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Smith, Benjamin E. "Characterization of the small scale ice sheet topography of Antarctica and Greenland /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6812.
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McGovern, Jonathan. "Forward and adjoint ice sheet model sensitivities with an application to the Greenland Ice Sheet." Thesis, Swansea University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678316.
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Selmes, Nick. "Remote sensing of supraglacial lakes on the Greenland Ice Sheet." Thesis, Swansea University, 2011. https://cronfa.swan.ac.uk/Record/cronfa42597.
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The dynamic mass loss from the Greenland Ice Sheet has prompted considerable research into the role of supraglacial lakes in causing dynamic thinning. These lakes can drain through 1000 m of ice to the bed and are thought to play an important role in connecting the surface and basal hydrologies of the ice sheet, allowing water to reach the bed and cause the ice to accelerate. Despite this apparent importance little research has been carried out on lakes outside of SVV Greenland, and no research has examined the occurrence of lake drainage over the whole of Greenland. The aim of this thesis is to discover where lakes occur for the entire Greenland ice Sheet, and how these lakes drain. New remote sensing techniques for monitoring lakes through the melt season were developed and tested. The evolution of 2600 lakes (those lakes larger than > 0.125 km2) was studied over five years (2005-2009) using 3704 MODIS images. Lakes were discovered to either drain fast to the bed, more slowly over the surface, or to freeze at the end of the melt season. There were 263 fast lake drainages per year of which 61% were in the SW region and a further 17% in the NE, both regions where mass loss is mainly due to surface mass balance. In the dynamically thinning SE region there were only three fast lake drainages per year along a 1300 km coastline. In the NW, fast lake drainage did not occur on five of the ten glaciers with the most rapid dynamic thinning. The results of this thesis show that the drainage of supraglacial lakes cannot have been responsible for dynamic mass loss from the Greenland Ice Sheet.
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Tedstone, Andrew Jachnik. "Hydrological controls on Greenland Ice Sheet motion." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/14169.
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An improved understanding of the processes controlling the dynamics of the Greenland Ice Sheet is needed to enable more accurate determination of the response of the ice sheet to projected climate change. Meltwater produced on the ice sheet surface can penetrate to the bed and cause ice motion to speed up through enhanced basal sliding. However, the importance of coupled hydro-dynamics both to current ice sheet motion and future stability over the coming century is unclear. This thesis presents observations from the south-west Greenland Ice Sheet which improve our understanding of coupled hydro-dynamics. It commences with an investigation of the response of ice motion to exceptional meltwater forcing during summer 2012. Simultaneous field observations of ice motion (by GPS) and proglacial discharge show that, despite two extreme melt events during July 2012 and summer ice sheet runoff 3.9 s.d. above the 1958– 2011 mean which resulted in faster summer motion, net annual motion was slower than in the average melt year of 2009. This suggests that surface melt-induced acceleration of land-terminating regions of the ice sheet will remain insignificant even under extreme melting scenarios. The thesis then examines spatial variability in ice motion, in relation to an inferred subglacial drainage axis, using GPS and satellite radar observations from a land-terminating margin up to 20 km inland where ice is 800 m thick. Whilst spatial variability in subglacial drainage system configuration is found to control ice motion at short timescales, the proportional contribution of summer motion to annual motion is almost invariant. The structure of the subglacial drainage system does not therefore appear to significantly influence spatial variations in net summer speedup. Lastly, observations are made by applying feature tracking to 30 years of optical satellite imagery in a ~170 by 50 km area along the ice sheet margin (where ice reaches ~850 m thick) to examine whether coupled hydrology-dynamics affects inter-annual ice motion. Hydro-dynamic coupling resulted in net ice motion slowdown during a period of clear climate warming. Further increases in meltwater production may therefore reduce ice sheet motion. The thesis concludes that at land-terminating margins of the Greenland Ice Sheet, (1) larger annual meltwater volumes do not result in faster annual ice motion; (2) the detailed structure of the subglacial drainage network appears unimportant to the role of summer motion in determining annual motion; and (3) atmospheric warming over several decades has been accompanied by a slowdown in ice motion. As such, hydro-dynamic coupling is unlikely to form a significant positive feedback between surface melting and ice motion in response to projected climate warming. The wider relevance of these findings to tidewater systems requires further investigation.
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Sturgis, Daniel J. "Meltwater infilltration [sic] in the accumulation zone, West Greenland Ice Sheet." Laramie, Wyo. : University of Wyoming, 2009. http://proquest.umi.com/pqdweb?did=1939351861&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Beal, Samuel A. "Chemical weathering along the Greenland ice sheet margin /." Norton, Mass. : Wheaton College, 2009. http://hdl.handle.net/10090/8391.
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Yang, Lei. "Greenland ice sheet change surface climate variability and glacier dynamics /." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1180121203.
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Lecavalier, Benoit. "A Model of the Greenland Ice Sheet Deglaciation." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/30362.
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The goal of this thesis is to improve our understanding of the Greenland ice sheet (GrIS) and how it responds to climate change. This was achieved using ice core records to infer elevation changes of the GrIS during the Holocene (11.7 ka BP to Present). The inferred elevation changes show the response of the ice sheet interior to the Holocene Thermal Maximum (HTM; 9-5 ka BP) when temperatures across Greenland were warmer than present. These ice-core derived thinning curves act as a new set of key constraints on the deglacial history of the GrIS. Furthermore, a calibration was conducted on a three-dimensional thermomechanical ice sheet, glacial isostatic adjustment, and relative sea-level model of GrIS evolution during the most recent deglaciation (21 ka BP to present). The model was data-constrained to a variety of proxy records from paleoclimate archives and present-day observations of ice thickness and extent.
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Rumrill, Julie. "Analysis of Spatial and Temporal Variations in Strain Rates Near Swiss Camp, Greenland." ScholarWorks @ UVM, 2009. http://scholarworks.uvm.edu/graddis/205.
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In this thesis, I present results from a two-year study of strain-rate variations along a flow line on the western margin of the Greenland ice sheet. I used baseline network solutions to investigate variations in longitudinal strain rates over the 2006 and 2007 melt seasons. Analyses revealed high-magnitude, short-duration events of increased longitudinal strain early in the melt season coincident with a high melt year, suggesting a link between melt production and its effects on seasonal ice flow. Results from 2006 data show that longitudinal strain rates became variable shortly after the onset of melt (day 186) changing up to ~ 15 x 10-4 a-1 within 24 hours. The onset of melting occurred earlier in 2007 (day 153) and was also followed closely by strain-rate deviation from background rates calculated prior to melting. The data revealed rapid (hours to days), high-magnitude (two to ten times greater than background rates) changes in longitudinal strain rates (hereafter referred to as ‘high-strain’ events) that occurred both on the small-scale (affecting 1-4 baselines) and on the large-scale (affecting 5 or more baselines). Large-scale high-strain events were infrequent, on the order of two events per season. Events were likely caused by drainage of supraglacial meltwater that penetrated to the bed of the glacier raising the basal water pressure. The increase in pressure reduced the basal resistive stress, and allowed rapid local acceleration. The basal stress reduction was transmitted to areas of higher stress which resulted in longitudinal compression of the ice down glacier and longitudinal extension up glacier. The evolution of high-strain events altered longitudinal strain rates more than 15 km along flow from the site of initiation. I estimated the origin and spatial extent of highstrain events by assessing the magnitude of the strain-rate variations in various baselines, and observing whether the altered strain regime was extensive or compressive. Magnitude and timing of changes in strain suggest that high-strain events originated in the ablation zone, the equilibrium zone, and inland of the equilibrium zone, and indicate that short-term altered stress conditions are not confined to the ablation zone. The background strain-rate for 2007 (~ -7 x 10-4 a-1 for a 37 km longitudinal baseline) was similar to the 2006 longitudinal background rate. When extrapolating the 2006 background rate over the melt season, the expected change in baseline length (~ 11 m) was similar to the observed change (~ 9 m). In contrast, when extrapolating the 2007 background rate over the melt season, the expected shortening was ~ 6 m, but the observed shortening was less than 1 m. This result suggests that seasonal high-strain events have the ability to alter longitudinal baseline length, allowing a greater ice flux to lower elevations where melting occurs for a larger portion of the year. However, the cumulative seasonal effects of both large-scale and small-scale strain events are modest, and indicate that seasonal changes in strain rates have a minor effect on the overall stability of the ice sheet. Nevertheless, it is possible that over much longer timescales these seasonal changes may become more important with increasing temperatures and available melt. Results from this study may also be useful in making broader inferences regarding the response of grounded portions of the ice sheet to seasonal changes in basal resistive stress.
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Sun, Shihua. "Long-term elevation change of the southern Greenland ice sheet from Seasat, Geosat, and GFO satellite radar altimetry /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p1418069.
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Morris, Richard M. "Modelling melt, refreezing and runoff across the surfaces of high-latitude ice masses : Devon Ice Cap, Nunavut, Canada and the Greenland Ice Sheet." Thesis, University of Aberdeen, 2013. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=198040.
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Rising global air temperatures are causing increased melting across the surfaces of large ice masses such as the Greenland Ice Sheet and the ice caps of Arctic Canada. The fraction of this melt that refreezes within the snow and firn has a large spatial variability across the surfaces of these ice masses. This spatial variability is an important control on the surface mass balance, and has important implications for the interpretation of satellite radar altimetry data sets. The sensitivity of large ice masses to climate change depends on changes in the melt-runoff relationship, and changes in the spatial extents of surface snow zones within the accumulation zone. Therefore, this thesis develops a model used to calculate melt, near-surface refreezing and surface runoff across the surface of a large ice mass. The model is used to predict both stratigraphic changes and bulk snow and firn properties over a melt season across a transect of points. A high-resolution snow and firn data set from Devon Ice Cap is used to calibrate and validate the model. It is then run across a transect covering the entire altitude range of the ice cap for the summers of 2004 and 2006. The model matches measured trends in bulk snowpack variables across the transect in both years. Calculated fraction of melt running off is similar in both years at ~44%, though is sensitive to change in air temperature. Surface mass balance (including internal accumulation), found to be +0.26 Gt in 2004 and +0.18 Gt in 2006, changes in a parabolic way for a linear air temperature change. The model is then applied to the Greenland Ice Sheet without altering any of the calibrated parameters. It is run for two melt seasons, 2004 and 2005, over which model output compares well with measurements of snow depth, sub-surface density and altitudes of snow surface boundaries. The wet snow line responds in a linear way to change in air temperature, and the runoff line is sensitive to the specified depth within the firn of the impermeable layer. Over the next century, the model shows that the dry snow zone will disappear completely under moderate warming scenarios, and the percolation zone will also disappear under intense warming scenarios. Including a more complicated representation of vertical meltwater percolation through the snow and firn grid substantially alters modelled autumn density profiles, and produces more accurate values of meltwater percolation depth and ice fraction within the autumn snowpack. However, bulk snowpack properties are of similar accuracy to the un-modified model. Scaling up of the model, in both spatial and temporal terms, will make it useful for assistance in the interpretation of satellite radar altimetry data sets, as well as assessing future changes in the spatial variability of refreezing and runoff, reducing the uncertainty in long term surface mass balance predictions across large ice masses.
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Samuel, Welsh. "Applying GIS to Investigate the Spatial Variability of Sub-Glacial Hydrology under Land Terminating Ice Sheets in Western Greenland Ice Sheet." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-305434.
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With continued warming regional surface air temperatures around the Artic in recent decades, there is growing importance in understanding how ice sheet dynamics interact with a shifting global climate system. This research investigates the spatial variability of sub-glacial hydrology under land terminating ice sheets in Western GrIS, when applying varying overburden ice pressures within Shreve’s (1972) hydraulic potential equation. The application of ArcGIS is used with adjusted k-values in the equation to route hydrological network systems under the ice sheet and help identify the processes taking place within the sub-glacial system. With focus on processes such as water piracy, we are able illustrate the effects that water at the base can have on ice sheet behaviors. i.e. velocity and mas balance. The findings conclude that the ice sheet is operating under conditions at its base with a k-value somewhere within the range of 0.9 to 1.1. This assumption is based on comparisons between modelled pro-glacial output with observed data taken from studies by Mikkelsen et al. (2014) and Smith et al. (2015), using input melt data at the surface (Lindback et. al., 2015). At this level of hydraulic potential, water piracy is effectively changing the course pathways of the hydrological network and therefore manipulating the size and shape of the sub-glacial catchments. As a result, discharge may leave the glacier from a different location than what would be assumed. Identifying the location and volume of water under particular ice sheets, compared to neighboring ice sheets, can be used to explain spatial and temporal differences in ice sheet characteristics. Such research is important in understanding both environmental and socio-economic implications at local to global scale. Although the application of GIS methodology is extremely useful is producing such results, it must be recognised that a high level of uncertainty and error exists in the data results.<br>Temperatur kan ha en särskilt stark inverkan på hur istäcken (glaciärer) beter sig. Även om det är väl känt att temperaturerna ökar både globalt och runt Arktis så har vi bara börjat förstå vikten av effekten av detta på glaciärer. Med ökande temperaturer har vi börjat se att en ökad avsmältning och en ökad mängd smältvatten i glaciala system kan ändra sättet en ismassa beter sig. Ett exempel på en sådan förändring är en ökad hastighet som ismassan rör sig i eftersom vatten fungerar som ett glidmedel mellan glaciären och den underliggande marken. Var vattnet finns under isen påverkar var istäcket rör sig. Man tror att en ökning i hastighet vid vissa delar av istäcket kan ledda till att det tunnas ut. Med tiden lämnar en allt större mängd vatten systemet vilket bidrar till mindre, retirerande glaciärer och en höjning av den globala havsytenivån då vattnet via vattendrag till slut rinner ut i havet. I den här studien användes ett kartläggningsprogram, Geografiskt Informationssystem (GIS), för att förutsäga var flodsystem under isen befinner sig. Detta kartläggningsprogram används eftersom dessa regioner inte är tillgängliga för observationer i fält. Tjockleken på istäcket som ligger ovanpå flodsystemet utövar ett tryck på vattnet och gör att det kan flöda emot gravitationen och i riktningar och med hastigheter som inte är typiska för flodsystem i varmare klimat. Denna process kallas vattenavlänkning. I denna studie används en ekvation i GIS för att variera trycket från det ovanliggande istäcket. Genom att ändra detta ändras hur stor vattenavlänkningen blir och därför även vilken väg vattnet tar under isen. Denna teknik tillåter oss att se vilken väg vattnet tar från att det kommer in i systemet vid toppen av istäcket till var det lämnar systemet genom vattendrag nedströms. Genom att veta var vattnet befinner sig kan man utröna varför isen rör sig annorlunda gentemot omkringliggande istäcken, och därför också dess påverkan på omgivande miljö såväl som sociala konsekvenser. Även om detta är en väldigt användbar metod för att kartlägga kanalsystem så finns det osäkerheter, till exempel i hur resultatet stämmer överens med verkliga scenarion. Så även om detta är användbart för att förstå teorin bakom processerna så är resultatet kanske inte helt tillförlitligt.
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Pingree, Katherine A. "The Greenland Ice Sheet: Reconstruction under Modern-Day Conditions and Sensitivity to the North Atlantic Oscillation." Fogler Library, University of Maine, 2010. http://www.library.umaine.edu/theses/pdf/PingreeKA2010.pdf.
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Gao, Xin. "Tracing of internal layers in radar echograms from a Greenland study region." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4645.
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Thesis (M.S.) University of Missouri-Columbia, 2006.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research .pdf file viewed on (June 25, 2007) Includes bibliographical references.
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Habermann, Marijke. "Basal shear strength inversions for ice sheets with an application to Jakobshavn Isbrae, Greenland." Thesis, University of Alaska Fairbanks, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3607054.
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<p> Satellite and <i>in situ</i> observations of ice sheet outlet glaciers around the turn of the 21<sup>st</sup> century showed that rapid changes in ice dynamics are possible and important for the evolution of ice sheets. When attempting to model these dynamic changes the conditions at the ice-bed interface are crucial. Inverse methods can be used to infer basal properties, such as the basal yield stress, from abundant surface velocity observations by using a physical model of ice flow. Inverse methods are very powerful, but they need to be applied with care, otherwise errors can dominate the solution. In this study we investigate the potentials and caveats of inverse methods.</p><p> Synthetic experiments can be designed where basal conditions are assumed and an ice flow model is used to produce a set of 'synthetic' surface velocities. These can then be used to examine and evaluate inverse methods. We find that in iterative inverse methods it is essential to use a stopping criterion that will prevent overfitting the data. We introduce a new and rapidly-converging iterative inverse method called Incomplete Gauss Newton method, where the linearized problem is partly minimized in each step.</p><p> In a practical application of inverse methods to the terminus region of Jakobshavn Isbræ, Greenland we investigate changes in basal conditions over time by performing inversions for different years of available surface velocity data. We find a decrease in basal yield stress in the lower areas of the glacier that agrees with effective pressure changes due to the changes in ice geometry. This supports an ocean and terminus driven system.</p><p> The difference between the modeled and observed velocity fields, called residual, contains information about the ability to reproduce the velocities when only adjustment of the basal condition is allowed. With a properly regularized inversion the residual patterns can be used to investigate sources of error in the system. We find that the ice geometry and the model simplifications influence the ability to reproduce observed velocity fields more than the error in observed velocity does. This indicates that further progress must come from model improvements and improved capabilities to measure bedrock geometry.</p>
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Ashcraft, Ivan S. "Microwave Remote Sensing of the Greenland Ice Sheet: Models and Applications." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd532.pdf.
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de, Pomereu Jean. "The exploration of 'indlandsis' : a cultural and scientific history of ice sheets to 1970." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18332.
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Despite their central importance to the Earth system, nowhere within the literatures of Polar Studies or the Humanities does there exist a comprehensive cultural and scientific history of ice sheets that takes into consideration both Greenland and Antarctica, or that is not constrained to a particular exploratory, technological, or geopolitical period or framing. My thesis addresses this lacunae by contributing a bi-polar, empirical history and analysis of the different scientific and cultural processes, transformations, and discontinuities through which ice sheets have been transformed from unexplored realms of the imagination, into tangible, material objects of investigation and meaning. Its scope extends from early Greek mapping to 1970. Within this timeframe, it identifies three broad phases in the perception of ice sheets. The first, preceding their earliest physical exploration, corresponds to the perception of ice sheets as one-dimensional realms defined and bounded by the human imagination. The second phase, associated with their early surface exploration between 1870 and 1930, corresponds to the perception of ice sheets as undifferentiated, two-dimensional 'topographies of absence', best characterized by their horizontal desolation. The third phase, triggered by the deployment of new technologies of sub-surface investigation such as seismic sounding, radio echo sounding (RES), and the practice of ice coring, corresponds to the perception of ice sheets as three-dimensional, super-massive, and interdependent objects of internal and material complexity. Although primarily rooted in archival research and the study of first hand textual and visual materials, my arguments and observations also draw on secondary literatures from the history of science and technology, geopolitics, visual culture, and the geography of space and place. These literatures allow me to contextualize and substantiate my analysis of historical processes within broader perspectives, notably Humboldtian science, Romanticism, visual abstraction, scientific imagery, and the Cold War.
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Bathke, Deborah J. "Meteorological processes controlling the variability of net annual accumulation over the Greenland ice sheet." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1073073721.
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Thesis (Ph. D.)--Ohio State University, 2004.<br>Title from first page of PDF file. Document formatted into pages; contains xv, 200 p.; also includes graphics. Includes bibliographical references (p. 173-184).
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Clason, Caroline. "Quantitative controls on the routing of supraglacial meltwater to the bed of glaciers and ice sheets." Doctoral thesis, Geography and Environment, University of Aberdeen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-85178.
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The influence of seasonal influx of supraglacial meltwater on basal water pressures and consequent changes in ice surface velocity has been a focus of research spanning over three decades, particularly focussing on alpine glaciers. Now, with increased recognition for a need to better include glacial hydrology within models of ice dynamics and ice sheet evolution, the ability to predict where and when meltwater is delivered to the subglacial system is paramount, both for understanding the dynamics of alpine glaciers, and of large Arctic ice masses. Studies of the dynamics of outlet glaciers on the Greenland Ice Sheet have received particular attention in recent years, as links between ice acceleration and increased surface melt production are explored. Responses of horizontal and vertical ice velocities to meltwater generated suggest efficient transmission of meltwater from the supraglacial to subglacial hydrological systems. Indeed, in the case of meltwater transfer through the drainage of supraglacial lakes, it has been shown that such build-ups of stored meltwater can force crevasse penetration through many hundreds of metres of ice. This thesis presents a new modelling routine for the prediction of moulin formation and delivery of meltwater to the ice-bed interface. Temporal and spatial patterns of moulin formation through propagation of crevasses and drainage of supraglacial lakes are presented, and quantitative controls on water-driven crevasse propagation are investigated through a series of sensitivity tests. The model is applied to two glacial catchments: the Croker Bay catchment of Devon Ice Cap in High Arctic Canada; and Leverett Glacier catchment of the southwest Greenland Ice Sheet. Through model application to these sites, sensitivities to crevasse surface dimensions, ice tensile strength, ice fracture toughness and enhanced production of surface meltwater are investigated. Model predictions of moulin formation are compared with field observations and remotely sensed data, including ice surface velocities, dynamic flow regimes, and visible surface features. Additionally, model quantification of meltwater delivered to the ice-bed interface of Leverett Glacier is compared with profiles of measured proglacial discharge. Moulin formation is predicted at increasingly high elevation with time into the ablation season in both4catchments, and furthermore, the model predicts an increase in both the number of moulins and the number of lake drainages in response to increased melt scenarios. Sensitivity testing confirms that the model is most sensitive to factors influencing the rate at which meltwater fills a crevasse, and results highlight the importance of accurate parameterisation of crevasse surface dimensions and the tensile strength of the ice. Further applications of the model are discussed, with a focus on incorporation into coupled models of glacial hydrology and dynamics, including larger scale ice sheet modelling. The inclusion of spatially distributed points of temporally varying meltwater delivery to the subglacial system is imperative to fully understand the behaviour of the subglacial drainage system. Furthermore, dynamic response to future climatic change and increased melt scenarios, and the consequent evolution of ice masses, including those in the Canadian Arctic and Greenland, cannot be fully understood without first understanding the glacial hydrological processes driving many of these changes.
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Strellis, Brandon Mitchell. "Aerosol radiative forcing over central Greenland: estimates based on field measurements." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49063.
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Measurements of the key aerosol properties including light scattering and backscattering coefficients (σsp and σbsp), light absorption coefficient (σap), and particle concentration were made at Summit, Greenland, in the summer of 2011. From these quantities, the single scattering albedo (ω) and angstrom scattering and absorption exponents (åsp, åap) were calculated. In conjunction with these measurements, aerosol optical depth (AOD or τ) and the spectral surface albedo, Rs, were measured. Additionally, the aerosol chemical composition was characterized through snow and air filter analyses. A radiative transfer model was used to estimate the direct aerosol radiative forcing and radiative forcing efficiency using the measurements as inputs. Taken as a whole, this project allowed for the first ever measurement-based characterization of aerosol radiative forcing over central Greenland.
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Wheelock-Davis, Emily J. "Elevation Changes in Greenland over Two Decades from Cross-Platform LIDAR Analysis." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366223499.
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Hulton, Nicholas R. J. "Modelling the Greenland ice sheet." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/19859.
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A dynamic, vertically integrated, three-dimensional, mass continuity, computer model of the Greenland ice sheet is used to predict the ice sheet's response to climatic perturbation. The ice flow is gravity driven according to glaciological physics, whereby ice flow is claculated as the sum of deformation and sliding components averaged over the ice thickness where longitudinal stresses are considered negligible. The model has inputs of the present-day ice surface and basal topography, and is forced by changes in sea level and surface mass balance, which are modelled by separately described and forced accumulation and ablation parts. The mass balance and the forcing terms are parametized against present-day values and the present-day ice sheet is initially used as the starting condition for model experiments. By repeating model experiments from the same starting point and varying only one model parameter at a time the model's sensitivity to individual parameters is assessed. Characteristic behaviour patterns, reaction times and significant parameters are identified. The model is seen to produce a realistic simulation of present-day conditions. The ice dynamics model is robust compared to the changes that can be introduced by small variations in sea-level. The relationship between forcing temperatures and ablation rates exerts most control on the model. Confidence in the model allows a series of predictive runs to be undertaken to smiulate three types of glacial fluctuation: Short term change, behaviour under maximum ice conditions and deglaciation trends. Whilst climatic forcing is important in driving the model overall, topographic effects and the influences of calving are crucial to understanding maximum state conditions and retreat behaviour. In each of the three cases, the model results corroborate well with what is known about the real world. These matches and the closeness with which the present-day conditions are simulated are mutually supportive to the conclusion that the model is effective and realistic in the way long term ice sheet change in Greenland is represented. The theoretical processes and the model results are considered to describe real processes and events. Modelling, in conjunction with field techniques, is seen as an powerful means of understanding nature.
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Butler, Catriona Elizabeth Hamilton. "Hydrochemistry of the Greenland Ice Sheet." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683692.
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The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly understood, in terms of hydrology, water storage and biogeochemical processes. High temporal resolution biogeochemical sampling of bulk meltwaters at a typical, land-terminating outlet glacier of the GrIS was employed in order to infer processes at the ice sheet bed over three contrasting melt seasons. No high temporal resolution geochemical datasets previously existed for ice sheet environments, mainly due to inaccessibility. Bulk meltwaters comprised differing propOltions of waters originating from a widespread, distributed subglacial drainage system (these delayed flow waters being solute enriched due to prolonged residence times and high rock:water ratios in the contributing environments), and an efficient channelized system (dilute surface waters rapidly transmitted to the margin). Two-component chemical mixing models, in combination with MODIS satellite imagery, revealed that delayed flow was released continuously. However, higher volumes were released at times of subglacial outburst events when draining surface lakes interacted with the bed and expelled stored waters. Dissolution experiments and geochemical data indicated that these waters may have been stored at the bed over winter, or longer, and comprised one-third of delayed flow release in any given year (~O.02 km\ The geochemical data, in combination with 01 80 -H20 isotope data from bulk meltwaters and surface ice, were able to identify subglacial drainage system evolution and increasingly distant water sources contributing to bulk meltwaters. Enhanced silicate dissolution was observed compared to smaller valley glaciers, which may lead to enhanced CO2 sequestration compared to carbonate weathering' environments. Chemical weathering rates were lower than would be expected for a poly thermal ice mass, likely due to low reactivity bedrock. Ionic fluxes were higher in high melt years, which is a further indication of stored water release due to extensive basal flushing. Finally, isotopes of sulphate demonstrated that there are both oxic and anoxic conditions at the bed of the GrIS, with potential for highly anoxic sulphate reducing conditions in the interior.
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Banwell, Alison Frances. "Modelling the hydrology of the Greenland Ice Sheet." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/267715.
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There is increasing recognition that the hydrology of the Greenland Ice Sheet plays an important role in the dynamics and therefore mass balance of the ice sheet. Understanding the hydrology of the ice sheet and being able to predict its future behaviour is therefore a key aspect of glaciological research. To date, the ice sheet’s hydrology has tended to be inferred from the analysis of surface velocity measurements, or modelled in a theoretical, idealised way. This study focuses on the development of a high spatial (100 m) and temporal (1 hour) resolution, physically based, time-dependent hydrological model which is applied to the ~2,300 km2 Paakitsoq region, West Greenland, and is driven, calibrated, and evaluated using measured data. The model consists of three components. First, net runoff is calculated across the ice sheet from a distributed, surface energy- balance melt model coupled to a subsurface model, which calculates changes in temperature, density and water content in the snow, firn and upper-ice layers, and hence refreezing. The model is calibrated by adjusting key parameter values to minimize the error between modelled output and surface height and albedo measurements from the three Greenland Climate Network (GC-Net) stations, JAR 1, JAR 2 and Swiss Camp. Model performance is evaluated in two ways by comparing: i) modelled snow and ice distribution with that derived from Landsat-7 ETM+ satellite imagery using Normalised Difference Snow Index (NDSI) classification and supervised image thresholding; and ii) modelled albedo with that retrieved from the Moderate- resolution Imaging Spectroradiometer (MODIS) sensor MOD10A1 product. Second, a surface routing / lake filling model takes the time-series of calculated net runoff over the ice sheet and calculates flow paths and water velocities over the snow / ice covered surface, routing the water into ‘open’ moulins or into topographic depressions which can fill to form supraglacial lakes. This model component is calibrated against field measurements of a filling lake in the study area made during June 2011. Supraglacial lakes are able to drain by a simulated hydrofracture mechanism if they reach a critical volume. Once water is at the ice / bed interface, discharge and hydraulic head within subglacial drainage pathways are modelled using the third model component. This consists of an adaptation of a component (EXTRAN) of the U.S. Environmental Protection Agency Storm Water Management Model (SWMM), modified to allow for enlargement and closure of ice-walled conduits. The model is used to identify how the subglacial hydrological system evolves in space and time in response to varying surface water inputs due to melt and lake drainage events, driven ultimately by climate data. A key output from the model is the spatially and temporally varying water pressures which are of interest in helping to explain patterns of surface velocity and uplift found by others, and will ultimately be of interest for driving ice dynamics models.
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Karatay, Mehmet Rahmi. "Modelling the hydrology of the Greenland ice sheet." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5282.
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This thesis aims to better understand the relationships between basal water pressure, friction, and sliding mechanisms at ice sheet scales. In particular, it develops a new subglacial hydrology model (Hydro) to explicitly predict water pressures in response to basal water production and water injection from the surface. Recent research suggests that the Greenland ice sheet (gis) is losing a substantial volume of ice through dynamic thinning. This process must be modelled to accurately assess the contribution of the gis to sea-level rise in future warming scenarios. A key control on dynamic thinning is the presence of water at the ice-bed interface; Zwally et al. (2002) highlight the importance of supraglacial lakes' impact on basal ice dynamics, a process now con rmed by Das et al. (2008) and Shepherd et al. (2009). Many studies focus on the effects of surface meltwater reaching the bed of the gis but the underlying processes are often ignored. Geothermal, strain, and frictional melting, which evolves with basal hydrology, provide the background basal pressure profile that surface meltwater perturbates. Without understanding how these heat terms affect the background profile it is difficult to define basal boundary conditions in models and therefore difficult to model the dynamic response of the gis to surface melting. Hydro tracks subglacial water pressures and the evolution of efficient drainage networks. Coupled with the existing 3D thermomechanical ice sheet model Glimmer, model outputs include effective pressure N and the efficient hydraulic area. Defining frictional heat flux and basal traction as functions of N allow the modelling of seasonal dynamic response to randomly draining supraglacial lakes. Key results are that frictional heat flux, as a function of N, caps potential runaway feedback mechanisms and that water converges in topographic troughs under Greenland's outlet glaciers. This leads to a background profile with low N under outlet glaciers. Therefore, outlet glaciers show a muted dynamic speedup to the seasonal surface signal reaching the bed. Land-terminating ice does not tend to have subglacial troughs and so has higher background N and consequently a larger seasonal response. This, coupled with effects of ice rheology, can explain the hitherto puzzling lack of observed seasonal velocity change on Jakobshavn Isbræ and other outlet glaciers.
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Doyle, Samuel Huckerby. "GPS-based investigations of Greenland Ice Sheet dynamics." Thesis, Aberystwyth University, 2014. http://hdl.handle.net/2160/3040645e-18ac-496b-9428-ebbf4696cddb.
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Accurate forecasting of the Greenland Ice Sheet's contribution to global sea level change requires detailed knowledge of how ice ow responds to surface water inputs. Both ice velocities and surface melt have increased significantly over the last decade but recent research suggests that ice ow acceleration over the summer is regulated by the seasonal evolution of the subglacial drainage system. To investigate these and associated processes, a network of continuously-operating, dual-frequency global positioning system (GPS) receivers was deployed on a 140-km-long land-terminating transect in West Greenland, providing centimetre-precise, high-frequency records of ice motion. These data reveal that the enhanced summer ow regime is comprised of discrete, transient accelerations driven by the diurnal melt cycle, rapid in situ supraglacial lake drainage and rainfall/melt events. In 2010, a comprehensive array of instruments captured the rapid ( ~ 2 hour) drainage of a large supraglacial lake via a 3-km-long fracture, hydraulically-driven through km-thick ice. A further pronounced, widespread and sustained acceleration driven by rainfall and melt, observed in late August 2011, suggests that the predicted increase in cyclonic activity over Greenland may drive widespread off-season melt, rainfall and ow acceleration across the ice sheet. Together these events provide new insights into the basal hydrodynamic controls on ice sheet motion. Furthermore, observations of a persistent year-on-year acceleration in ice ow between 2009 and 2012 at a high elevation site located ~ 50 km inland of the equilibrium line support the hypothesis that the observed inland expansion of supraglacial lakes is driving faster ice ow at high elevations. These observations contrast with the prevailing self-regulation model and reveal that despite surface melt increasing water inputs to the bed are still insuffcient to develop effective subglacial drainage in the ice sheet's interior.
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Stevens, Laura A. "Influence of meltwater on Greenland Ice Sheet dynamics." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113800.
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Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>Seasonal fluxes of meltwater control ice-flow processes across the Greenland Ice Sheet ablation zone and subglacial discharge at marine-terminating outlet glaciers. With the increase in annual ice sheet meltwater production observed over recent decades and predicted into future decades, understanding mechanisms driving the hourly to decadal impact of meltwater on ice flow is critical for predicting Greenland Ice Sheet dynamic mass loss. This thesis investigates a wide range of meltwater-driven processes using empirical and theoretical methods for a region of the western margin of the Greenland Ice Sheet. I begin with an examination of the seasonal and annual ice flow record for the region using in situ observations of ice flow from a network of Global Positioning System (GPS) stations. Annual velocities decrease over the seven-year time-series at a rate consistent with the negative trend in annual velocities observed in neighboring regions. Using observations from the same GPS network, I next determine the trigger mechanism for rapid drainage of a supraglacial lake. In three consecutive years, I find precursory basal slip and uplift in the lake basin generates tensile stresses that promote hydrofracture beneath the lake. As these precursors are likely associated with the introduction of meltwater to the bed through neighboring moulin systems, our results imply that lakes may be less able to drain in the less crevassed, interior regions of the ice sheet. Expanding spatial scales to the full ablation zone, I then use a numerical model of subglacial hydrology to test whether model-derived effective pressures exhibit the theorized inverse relationship with melt-season ice sheet surface velocities. Finally, I pair near-ice fjord hydrographic observations with modeled and observed subglacial discharge for the Saqqardliup sermia-Sarqardleq Fjord system. I find evidence of two types of glacially modified waters whose distinct properties and locations in the fjord align with subglacial discharge from two prominent subcatchments beneath Saqqardliup sermia. Continued observational and theoretical work reaching across discipline boundaries is required to further narrow our gap in understanding the forcing mechanisms and magnitude of Greenland Ice Sheet dynamic mass loss.<br>by Laura A. Stevens.<br>Ph. D.
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Young, Tun Jan. "Investigating fast flow of the Greenland Ice Sheet." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/279019.
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The dynamic response of a faster-flowing Greenland Ice Sheet to climate change is modulated by feedbacks between ice flow and surface meltwater delivery to the basal environment. While supraglacial melt processes have been thoroughly examined and are well constrained, the response of the englacial and subglacial environment to these seasonal perturbations still represent the least-studied, understood, and parameterised processes of glacier dynamics due to a paucity of direct observation. To better understand these processes in the wake of a changing climate, novel in-situ geophysical experiments were undertaken on Store Glacier in west Greenland to quantify rates of englacial deformation and basal melting. The records produced from these experiments yield new insights into the thermodynamic setting of a major outlet glacier, and the physical mechanisms underlying and resulting from fast glacier motion. The deployment of autonomous phase-sensitive radio-echo sounders (ApRES) $\SI{30}{\kilo\metre}$ from the calving terminus of Store Glacier between 2014 and 2016 revealed high rates of both englacial deformation and basal melting, driven primarily by the dynamic response of the basal hydrological system to seasonal surface meltwater influxes. Thermodynamic modelling of this process revealed a convergence of large-scale basal hydrological pathways that aggregated large amounts of water towards the field site. The warm, turbulent water routed from surface melt contained and dissipated enough energy at the ice-bed interface to explain the observed high melt rates. Simultaneously, changes in the local strain field, involving seasonal variations in the morphology of internal layers, were found to be the result of far-field perturbations in downstream ice flow which propagated tens of kilometres upglacier through longitudinal stress coupling. When observed in multiple dimensions, the layer structure revealed complex internal reflection geometries, demonstrating ApRES as not just a monitor of depth changes in ice thickness, but also as an imaging instrument capable of characterising the subsurface environment within and beneath ice sheets. Altogether, the observations and analyses comprising this thesis provide new and significant insight and understanding into the structural, thermal, and mechanical processes tied to Store Glacier and its fast, complex, and dynamic ice flow.
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Guo, Wenkai. "The relationship between sea ice retreat and Greenland ice sheet surface-melt." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397692613.
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Warren, Charles Raymond. "Iceberg calving and ice sheet margin dynamics, West Greenland." Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/20284.
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Ice sheets are integral to the earth's climate system, both modulating and responding to climatic change. Iceberg calving fronts are the only dynamic interface at which the atmosphere, oceans and ice sheets directly interact. Calving introduces mechanical instability to glacier systems such that the response of calving glaciers to climatic forcing is commonly nonlinear. The interaction between calving dynamics and the ice-marginal environment, notably the topographic geometry of glacier troughs, can partially or totally decouple glacier fluctuations from climate for periods of several centuries. In West Greenland these instability mechanisms appear to have been important both during deglaciation and recently. In the Late Glacial/early Holocene, trough geometry controlled the retreat stages of the ice sheet margin in the Ilulissat (Jakobshavn) area of central west Greenland. During the second half of the twentieth century, the oscillations of 72 outlet glaciers between 61 °N and 72°N show that land- terminating glaciers respond directly to climate change (albeit with variable time lags) but that calving glaciers behave non- linearly. Freshwater calving glaciers have lower calving fluxes and calving rates than tidewater glaciers, and may be the first to respond to climatic cooling. It is not clear whether ice sheet outlet glaciers oscillate cyclically as do calving mountain glaciers, but the instabilities introduced by calving cause many glaciers to respond more directly to topographic than climatic factors. It is therefore hazardous to attach palaeoclimatic significance to the glacial geomorphological record of the fluctuations of former calving margins, or to regard the behaviour of contemporary calving outlets as indicative of climative trends. Factors affecting the stability of ice margins have a fundamental impact on the dynamics of ice sheets, and are important controls on the timing and patterns of ice sheet response to climate change.
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Ryan, Jonathan. "UAV investigation of surface and tidewater mass loss processes across the Greenland Ice Sheet." Thesis, Aberystwyth University, 2018. http://hdl.handle.net/2160/018cf7b7-fc9b-4327-a80e-6ec866193d5f.
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Accurately forecasting the contribution of the Greenland Ice Sheet to global sea-level requires precise observations to constrain present-day processes and incorporate them into models. However, the spatial and temporal resolution of satellite imagery and representativeness of in situ measurements often precludes or obscures our understanding of mass loss processes. This thesis investigates whether imagery from unmanned aerial vehicles (UAVs) have the potential to 1) bridge the scale gap between in situ and satellite observations and, 2) resolve processes of mass loss which are beyond the resolution of satellite imagery. It is found that the footprints of ground-based pyranometers are insufficient to capture the spatial heterogeneity of the ice surface as it progressively ablates and darkens. Point-to-pixel albedo comparisons are therefore often invalid, meaning that satellite-derived albedo measurements may be more accurate than previously thought. A 25 km transect intersecting the dark zone reveals that distributed impurities, not cryoconite nor surface water, govern spatial albedo patterns and may have implications for the future expansion of the dark zone. Repeat surveys over Store Glacier show that UAVs can be used to quantify calving rates and surface velocities of tidewater glaciers. The surveys indicate that large calving events cause short-term terminus velocity accelerations and can explain the seasonal pattern of acceleration and retreat. Any process which accelerates calving, such as removal of the ice m ́elange, therefore has important implications for the glaciers future behaviour.
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Vernon, Christopher L. "Surface mass balance model intercomparison for the Greenland ice sheet." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633454.
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our simulations of the surface mass balance (SMB) of the Greenland ice sheet (GrIS) are compared over the period 1960-2008. Three use a regional climate model to downscale ECMWF reanalysis (ERA-40) and operational analysis data, while the fourth uses the same inputs but an empirical downscaling approach and melt model. These reconstructions have been used in a variety of applications but prior to this study little was known about their consistency with each other and the impact of the downscaling method on the result. The reconstructions are compared to assess the consistency in regional, seasonal and integrated 5MB components and evaluated against a suite of observational data. Three key areas of difference between the models have been identified. Firstly differences in how the ERA-40 reanalysis data are downscaled by the models. Secondly differences in how the 5MB components are calculated. And thirdly differences in the domain, the ice sheet mask used. Total 5MB estimates for the GrIS are in agreement within 34% of the four-model average when a common ice sheet mask is used. When models' native land/ice/sea masks are used this spread increases to 57%. The components of 5MB, with the exception of refreeze, show a similar level of agreement once a common mask is used. Previously noted differences in the models I estimates are partially explained by ice sheet mask differences. Agreement is higher (18% spread) in the accumulation area than the ablation area (38% spread) suggesting relatively high uncertainty in the estimation of ablation processes. Regionally there is less agreement, suggesting spatially compensating errors improve the integrated estimates. Modelled 5MB estimates are compared with in situ observations, gravimetric observations from GRACE and altimetry observations from ICESat. Through the use of a surface density and firn compaction model individual components of 5MB are, indirectly, able to be evaluated against altimetry observation.
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Bhatia, Maya Pilar 1979. "Hydrological and biogeochemical cycling along the Greenland ice sheet margin." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70775.
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Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>Global warming has led to a significant increase in Greenland ice sheet (GrIS) melt and runoff since 1990, resulting in escalated export of fresh water and associated sediment to the surrounding North Atlantic and Arctic Oceans. Similar to alpine glacial systems, surface meltwater on ice sheet surface drains to the base (subglacial) where it joins a drainage system and can become chemically enriched from its origin as dilute snow- and ice-melt. In this thesis, I examine the interdependence of glacial hydrology and biogeochemical cycling in terms of export of carbon and iron from the Greenland ice sheet. I develop a new isotope mixing-model to quantify water source contributions to the bulk meltwater discharge draining a GrIS outlet glacier. Results illustrate (a) the new application of a naturally occurring radioisotope (radon-222) as a quantitative tracer for waters stored at the glacier bed, and (b) the seasonal evolution of the subglacial drainage network from a delayed-flow to a quick-flow system. Model results also provide the necessary hydrological context to interpret and quantify glacially-derived organic carbon and iron fluxes. I combine bulk- and molecular-level studies of subglacial organic carbon to show that GrIS discharge exports old (radiocarbon depleted), labile organic matter. Similar investigations of dissolved and particulate iron reveal that GrIS discharge may be a significant flux of labile iron to the North Atlantic Ocean during the summer meltseason. Both carbon and iron are subject to proglacial processing prior to export to the marine environment, and exhibit strong seasonal variability in correlation with the subglacial drainage evolution. Low, chemically concentrated fluxes characterize the spring discharge, whereas higher, chemically dilute fluxes typify the summer discharge. Collectively, this thesis provides some of the first descriptions and flux estimates of carbon and iron, key elements in ocean biogeochemical cycles, in GrIS meltwater runoff.<br>by Maya Pilar Bhatia.<br>Ph.D.
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Burkhart, John F. "Variability of nitrogen deposition and preservation over the Greenland Ice Sheet." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1069%5F1%5Fm.pdf&type=application/pdf.
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Svensson, Anna. "Mapping of Water under a Part of the Greenland Ice Sheet Using Ice-Penetrating Radar." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-265300.
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The contribution to the global sea level change from the large ice sheet of Greenland and Antarctica if both ice sheet where to melt completely, is estimated to be approximately 70 meters. How much the actual contribution would be, is due to complex ice dynamics still unclear. It is crucial to gain knowledge about the spatial distribution of wet and frozen beds, in order to increase the understanding of ice-sheet flow. There are yet no complete models available that can fully explain and describe ice sheet motion and the feedback mechanisms that are involved, making this topic important for future predictions and modelling of the impact of a warming climate. Radar sounding can be used for distinguish the different reflectivity between wet and frozen beds, this is however limited by uncertainties caused by scattering and attenuation. To be able to map the spatial distribution of subglacial water, attenuation needs to be taken into account. Here, mapping of water under a smaller part of the Greenland ice sheet was performed, and three different methods for acquiring attenuation values was used to obtain a suitable value of the attenuation. A CMP analysis, an attenuation model based on temperature data and an attenuation estimation derived from common-offset radar data, the mean attenuation value from these methods was used for the determination of the reflectivity. Hydraulic potential calculations was also performed, analyzed and compared with the result from the mapping of the reflectivity. Higher reflectivity was observed closer to the front of the glacier, indicating wetter basal condition in that area. This area did also have more moulins and sinks which could lead water from the surface down to the base of the ice.<br>De båda istäckena Grönland och Antarktis uppskattas kunna bidra till den globala havsytehöjningen med ungefär 70 meter om de bägge istäckena skulle smälta helt och hållet. Hur mycket det faktiska bidraget skulle bli, är på grund av komplex isdynamik fortfarande oklart. Det är av yttersta vikt att öka kunskapen om den rumsliga fördelningen av frusna och icke-frusna bottnar under ett istäcke, för att öka förståelsen om isrörelse. Det finns i nuläget inga modeller som helt och fullt kan beskriva och förklara istäckens rörelse och de återkopplingsmekanismer som är involverade, vilket gör detta ämne viktigt för framtida förutsägelser och modellering av inverkan av ett allt varmare klimat.Radar kan användas för att särskilja den olika reflektivitet som uppvisas mellan frusna och icke-frusna bottnar, detta är dock begränsat på grund av dämpning och spridning av radarvågor genom isen. För att kunna kartera den rumsliga fördelningen av subglacialt vatten, behövs bland annat dämpningen i isen tas med i beräkningarna.Kartering av vatten under en mindre del av istäcket på Grönland har utförts i detta arbete, och för att erhålla ett bättre värde på dämpningen i isen användes tre olika metoder. En CMP-analys, en dämpningsmodell baserad på temperatur data och en dämpningsbedömning baserad på common-offset radardata, och medelvärdet på dämpningen från dessa tre metoder användes för fastställandet av reflektivitet i det undersökta området. Beräkningar av hydraulisk potential utfördes också, vilket analyserades och jämfördes med resultatet från karteringen av reflektivitet.Högre reflektivitet observerades närmre fronten av glaciären, vilket är en indikation på att vatten finns vid botten i det området. I detta område fanns också fler brunnar som skulle kunna leda ner vatten från ytan till botten av glaciären.
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Slater, Donald Alexander. "Modelling submarine melting at tidewater glaciers in Greenland." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28899.
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The recent thinning, acceleration and retreat of tidewater glaciers around Greenland suggests that these systems are highly sensitive to a change in climate. Tidewater glacier dynamics have already had a significant impact on global sea level, and, given projected future climate warming, will likely continue to do so over the coming century. Understanding of the processes connecting climatic change to tidewater glacier response is, however, at an early stage. Current leading thinking links tidewater glacier change to ocean warming by submarine melting of glacier calving fronts, yet the process of submarine melting remains poorly understood. This thesis combines modelling and field data to investigate submarine melting at tidewater glaciers, ultimately seeking to constrain the sensitivity of the Greenland Ice Sheet to climate change. Submarine melting is thought to be enhanced where subglacial runoff enters the ocean and drives energetic ice-marginal plumes. In this thesis, two contrasting models are used to examine the dynamics of these plumes; the Massachusetts Institute of Technology general circulation model (MITgcm) and the simpler buoyant plume theory (BPT). The first result of this thesis, obtained with the MITgcm, is that the spatial distribution of subglacial runoff at the grounding line of a tidewater glacier is a key control on the rate and spatial distribution of submarine melting. Focussed subglacial runoff induces rapid but localised melting, while diffuse runoff induces slower but spatially homogeneous melting. Furthermore, for the same subglacial runoff, total ablation by submarine melting from diffuse runoff exceeds that from focussed runoff by at least a factor of five. BPT is then used to examine the relationship between plume-induced submarine melting and key physical parameters, such as plume geometry, fjord stratification, and the magnitude of subglacial runoff. It is shown that submarine melt rate is proportional to the magnitude of subglacial runoff raised to the exponent of 1/3, regardless of plume geometry, provided runoff lies below a critical threshold and the fjord is weakly stratified. Above the runoff threshold and for strongly stratified fjords, the exponent respectively decreases and increases. The obtained relationships are combined into a single parameterisation thereby providing a useful first-order estimate of submarine melt rate with potential for incorporation into predictive ice flow models. Having investigated many of the factors affecting submarine melt rate, this thesis turns to the effect of melting on tidewater glacier dynamics and calving processes. Specifically, feedbacks between submarine melting and calving front shape are evaluated by coupling BPT to a dynamic ice-ocean boundary which evolves according to modelled submarine melt rates. In agreement with observations, the model shows calving fronts becoming undercut by submarine melting, but hints at a critical role for subglacial channels in this process. The total ablation by submarine melting increases with the degree of undercutting due to increased ice-ocean surface area. It is suggested that the relative pace of undercutting versus ice velocity may define the dominant calving style at a tidewater glacier. Finally, comparison of plumes modelled in both MITgcm and BPT with those observed at Kangiata Nunata Sermia (KNS), a large tidewater glacier in south-west Greenland, suggests that subglacial runoff at KNS is often diffuse in nature. In addition to the above implications for submarine melting, diffuse drainage may enhance basal sliding during warmer summers, thereby providing a potential link between increasing atmospheric temperature and tidewater glacier acceleration which does not invoke the role of the ocean. This thesis provides a comprehensive investigation and quantification of the factors affecting submarine melting at tidewater glaciers, a complex process that is believed to be one of the key influences on the current and future stability of the Greenland Ice Sheet. Based on the magnitude of modelled melt rates, and their effect on calving front shape, the process of submarine melting is a likely driver of retreat at slower-flowing tidewater glaciers in Greenland. For melting to influence the largest and fastest-flowing glaciers requires invoking a sensitive coupling between melting and calving which is as yet obscure. It should however be noted that modelled melt rates depend critically on parameters which are poorly constrained. The results and parameterisations developed in this thesis should now be taken forward through testing against field observations - which are currently rare - and, from a modelling perspective, coupling with ice flow models to provide a more complete picture of the interaction of the Greenland Ice Sheet with the ocean.
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Johansson, A. Malin. "Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet." Doctoral thesis, Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-74509.
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The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concerns about the stability of the ice sheet. Melt water generated at the surface is temporarily stored in supra-glacial lakes on the ice sheet. Connections between melt water generation, storage and ice sheet dynamics highlight the importance of the surface hydrological system. In this thesis different methods are used that improve our ability to observe the supra-glacial lake system on the west Greenland Ice Sheet. This region of the Greenland Ice Sheet has the most extensive supra-glacial hydrological system with a dense network of streams connecting lakes that can exceed several square kilometres in area. Synthetic Aperture Radar (SAR) and visible-near infrared (VNIR) images are used to explore the potential of different sensor systems for regular observations of the supra-glacial lakes. SAR imagery is found to be a useful complement to VNIR data. VNIR data from moderate resolution sensors are preferred as these provide high temporal resolution data, ameliorating problems with cloud cover. The dynamic nature of the lakes makes automated classification difficult and manual mapping has been widely used. Here a new method is proposed that improves on existing methods by automating the identification and classification of lakes, and by introducing a flexible system that can capture the full range of lake forms. Applying our new method we are better able to analyse the evolution of lakes over a number of melt seasons. We find that lakes initiate after approximately 40 positive degree days. Most lakes exist for less than 20 days before draining, or later in the season, and less often, freezing over. Using the automated method developed in this thesis lakes have been mapped in imagery from 2001–2010 at approximately five day intervals.<br><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p>
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Lindbäck, Katrin. "Hydrology and Bed Topography of the Greenland Ice Sheet : Last known surroundings." Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-259076.
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The increased temperatures in the Arctic accelerate the loss of land based ice stored in glaciers. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and holds ~10% of all the freshwater on Earth, equivalent to ~7 metres of global sea level rise. A few decades ago, the mass balance of the Greenland Ice Sheet was poorly known and assumed to have little impact on global sea level rise. The development of regional climate models and remote sensing of the ice sheet during the past decade have revealed a significant mass loss. To monitor how the Greenland Ice Sheet will affect sea levels in the future requires understanding the physical processes that govern its mass balance and movement. In the southeastern and central western regions, mass loss is dominated by the dynamic behaviour of ice streams calving into the ocean. Changes in surface mass balance dominate mass loss from the Greenland Ice Sheet in the central northern, southwestern and northeastern regions. Little is known about what the hydrological system looks like beneath the ice sheet; how well the hydrological system is developed decides the water’s impact on ice movement. In this thesis, I have focused on radar sounding measurements to map the subglacial topography in detail for a land-terminating section of the western Greenland Ice Sheet. This knowledge is a critical prerequisite for any subglacial hydrological modelling. Using the high-resolution ice thickness and bed topography data, I have made the following specific studies: First, I have analysed the geological setting and glaciological history of the region by comparing proglacial and subglacial spectral roughness. Second, I have analysed the subglacial water drainage routing and revealed a potential for subglacial water piracy between adjacent subglacial water catchments with changes in the subglacial water pressure regime. Finally, I have looked in more detail into englacial features that are commonly observed in radar sounding data from western Greenland. In all, the thesis highlights the need not only for accurate high-resolution subglacial digital elevation models, but also for regionally optimised interpolation when conducting detailed hydrological studies of the Greenland Ice Sheet.<br>De ökade temperaturerna i Arktis påskyndar förlusten av landbaserad is lagrad i glaciärer och permafrost. Grönlands inlandsis är den största ismassan på norra halvklotet och lagrar ca 10% av allt sötvatten på jorden, vilket motsvarar ca 7 meter global havsnivåhöjning. För ett par decennier sedan var inlandsisens massbalans dåligt känd och antogs ha liten inverkan på dagens havsnivåhöjning. Utvecklingen av regionala klimatmodeller och satellitbaserad fjärranalys av inlandsisen har under de senaste decenniet påvisat en betydande massförlust. För att förutse vilken inverkan inlandsisen har på framtida havsnivåhöjningar krävs en förståelse för de fysikaliska processerna som styr dess massbalans och isrörelse. I de sydöstra och centrala västra delarna av inlandsisen domineras massförlusten av dynamiska processer i isströmmar som kalvar ut i havet. Massförlusten i de centrala norra, sydvästra och nordöstra delarna domineras av isytans massbalans. Ytterst lite är känt om hur det hydrologiska systemet ser ut under inlandsisen; hur väl det hydrologiska systemet är utvecklat avgör vattnets påverkan på isrörelsen. I denna doktorsavhandling har jag använt markbaserade radarmätningar för att kartlägga den subglaciala topografin för en del av den västra landbaserade inlandsisen. Denna kunskap är en viktig förutsättning för att kunna modellera den subglaciala hydrologin. Med hjälp av rumsligt högupplöst data över istjockleken och bottentopografin har jag gjort följande specifika studier: Först har jag analyserat de geologiska och glaciologiska förhållandena i regionen genom att jämföra proglacial och subglacial spektralanalys av terrängens ytojämnheter. Sedan har jag analyserat den subglaciala vattenavrinningen och påvisat en potential för att avrinningsområdena kan ändras beroende på vattentryckförhållandena på botten. Slutligen har jag tittat mer i detalj på englaciala radarstrukturer som ofta observerats i radardata från västra Grönland. Sammanfattningsvis belyser avhandlingen behovet av inte bara noggranna rumsligt högupplösta subglaciala digitala höjdmodeller, utan även regionalt optimerad interpolering när detaljerade hydrologiska studier ska utföras på Grönlands inlandsis.
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Williamson, Andrew Graham. "Remote sensing of rapidly draining supraglacial lakes on the Greenland Ice Sheet." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/276910.
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Supraglacial lakes in the ablation zone of the Greenland Ice Sheet (GrIS) often drain rapidly (in hours to days) by hydraulically-driven fracture (“hydrofracture”) in the summer. Hydrofracture can deliver large meltwater volumes to the ice-bed interface and open-up surface-to-bed connections, thereby routing surface meltwater to the subglacial system, altering basal water pressures and, consequently, the velocity profile of the GrIS. The study of rapidly draining lakes is thus important for developing coupled hydrology and ice-dynamics models, which can help predict the GrIS’s future mass balance. Remote sensing is commonly used to identify the location, timing and magnitude of rapid lake-drainage events for different regions of the GrIS and, with the increased availability of high-quality satellite data, may be able to offer additional insights into the GrIS’s surface hydrology. This study uses new remote-sensing datasets and develops novel analytical techniques to produce improved knowledge of rapidly draining lake behaviour in west Greenland over recent years. While many studies use 250 m MODerate-resolution Imaging Spectroradiometer (MODIS) imagery to monitor intra- and inter-annual changes to lakes on the GrIS, no existing research with MODIS calculates changes to individual and total lake volume using a physically-based method. The first aim of this research is to overcome this shortfall by developing a fully-automated lake area and volume tracking method (“the FAST algorithm”). For this, various methods for automatically calculating lake areas and volumes with MODIS are tested, and the best techniques are incorporated into the FAST algorithm. The FAST algorithm is applied to the land-terminating Paakitsoq and marine-terminating Store Glacier regions of west Greenland to investigate the incidence of rapid lake drainage in summer 2014. The validation and application of the FAST algorithm show that lake areas and volumes (using a physically-based method) can be calculated accurately using MODIS, that the new algorithm can identify rapidly draining lakes reliably, and that it therefore has the potential to be used widely across the GrIS to generate novel insights into rapidly draining lakes. The controls on rapid lake drainage remain unclear, making it difficult to incorporate lake drainage into models of GrIS hydrology. The second aspect of this study therefore investigates whether various hydrological, morphological, glaciological and surface-mass-balance controls can explain the incidence of rapid lake drainage on the GrIS. These potential controlling factors are examined within an Exploratory Data Analysis statistical technique to elicit statistical similarities and differences between the rapidly and non-rapidly draining lake types. The results show that the lake types are statistically indistinguishable for almost all factors, except lake area. It is impossible, therefore, to elicit an empirically-supported, deterministic method for predicting hydrofracture in models of GrIS hydrology. A frequent problem in remote sensing is the need to trade-off high spatial resolution for low temporal resolution, or vice versa. The final element of this thesis overcomes this problem in the context of monitoring lakes on the GrIS by adapting the FAST algorithm (to become “the FASTER algorithm”) to use with a combined Landsat 8 and Sentinel-2 satellite dataset. The FASTER algorithm is applied to a large, predominantly land-terminating region of west Greenland in summers 2016 and 2017 to track changes to lakes, identify rapidly draining lakes, and ascertain the extra quantity of information that can be generated by using the two satellites simultaneously rather than individually. The FASTER algorithm can monitor changes to lakes at both high spatial (10 to 30 m) and temporal (~3 days) resolution, overcoming the limitation of low spatial or temporal resolution associated with previous remote sensing of lakes on the GrIS. The combined dataset identifies many additional rapid lake-drainage events than would be possible with Landsat 8 or Sentinel-2 alone, due to their low temporal resolutions, or with MODIS, due to its inferior spatial resolution.
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Reeves, Eyre James Edward Jack, and Eyre James Edward Jack Reeves. "Evaluation of Greenland Near Surface Air Temperature Datasets." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/622907.
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Near-surface air temperature (SAT) over Greenland has important effects on mass balance of the ice sheet, but it is unclear which SAT datasets are reliable in the region. Here extensive in-situ SAT measurements are used to assess monthly mean SAT from seven global reanalysis datasets, four gridded SAT analyses, one satellite retrieval and two dynamically downscaled reanalyses. Strengths and weaknesses of these products are identified, and their biases are found to vary by season and glaciological regime. MERRA2 reanalysis overall performs best with mean absolute error less than 2 °C in all months. Ice sheet-average annual mean SAT from different datasets are highly correlated in recent decades, but their 1901–2000 trends differ in sign. Compared with the MERRA2 climatology combined with gridded SAT analysis anomalies, thirty-one earth system model historical runs from the CMIP5 archive reach ~5 °C for the 1901–2000 average bias and have opposite trends for a number of sub-periods.
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Jung, Jihoon. "Temporal and spatial characteristics of Greenland ice sheet net snow accumulation (1781–2008)." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343848275.
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Wilcox, Paul. "Late-Holocene Expansion of the Greenland Ice Sheet as recorded by the Vendue Glacier, Graben Land, East Greenland." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1368013796.
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Duncan, Kyle. "Reconstructing surface elevation changes for the Greenland Ice Sheet (1993-2013) and analysis of Zachariae Isstrom, northeast Greenland." Thesis, State University of New York at Buffalo, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1600748.
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<p> Previous studies investigating the velocity and elevation change records of the Greenland Ice Sheet (GrIS) revealed rapid and complex changes. It is therefore imperative to determine changes with both high spatial and temporal resolutions. By fusing multiple laser altimetry data sets, the Surface Elevation Reconstruction and Change (SERAC) program is capable of reconstructing surface elevation changes with high spatial and temporal resolution over the entire GrIS. The input data include observations from NASA’s Ice, Cloud and land Elevation Satellite (ICESat) mission (2003-2009) as well as data collected by NASA’s Airborne Topographic Mapper (ATM) (1993-2013) and Land, Vegetation and Ice Sensor (LVIS) (2007-2012) airborne laser altimetry systems. This study extends the record of surface elevation changes over the GrIS by adding 2012 and 2013 laser altimetry data to the previous 1993-2011 record. Extending the record leads to a new, more accurate and detailed altimetry record for 1993-2013. </p><p> Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Models (DEMs) are fused with laser altimetry data over Zachariæ Isstrøm, northeast Greenland to analyze surface elevation changes and associated thinning rates during 1978-2014. Little to no elevation change occurred over Zachariæ Isstrøm from 1978-1999, however, from 1999-2014 elevation changes near the calving front became increasingly negative and accelerated. Calving front position showed steady retreat and grounding line position has been retreating towards the interior of the ice sheet at an increasing rate from 2010-2014 when compared to the 1996-2010 period. The measured elevation changes near the calving front have brought a large portion of the glacier close to the height of flotation. If the current thinning trend continues this portion of the glacier will reach flotation within the next 2-5 years allowing for further retreat and increased vulnerability to retreat for sections of the glacier further upstream.</p>
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Koziol, Conrad Pawel. "Modelling the impact of surface melt on the hydrology and dynamics of the Greenland Ice Sheet." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273345.
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Increasing surface runoff from the Greenland Ice Sheet due to a warming climate not only accelerates ice mass loss by altering surface mass balance, but may also lead to increased dynamic losses. This is because surface melt draining to the bed can reduce ice-bed coupling, leading to faster ice flow. Understanding the impact of surface melt on ice dynamics is important for constraining the contribution of the Greenland Ice Sheet to sea level rise. The aim of this thesis is to numerically model the influence of surface runoff on ice velocities. Three new models are presented: an updated supraglacial hydrology model incorporating moulin and crevasse drainage, along with lake drainage over the ice surface via channel incision; an ice sheet model implementing a numerically efficient formulation of ice flow; an adjoint code of the ice flow model based on automatic differentiation. Together with a subglacial hydrology model, these represent the key components of the ice sheet system. The supraglacial hydrology model is calibrated in the Paakitsoq region. Model output shows the partitioning of melt between different drainage pathways and the spatial distribution of surface drainage. Melt season intensity is found to be a relevant factor for both. A key challenge for simulations applying a coupled ice-flow/hydrology model is state and parameter initialization. This challenge is addressed by developing a new workflow for incorporating modelled subglacial water pressures into inversions of basal drag. A current subglacial hydrology model is run for a winter season, and the output is incorporated into the workflow to invert for basal drag at the start of summer in the Russell Glacier area. Comparison of the modelled subglacial system to observations suggests that model output is more in line with summer conditions than winter conditions. A multicomponent model integrating the main components of the ice sheet system is developed and applied to the Russell Glacier area. A coupled ice-flow/hydrology model is initialized using the proposed workflow, and driven using output from the supraglacial hydrology model. Three recent melt seasons are modelled. To a first order, predicted ice velocities match measured velocities at multiple GPS sites. This affirms the conceptual model that summer velocity patterns are driven by transitions between distributed and channelized subglacial hydrological systems.
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Perner, Kerstin [Verfasser]. "Holocene interaction between ocean circulation and the West Greenland ice sheet / Kerstin Perner." Greifswald : Universitätsbibliothek Greifswald, 2012. http://d-nb.info/1025666917/34.
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Igneczi, Adam. "Greenland Ice Sheet hydrology and dynamics : the role of surface and basal topography." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/22746/.
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The Greenland Ice Sheet (GrIS) is an important and growing contributor to global sea level rise. However, the long-term influence of meltwater hydrology on GrIS dynamics (i.e. hydro-dynamics) and mass balance in a warming climate remains uncertain, partly due to our limited understanding of controls governing the large-scale spatial structure of surface drainage. Although the bed-to-surface transfer of basal topographical variations is thought to exert a key influence on surface hydrology, this is yet to be tested at the ice sheet-scale. Focussing on the contemporary GrIS, I use recent developments in the theory of bed-to-surface transfer to demonstrate that bed properties can be used to predict the surface relief of the ice sheet. Although the approach is approximate, the magnitude and spatial pattern of discrepancies with real topography are consistent with the limitations of the theory and known uncertainties of the input datasets. Additional analyses show that surface relief, which is predominantly controlled by the bed-to-surface transfer of basal topography, preconditions the large scale spatial structure of surface drainage. It follows that the spatial structure of surface drainage depends strongly on the transfer of basal topography to the ice surface. Based on these findings, I estimate the changing future distribution of surface lakes on the GrIS, which is crucial for hydro-dynamics as lakes can initiate surface-to-bed hydraulic connections through thick ice. The total volume of surface lakes is projected to increase sharply - by 172-270% - during the 21st century though the rate of increase slows between 2100 and 2300. The regional distribution of surface lakes is also projected to shift on the GrIS, from the SW to the W, NW and NE. Effects of the changing surface relief on surface lake distribution can be neglected during the 21st century, but projections beyond 2100 should incorporate them.
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Rick, Ursula Kay. "Meltwater transport through firn in the accumulation zone of the Greenland Ice Sheet." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337144.
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Moon, Kevin Randall. "Investigations of the Dry Snow Zone of the Greenland Ice Sheet Using QuikSCAT." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3310.
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The Greenland ice sheet is an area of great interest to the scientific community due to its role as an important bellwether for the global climate. Satellite-borne scatterometers are particularly well-suited to studying temporal changes in the Greenland ice sheet because of their high spatial coverage, frequent sampling, and sensitivity to the presence of liquid water. The dry snow zone is the largest component of the Greenland ice sheet and is identified as the region that experiences negligible annual melt. Due to the lack of melt in the dry snow zone, backscatter was previously assumed to be relatively constant over time in this region. However, this thesis shows that a small seasonal variation in backscatter is present in QuikSCAT data in the dry snow zone. Understanding the cause of this seasonal variability is important to verify the accuracy of QuikSCAT measurements, to better understand the ice sheet conditions, and to improve future scatterometer calibration efforts that may use ice sheets as calibration targets.This thesis provides a study of the temporal behavior of backscatter in the dry snow zone of the Greenland ice sheet focusing on seasonal variation. Spatial averaging of backscatter and the Karhunen-Lo`eve transform are used to identify and study the dominant patterns in annual backscatter behavior. Several QuikSCAT instrumental parameters are tested as possible causes of seasonal variation in backscatter in the dry snow zone to verify the accuracy of QuikSCAT products. None of the tested parameters are found to be related to seasonal variation. Further evidence is given that suggests that the cause of the seasonal variation is geophysical and several geophysical factors are tested. Temperature is found to be highly related to dry snow backscatter and therefore may be driving the seasonal variation in backscatter in the dry snow zone.
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Beadling, Rebecca Lynn. "Impact of the Melting of the Greenland Ice Sheet on the Atlantic Meridional Overturning Circulation in 21st Century Model Projections." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/613379.
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Contemporary observations show an increase in the melting of the Greenland Ice Sheet (GrIS) since the early 21st century. Located near the critical sites of oceanic deep convection and deep water formation, the melting of the GrIS has the potential to directly impact the Atlantic Meridional Overturning Circulation (AMOC) by freshening ocean surface waters in these regions. The majority of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models project a decline in AMOC strength by 10-50% during the 21st century, in response to the increase in atmospheric greenhouse gas (GHG) concentrations. However, due to the simple treatment of polar ice sheets and the lack of a dynamical ice sheet component in these models, these projections likely underestimated the impacts of the GrIS melt, leading to uncertainty in projecting future AMOC evolution and climate change around Greenland. To better understand the impact of the GrIS melt on the AMOC, we perform a series of 21st century projection runs with a state-of-the-art Earth System Model-GFDL ESM2Mb. We consider a medium and a high Representative Concentration Pathway (RCP) scenario (RCP4.5 and RCP8.5, respectively). Unlike the CMIP5-standard RCP runs which included only radiative forcing, the new model experiments are also forced with additional and potentially more realistic meltwater discharge from the GrIS. This meltwater discharge is estimated based on a model-based relationship between the GrIS surface melt and the 500hPa atmospheric temperature anomalies over Greenland. The model simulations indicate that compared to the RCP4.5-only and RCP8.5-only projections, the additional melt water from the GrIS can further weaken the AMOC, but with a relatively small magnitude. The reason is that radiative forcing already weakens the deep convection and deep water formation in the North Atlantic, therefore limiting the magnitude of further weakening of AMOC due to the additional meltwater. The modeling results suggest that the AMOC's sensitivity to freshwater forcing due to the GrIS melt is highly dependent on the location and strength of oceanic deep convection sites in ESM2Mb as well as the pathways of the meltwater towards these regions. The additional meltwater contributes to the minimum surface warming (so-called "warming hole") south of Greenland. These simulations with ESM2Mb contribute to the Atlantic Meridional Overturning Circulation Model Intercomparison Project (AMOCMIP), a community effort between international modeling centers to investigate the impacts of the melting of the GrIS on the AMOC and quantify the associated uncertainty.
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Corbett, Lee B. "Investigating the Timing of Deglaciation and the Efficiency of Subglacial Erosion in Central-Western Greenland with Cosmogenic 10Be and 26Al." ScholarWorks @ UVM, 2011. http://scholarworks.uvm.edu/graddis/53.
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This work aims to study the behavior of the western margin of the Greenland Ice Sheet during a period of pronounced ice retreat roughly 10,000 years ago, after the end of the last glacial period. It explores the efficiency of subglacial erosion, the spatial dynamics of ice retreat, and the rates of ice retreat. To address these questions, I use the radionuclides 10Be and 26Al, which form in rocks due to the bombardment of cosmic rays, only after the rocks have been exposed from underneath retreating ice. These nuclides can be used as a geologic dating technique to explore exposure history. Before applying this dating technique to address geological questions, it was critical to first perform methodological development. My work in the University of Vermont‘s new Cosmogenic Nuclide Laboratory served to improve the precision and efficiency of the pre-existing laboratory methods. New methodological advances ensured that samples from Greenland, which contained only low concentrations of 10Be and 26Al, could be used to yield meaningful results about ice behavior. Cosmogenic nuclide dating was applied at two sites along the ice sheet margin in central-western Greenland. At both of these sites, I collected paired bedrock and boulder samples in a transect normal to and outside of the present-day ice sheet margin. Samples were collected from a variety of elevations at numerous locations along the transects, thus providing three-dimensional coverage of the field area. After isolating the mineral quartz from the rocks, and isolating the elements Be and Al from the quartz, isotopic analysis was performed using accelerator mass spectrometry to quantify the relative abundances of the radionuclides against their respective stable isotopes. The southern study site, Ilulissat, is located on the western coast of Greenland at a latitude of 69N. Much previous work has been conducted here due to the presence of one of the largest ice streams in the northern hemisphere, Jakobshavn Isbræ. My work in Ilulissat demonstrated that subglacial erosion rates were high during previous glacial periods, efficiently sculpting and eroding the landscape. Ice retreat across the land surface began around 10,300 years ago, and the ice sheet retreated behind its present-day margin about 7,600 years ago. Ice retreat occurred at a rate of about 100 meters per year. My work in this area suggests that retreat in the large ice stream set the pace and timing for retreat of the neighboring ice sheet margin. The northern site, Upernavik, is located on the western coast of Greenland at a latitude of 73N. Little research has been conducted here in the past. Unlike in Ilulissat, my work here shows that the ice sheet did not efficiently erode the landscape, especially at high elevations, during previous glacial periods. This is likely because the ice was thinner, and therefore had a colder base, than the ice in Ilulissat. My work suggests that ice cover was lost from this area very rapidly, likely at rates of about 170 meters per year, in a single episode around 11,300 years ago. Comparison between the two study sites reveals that ice characteristics can vary appreciably over relatively small distances.