Sea Levels, Land Levels, and Tide Gauges K.O. Emery David G. Aubrey Sea Levels, Land Levels, and Tide Gauges With 113 Illustrations Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona K.o. Emery Woods Hole Oceanographic Institution Coastal Research Center Woods Hole, MA 02543 USA David G. Aubrey Woods Hole Oceanographic Institution Coastal Research Center Woods Hole, MA 02543 USA Library of Congress Cataloging-in-Publication Data Emery, K. O. (Kenneth Orris), 1914- Sea levels, land levels, and tide gauges / K.O. Emery, David G. Aubrey. p. cm. Includes bibliographical references and index. ISBN-13: 978-1-4613-9103-6 e-ISBN-13: 978-1-4613-9101-2 DOl: 10.1007/978-1-4613-9101-2 1. Sea level. 2. Subsidences (Earth movements) 3. Tide-gauges. I. Aubrey, David G. II. Title. GC89.E54 1991 551.4'58-dc20 90-49743 Printed on acid-free paper. © 1991 Springer-Verlag New York Inc. Softcover reprint of the hardcover 1s t edition 1991 All rights reserved. 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Typeset by Publishers Service of Montana, Bozeman, Montana. 98765 4 3 2 1 With appreciation for the long forebearance of our spouses, Phyllis and Sandy Preface This book reinterprets and discusses tide-gauge records to investigate the eustatic rise of sea level caused by Holocene climatic warming and melting of ice sheets and glaciers thought by some to have been augmented since the beginning of the Industrial Revolution by the green house effect of gases from burning of fossil fuels, making of cement, and other sources. This new view is necessary, because about as many tide-gauge records of the world show a fall of relative sea level as show a rise. A tide-gauge record at any site could indicate rising or falling land level as well as changing sea level. A rise of land level by coastal rebound in areas of now-melted ice sheets has long been accepted by scientists and the public, but less widely rec ognized is the concurrent post-glacial sinking of a ridge peripheral to the ice sheets. Local sinking of large deltas also has been observed, because their sediments are deposited with a high percentage of interstitial water and are compacted easily. During recent decades, sinking also has been noted in areas where fluids have been pumped excessively from the ground. Volcanic regions are known to exhibit both upward and downward changes in level probably because of movements of magma in chambers beneath the volcanoes; some of these changes occur along seacoasts of the world. Less well noted, however, are vertical movements ofland levels in modern times because of crustal cooling of rifted continental crust and because of underthrusting of oceanic crust beneath continental margins. Adding to this geological com plexity are the many space and time scales of ocean movement owing to vastly differing dynamics (meanders in western boundary currents, steric changes, shelf waves, tides, and surface waves, for instance). The book begins with an introduction that describes recorded ancient water movements, continues with a description of the more precisely measured early-to-modern variations of tides and currents, and concludes with a description of the stages in development of tide prediction tables. The next chapter addresses the causes and time scales of different kinds of vertical shifts of relative sea levels. Next is a discussion of plate tectonics and how plate movements have affected past emergence and submergence of continents, and the nature of resulting control exerted by these movements on the chemistry of seawater and the distribu tion and evolution of plant and animal life both on the land and in the ocean. Background information about past shifts in levels of the ocean and land derived from ocean-floor cores, archaeology, radiocarbon dating, and historical records sets the scene for discussion of tide gauges, whose recording began in earnest less than a century ago. Most tide gauges were installed within seaports to facilitate the entrance and exit of com mercial shipping, chiefly sailing ships that were at the mercy of flooding and ebbing currents. During the early part of the present century a few scientists began to study long-term tide gauge records to measure temporal changes of relative sea level, some inferring a rise of sea level and others a change of land level, as discussed in a chapter on early studies of the records. These studies were hampered (and still are) by the poor worldwide distribution of tide gauges: mainly, they are concentrated along the coasts of industrial nations of the north ern hemisphere. By about 1970 many scientists and the mass media began to advocate the possibility that heating of the atmosphere by the greenhouse effect of industrial waste gases might have increased the rate of melt of ice sheets and caused a faster rise of sea level that would be destructive to human habitation, industry, and agriculture along coasts of the world. Accordingly, some climatologists studied tide-gauge records in a search for a possible VII viii Preface increase in eustatic rise of sea levels. They mainly ignored the vertical movements of the land beneath the tide gauges and tried various strategems for averaging records of indicated rela tive sea-level change to avoid some effects of poor geographical distribution of useful tide gauge records and to minimize differences within groups of records. We chose an alternate method of study: the investigation of the same differences in direc tion and rates within regional groups of tide gauges. Immediately obvious was the presence within the regions of systematic changes, some of which are related to deglaciation, others to sinking of cooling rifted continental crusts, and still others to plate subduction. In a sort of tour of the world's coasts we classified the indicated land movements according to inferred origin, finding good correlation between direction and rates of land movements and the regional geology. In other words, the noise in the tide-gauge records caused by land move ments that obscure the signal for change of sea level is a source of information about plate tec tonics and the role of tectonism in causing modern vertical movements of the land. In a chapter on significance of results, the direction and rates of relative sea-level change for different causes of land movements were compared and found to differ in a systematic way for different coasts of the world. This knowledge provides some insight into likely future changes of level and their impacts on society. For example, protection by sea walls along all coasts is unnecessary because some coasts are rising, not sinking. In addition, much shore destruction is caused not by natural sinking of lands or eustatic rise of oceans, but instead it is among the unexpected results of human intervention through engineering works. Some of these works cause coastal subsidence owing to extraction of fluids, others reduce the natural sediment supply to beaches and thus accelerate coastal erosion, and others (dams and bar rages) alter the sediment supply to deltas, thereby accelerating relative sea-level rise. Con struction of groins and breakwaters often traps beach sand in its movement along coasts, thereby causing erosion of beaches that are located down-current from the structures. Understanding of the cause of changes in level of the land and the ocean is paramount in importance to the proper development of coastal regions. Results of this study provide guid ing data for scientific, engineering, or policy solutions to coastal flooding, by helping to assure that the true causes of relative subsidence are understood along each coastal compart ment. Although we still cannot quantify unambiguously the contributions to relative sea levels from tectonism and oceanographic variability, we can describe the apparent dominant factors for most of the globe. Hopefully, our study can provide some impetus to gaining better understanding and use of geological and oceanological controls rather than the usual reliance on legal "remedies" or of trying to force nature by engineering means. An old Newfoundland skipper said, "We don't be takin' nothin' from the sea. We has to sneak up on what we wants, and wiggle it away" (Mowatt 1958). K. O. Emery D. G. Aubrey Acknowledgments This book has been in progress for about a decade, and there have been numerous occasions to discuss its objectives with many individuals and organizations. These discussions were supplemented by our publication in scientific journals of articles that were written for regions having densely spaced tide gauges (for example, Fennoscandia, Japan, and the United States) or having special geological situations (Australia, India, South America). This early work aroused some discussion that led to strengthening of later analyses. In essence, we have concluded that 'noise' in the records produced by tectonic movements and both meteorologi cal and oceanographical factors so obscures any signal of eustatic rise of sea level that the tide-gauge records are more useful for learning about plate tectonics than about effects of the greenhouse heating of the atmosphere, glaciers, and ocean water. To these early discussants and writers on related aspects of the subject, we perhaps owe more thanks and appreciation than to those who fully agreed with our views. Among them were T. P. Barnett and Roger Revelle of the Scripps Institution of Oceanography; R. 1. N. Devoy of University College, Cork, Ireland; V. Gornitz of Goddard Space Flight Center, Institute for Space Studies, New York; A. L. Bloom of Cornell University; N. C. Flemming of the Institute of Oceanographic Sciences, Godalming, England; N.-A. Marner of the University of Stockholm, Sweden; W. A. Peltier of the University of Toronto, Canada; P. A. Pirazzoli of the Laboratoire de Geo graphie Physique, Montrouge, France; and P. S. Roy of the University of Sydney, Australia, some of whom favored only limited tectonism. To these people and the anonymous reviewers we express sincere appreciation for their interest, thoughts, and suggestions. Special thanks are due D. T. Pugh formerly of the Permanent Service for Mean Sea Level at Merseyside, England, D. B. Enfield of University of Oregon, You Fanghu of the Institute of Oceanology at Qingdao, China, and V. Goldsmith of Hunter College, New York, for pro viding magnetic tapes of tide-gauge records of the world and tabulations of some records from South America, China, and Israel, respectively. We also thank our many colleagues and students at Woods Hole Oceanographic Institution for discussions on these topics, including B. V. Braatz, 1. D. Milliman, A. Solow, Elazar Uchupi, and A. 1. Withnell. We gladly acknowledge the aid of others in translating the summary chapter into various languages (French-Lucienne Taillebot, 1. P. Eliet, Maureen Eliet; German-w. G. Deuser; Hebrew David Neev; Japanese-Susumu Honjo; Russian-A. P. Lisitzin; Spanish-Carlos Palomo, Juan Acosta, Yuri Budenko). Finally, we happily received financial aid from the Woods Hole Oceanographic Institu tion's Ocean Industry Program and Coastal Research Center, the A. W. Mellon Foundation, National Science Foundation under Grant Number OCE- 8501174, NOAA National Office of Sea Grant under Grant Number NA83-AA -D-0049, and Aubrey Consulting, Incorporated, the latter for covering costs of photography and xerographic duplicating of drawings and texts. The Woods Hole Oceanographic Institution also aided by providing pension funds for Emery. Pamela Barrows edited the final computer disk to fit Springer-Verlag's format. The Editorial Department of Springer-Verlag provided encouragement during the late phases of completion of the manuscript. IX Contents Preface ........................................................ vii Acknowledgments ............................................... ix 1. Introduction................................................. 1 Objective I Early Knowledge of Relative Sea-Level Changes 2 Prehistoric 2 Epic Flood 2 Charybdis and Maelstrom 3 Periodic Movement-Tides 4 Early Substitutes for Laws of Nature 4 Identification of the Moon as the Cause of Tides 5 Tide Tables 6 Developments in Europe 6 Developments in China 7 The Chinese Tables of A.D. 1056 8 Modern Prediction Tables 10 Devices for Measurement of Water Level 12 Fixed Scales 12 Mechanical Recorders 13 Electronic-Digital Recorders 13 Satellite Altimetry 14 Frequency Realms of Tide-Gauge Records 14 Semi diurnal and Diurnal Tidal Frequencies 17 2. Causes of Relative Sea-Level Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Sea Levels Versus Land Levels 23 Plate Tectonics/Sea-Floor Spreading 23 General 23 Changes in Spreading Rates 23 Changes in Areas of Oceans and Land 23 Changes in Direction of Plate Motions 24 Other Thermal Effects 24 Deep-Ocean Sedimentation 24 Isostasy 24 General 24 Glacio-Isostasy 24 Hydro-Isostasy 25 Sediment-Isostasy 25 Glacial Surge/Melting 25 Ocean Surface Topography 26 Geoid 26 Geological Faulting 27 Xl xii Contents Sediment Compaction and Subsidence 31 Processes 31 Examples of Subsidence 33 Sinkholes 40 Climatic Effects 40 Overview 40 El Nino/Southern Oscillation 41 River Runoff/Floods 45 Steric Ocean Response 46 General 46 Temperature Effects 46 Salinity Effects 46 Long-Period Tides 47 General 47 Long Time Scales 47 Amplitude Variation Through Time 48 Changes in Hydrodynamical Conditions 48 Shelf Waves and Seiches 50 Tsunamis 51 Surface Gravity Waves 51 3. Ancient to Modern Changes in Relative Sea Levels. . . . . . . . . . . . . . . . . 53 Source Materials 53 Background 53 Rocks on Continents 53 Sediments and Rocks on the Ocean Floor 54 Pleistocene Glacial Deposits and Ice 54 Shoreline Classification 55 Dating of Shore Fossils 56 Archaeology 56 Tide Gauges 57 Phanerozoic 57 General 57 Seismic Stratigraphy 57 Volumes of Igneous Rocks 59 Sequence of Plate Movements 59 Late Archaean to Present 61 Orogenies 61 Relative Sea Levels 62 Tides 62 Continental Glaciation 62 Isotopes in Marine Sediments 63 Evolution of Life 63 Late Pleistocene 64 Oxygen Isotopes 64 Solar Insolation 64 Latest Pleistocene and Holocene 65 4. Previous Studies of Relative Sea Levels from Tide Gauges. . . . . . . . . . . 69 Data Base 69 Previous Methods and Interpretations 69 United States 69 Europe 72 World (Through 1980) 72 Contents Xlii World (After 1980) 76 Summary 78 5. Detailed Mapping of Tide-Gauge Records in Specific Regions. . . . . . . . 81 General 81 Northern Europe 82 Southwestern Europe 88 Mediterranean Sea 89 Africa 93 Antarctica 95 India 96 Southeastern Asia 100 Australia 10 1 New Zealand 104 Eastern Asia 105 Japan 107 Northern Eurasia 114 Western North America 114 Central America 118 South America 123 Caribbean Sea 125 Gulf of Mexico 125 Eastern North America 127 Islands of the Atlantic Ocean 134 Islands of the Indian Ocean 137 Islands of the Pacific Ocean 139 Island Arcs 139 Hot-Spot Chains 141 Long-Term Tide-Gauge Records of the World 143 6. Significance of Tide-Gauge Records. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 151 General 151 Glacial Loading and Unloading 151 Subduction and Rifting 152 Volcanism 153 Faults and Folds 154 Deltaic Loading 154 Extraction of Fluids 155 "Stable" Coasts 155 Observation 155 Interpretation 156 Eustatic Sea-Level Change 158 Statistical Summary 160 7. Future Eustatic Sea-Level Change. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 163 Climate Change Scenarios 163 Sea-Level Change Scenarios 165 8. Impact of Sea-LevellLand-Level Change on Society. . . . . . . . . . . . . . .. 167 General 167 Physical, Chemical, and Biological Impacts of Rising Relative Sea Level 169 Socio-Economic Impacts 174