with the majority of studies focussing on dynamics over the last two decades. Although numerical model based projections exist anticipating the future dynamics of major GrIS outlets, these have been made using temporally limited model calibration periods (5 years) compared to the centennial timescales that they seek to predict over. The ability of these numerical models to simulate the centennial timescale dynamics of GrIS tidewater glaciers has therefore not been explicitly tested. This thesis seeks to calibrate a well-established one-dimensional tidewater glacier numerical model against post-Little Ice Age maximum (LIAmax) observations of a major tidewater glacier outlet of GrIS. The study site chosen is Kangiata Nunaata Sermia (KNS); the largest tidewater outlet in SW Greenland south of Jakobshavn Isbræ. This glacier is known to have undergone retreat of20 km since its LIAmax, though the timing of this retreat and response to climate forcing is currently poorly constrained. Utilising a range of source material, it is demonstrated that KNS is likely to have achieved its LIAmax by 1761, experiencing either one, or two multi-kilometre retreats by 1859, and retreats of a similar scale between 1921-1968, and 1997-2012. Terminus fluctuations of KNS were in phase with climate anomalies, where data were available for comparison (1871-2012). To allow accurate comparison to numerical model output, the accuracy of different methods of quantifying glacier terminus change was also evaluated. Two new methods were devised so observations could be matched with greater accuracy than existing methods allowed. Glacier sensitivity to climate forcing was evaluated using the numerical model.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 205
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The Greenland Ice Sheet contains enough water to raise global sea levels by ~7 metres, but predictions of the actual potential future contribution in a warming climate vary widely. These can be improved through a better understanding of how the whole ice sheet and its outlet glaciers have responded to past and present climate fluctuations. Recent studies have observed that Greenland Ice Sheet outlet glaciers have been retreating and thinning at increasingly faster rates since the 1990s. However, few studies have investigated the behaviour of the numerous independent ice caps that surround the ice sheet, or the land-terminating outlet glaciers. In addition, recent retreat is rarely put into context with long-term twentieth century fluctuations. This study has mapped ice sheet outlet glaciers and margins, independent ice cap outlets and mountain/valley glaciers at 11 time steps between the Little Ice Age and 2009 in northwest and southwest Greenland. Length changes of different glacier classes and terminus environments are examined, and overall glacier fluctuations compared to regional air temperatures and precipitation. Glaciers in the northwest have retreated further than those in the southwest at most time periods, with the exception of 1943/53-1964 when southwest glaciers underwent their most rapid rate of retreat. Length changes in both regions are driven by air temperature and precipitation changes. Tidewater outlet glaciers have generally retreated shorter distances than land-terminating glaciers in both absolute and relative terms over long time periods. These results imply that recent rapid retreat of many tidewater outlet glaciers in Greenland is not unprecedented, and may represent natural cyclical fluctuations rather than a long-term shift in behaviour. Ice sheet outlet glaciers have retreated shorter relative distances than independent ice caps and mountain/valley glaciers. Ice sheet margins advanced in the southwest between 1964 and 2001, and a slight and a slight advance of independent glaciers was observed from ~1964-1987. It is unclear why this advance occurred. This study highlights the need for more research into the fluctuations of the independent ice caps and land-terminating glaciers in all regions of Greenland. In addition, more detailed research into the response of glaciers of all classes and terminus environments to climate change during the whole of the twentieth century is required to put recent changes into context.
Author: Mason Joseph Fried
Publisher:
ISBN:
Category :
Languages : en
Pages : 270
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The Greenland Ice Sheet rapidly lost mass over the last two decades, in part due to increases in ice loss from termini of large tidewater glaciers. Terminus melting and calving can drive glacier retreat and the pattern of ice sheet mass loss through reductions in resistive stresses near the glacier front and, in turn, increases in ice flow to the ocean. Despite their importance to ice sheet mass balance, factors controlling terminus positions are poorly constrained in ice sheet models, which fundamentally obscures sea level rise predictions. In this dissertation, I use a suite of novel observations and techniques to quantify controls on frontal ablation and terminus positions at tidewater glaciers in central west Greenland. Until recently, frontal ablation processes were obscured due to limited observations of submarine termini. Here, I use observations from multibeam echo sonar to show the morphological complexity of the submarine terminus face and identify previously unrecognized melting and calving processes. The terminus features numerous secondary subglacial plume outlets outside of the main subglacial channel system that drive and disperse large submarine melt rates across the glacier front. Submarine melting drives steep, localized terminus undercutting that can trigger calving by connecting to finely-spaced surface crevasses. In turn, large calving events cause the terminus face to become anomalously overcut. Incorporating observed outlet geometries in a numerical plume model, I estimate small subglacial discharge fluxes feeding secondary plume outlets that are reminiscent of a distributed subglacial network. Regional remote-sensing observations reveal that, for most glaciers in central west Greenland, seasonal terminus positions are more sensitive to glacial runoff than ice mélange or ocean thermal forcing. Shallow, serac-failing tidewater glaciers are most sensitive, where subglacial plumes melt the terminus and locally enhance retreat. Glaciers with large ice fluxes and deep termini retreat sporadically through full ice-thickness calving events less dependent on runoff. Together, these results provide process-oriented constraints on the shape of the submarine terminus face, the geometry of subglacial discharge and submarine melting, the influence of environmental forcing mechanisms and the impact that these variables have on terminus positions and dynamics in a warming climate.
Author: John A. Matthews
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 126
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Author: George Frederick Wright
Publisher: London : K. Paul, Trench, Trübner
ISBN:
Category : Geology
Languages : en
Pages : 454
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Describes excursion to Greenland in 1894 with Dr. F.A. Cook, with observations on land and sea ice, peoples, plants and animals. Discusses Pleistocene glaciation and its causes. (AB 19714).
Author: Per Holmlund
Publisher:
ISBN:
Category :
Languages : en
Pages : 13
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Author: Hans Wilhelmsson Ahlmann
Publisher:
ISBN:
Category : Climatology
Languages : en
Pages : 76
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Author: Laura B. Levy
Publisher:
ISBN:
Category :
Languages : en
Pages : 408
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"The Greenland Ice Sheet (GrIS) is responding sensitively to climate change and its meltwater has the potential to influence global sea level. Recently, large changes in the GrIS have occurred including increased velocities of outlet glaciers and melt over ~97% of the ice sheet. One means to understand modern and help predict future changes in the GrIS is to examine how it responded to past climate conditions. In this dissertation I provide a longer-term perspective of changes in the GrIS as well as in smaller, independent glaciers near the ice sheet margins (i.e., "local" glaciers). My research documents the past extents of the GrIS in central East and southern West Greenland during the Holocene Epoch (11,600 yrs ago-present) and provides evidence for climate conditions along the ice sheet margin during late glacial time (~17,500-11,600 yrs ago) and the Holocene Epoch. I use geomorphic mapping, surface exposure dating and lake sediment analyses to demonstrate that the GrIS and local glaciers in central East Greenland were receding during the Younger Dryas cold event (~12,900-11,600 yrs ago) and deposited the Milne Land stade moraines at the end of the Younger Dryas. I hypothesize that these ice marginal fluctuations were primarily influenced by air or ocean surface temperatures. I document the Holocene fluctuations of a local glacier that completely disappeared indicating peak warm conditions between ~9.3 and 6.0 cal kyr BP. The formation of this glacier at 2.6 cal kyr BP and its persistence from ~1.9 cal kyr BP-present suggests cold conditions during late Holocene time. I also use geomorphic mapping and surface exposure dating to document the extents of the GrIS in southern West Greenland, near Kangerlussuaq. I show that the Keglen, Ørkendalen and Historical moraines were deposited at 7.3 ka, 6.3 ka, and by ~AD 1950, respectively. These data indicate that the GrIS was as small as or smaller than at present during much of middle to late Holocene time. Finally, I synthesize my results and discuss possible causes of GrIS marginal changes in central East and southern West Greenland including changes in air and ocean temperatures and changes in sea level."
Author: John Anthony Matthews
Publisher:
ISBN:
Category :
Languages : en
Pages : 43
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Author: Yun Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 138
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The Greenland Ice Sheet has been experiencing accelerating mass loss in the past two decades, due to enhanced surface melting and accelerated ice discharge into the ocean through tidewater glaciers. Many tidewater glaciers accelerated as anomalous warm water intruded into their glacial fjords. Subaqueous melting of the glaciers in the ocean is a potential trigger of glacier acceleration. However, the processes of subaqueous melting are not well understood. In this dissertation, we modify an ocean general circulation model, MITgcm, to include the melting/freezing processes on the vertical calving face of tidewater glaciers. We simulate the subaqueous melting using 2D and 3D configurations of the numerical model at high resolution (20-m to 1-m grid spacing). The model well represents the turbulent buoyant plume we simulate in a laboratory tank, and is then applied to a glacial fjord domain configured from oceanographic data we collected in several Greenland tidewater glacier fjords in August 2010 and 2012. The rate and distribution of subglacial freshwater discharge is estimated and used to force model simulations. The numerical simulations show the turbulent upwelling and expansion of subglacial freshwater plumes, which induce high rates of subaqueous melting along their routes. Average rates of subaqueous melting of Greenland tidewater glaciers could be several meters per day in summer and an order of magnitude smaller in winter. The melt rate increases less than linearly with subglacial freshwater discharge and more than linearly with ocean thermal forcing. The uncertainty of the distribution of subglacial freshwater discharge leads to ±15% error on the melt rate. We derive a sensitivity relationship between the melt rate and ocean thermal forcing and subglacial water discharge for Store Glacier, and calculate the daily melt rate of Store Glacier between 2008 and 2011. The simulated melt rate in August 2010 compares well with the melt rate derived from the oceanographic data. This study provides simple guidelines for interpreting recent changes in glacier fronts as a result of climate warming and the inclusion of ice-ocean interactions along the calving fronts of Greenland glaciers in ice sheet numerical models.
