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Ice Composition and Glacier Dynamics PDF

213 Pages·1991·5.472 MB·English
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Springer Series 8 in Physical Environment Managing Editor D. Barsch, Heidelberg Editors I. Douglas, Manchester • F. Joly, Paris M. Marcus, Tempe • B. Messerli, Bern Advisory Board F. Ahnert, Aachen • V.R. Baker, Tucson • R.G. Barry, Boulder H. Bremer, Köln • D. Brunsden, London • R.U. Cooke, London R. Coque, Paris • Y. Dewolf, Paris • P. Fogelberg, Helsinki O. Fränzle, Kiel • I. Gams, Ljubljana • A. Godard, Meudon A. Guilcher, Brest • H. Hagedorn, Würzburg • J. Ives, Boulder S. Kozarski, Poznan • H. Leser, Basel • J.R. Mather, Newark J. Nicod, Aix-en-Provence • A.R. Orme, Los Angeles G. 0strem, Oslo • T.L. Pewe, Tempe • P. Rognon, Paris A. Semmel, Frankfurt/Main • G. Stäblein, Bremen H. Svensson, Kobenhavn • M.M. Sweeting, Oxford R.W. Young, Wollongong Volumes already published Vol 1: Earth Surface Systems R. Huggett Vol 2: Karst Hydrology O. Bonacci Vol 3: Fluvial Processes in Dryland Rivers W.L. Graf Vol 4: Processes in Karst Systems. Physics, Chemistry and Geology W. Dreybrodt Vol 5: Loess in China T. Liu Vol 7: River Morphology J. Mangelsdorf, K. Scheurmann and F.H. Weiß Vol 8: Ice Composition and Glacier Dynamics R.A. Souchez and R.D. Lorrain Volumes in preparation Vol 6: System-Theoretical Modelling in Surface Water Hydrology A. Lattermann Vol 9: Desertification. Natural Background and Human Mismanagement M. Mainguet Vol 10: Fertility of Soils. A Future for Farming in the West African Savannah C. Pieri R.A. Souchez R.D. Lorrain Ice Composition and Glacier Dynamics With 119 Figures Springer-Verlag Berlin Heidelberg GmbH Dr. ROLAND A. SOUCHEZ Dr. REGINALD D. LORRAIN Universite Libre de Bruxelles Faculte des Sciences, CR 160 Departement des Sciences de la Terre et de PEnvironnement Avenue F.D. Roosevelt, 50 1050 Bruxelles, Belgium Cover illustration' The margin of Sydkap Ice Cap (S-W Ellesmere Island, Arctic Canada). The upward movement of ice is visible when not masked by a snow cover. Debris is transferred from the ice-bedrock interface towards the ice cap surface and forms an ice-perched morain eT.he com position of these basal ice layers gives some clues about their formation. (Photo by R. Souchez) ISSN 0937-3047 ISBN 978-3-642-63497-0 ISBN 978-3-642-58187-8 (eBook) DOI 10.1007/978-3-642-58187-8 This work is subject ot copyright. All rights are reserved, whether the whole or part of the materi al is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplica tion of this publication or parts thereof is only permitted under the provision osf the German Copyright Law of September 9, 1965, in its current version, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1991 Originally published by Springer-Verlag Berlin Heidelberg in 1991 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the rele vant protective laws and regulations and therefore free for general use. Typesetting: K+V Fotosatz GmbH, Beerfelden 32/3145-543210 - Printed on acid-free paper To E. Picciotto, who introduced us into the field of isotope glaciology Preface Ice composition has until now been mostly used for reconstructing the environment of the past. A great research effort is made today to model the climate system in which the ice cover at the earth sur face plays a prominent role. To obtain a correct model of the ice sheets, due attention must be paid to the physical processes operating at the interfaces, i.e. the boundary conditions. The idea behind the title of this book is that the study of ice composition can shed some light on the various processes operating at the ice bedrock and ice-ocean interfaces and more generally on glacier dy namics. The book is not intended as a treatise on some specialized topic of glaciology. It is mainly the product of the experience of the two authors gained over several years research on the subject. The two authors are both members of the same university department and personal friends. The book was prepared in the following way. After a first draft of the complete book had been written by the first author, it was put in the hands of the second. The final version sent to the publishers is therefore the result of ex tended discussion, while at the same time preserving the unity of style that would have been lost had the two authors written selected chapters of the book individually. The book is organized into two distinct parts. The first part is devoted to fundamentals which must be understood before attempts at ice composition study can be undertaken from the perspective of glacier dynamics. The reader is first introduced to the glacier system, its main characteristics and how it works (Chap. 1). The various ice types which are produced within the glacier system by specific processes of formation are considered. Chapter 2 is then devoted to ice composition with emphasis on isotopes in ice. Phase equilibria, self-purification and leaching are considered in order to understand the distribution of impurities in ice. Ice also contains mineral particles and gas bubbles, representing a tiny part of the at mospheric reservoir imprisoned during ice formation as the pores of the firn close off and entrap the air. These factors are considered as they can also help to understand glacier dynamics. The second part of the book is concerned with the implications on glacier dynamics. A general view of the relationships between ice composition and ice flow is first considered in Chapter 3. A more VIII Preface detailed view of the key basal zone of ice caps, ice sheets and alpine glaciers is then given in Chapters 4 and 5. In the polar regions, glacier ice comes into contact with the sea (Chap. 6). This contact zone between glacier and ocean plays an important environmental role. It is considered here since ice composition studies further the understanding of floating ice dynamics. Finally, implications at the global scale are considered. The authors are aware that important work may have been omit ted and that imperfections may remain in the text. Their only excuse is that they can devote only a limited amount of time to this activity, as they are continuously involved with ongoing research. Whilst apologizing for any inexactitudes, the authors sincerely hope that this book will serve the cause of glaciology. This book would probably never have been written without the support of many individuals. Professor D. Barsch from the Univer sity of Heidelberg is gratefully acknowledged for encouraging the authors to write this book. The help of Dr. M. Lemmens, who reviewed a first version of the manuscript, is also appreciated. The work greatly benefited from considerable improvement of the English and constructive comments by Dr. M. Sharp and Mr. B. Hubbard from the University of Cambridge during a stay at the authors' laboratory. Critical-comments of Dr. D. Wagenbach from the University of Heidelberg resulted in significant improvements of the structure of the book. The tables and the drafts of diagrams for this book were prepared by Mrs. J. Escande. Most of the typing was done by Mrs. E. Rondou. Many thanks are due to them both for their skill and patience. Brussels, Winter 1990/91 R. A. SOUCHEZ R. D. LORRAIN Contents Part I Fundamentals 1 The Glacier System 3 1.1 General ......................................... 3 1.2 Input and Output ................................ 4 1.3 Ice Flow .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.4 Ice Residence Time ............................... 13 1.5 Distribution of Ice Fabrics and Textures ............. 14 1.6 Ice Foliation ..................................... 18 1.7 Basic Ice 1YJ>es in Different Glacial Systems ......... 22 2 Ice Composition .................................. 29 2.1 Stable Isotopes and the Water Cycle ................ 29 2.2 Stable Isotopes in Snow ........................... 33 2.3 Isotopic Changes During the Transformation of Snow into Ice ......................................... 39 2.4 Stable Isotope Fractionation by Freezing . . . . . . . . . . . . . 45 2.5 Impurities and Phase Equilibria .................... 60 2.6 Self-Purification and Leaching of Impurities ......... 64 2.7 Mineral Particles in Ice. . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 2.8 Gases in Ice ..................................... 74 Part II Implications on Glacier Dynamics 3 Ice Composition and Ice Flow: a General View . . . . . . . 79 3.1 Gas Content and Ice Sheet Profiles ................. 79 3.2 Impurities in Ice and Ice Creep .................... 83 3.3 Isotopes and Flow in Ice Sheets and Ice Caps ..... , . . 86 3.4 Lead 210 in Ice and Alpine Glacier Flow ............ 97 3.5 Mineral Particles in Ice and Glacier Flow ............ 101 3.6 Evidence for Buried Glacier Ice .................... 108 4 The Basal Zone of Ice Caps and Ice Sheets .......... 114 4.1 Thermal Conditions at the Glacier Sole ............. 114 4.2 The Effective Bed ................................ 117 x Contents 4.3 The Basal Zone in Ice Cores 123 4.4 Investigations in Marginal Areas ................... . 130 5 The Basal Zone of Alpine Glaciers ................. 140 5.1 Water Flow in the Basal Zone. . . . . . . . . . . . .. . . . . . . .. 140 5.2 Phase Changes at the Base of Alpine Glaciers. . . . . . .. 143 5.3 Incorporation of Debris into Basal Ice .............. 145 5.4 Basal Ice Chemistry .............................. 148 5.5 Subglacial Precipitates and Basal Ice ................ 155 5.6 Isotopes in the Basal Zone of Alpine Glaciers ........ 158 6 The Contact Zone Between Glacier and Ocean ....... 164 6.1 Ice Shelves and Tidewater Glaciers .................. 164 6.2 Melting and Freezing at the Base of Ice Shelves ...... 166 6.3 Frazil and Congelation Ice ......................... 170 6.4 Isotope and Impurity Distribution .................. 172 6.5 The Case of the Ward Hunt Ice Shelf ............... 177 6.6 Freezing Rates in the Marine Environment ........... 179 6.7 The Glacial Supply to the Ocean ................... 183 Conclusion: Ice Composition, Glacier Dynamics and Global Changes .................................. 187 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Subject Index .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 201 Part I Fundamentals

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