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Download or read book GPS-based Investigations of Greenland Ice Sheet Dynamics written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Samuel Huckerby Doyle
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (16 download)
Download or read book GPS-based Investigations of Greenland Ice Sheet Dynamics written by Samuel Huckerby Doyle and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Thomas Chudley
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (123 download)
Download or read book UAV-based Investigations Into the Hydrology and Dynamics of the Greenland Ice Sheet written by Thomas Chudley and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Hans-Joachim Schellnhuber
Publisher : Springer Science & Business Media
ISBN 13 : 3642523544
Total Pages : 548 pages
Book Rating : 4.6/5 (425 download)
Download or read book Earth System Analysis written by Hans-Joachim Schellnhuber and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 548 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since this new science is of an unprecedented interdisciplinary nature, the book does not merely take stock of its numerous ingredients, but also delivers their multifaceted integration. The resulting master paradigm - the co-evolution of nature and anthroposphere within a geo-cybernetic continuum of processes - is based on a structured manifold of partial paradigms with their specific ranges. Most importantly, this serves the scientific foundation of a meaningful, safe and efficient environment and development management for solving the most burning questions concerning humankind and its natural environment. The more concrete elucidation of the natural and human dimensions, as well as various attempts and instruments of integration are represented in the different parts of the book, while the didactic quality is heightened by many allegoric illustrations.
Author : Lei Yang
Publisher :
ISBN 13 :
Total Pages : 160 pages
Book Rating : 4.:/5 (637 download)
Download or read book Greenland Ice Sheet Change: Surface Climate Variability and Glacier Dynamics written by Lei Yang and published by . This book was released on 2007 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: The co-variability of glacier ice discharges and climate variability is also examined by using Polar MM5 V1 modeled summer temperature and April-September Positive Degree Day (PDD) anomalies. Ice discharges from south Greenland glaciers are found to be sensitive to temperature change. Based on sensitivities of ice discharge to melt index anomalies, time series of total ice discharge from 28 major glaciers since 1958 are modeled. The global sea level rise contribution from Greenland ice sheet during past 50 years is estimated be ∼0.6 mm yr-1 in average.
Author : Kate Hannah Briggs
Publisher :
ISBN 13 :
Total Pages : 174 pages
Book Rating : 4.:/5 (827 download)
Download or read book Satellite Investigations of Ice Dynamics and Supraglacial Lake Development in Greenland written by Kate Hannah Briggs and published by . This book was released on 2012 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis aims to improve the current understanding of the processes which control the flow variability of Greenland Ice Sheet (GrIS) outlet glaciers. The most recent Intergovernmental Governmental Panel on Climate Change (IPCC) report (Meehl et al., 2007) identifies that a critical limitation to forecasts of sea-level rise are uncertainties in modelling the ice dynamics of the GrIS. Using Synthetic Aperture Radar (SAR) feature tracking, seasonal velocities of land- and marine- terminating glaciers in a region in the northeast of Greenland are measured. Records of air temperature in conjunction with seasonal observations of supraglacial lake development, sea ice conditions and ice front positions, derived from SAR imagery, are used to investigate the controls on the observed variations in ice velocity. A clear link between ice velocities and glacier hydrology is found. These findings are consistent with observations from other glaciers in Greenland and are suggestive of a universal hydrological forcing of ice velocity for the whole of the GrIS ablation zone. Lake drainage events have been identified as a key factor in linking atmospheric changes, glacier hydrology and ice velocities in Greenland. For modelling purposes, a means of parameterising the distribution and evolution of supraglacial lakes is therefore needed. Assuming that water will pond in surface depressions, this thesis assesses the ability of using Digital Elevation Models (DEMs) for this purpose. High resolution DEMs are created using Interferometric SAR (InSAR) for two, separate regions of the GrIS. The positions and areal extent of surface depressions are compared with those of lakes observed in optical satellite imagery. The level of correspondence between the two datasets is found to be poor as a result of the resolution of the DEMs and the physical differences between surface depressions and lakes (e.g. lakes may not fill the capacity of the depression). An alternative method for parameterising the seasonal distribution of supra-glacial lakes, by extrapolating trends observed in current lake distributions, is investigated. The locations and evolution of lakes in the west of Greenland during the summer of 2003 are mapped using 47 Moderate Resolution Imaging Spectroradiometer (MODIS) images. Clear trends are identified in the distributions of lakes with elevation and are linked to the seasonal melt-cycle and to changes in ice thickness and its influence on surface depressions, tensile stresses and hydrofracturing. It may be possible to extrapolate these trends to other regions and higher elevations on the ice sheet, thereby enabling the distribution of lakes to be parameterised in ice sheet models. The findings of this thesis help to contribute to the understanding of the interaction between climate and ice dynamics in the context of the GrIS.
Author : Lina Madaj
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (128 download)
Download or read book Holocene Ice Sheet Dynamics and Detrital Provenance Shifts Along the West Greenland Margin written by Lina Madaj and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the effect of Arctic Amplification the Arctic is currently warming at least twice as fast as the rest of the planet. Seasonal sea-ice extent has been alarmingly declining in the past decade. Glaciers and ice caps along the Greenland coast and in the Canadian Arctic have been losing mass on an accelerated rate during the past century. As the global climate system is a complex system connecting different regions via atmospheric transport, changes in Arctic climate patterns are affecting the climate and weather conditions in the lower latitudes. The Greenland Ice Sheet as well as glaciers and ice caps in the Canadian Arctic are the largest freshwater storages on the northern hemisphere and expected to be among the highest contributors to global sea level rise. Freshwater input through meltwater discharge is not only affecting sea level rise but further influencing deep water formation in the Labrador Sea and the subpolar North Atlantic and hence global ocean circulation and climate patterns. To be able to sufficiently predict future developments of the Greenland Ice Sheet with respect to mass loss and resulting impacts on the global climate, data from past climate and Greenland Ice Sheet extents are crucially important. The Holocene spanning the last period of the deglaciation after the Last Glacial Maximum culminating in the Holocene Thermal Maximum when atmospheric temperatures were warmer and glacier and ice-sheet extent smaller than today represents the closest analogue to current atmospheric warming and Greenland Ice Sheet mass loss. The wide west Greenland shelf of Baffin Bay and Labrador Sea hosts thick marine sediments archiving around ten thousand years of this past climate and ice-sheet history. Siliciclastic detrital material discharged into Baffin Bay and the Labrador Sea via meltwater and erosion can be separated from those sedimentary archives and traced back to its source region. Radiogenic isotopes (Sr, Nd, Pb) label the source regions of those sediments by fingerprinting the isotopic composition of the prevailing bedrock. Hence, they can be used as reliable provenance tracers. Retreating land-ice masses expose bedrock that before was not subject to erosion, influencing the isotopic signatures delivered into the surrounding ocean. Based on this theory, radiogenic isotopes can record changes in siliciclastic detrital sediment provenance and hence, indirectly trace ice-sheet dynamics. The overall aim of this thesis work is to reconstruct changes in detrital sediment provenance along the west Greenland shelf to gain new insights into Holocene Greenland Ice Sheet dynamics and ocean current-induced sediment transport. Sedimentary archives from three main research areas (eastern Labrador Sea, northeastern Baffin Bay, and Kane Basin, central Nares Strait) record obvious shifts in sediment provenance throughout the Holocene. Those shifts coincide with major regional climatic changes in the research area. Generally, all records reveal the local bedrock as the main source region of detrital material and distal-sourced material transported along the coast via the West Greenland Current as a secondary source. Although the proportion of distal sourced material appears to be small, changes in West Greenland Current strength have been recorded in the isotopic composition. In southwestern Greenland and the Labrador Sea radiogenic isotope records reveal a shift towards a higher proportion of the local Archean Block in the late Holocene caused by Neoglacial ice advance and a reduction in West Greenland Current speed delivering less material from southern most Greenland. Farther north in the Upernavik region, midwest Greenland coast, the isotopic composition marks a change with the transition from early to mid Holocene caused by increased West Greenland Current strength and the opening of Vaigat Strait which enabled erosion and transport of freshly exposed basalts from the Disko Bay area due to ice-sheet retreat. This basalt input is, however, not transported all the way to northernmost Melville Bay (northern Baffin Bay) where the detrital sediment composition is clearly dominated by contribution of the local Committee-Melville Belt without any significant provenance changes throughout the Holocene. Farthest north, the sedimentary record from Kane Basin records provenance shifts that confirm the opening of Nares Strait around 8.3 ka BP. This event is followed by an increased delivery of carbonate-rich detrital sediments from northern Ellesmere Island due to the newly established gateway of Arctic Ocean water transporting sediments from further north to the core location. Additionally determined mineralogical composition of the sedimentary records along the west Greenland coast supports the interpretation drawn from the radiogenic isotopic composition. Furthermore, it points out the additional value of radiogenic isotopes through variations only visible in isotopic composition but not in the mineralogical composition. Further comparison to other studies from the region based on different tracers confirms the reliability and sufficient application of radiogenic isotopes in provenance studies as well as the advantage of multi-proxy approaches in paleoclimatological studies. Overall, this study highlights the advantages and reliability of radiogenic isotopes in provenance studies with regards to reconstructions of ice-sheet dynamics. The combination of the three isotopic systems (Sr, Nd, Pb) enables source region determination with a higher probability compensating for overlapping signatures within individual isotopic systems. The transect of sedimentary records along the west Greenland coast identifies clearly distinguishable isotopic ranges for the different Greenland bedrock terrains, qualifying this approach for further high-resolution investigation in past Greenland Ice Sheet development.
Author : David John McCarthy
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (757 download)
Download or read book Late Quaternary Ice-ocean Interactions in Central West Greenland written by David John McCarthy and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A greater knowledge of the interactions between the Greenland Ice Sheet and climate is critical to understanding the possible impacts of future global warming, including ice sheet contribution to global sea-level rise and perturbations to ocean circulation. Recent acceleration, thinning and retreat of major tidewater glaciers in Greenland and Antarctica during the past two decades demonstrate the potential for ice sheets to respond to climate change much faster than previously assumed. One approach to understanding the role of atmospheric and oceanic warming to ice sheet dynamics is to investigate how ice sheets responded to past periods of climate change. This thesis uses benthic foraminifera as a proxy to reconstruct past changes in the temperature of the relatively warm West Greenland Current, to investigate the possible influence of ocean warming on ice sheet dynamics during the initial marine-based deglaciation phase, and throughout the Holocene, when the ice was positioned close to the present margin. This thesis finds that the marine-based ice sheet in central West Greenland collapsed rapidly due to a combination of high relative sea-level and ice sheet thinning due to climatic warming. Foraminiferal evidence does not support a major influence of ocean forcing on initial deglaciation. However, Holocene changes in the relative temperature of the West Greenland Current may have had a more significant influence on ice stream dynamics following the marine-based ice retreat, when outlet glaciers were positioned within coastal fjords. Changes in the relative temperature of the West Greenland Current are determined?upstream? by wider scale changes in the North Atlantic region.
Author : Kiya Riverman
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (992 download)
Download or read book Flow Dynamics of the NE Greenland Ice Stream with Hydrological Insights from Englacial Exploration of Larsbreen, Svalbard written by Kiya Riverman and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Glaciers and ice sheets are large reservoirs of freshwater. In order to project how these icy reservoirs will respond to future climate, predictive models must incorporate all relevant ice flow processes and dynamics. Here, I present observations of glaciers in Greenland and Svalbard that advance our understanding of the role of meltwater in rapid ice flow. Chapters 1-4 concern the North East Greenland Ice Stream (NEGIS), a large flow feature of the Greenland Ice Sheet that drains a catchment spanning ~11% of the ice sheet area. I investigate the controls on ice stream location using geophyscial and remote sensing techniques. I find water flow at the base of the ice is, in part, controlled by enhanced firn densification and surface elevation changes in areas of high stress. The basal conditions across the ice stream are very heterogeneous, with variable water content and till thickness (Chapters 2, 3). Under both shear margins, I find shear-marginal moraines, as well as mega-scale glacial lineations within the central trunk of the ice stream (Chapter 4). Chapters 5 and 6 concern the hydrology of cold glacier on Svalbard. I use glaciospeleology (ice caving) to map the englacial and subglacial channels on Larsbreen, Spitsbergen across 3 years. Waterfalls within the glacier migrate rapidly and dominate change within the englacial system each year. I suggest that formation and migration of the final waterfall to the bed of the glacier is a potentially large source of erosion.
Author : Roger G. Barry
Publisher : Cambridge University Press
ISBN 13 : 1108423167
Total Pages : 445 pages
Book Rating : 4.1/5 (84 download)
Download or read book Polar Environments and Global Change written by Roger G. Barry and published by Cambridge University Press. This book was released on 2018-08-09 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surveys atmospheric, oceanic and cryospheric processes, present and past conditions, and changes in polar environments.
Author : Vena Chu
Publisher :
ISBN 13 :
Total Pages : 221 pages
Book Rating : 4.:/5 (926 download)
Download or read book Hydrologic Dynamics of the Greenland Ice Sheet from Remote Sensing and Field Measurements written by Vena Chu and published by . This book was released on 2015 with total page 221 pages. Available in PDF, EPUB and Kindle. Book excerpt: The current need for forecasting Greenland Ice Sheet contributions to global sea level rise is complicated by the lack of understanding of ice sheet hydrology. The proportion of meltwater contributing to sea level rise, as well as the pathways transporting meltwater on, through, and out of the ice sheet, are not well understood. Remote sensing of hydrologic dynamics in combination with small-scale fieldwork allows examination of broad spatial and temporal trends in the Greenland hydrologic system responding to a changing climate. This dissertation reviews the current state of knowledge on Greenland Ice Sheet hydrology, and examines three components of the Greenland hydrologic system: (1) fjord sediment plumes as an indicator of meltwater output, (2) supraglacial streamflow as an indicator of meltwater input to the ice sheet, and (3) moulin distribution and formation as a mechanism diverting meltwater from the surface of the ice sheet to the bed. Buoyant sediment plumes that develop in fjords downstream of outlet glaciers are controlled by numerous factors, including meltwater runoff. MODIS retrievals of sediment plume concentration show a strong regional and seasonal response to meltwater production on the ice sheet surface, despite limitations in fjords with rapidly calving glaciers, providing a tool for tracking meltwater release to the ocean. Summertime field observations and high-resolution satellite imagery reveal extensive supraglacial river networks across the southwestern ablation zone transporting large volumes of meltwater to moulins, yet these features remain poorly mapped and their discharges unquantified. A GIS modeling framework is developed to spatially adapt Manning's equation for use with high-resolution WorldView-2 imagery to map supraglacial river discharge. Moulins represent connections between surface meltwater on the Greenland ice sheet and subglacial drainage networks, where increased meltwater can enhance ice sliding dynamics. A new high-resolution moulin dataset in western Greenland created from WorldView-1/2 imagery in the 2012 record melt year is used to assess moulin distribution and formation. Moulin locations show a significantly different distribution compared to geospatial variables in the entire study area, with moulins forming in areas of thinner ice, higher velocity and extensional strain rate, as well as lower surface elevation and slope, and higher bed elevation and slope.
Author : Kate Hannah Briggs
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (874 download)
Download or read book Satellite Investigations of Ice Dynamics and Supraglacial Lake Development in Greenland written by Kate Hannah Briggs and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : H. Jay Zwally
Publisher :
ISBN 13 :
Total Pages : 22 pages
Book Rating : 4.:/5 (31 download)
Download or read book ICESat written by H. Jay Zwally and published by . This book was released on 2002 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Soroush Rezvanbehbahani
Publisher :
ISBN 13 :
Total Pages : 102 pages
Book Rating : 4.:/5 (845 download)
Download or read book Temporal History of Ice Dynamics Contribution to Volume Changes of the Southeast Greenland Ice Sheet written by Soroush Rezvanbehbahani and published by . This book was released on 2013 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: Current estimations of the contribution of ice sheets to future sea level rise are solely based on changes in Surface Mass Balance (SMB) of Antarctic and Greenland Ice Sheets. However, the reported SMB changes over the Greenland Ice Sheet explain only about 50% of the observed total mass loss of the Greenland Ice Sheet (GrIS). The other 50% is caused by ice dynamic processes, which have not been included in most sea level rise predictions. The goal of this study was to investigate surface elevation changes of the entire GrIS in 2003-2009. In addition to the total elevation changes, elevation changes due to ice dynamics were also estimated by computing the difference between surface elevation changes measured by laser altimetry and those caused by SMB processes. I applied the Surface Elevation And Change Detection (SERAC) approach to derive surface elevation changes from laser altimetry observations. By fusing satellite laser altimetry (Ice, Cloud, and land Elevation Satellite (ICESat)) and airborne laser altimetry (Airborne Topographic Mapper (ATM) and Land, Vegetation, and Ice Sensor (LVIS)) data, I have reconstructed the elevation and volume change history of the GrIS at more than 55,000 locations. To estimate elevation changes due to SMB, SMB anomalies from RACMO2/GR were converted into height changes using a simple firn-densification model. To facilitate the visualization of elevation changes and the computation of volume changes I interpolated the irregularly distributed observations of ice sheet elevation changes into regular grids. Finally, I partitioned the ice sheet elevation and volume changes into SMB-related and ice dynamics-related changes and computed the contributions of major drainage basins. I have shown that the southeast GrIS was the main contributor of ice loss in Greenland inx2003-2009. The Kangerlussuaq Glacier drainage basin exhibited the largest ice-dynamics related volume loss from the twelve major drainage basins of southeast Greenland. The regions below 2000 m elevation, despite constituting only about 28% of the southeast GrIS, contribute to more than 92% to its ice-dynamics related volume loss. Ice sheet elevation changes, as well as annual volume changes of the twelve major southeast Greenland drainage basins, show a complex spatial and temporal pattern. Finally, the effect of ocean and air temperature changes as external forcing mechanisms on the observed volume change patterns is also discussed. I have shown that the trend of ocean temperatures anomalies along the southeast coast of the GrIS shows a close similarity to the estimated ice-dynamics related volume change pattern.
Author : Nicole-Jeanne Schlegel
Publisher :
ISBN 13 :
Total Pages : 94 pages
Book Rating : 4.:/5 (816 download)
Download or read book Determining Greenland Ice Sheet Sensitivity to Regional Climate Change written by Nicole-Jeanne Schlegel and published by . This book was released on 2011 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Greenland Ice Sheet, which extends south of the Arctic Circle, is vulnerable to melt in a warming climate. Complete melt of the ice sheet would raise global sea level by about 7 meters. Prediction of how the ice sheet will react to climate change requires inputs with a high degree of spatial resolution and improved simulation of the ice-dynamical responses to evolving surface mass balance. No Greenland Ice Sheet model has yet met these requirements. A three-dimensional thermo-mechanical ice sheet model of Greenland was enhanced to address these challenges. First, it was modified to accept high-resolution surface mass balance forcings. Second, a parameterization for basal drainage (of the sort responsible for sustaining the Northeast Greenland Ice Stream) was incorporated into the model. The enhanced model was used to investigate the century to millennial-scale evolution of the Greenland Ice Sheet in response to persistent climate trends. During initial experiments, the mechanism of flow in the outlet glaciers was assumed to be independent of climate change, and the outlet glaciers' dominant behavior was to counteract changes in surface mass balance. Around much of the ice sheet, warming resulted in calving front retreat and reduction of total ice sheet discharge. Observations show, however, that the character of outlet glacier flow changes with the climate. The ice sheet model was further developed to simulate observed dynamical responses of Greenland's outlet glaciers. A phenomenological description of the relation between outlet glacier discharge and surface mass balance was calibrated against recent observations. This model was used to investigate the ice sheet's response to a hypothesized 21st century warming trend. Enhanced discharge accounted for a 60% increase in Greenland mass loss, resulting in a net sea level increment of 7.3 cm by year 2100. By this time, the average surface mass balance had become negative, and widespread marginal thinning had caused 30% of historically active calving fronts to retreat. Mass losses persisted throughout the century due to flow of dynamically responsive outlets capable of sustaining high calving rates. Thinning in these areas propagated upstream into higher elevation catchments. Large drainage basins with low-lying outlets, especially those along Greenland's west coast and those fed by the Northeast Greenland Ice Stream, were most susceptible to dynamic mass loss in the 21st century.
Author : Roderik van de Wal
Publisher :
ISBN 13 : 9789039303740
Total Pages : 144 pages
Book Rating : 4.3/5 (37 download)
Download or read book Ijs en Klimaat written by Roderik van de Wal and published by . This book was released on 1992 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Heather Stewart
Publisher :
ISBN 13 :
Total Pages : 94 pages
Book Rating : 4.:/5 (641 download)
Download or read book Climate Vs. Dynamic Forcing of Greenland's Largest Glacier written by Heather Stewart and published by . This book was released on 2010 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Greenland Ice Sheet's (GIS) magnitude of change has been of the utmost importance in understanding cryospheric contributions to the earth's climate change. Of particular interest is the long-term record of Jakobshavn Isbræ, one of the largest outlet glaciers draining an estimated 6.5% of the GIS. Its recent rapid thinning, associated with nearly doubled velocities, indicates that Greenland's outlet glaciers are likely to make faster contributions to sea-level rise than previously believed. To evaluate whether ongoing observed changes are climatically significant, changes must be determined over longer time frames. Although the 35 km retreat of its calving front since the LIA (1850) is well documented, it cannot be used to accurately reconstruct the glacier's history; in particular, since much of its recent retreat, the terminus was likely floating and thus susceptible to small and short-lived climate perturbations.^Here, we combine a chronology of the LIA readvance and subsequent retreat determined from ice sheet threshold lake sediments, along with a 3D reconstruction of ice marginal retreat, measured from stereo imagery to investigate the evolution of the floating ice tongue and land-based margins in the Jakobshavn drainage basin. For this study, we constrain Jakobshavn Isbræ's longer-term context with proglacial threshold lake sediments. Four AMS radiocarbon dates from macrofossils immediately below the LIA sediments from three lake basins to the north of the fjord reveal that Jakobshavn Isbrae reached its LIA maximum extent between 530"10 and 370"60 cal yr BP (1400-1640 AD). Two AMS radiocarbon dates from a lake south of the fjord state that Jakobshavn reached its LIA maximum between 2250"70 and 2420"60 cal yr BP.^Furthermore, the continuous nature of the LIA-sediment units in all sites indicates that Jakobshavn remained at or near its LIA maximum position between 1400-1640 AD and into the 20th century. Using stereoscopic pairs of aerial images taken in 1985, and SPOT satellite images acquired in 2007, vegetation trimlines marking the LIA ice extent and 1985 and 2007 ice sheet margins were mapped in 3D by using a soft-copy workstation. Maximum retreat and thinning rates were measured at Jakobshavn Isbræ, where the calving front retreated at an average rate of 0.178 km yr-1 between the LIA and 1985. Retreat rates increased to 0.545 km yr-1 between 1985 and 2007. Land based margins in the Jakobshavn area record average retreat rates from the LIA to 1985 at .007 km yr-1 and increasing from 1985 to 2007 at 0.030 km yr-1.^However, an outlet glacier just 30 km south of Jakobshavn Isbræ, Alanngorliup Sermia, is at or just above its LIA margin, and has only retreated at a rate of 0.017 km yr-1 since 1985. Thinning rates had a similar trend of increasing at the calving front at a rate of -2.15 m yr-1 from the LIA to 1985 and increased to -4.48 m yr-1 between 1985 and 2007. Land based margins in the Jakobshavn Isbræ area averaged -0.67 m yr-1 from the LIA to 1985 and increased to -1.34 m yr-1 thinning rate between 1985 and 2007. Alanngorliup Sermia has no thinning rate recorded between the LIA and 1985 because of its position at the LIA trimline and has thinned at a rate of -0.31 m yr-1 between 1985 and 2007. These results suggest the greatest retreat and thinning occurred between 1985 and 2007. They also suggest different termini environments respond differently to the same climatic changes.^Varied patterns of retreat and elevation indicate dynamic controls of the Jakobshavn study area. These data suggest that although climate may be the greater driving force of the Jakobshavn margin, ice dynamics play a key role in the marginal evolution since the LIA. The net loss of ice from the GIS plays an important role in global sea-level rise, and therefore more detailed investigations of the causes for marked changes of margins are needed to assess ongoing future changes.
