Climate Vs. Dynamic Forcing of Greenland's Largest Glacier PDF Download

Author: Heather Stewart
Publisher:
ISBN:
Category :
Languages : en
Pages : 94

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Book Description
The Greenland Ice Sheet's (GIS) magnitude of change has been of the utmost importance in understanding cryospheric contributions to the earth's climate change. Of particular interest is the long-term record of Jakobshavn Isbræ, one of the largest outlet glaciers draining an estimated 6.5% of the GIS. Its recent rapid thinning, associated with nearly doubled velocities, indicates that Greenland's outlet glaciers are likely to make faster contributions to sea-level rise than previously believed. To evaluate whether ongoing observed changes are climatically significant, changes must be determined over longer time frames. Although the 35 km retreat of its calving front since the LIA (1850) is well documented, it cannot be used to accurately reconstruct the glacier's history; in particular, since much of its recent retreat, the terminus was likely floating and thus susceptible to small and short-lived climate perturbations.^Here, we combine a chronology of the LIA readvance and subsequent retreat determined from ice sheet threshold lake sediments, along with a 3D reconstruction of ice marginal retreat, measured from stereo imagery to investigate the evolution of the floating ice tongue and land-based margins in the Jakobshavn drainage basin. For this study, we constrain Jakobshavn Isbræ's longer-term context with proglacial threshold lake sediments. Four AMS radiocarbon dates from macrofossils immediately below the LIA sediments from three lake basins to the north of the fjord reveal that Jakobshavn Isbrae reached its LIA maximum extent between 530"10 and 370"60 cal yr BP (1400-1640 AD). Two AMS radiocarbon dates from a lake south of the fjord state that Jakobshavn reached its LIA maximum between 2250"70 and 2420"60 cal yr BP.^Furthermore, the continuous nature of the LIA-sediment units in all sites indicates that Jakobshavn remained at or near its LIA maximum position between 1400-1640 AD and into the 20th century. Using stereoscopic pairs of aerial images taken in 1985, and SPOT satellite images acquired in 2007, vegetation trimlines marking the LIA ice extent and 1985 and 2007 ice sheet margins were mapped in 3D by using a soft-copy workstation. Maximum retreat and thinning rates were measured at Jakobshavn Isbræ, where the calving front retreated at an average rate of 0.178 km yr-1 between the LIA and 1985. Retreat rates increased to 0.545 km yr-1 between 1985 and 2007. Land based margins in the Jakobshavn area record average retreat rates from the LIA to 1985 at .007 km yr-1 and increasing from 1985 to 2007 at 0.030 km yr-1.^However, an outlet glacier just 30 km south of Jakobshavn Isbræ, Alanngorliup Sermia, is at or just above its LIA margin, and has only retreated at a rate of 0.017 km yr-1 since 1985. Thinning rates had a similar trend of increasing at the calving front at a rate of -2.15 m yr-1 from the LIA to 1985 and increased to -4.48 m yr-1 between 1985 and 2007. Land based margins in the Jakobshavn Isbræ area averaged -0.67 m yr-1 from the LIA to 1985 and increased to -1.34 m yr-1 thinning rate between 1985 and 2007. Alanngorliup Sermia has no thinning rate recorded between the LIA and 1985 because of its position at the LIA trimline and has thinned at a rate of -0.31 m yr-1 between 1985 and 2007. These results suggest the greatest retreat and thinning occurred between 1985 and 2007. They also suggest different termini environments respond differently to the same climatic changes.^Varied patterns of retreat and elevation indicate dynamic controls of the Jakobshavn study area. These data suggest that although climate may be the greater driving force of the Jakobshavn margin, ice dynamics play a key role in the marginal evolution since the LIA. The net loss of ice from the GIS plays an important role in global sea-level rise, and therefore more detailed investigations of the causes for marked changes of margins are needed to assess ongoing future changes.

Author: Lei Yang
Publisher:
ISBN:
Category :
Languages : en
Pages : 160

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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: Jamie Brooke Mitchell
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 242

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Abstract: The Greenland ice sheet, the planets second largest ice mass, has most recently been in a state of negative mass balance, contributing to about 15% of global sea level rise between 1991 and 2000 (Box et al., 2004). Results from NASA's Airborne Topographic Mapper (ATM) show an increase in the rate of Greenland's ice loss from 50 to 90 km3/yr in the past 11 years (Krabill et al., 2004) corresponding to a global sea level rise of .25 mm/year since 1997. Debate exists as to whether or not this loss is caused by recent increases in temperature, or by dynamic processes.

Author: Paul Andrew Mayewski
Publisher: UPNE
ISBN: 161168384X
Category : Nature
Languages : en
Pages : 266

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Book Description
An exciting account of revolutionary new discoveries for understanding the earth's climate, and their implications for future scientific research and global environmental policy.

Author: Intergovernmental Panel on Climate Change (IPCC)
Publisher: Cambridge University Press
ISBN: 1009175351
Category : Science
Languages : en
Pages : 2410

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Book Description
The Working Group I contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) provides a comprehensive assessment of the physical science basis of climate change. It considers in situ and remote observations; paleoclimate information; understanding of climate drivers and physical, chemical, and biological processes and feedbacks; global and regional climate modelling; advances in methods of analyses; and insights from climate services. It assesses the current state of the climate; human influence on climate in all regions; future climate change including sea level rise; global warming effects including extremes; climate information for risk assessment and regional adaptation; limiting climate change by reaching net zero carbon dioxide emissions and reducing other greenhouse gas emissions; and benefits for air quality. The report serves policymakers, decision makers, stakeholders, and all interested parties with the latest policy-relevant information on climate change. Available as Open Access on Cambridge Core.

Author: Jeffrey S. Kargel
Publisher: Springer
ISBN: 3540798188
Category : Technology & Engineering
Languages : en
Pages : 936

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Book Description
An international team of over 150 experts provide up-to-date satellite imaging and quantitative analysis of the state and dynamics of the glaciers around the world, and they provide an in-depth review of analysis methodologies. Includes an e-published supplement. Global Land Ice Measurements from Space - Satellite Multispectral Imaging of Glaciers (GLIMS book for short) is the leading state-of-the-art technical and interpretive presentation of satellite image data and analysis of the changing state of the world's glaciers. The book is the most definitive, comprehensive product of a global glacier remote sensing consortium, Global Land Ice Measurements from Space (GLIMS, http://www.glims.org). With 33 chapters and a companion e-supplement, the world's foremost experts in satellite image analysis of glaciers analyze the current state and recent and possible future changes of glaciers across the globe and interpret these findings for policy planners. Climate change is with us for some time to come, and its impacts are being felt by the world's population. The GLIMS Book, to be released about the same time as the IPCC's 5th Assessment report on global climate warming, buttresses and adds rich details and authority to the global change community's understanding of climate change impacts on the cryosphere. This will be a definitive and technically complete reference for experts and students examining the responses of glaciers to climate change. World experts demonstrate that glaciers are changing in response to the ongoing climatic upheaval in addition to other factors that pertain to the circumstances of individual glaciers. The global mosaic of glacier changes is documented by quantitative analyses and are placed into a perspective of causative factors. Starting with a Foreword, Preface, and Introduction, the GLIMS book gives the rationale for and history of glacier monitoring and satellite data analysis. It includes a comprehensive set of six "how-to" methodology chapters, twenty-five chapters detailing regional glacier state and dynamical changes, and an in-depth summary and interpretation chapter placing the observed glacier changes into a global context of the coupled atmosphere-land-ocean system. An accompanying e-supplement will include oversize imagery and other other highly visual renderings of scientific data.

Author: Mason Joseph Fried
Publisher:
ISBN:
Category :
Languages : en
Pages : 270

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The Greenland Ice Sheet rapidly lost mass over the last two decades, in part due to increases in ice loss from termini of large tidewater glaciers. Terminus melting and calving can drive glacier retreat and the pattern of ice sheet mass loss through reductions in resistive stresses near the glacier front and, in turn, increases in ice flow to the ocean. Despite their importance to ice sheet mass balance, factors controlling terminus positions are poorly constrained in ice sheet models, which fundamentally obscures sea level rise predictions. In this dissertation, I use a suite of novel observations and techniques to quantify controls on frontal ablation and terminus positions at tidewater glaciers in central west Greenland. Until recently, frontal ablation processes were obscured due to limited observations of submarine termini. Here, I use observations from multibeam echo sonar to show the morphological complexity of the submarine terminus face and identify previously unrecognized melting and calving processes. The terminus features numerous secondary subglacial plume outlets outside of the main subglacial channel system that drive and disperse large submarine melt rates across the glacier front. Submarine melting drives steep, localized terminus undercutting that can trigger calving by connecting to finely-spaced surface crevasses. In turn, large calving events cause the terminus face to become anomalously overcut. Incorporating observed outlet geometries in a numerical plume model, I estimate small subglacial discharge fluxes feeding secondary plume outlets that are reminiscent of a distributed subglacial network. Regional remote-sensing observations reveal that, for most glaciers in central west Greenland, seasonal terminus positions are more sensitive to glacial runoff than ice mélange or ocean thermal forcing. Shallow, serac-failing tidewater glaciers are most sensitive, where subglacial plumes melt the terminus and locally enhance retreat. Glaciers with large ice fluxes and deep termini retreat sporadically through full ice-thickness calving events less dependent on runoff. Together, these results provide process-oriented constraints on the shape of the submarine terminus face, the geometry of subglacial discharge and submarine melting, the influence of environmental forcing mechanisms and the impact that these variables have on terminus positions and dynamics in a warming climate.

Author: Sebastian Jan Koenig
Publisher:
ISBN:
Category : Greenland
Languages : en
Pages : 196

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Book Description
The cryosphere and its interactions with other components of the climate system are considered to be major influences on global climate change through the Cenozoic and into the future. However, fundamental dynamics and secondary feedbacks that drive long-term ice sheet variability on Greenland remain poorly understood. Here, a numerical climate-ice sheet modeling study is conducted with the aim of reconstructing most likely locations, timing and variability of continental ice in the mid to late Pliocene and the transition into the Pleistocene. Simulations using the GENESIS v3 General Circulation Model coupled to the Penn State Ice Sheet-Shelf Model are compared with a range of independent numerical ice sheet model simulations under Pliocene boundary conditions and validated against available proxy reconstructions. This study aims at investigating the sensitivity of an ice-free and glaciated Greenland to changes in climate forcings, and the modulation of those forcings through internal feedbacks with focus on the dynamical thresholds involved in the growth and retreat of continental ice on Greenland. ^ Orbital changes of latitudinal and seasonal solar radiation, in combination with prevalent atmospheric pCO2 levels, are found to pace the timing of the cryospheric response. Internal feedbacks invoked though local surface characteristics on Greenland in concert with far field changes in Arctic sea surface temperature and sea ice conditions control the energy and moisture budget on Greenland with consequences for its mass balance. In the Pliocene, inception of Greenland ice is inhibited during interglacials and ice volume is limited even when orbits are favorable for ice sheet growth. During Pliocene warmth, a present-day Greenland Ice Sheet cannot be maintained and ice was most likely restricted to the highest elevations in the East and South, contributing around 6m of equivalent sea level rise. This assessment of the sensitivity and survivability of Greenland Ice Sheet in a warmer-than-modern world implies the potential for a long-term commitment to future sea level rise from a smaller Greenland Ice Sheet.

Author: Andrew Fowler
Publisher: Springer Nature
ISBN: 3030425843
Category : Science
Languages : en
Pages : 544

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Book Description
Our realisation of how profoundly glaciers and ice sheets respond to climate change and impact sea level and the environment has propelled their study to the forefront of Earth system science. Aspects of this multidisciplinary endeavour now constitute major areas of research. This book is named after the international summer school held annually in the beautiful alpine village of Karthaus, Northern Italy, and consists of twenty chapters based on lectures from the school. They cover theory, methods, and observations, and introduce readers to essential glaciological topics such as ice-flow dynamics, polar meteorology, mass balance, ice-core analysis, paleoclimatology, remote sensing and geophysical methods, glacial isostatic adjustment, modern and past glacial fluctuations, and ice sheet reconstruction. The chapters were written by thirty-four contributing authors who are leading international authorities in their fields. The book can be used as a graduate-level textbook for a university course, and as a valuable reference guide for practising glaciologists and climate scientists.

Author: Twila Moon
Publisher:
ISBN:
Category : Ice sheets
Languages : en
Pages : 116

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Book Description
Outlet glacier ice dynamics, including ice-flow speed, play a key role in determining Greenland Ice Sheet mass loss, which is a significant contributor to global sea-level rise. Mass loss from the Greenland Ice Sheet increased significantly over the last several decades and current mass losses of 260-380 Gt ice/yr contribute 0.7-1.1 mm/yr to global sea-level rise (~10%). Understanding the potentially complex interactions among glacier, ocean, and climate, however, remains a challenge and limits certainty in modeling and predicting future ice sheet behavior and associated risks to society. This thesis focuses on understanding the seasonal to interannual scale changes in outlet glacier velocity across the Greenland Ice Sheet and how velocity fluctuations are connected to other elements of the ice sheet-ocean-atmosphere system. 1) Interannual velocity patterns Earlier observations on several of Greenland's outlet glaciers, starting near the turn of the 21st century, indicated rapid (annual-scale) and large (>100%) increases in glacier velocity. Combining data from several satellites, we produce a decade-long (2000 to 2010) record documenting the ongoing velocity evolution of nearly all (200+) of Greenland's major outlet glaciers, revealing complex spatial and temporal patterns. Changes on fast-flow marine-terminating glaciers contrast with steady velocities on ice-shelf-terminating glaciers and slow speeds on land-terminating glaciers. Regionally, glaciers in the northwest accelerated steadily, with more variability in the southeast and relatively steady flow elsewhere. Intraregional variability shows a complex response to regional and local forcing. Observed acceleration indicates that sea level rise from Greenland may fall well below earlier proposed upper bounds. 2) Seasonal velocity patterns. Greenland mass loss includes runoff of surface melt and ice discharge via marine-terminating outlet glaciers, the latter now making up a third to a half of total ice loss. The magnitude of ice discharge depends in part on ice-flow speed, which has broadly increased since 2000 but varies locally, regionally, and from year-to-year. Research on a few Greenland glaciers also shows that speed varies seasonally. However, for many regions of the ice sheet, including wide swaths of the west, northwest, and southeast coasts where ice loss is increasing most rapidly, there are few or no records of seasonal velocity variation. We present 5-year records of seasonal velocity measurements for 55 glaciers distributed around the ice sheet margin. We find 3 distinct seasonal velocity patterns. The different patterns indicate varying glacier sensitivity to ice-front (terminus) position and likely regional differences in basal hydrology in which some subglacial systems do transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. Our findings highlight the need for modeling and observation of diverse glacier systems in order to understand the full spectrum of ice-sheet dynamics. 3) Seasonal to interannual glacier and sea ice behavior and interaction Focusing on 16 northwestern Greenland glaciers during 2009-2012, we examine terminus position, sea ice and ice m??lange conditions, seasonal velocity changes, topography, and climate, with extended 1999-2012 records for 4 glaciers. There is a strong correlation between near-terminus sea ice/mélange conditions and terminus position. In several cases, late-forming and inconsistent sea ice/mélange may induce sustained retreat. For all of the 13-year records and most of the 4-year records, sustained, multi-year retreat is accompanied by velocity increase. Seasonal speedup, which is observed across the region, may, however, be more heavily influenced by melt interacting with the subglacial hydrologic system than seasonal terminus variation. Projections of continued warming and longer ice-free periods around Greenland suggest that notable retreat over wide areas may continue. Sustained retreat is likely to be associated with multi-year speedup, though both processes are modulated by local topography. The timing of seasonal ice dynamics patterns may also shift.