Investigating the Dynamics of Greenland's Glacier-fjord Systems PDF Download

Author: Benjamin Joseph Davison
Publisher:
ISBN:
Category : Fjords
Languages : en
Pages : 229

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Author: Rebecca Harding Jackson
Publisher:
ISBN:
Category :
Languages : en
Pages : 172

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Glacial fjords form conduits between glaciers of the Greenland Ice Sheet and the North Atlantic. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Submarine melting in fjords has been implicated as a driver of recent glacier acceleration; however, there are no direct measurements of this melting, and little is known about the fjord processes that modulate melt rates. Combining observations, theory, and modeling, this thesis investigates the circulation, heat transport, and meltwater export in glacial fjords. While most recent studies focus on glacial buoyancy forcing, there are other drivers -e.g. tides, local wind, shelf variability - that can be important for fjord circulation. Using moored records from two major Greenlandic fjords, shelf forcing (from shelf density fluctuations) is found to dominate the fjord circulation, driving rapid exchange with the shelf and large heat content variability near the glacier. Contrary to the conventional paradigm, these flows mask any glacier-driven circulation in the non-summer months. During the summer, when shelf forcing is reduced and freshwater forcing peaks, a mean exchange flow transports warm Atlantic-origin water towards the glacier and exports glacial meltwater. Many recent studies have inferred submarine melt rates from oceanic heat transport, but the fjord budgets that underlie this method have been overlooked. Building on estuarine studies of salt fluxes, this thesis presents a new framework for assessing glacial fjord budgets and revised equations for inferring meltwater fluxes. Two different seasonal regimes are found in the heat/salt budgets for Sermilik Fjord, and the results provide the first time-series of submarine meltwater and subglacial discharge fluxes into a glacial fjord. Finally, building on the observations, ROMS numerical simulations and two analytical models are used to investigate the dynamics of shelf-driven flows and their importance relative to local wind forcing across the parameter space of Greenland's fjords. The fjord response is found to vary primarily with the width relative to the deformation radius and the fjord adjustment timescale relative to the forcing timescale. Understanding these modes of circulation is a step towards accurate modeling of ocean-glacier interactions.

Author: Robert M. Sanchez
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Mass loss of the Greenland Ice Sheet is expected to accelerate in the 21st century in response to both a warming atmosphere and ocean, with consequences for sea level rise, polar ecosystems and potentially the global overturning circulation. Glacial fjords connect Greenland's marine-terminating glaciers with the continental shelf, and fjord circulation plays a critical role in modulating the import of heat from the ocean and the export of freshwater from the ice sheet. Understanding fjord dynamics is crucial to predicting the cryosphere and ocean response to a changing climate. However, representing glacial fjord dynamics in climate models is an ongoing challenge because fjord circulation is complex and sensitive to glacial forcing that is poorly understood. Additionally, there are limited observations available for constraining models and theory. This dissertation aims to improve our understanding of fjord dynamics, focusing on key aspects (heat variability, freshwater residence time, and fjord exchange) which need to be included in glacial fjord parameterizations. We use three approaches combining novel observations, idealized, modeling and numerical simulations to investigate the dynamics of fjord circulation at different spatial scales. First, we investigate the heat content variability in the fjord using acoustic travel time (Chapter 2). We demonstrate that acoustic travel time can be used to model fjord stratification during winter months and monitor heat content variability at synoptic and seasonal timescales. Secondly, we use a combination of in situ observations and an idealized box model to evaluate freshwater residence time in a west Greenland Fjord (Chapter 3). We find that meltwater from the ice sheet is mixed downward across multiple layers near the glacier terminus resulting in freshwater storage and a delay in freshwater export from the fjord. Finally we analyze a multi-year realistically forced numerical simulation of Sermilik Fjord in southeast Greenland and identify the impact of shelf and glacial forcing on fjord exchange (Chapter 4). We show that the glacial-driven circulation is more efficient at renewing the fjord and that the sign of the exchange flow is related to the along-shelf wind stress. This dissertation strengthens our understanding of the fundamental connections between oceans and glaciers, and will lead to improved representation of ice-ocean interactions in climate models.

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

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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: Margaret Ruth Lindeman
Publisher:
ISBN:
Category :
Languages : en
Pages : 160

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The glacial fjords that connect the Greenland Ice Sheet to the North Atlantic control ocean heat transport toward the ice sheet and the downstream fate of glacier meltwater. This thesis builds on a growing body of research into Greenland fjord dynamics, focusing on aspects of glacier-fjord systems that are especially challenging to observe: sub-annual ocean variability beneath a floating ice tongue; iceberg meltwater properties and distribution; and the distribution and cycling of environmental mercury. Ice discharge to the ocean can be moderated by ice tongues, floating extensions of glaciers that buttress the upstream ice flow. In Chapter 3, an ice-tethered mooring record from beneath the 79 North Glacier ice tongue shows that ocean warming observed on the continental shelf is advected into the fjord and reaches the glacier grounding line within 6 months, indicating that basal melt of the ice tongue is sensitive to regional ocean variability. Icebergs calved from tidewater glaciers are a major component of fjord freshwater and heat budgets in fjords, but there are few observations to constrain iceberg melt models. In Chapter 4, meltwater plume intrusions are identified based on their temperature and salinity properties in two surveys of a large iceberg in Sermilik Fjord in southeast Greenland. The intrusions are distributed around the iceberg between 80-250 m depth and drive upwelling over vertical scales averaging 15-50 m, with the plume height primarily controlled by stratification. A standard melt plume model does not recreate the observed melt concentrations even with adjustments to the model coefficients, suggesting that more substantial modifications to the model physics are needed to accurately simulate iceberg melt and upwelling. In Chapter 5, results from a recent survey in Sermilik Fjord show that glacially modified waters are depleted in the toxic trace element mercury relative to regional ocean waters, indicating that glacier melt is not a significant source of environmental mercury in that system. We hypothesize that mercury is removed from the water column in the ice melange region near the glacier terminus through scavenging and settling of suspended sediments from iceberg melt and runoff.

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

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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: C.J. van der Veen
Publisher: CRC Press
ISBN: 1439835667
Category : Science
Languages : en
Pages : 407

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Measuring, monitoring, and modeling technologies and methods changed the field of glaciology significantly in the 14 years since the publication of the first edition of Fundamentals of Glacier Dynamics. Designed to help readers achieve the basic level of understanding required to describe and model the flow and dynamics of glaciers, this second edition provides a theoretical framework for quantitatively interpreting glacier changes and for developing models of glacier flow. See What’s New in the Second Edition: Streamlined organization focusing on theory, model development, and data interpretation Introductory chapter reviews the most important mathematical tools used throughout the remainder of the book New chapter on fracture mechanics and iceberg calving Consolidated chapter covers applications of the force-budget technique using measurements of surface velocity to locate mechanical controls on glacier flow The latest developments in theory and modeling, including the addition of a discussion of exact time-dependent similarity solutions that can be used for verification of numerical models The book emphasizes developing procedures and presents derivations leading to frequently used equations step by step to allow readers to grasp the mathematical details as well as physical approximations involved without having to consult the original works. As a result, readers will have gained the understanding needed to apply similar techniques to somewhat different applications. Extensively updated with new material and focusing more on presenting the theoretical foundations of glacier flow, the book provides the tools for model validation in the form of analytical steady-state and time-evolving solutions. It provides the necessary background and theoretical foundation for developing more realistic ice-sheet models, which is essential for better integration of data and observations as well as for better model development.

Author: C.J.van der Veen
Publisher: CRC Press
ISBN: 9789054104704
Category : Science
Languages : en
Pages : 472

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Fundamentals of Glacier Dynamics presents an introduction to modelling the flow and dynamics of glaciers. The emphasis is more on developing and outlining procedures than on providing a complete overview of all aspects of glacier dynamics. Derivations leading to frequently-used equations are presented step-by-step to allow the reader to grasp the mathematical details and approximations involved and gain the understanding needed to apply similar concepts to different applications. The first four chapters discuss the background and theory needed for glacier modelling. The central part of the book discusses simple analytical solutions and time-evolving numerical models that are used to study general aspects of glacier dynamics and important feedback mechanisms. The final three chapters discuss applications specific to smaller mountain glaciers, the Greenland Ice Sheet, and the Antarctic Ice Sheet, respectively. This book will be suitable for graduate courses in geophysics and will also serve as a reference volume for scientists active in all aspects of glaciology and related research. Standard undergraduate mathematics and physics are sufficient background for studying the text.

Author: Laura A. Stevens
Publisher:
ISBN:
Category : Glaciers
Languages : en
Pages : 220

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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.

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.