Developments in Marine Geology Volume 7
Earth and Life Processes Discovered from Subseafloor Environments
Developments in Marine Geology Volume 7
Earth and Life Processes Discovered from Subseafloor Environments A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP) Edited by
Ruediger Stein Division of Geosciences, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Donna K. Blackman Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
Fumio Inagaki Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Nankoku, Kochi, Japan
Hans-Christian Larsen
AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 225 Wyman Street, Waltham, MA 02451, USA First edition 2014 Copyright © 2014 Elsevier B.V. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN: 978-0-444-62617-2 ISSN: 1572-5480 For information on all Elsevier publications visit our web site at http://store.elsevier.com
Contents Contributors Preface Acknowledgments List of Reviewers
xv xix xxi xxiii
1. Major Scientific Achievements of the Integrated Ocean Drilling Program: Overview and Highlights Keir Becker
2.
1.1 Introduction 1.2 The Deep Biosphere and the Subseafloor Ocean (Initiatives in Deep Biosphere and Gas Hydrates) 1.2.1 Initiative: Deep Biosphere 1.2.2 Initiative: Gas Hydrates 1.3 Environmental Change, Processes, and Effects (Initiatives in Extreme Climates and Rapid Climate Change) 1.3.1 Initiative: Extreme Climates 1.3.2 Initiative: Rapid Climate Change 1.3.3 Sea Level Change 1.4 Solid Earth Cycles and Geodynamics (Initiatives in Continental Breakup and Sedimentary Basin Formation, LIPs, 21st Century Mohole, and Seismogenic Zone) 1.4.1 Initiative: Seismogenic Zone 1.4.2 Initiative: Continental Breakup and Sedimentary Basin Formation 1.4.3 Initiative: LIPs 1.4.4 Initiative: 21st Century Mohole 1.5 Borehole Observatory Accomplishments References
1 4 6 8 10 11 15 16 18 19 25 25 26 28 29
New Frontier of Subseafloor Life and the Biosphere
2.1. Exploration of Subseafloor Life and the Biosphere Through IODP (2003–2013) Fumio Inagaki and Victoria Orphan
2.1.1 Background: The Deep Subseafloor Biosphere
39 v
vi Contents
2.1.2 IODP Expeditions Relative to the Deep-Biosphere Research 2.1.2.1 Expedition 329: South Pacific Gyre Subseafloor Life 2.1.2.2 Expedition 331: Deep Hot Biosphere 2.1.2.3 Expedition 336: Mid-Atlantic Ridge Flank Microbiology 2.1.2.4 Expedition 337: Deep Coalbed Biosphere Off Shimokita 2.1.2.5 Other Microbiology-Integrated IODP Expeditions 2.1.3 Sample Storage for the Future Deep-Biosphere Research 2.1.4 Conclusion and Perspectives Acknowledgments References
44 46 46 47 48 49 54 55 56 57
2.2.1. Biomass, Diversity, and Metabolic Functions of Subseafloor Life Yuki Morono and Jens Kallmeyer
2.2.1.1 The History of Detection and Enumeration of Microbial Cells in Deep Subseafloor Sediment 2.2.1.2 Technical Challenges in Estimating Biomass and Microbial Diversity in Subseafloor Environments 2.2.1.3 Counting Statistics 2.2.1.4 Overcoming the Limitations 2.2.1.5 Combating Contamination 2.2.1.6 Lowering the Quantification Limit 2.2.1.7 Potential Alternatives for Detecting Life in Subsurface Environments 2.2.1.8 Concluding Remarks References
65 69 71 72 73 74 76 78 78
2.2.2. Genetic Evidence of Subseafloor Microbial Communities Andreas Teske, Jennifer F. Biddle and Mark A. Lever
2.2.2.1 Ribosomal RNA as Phylogenetic Marker 85 2.2.2.1.1 Ribosomal RNA Surveys in the Deep Sedimentary Biosphere 87 2.2.2.1.2 Bacterial Lineages 88 2.2.2.1.3 Archaeal Lineages 91 2.2.2.1.4 Eukaryotic Lineages 93 2.2.2.1.5 Distinct Subsurface Habitats and Their Microbial Communities 93 2.2.2.2 Functional Genes 96 2.2.2.2.1 Methanogenesis and Anaerobic Methane Oxidation 97 2.2.2.2.2 Sulfate Reduction 103
Contents vii
2.2.2.2.3 Acetogenesis 2.2.2.2.4 Reductive Dehalogenation 2.2.2.2.5 Future Perspectives of Functional Gene Analysis 2.2.2.3 Metagenomic Investigations of Complex Subseafloor Communities References
105 106 106 109 113
2.3. The Underground Economy (Energetic Constraints of Subseafloor Life) Steven D’Hondt, Guizhi Wang and Arthur J. Spivack
2.3.1 Introduction 127 2.3.2 Energy-Conserving Activities in Marine Sediment 127 2.3.2.1 Electron Acceptors and Electron Donors in Marine Sediment 128 2.3.2.2 Vertical Distribution of Electron-Accepting Activities 129 2.3.2.3 Co-occurrence of Electron-Accepting Processes 131 2.3.2.4 Vertical Distribution of Organic-Fueled Respiration 133 2.3.3 Life Under Extreme Energy Limitation 135 2.3.3.1 Respiration Rates in Subseafloor Sediment 135 2.3.3.2 Energy per Reaction (The Invisible Hand of Thermodynamics) 137 2.3.3.3 Biomass Turnover and Energy Use 138 2.3.4 Discussion 140 2.3.4.1 What Do We Know? 140 2.3.4.2 What Do We Not Know? 141 2.3.5 Conclusions 144 Acknowledgments144 References 144
2.4. Life at Subseafloor Extremes Ken Takai, Kentaro Nakamura, Douglas LaRowe and Jan P. Amend
2.4.1 Introduction 2.4.2 Possible Physical and Chemical Constraints on Life in Subseafloor Environments 2.4.3 Challenge for Limits of Biosphere in Ocean Drilling Expeditions of ODP and IODP 2.4.4 Thermodynamic Estimation of Abundance and Composition of Microbial Metabolisms in Subseafloor Boundary Biosphere 2.4.4.1 Catabolic Reaction Energetics 2.4.4.2 Anabolic Reaction Energetics 2.4.5 Concluding Remarks and Perspectives References
149 150 156 160 162 165 168 169
viii Contents
2.5. Life in the Ocean Crust: Lessons from Subseafloor Laboratories Beth N. Orcutt and Katrina J. Edwards
2.5.1 Introduction 2.5.2 General Overview of the Diversity, Activity, and Abundance of Microbial Life in Igneous Oceanic Crust 2.5.3 Subseafloor Observatories: Another Tool for Studying Life in Oceanic Crust 2.5.4 Recent Deep Biosphere Discoveries from Subseafloor Observatories 2.5.5 The Future of Subseafloor Laboratories for Deep Biosphere Research 2.5.6 The Size of the Deep Biosphere Hosted in Igneous Oceanic Crust 2.5.7 Conclusions References
175 176 180 184 189 190 190 191
2.6. Cultivation of Subseafloor Prokaryotic Life Bert Engelen and Hiroyuki Imachi
2.6.1 The Necessity of Culturing Subseafloor Prokaryotes 2.6.2 The Specific Challenges to Cultivate Prokaryotic Life from the Subseafloor 2.6.3 Cultivation Attempts Using Conventional Batch-type Cultivation 2.6.4 Metabolic Capabilities of Available Isolates from Subseafloor Sedimentary Environments 2.6.5 Novel Techniques for the Cultivation of Subseafloor Prokaryotic Life References
197 200 201 203 205 209
2.7. Biogeochemical Consequences of the Sedimentary Subseafloor Biosphere Laura M. Wehrmann and Timothy G. Ferdelman
2.7.1 Introduction 217 2.7.2 Biogeochemical Zonation in Subseafloor Sediments 219 2.7.3 Secondary Biogeochemical Reactions 222 2.7.4 Interaction of Biogeochemical Processes and the Sediment 223 2.7.5 Time and the Deep Subseafloor Biosphere 231 2.7.6 Beyond Interstitial Water and Solid Phase Chemistry? 234 2.7.7 Connecting the Pelagic Ocean and Subseafloor Sedimentary Ocean 237 2.7.8 Toward a Global Ocean View 240 Acknowledgments241 References 241
Contents ix
3.
Environmental Change, Processes and Effects
3.1. Introduction: Environmental Change, Processes and Effects—New Insights From Integrated Ocean Drilling Program (2003–2013) Ruediger Stein
3.2. Cenozoic Arctic Ocean Climate History: Some Highlights from the Integrated Ocean Drilling Program Arctic Coring Expedition Ruediger Stein, Petra Weller, Jan Backman, Henk Brinkhuis, Kate Moran and Heiko Pälike
3.2.1 Integrated Ocean Drilling Program Expedition 302: Background and Objectives 259 3.2.2 Main Lithologies and Stratigraphic Framework of the ACEX Sequence 265 3.2.3 Highlights of ACEX Studies 268 3.2.3.1 The Paleocene/Eocene Thermal Maximum Event 270 3.2.3.2 The Azolla Freshwater Episode 272 3.2.3.3 From a Euxinic “Lake Stage” to a Fully Ventilated “Ocean Phase” 273 3.2.3.4 Early Onset of Arctic Sea Ice Formation and Cooling of Sea-Surface Temperatures 276 3.2.4 Outlook: Need for Future Scientific Drilling in the Arctic Ocean 282 Acknowledgments285 References 285
3.3. From Greenhouse to Icehouse at the Wilkes Land Antarctic Margin: IODP Expedition 318 Synthesis of Results Carlota Escutia, Henk Brinkhuis & the Expedition 318 Scientists
3.3.1 Introduction 295 3.3.2 Expedition 318 Summary of Results 301 3.3.2.1 Tectonic Evolution 302 3.3.2.2 The Eocene Hothouse 303 3.3.2.3 From Greenhouse to Icehouse: The Latest Eocene and Early Oligocene 306 3.3.2.4 The Icehouse: Oligocene to Pleistocene Records of EAIS Variability 311 3.3.2.5 Ultrahigh Resolution Holocene Record of Climate Variability 315 3.3.3 Discussion of Results 316 3.3.4 Concluding Remarks 319 Acknowledgments321 References 322
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3.4. The Pacific Equatorial Age Transect: Cenozoic Ocean and Climate History (Integrated Ocean Drilling Program Expeditions 320 & 321) Heiko Pälike, Mitchell W. Lyle, Hiroshi Nishi and Isabella Raffi
3.4.1 Integrated Ocean Drilling Program Expeditions 320 & 321 Introduction: Background, Objectives, and Drilling Strategy 329 3.4.1.1 Background 329 3.4.1.2 Scientific Objectives of PEAT IODP Expeditions 320 & 321 333 3.4.1.3 Drilling Design and Strategy 335 3.4.2 Main Sediment Sequence 337 3.4.3 Results from Postcruise Investigations 339 3.4.3.1 Integration with Seismic Stratigraphy 339 3.4.3.2 Integrated Bio-Magneto-Cyclostratigraphy and Sedimentation Rates 340 3.4.3.3 Progress on the Cenozoic Megasplice 345 3.4.3.4 Paleoceanographic, Sedimentological, Geochemical, and Microbiology Results 349 3.4.4 Outlook 350 Acknowledgments351 References 351
3.5. North Atlantic Paleoceanography from Integrated Ocean Drilling Program Expeditions (2003–2013) James E.T. Channell and David A. Hodell
3.5.1 Introduction 359 3.5.2 IODP Expedition 303/306 (North Atlantic Climate) 361 3.5.2.1 Sites U1302/03, U1308, U1312, and U1313 (North Atlantic IRD Belt) 362 3.5.2.2 Sites U1304 and U1314 (Gardar Drift) 373 3.5.2.3 Sites U1305, U1306, and U1307 (Eirik Drift) 375 3.5.2.4 Site U1315 (CORK in ODP Hole 642E) 378 3.5.3 IODP Expedition 339 (Mediterranean Outflow) 379 3.5.4 IODP Expedition 342 (Paleogene Newfoundland Sediment Drifts) 383 3.5.5 Summary 385 Acknowledgments386 References 386
3.6. Coral Reefs and Sea-Level Change Gilbert Camoin and Jody Webster
3.6.1 Introduction/Rationale
395
Contents xi
3.6.2 Coral Reefs: Archives of Past Sea-Level and Environmental Changes 3.6.3 The Last Deglacial Sea-Level Rise in the South Pacific 3.6.4 Expedition 310 “Tahiti Sea Level” 3.6.4.1 Introduction 3.6.4.2 Operational Results 3.6.4.3 Scientific Results 3.6.5 Expedition 325 (GBR Environmental Changes) 3.6.5.1 Introduction 3.6.5.2 Operation Results 3.6.5.3 Initial Science Results 3.6.6 Conclusions References
4.
Solid Earth Cycles and Geodynamics
4.1.
Introduction
398 401 402 402 404 406 419 419 423 424 428 432
Donna K. Blackman
4.2.1. Formation and Evolution of Oceanic Lithosphere: New Insights on Crustal Structure and Igneous Geochemistry from ODP/IODP Sites 1256, U1309, and U1415 Benoit Ildefonse, Natsue Abe, Marguerite Godard, Antony Morris, Damon A.H. Teagle and Susumu Umino
4.2.1.1 Introduction 4.2.1.2 Deep Drilling in Slow-Spread Crust: The Atlantis Massif 4.2.1.2.1 Background 4.2.1.2.2 Revisiting the Geophysical Signature of the Atlantis Massif 4.2.1.2.3 The Interplay between Magmatism and Tectonics Controls the Development of OCCs 4.2.1.2.4 Paleomagnetic Data and Borehole Imaging Constrain Tectonic Rotation in OCCs 4.2.1.2.5 Protracted Construction of the Lower Crust 4.2.1.2.6 Olivine-Rich Troctolites: Mantle Contribution to the Igneous Lower Crust 4.2.1.3 Deep Drilling of Intact Ocean Crust Formed at a Superfast Spreading Rate: Hole 1256D 4.2.1.3.1 Background 4.2.1.3.2 Summary of Upper Crustal Lithology at Site 1256 4.2.1.3.3 A Thin Upper Crust at Superfast Spreading Rate 4.2.1.3.4 Where Is the Layer 2/3 Transition at Site 1256? 4.2.1.3.5 Geochemical Characteristics of the Upper Crust at Site 1256
449 464 464 466 468 470 472 475 477 477 479 487 488 488
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4.2.1.4 Shallow Drilling in Fast-Spread Lower Crust at Hess Deep 491 4.2.1.5 Conclusion 493 Acknowledgments495 References 495
4.2.2. Hydrogeologic Properties, Processes, and Alteration in the Igneous Ocean Crust Andrew T. Fisher, Jeffrey Alt and Wolfgang Bach
4.2.2.1 Introduction 507 4.2.2.1.1 Motivation 507 4.2.2.1.2 Drilling, Coring, and Measurement Methods for the Igneous Ocean Crust 508 4.2.2.1.3 IODP Sites and Results Discussed 510 4.2.2.2 Crustal Hydrogeology and Alteration 514 4.2.2.2.1 Eastern Flank of the Juan De Fuca Ridge, Northeastern Pacific Ocean, ∼3.5-my-old Upper Crust (IODP Expeditions 301 and 327) 514 4.2.2.2.2 Western Flank of the Mid-Atlantic Ridge, Northern Atlantic Ocean, 7.3-my-old Upper Crust (IODP Expedition 336) 523 4.2.2.2.3 Eastern Flank of the East Pacific Rise, Eastern Pacific Ocean, ∼15-my-old Upper to Middle Crust (IODP Expeditions 309, 312, and 335) 525 4.2.2.2.4 Adjacent to the MAR and Atlantis Transform Fault, Northern Atlantic Ocean, Approximately 1.1–1.3-my-old Upper and Lower Crust (IODP Expeditions 304 and 305) 530 4.2.2.3 Synthesis: Method and Site Comparisons and Trends 533 4.2.2.3.1 Hydrogeologic Properties of the Ocean Crust 533 4.2.2.3.2 The Integrated Record of Fluid–Rock Interactions in the Ocean Crust 535 4.2.2.3.3 Future Needs and Frontiers 540 Acknowledgments541 References 541
4.3. Large-Scale and Long-Term Volcanism on Oceanic Lithosphere Anthony A.P. Koppers and William W. Sager
4.3.1 Introduction 4.3.2 History of Drilling LIPs and Hotspot Trails During DSDP and ODP 4.3.2.1 DSDP 4.3.2.2 ODP 4.3.3 IODP Expedition 324 to the Shatsky Rise
553 557 557 559 561
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4.3.4 4.3.5 4.3.6 4.3.7
4.3.3.1 Rationale and Objectives: A Shift in Focus 4.3.3.2 Outcomes IODP Expedition 330 to the Louisville Seamount Trail 4.3.4.1 Rationale and Objectives: Mirroring ODP Leg 197 4.3.4.2 Outcomes Oceanic Plateaus: Plumes or Plate Boundaries? Large-Scale Mantle Movements Traced by Seamount Trails Conclusions and Future Work References
561 563 571 571 574 583 586 587 589
4.4.1. Subduction Zones: Structure and Deformation History Harold Tobin, Pierre Henry, Paola Vannucchi and Elizabeth Screaton
4.4.1.1 Introduction 599 4.4.1.2 IODP Drilling at Three Subduction Zones: Targets and Objectives 607 4.4.1.2.1 Nankai Trough Seismogenic Zone Experiment 607 4.4.1.2.2 Costa Rica Seismogenesis Project 609 4.4.1.2.3 Japan Trench Fast Drilling Project 610 4.4.1.3 Highlights of Scientific Results from IODP Subduction Zone Drilling 611 4.4.1.3.1 Tectonic History and Evolution 612 4.4.1.3.2 Feedbacks with Sediment Supply and Role of Forearc Basins 615 4.4.1.3.3 Impact of Basement Topography on Deformation Near the Trench 616 4.4.1.3.4 Fluid Pressures and Deformation 617 4.4.1.3.5 Fault Zone Development and Mechanical Properties 619 4.4.1.3.6 Frictional Properties and Implications for Deformation 622 4.4.1.3.7 Stress State: Observations and Modeling 623 4.4.1.4 Future Directions 626 4.4.1.5 Summary and Conclusions 628 Acknowledgments629 References 630
4.4.2. Seismogenic Processes Revealed Through the Nankai Trough Seismogenic Zone Experiments: Core, Log, Geophysics, and Observatory Measurements Masataka Kinoshita, Gaku Kimura and Saneatsu Saito
4.4.2.1 Introduction 4.4.2.2 Stress State and Physical Properties in Shallow Formations 4.4.2.2.1 Stress State 4.4.2.2.2 In Situ Physical Properties
641 642 642 649
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4.4.2.3 Fault Zone State and Properties 654 4.4.2.3.1 Friction 654 4.4.2.3.2 Activity of Shallow Faults 656 4.4.2.4 Borehole Observatory 659 4.4.2.4.1 SmartPlug 659 4.4.2.4.2 GeniusPlug 661 4.4.2.4.3 Long-Term Borehole Monitoring System 661 4.4.2.5 Summary and Implications 663 Acknowledgments664 References 665
4.4.3. Fluid Origins, Thermal Regimes, and Fluid and Solute Fluxes in the Forearc of Subduction Zones Miriam Kastner, Evan A. Solomon, Robert N. Harris and Marta E. Torres
5.
4.4.3.1 Introduction 671 4.4.3.2 Accretionary and Erosive Convergent Margins 676 4.4.3.3 Global Estimates of Fluid Sources and Input Fluxes 678 4.4.3.3.1 The Role of Serpentine Minerals in Volatile Cycling in the Forearc 681 4.4.3.4 Forearc Thermal Regimes 681 4.4.3.5 Fluid Outputs, Flow Rates and Fluxes 688 4.4.3.5.1 Fluid Geochemistry 688 4.4.3.5.2 Flow Pathways 693 4.4.3.5.3 Flow Rates 695 4.4.3.5.4 Global Fluid Fluxes 702 4.4.3.5.5 Solute Fluxes 705 4.4.3.6 Global Volatile and Mass Cycling in SZs, has it Evolved or Fluctuated through Time? 709 4.4.3.7 Concluding Remarks 710 4.4.3.8 Appendices 711 4.4.3.8.1 Appendix 1. The Role of Serpentine Minerals in Volatile Cycling in the Forearc 711 4.4.3.8.2 Appendix 2 712 4.4.3.8.3 Appendix 3. The Most Important Chemical and Isotopic Compositions in Pore Fluids Used for Interpreting Fluid-Rock Reactions 712 Acknowledgments723 References 723
ppendix: One-Page Summaries of IODP A Expeditions 301–348
735
Jeannette Lezius and Ruediger Stein Index
789
Contributors Natsue Abe Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and, Technology (JAMSTEC), Yokosuka, Japan Jeffrey Alt Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA Jan P. Amend Department of Earth Sciences, and Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA Wolfgang Bach Department of Geosciences, Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany Jan Backman Department of Geology and Geochemistry, Stockholm University, Stockholm, Sweden Keir Becker Department of Marine Geosciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Coral Gables, FL, USA Jennifer F. Biddle School of Marine Science and Policy, University of Delaware, Lewes, DE, USA Donna K. Blackman Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA Henk Brinkhuis Royal Netherlands Institute for Sea Research NIOZ, Netherlands; and Instituto Andaluz de Ciencias de la Tierra, CSIC-Univ. Granada, Granada, Spain Gilbert Camoin CEREGE, UMR 7330 CNRS, Europôle Méditerranéen de l’Arbois, Aix-en-Provence, France James E.T. Channell Department of Geological Sciences, University of Florida, Gainesville, FL, USA Steven D’Hondt Graduate School of Oceanography, University of Rhode Island, RI, USA Katrina J. Edwards Department of Earth Sciences, and Department of Biological Sciences, University of Southern California, Los Angeles, CA, USA Bert Engelen Institut für Chemie und Biologie des Meeres (ICBM), Carl von Ossietzky Universität Oldenburg, Postfach, Oldenburg, Germany Carlota Escutia Instituto Andaluz de Ciencias de la Tierra, CSIC-Univ. Granada, Granada, Spain Timothy G. Ferdelman Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Bremen, Germany Andrew T. Fisher Earth and Planetary Sciences Department, University of California, Santa Cruz, CA, USA xv
xvi Contributors Marguerite Godard Géosciences Montpellier, Université Montpellier, Montpellier, France Robert N. Harris Oregon State University, Corvallis, OR, USA Pierre Henry CEREGE, Aix-Marseille Université, Marseille, France David A. Hodell Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge, UK Benoit Ildefonse Géosciences Montpellier, Université Montpellier, Montpellier, France Hiroyuki Imachi Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan Fumio Inagaki Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Nankoku, Kochi, Japan Jens Kallmeyer Deutsches GeoForschungsZentrum GFZ, Section 4.5 Geomicrobiology, Telegrafenberg, Potsdam, Germany Miriam Kastner Scripps Institution of Oceanography, La Jolla, CA, USA Gaku Kimura Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Japan Masataka Kinoshita Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Nankoku, Kochi, Japan Anthony A.P. Koppers College of Earth, Ocean & Atmospheric Sciences, Oregon State University, Corvallis, OR, USA Douglas LaRowe Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA Mark A. Lever Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland Jeannette Lezius Geosciences Department, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany Mitchell W. Lyle College of Geosciences, Texas A&M University, TX, USA Kate Moran Neptune Ocean Networks Canada, University of Victoria, Victoria, BC, Canada Yuki Morono Kochi Institute for Core Sample Research, Japan Agency for MarineEarth Science & Technology (JAMSTEC), Nankoku, Kochi, Japan Antony Morris School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth, UK Kentaro Nakamura Laboratory of Ocean-Earth Life Evolution Research (OELE), Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan; Submarine Hydrothermal System Research Group, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan; Department of Systems Innovation, School of Engineering, University of Tokyo, Tokyo, Japan Hiroshi Nishi The Center for Academic Resources and Archives, Tohoku University Museum, Tohoku University, Sendai, Japan
Contributors xvii
Beth N. Orcutt Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, USA Victoria Orphan Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA Heiko Pälike MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, Bremen, Germany Isabella Raffi Dipartimento di Ingegneria e Geologia (InGeo)–CeRSGeo, Università “G. d’Annunzio” di Chieti-Pescara, Chieti Scalo, Italy William W. Sager Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA Saneatsu Saito R&D Center for Ocean Drilling Sciences, JAMSTEC, Japan Elizabeth Screaton Department of Geological Science, University of Florida, Gainesville, FL, USA Evan A. Solomon School of Oceanography, University of Washington, Seattle, WA, USA Arthur J. Spivack Graduate School of Oceanography, University of Rhode Island, RI, USA Ruediger Stein Geosciences Department, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany Ken Takai Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan; Laboratory of Ocean-Earth Life Evolution Research (OELE), Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan; Submarine Hydrothermal System Research Group, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Japan; Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Tokyo, Japan Damon A.H. Teagle National Oceanography Centre Southampton, University of Southampton, Southampton, UK Andreas Teske Department of Marine Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Harold Tobin Department of Geoscience, University of Wisconsin–Madison, Madison, WI, USA Marta E. Torres Oregon State University, Corvallis, OR, USA Susumu Umino Department of Earth Sciences, Kanazawa University, Kanazawa, Japan Paola Vannucchi Department of Earth Sciences, University of London, London, UK Guizhi Wang State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China Jody Webster Geocoastal Research Group, School of Geosciences, University of Sydney, NSW, Australia Laura M. Wehrmann School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, USA Petra Weller Geosciences Department, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Chapter 3.6
Coral Reefs and Sea-Level Change Gilbert Camoin1,* and Jody Webster2 1CEREGE,
UMR 7330 CNRS, Europôle Méditerranéen de l’Arbois, Aix-en-Provence, France; Research Group, School of Geosciences, University of Sydney, NSW, Australia *Corresponding author: E-mail:
[email protected] 2Geocoastal
3.6.1 INTRODUCTION/RATIONALE One of the most societally relevant objectives of Earth Sciences is to successfully meet the challenges of recent and projected changes in Earth’s surface environment, including sea-level rise related to ice sheet instability, changes in hydrological cycle, and increasing atmospheric pCO2 that is expected to be the main driving force for future climatic and ocean ecological changes. In the last decade, most of the measured sea-level rise has resulted from thermal expansion of the ocean, but the Greenland and Antarctic ice sheets provide the greatest potential risk for future sea-level rise because of their huge volume, equivalent to ∼65 m of sea level. Satellite-based mass balance estimates show that the ice sheets are losing mass and that the rate is accelerating. Currently, they are contributing about half of the current global mean sea-level rise (now ∼3.4 mm/year), and in coming decades they will be by far the largest source (Bertler & Barrett, 2010). However, uncertainties in sea-level projections remain large (0.5–2.0 m by 2100) because the vulnerability of Greenland and Antarctica ice sheets to ongoing warming and related discharge feedbacks in response to a warming Earth are still poorly understood (Bamber, Riva, Vermeersen, & LeBrocq, 2009; Milne, Gehrels, Hughes, & Tamisiea, 2009; Pfeffer, Harper, & O’Neel, 2008). The improvement of past and future sea-level change models will rely on the quantification of the relative contributions of Northern and Southern Hemisphere ice sheets, especially based on a better understanding of their instability during recent natural events. The instrumental record of sea-level and climate variability extends back only about 150 years, a period when sea level has risen only 0.2 m and which does not reflect the conditions that are predicted for the future. Exploiting geological archives is therefore the only way to understand instrumental records of recent Developments in Marine Geology, Volume 7. http://dx.doi.org/10.1016/B978-0-444-62617-2.00015-3 Copyright © 2014 Elsevier B.V. All rights reserved.
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environmental and climate change in the larger context of natural variability, and to examine the response of the earth system to a large dynamic range of boundary conditions, on timescales ranging from annual through geological. Furthermore, geological archives give access to past periods of Earth’s environmental history which more closely resemble warm conditions predicted for the next few centuries and beyond, thus providing critical tests to improve climate and Earth System models. The full extent of sea-level variability can be constrained only by sea-level records from the geological past which provide the most direct estimates of changes in ice volume, including warm periods characterized by sea levels that are meters to tens of meters higher than today, and abrupt climate changes when sea level increased rapidly and dramatically as a consequence of large-amplitude and rapid discharges of freshwater following the collapse of continental ice sheets. Over the past ∼800,000 years, the cyclic growth and decay of northern ice sheets induced rapid sea-level change at intervals of ∼100,000 years, with maximum amplitudes of 120–140 m (e.g., Lambeck, Yokoyama, & Purcell, 2002; Milne & Mitrovica, 2008; Milne, Mitrovica, & Schrag, 2002; Waelbrock et al., 2002) (Figure 3.6.1). Current discrepancies between models and sea-level reconstructions of past changes are due largely to poor constraints on the timing, rates, and
FIGURE 3.6.1 Eustatic sea-level curve for the version of the ICE-5G (VM2) model and relative sea levels (RSL) observations from Barbados with individual data points show as meters below present sea level and corrected for a rate of vertical tectonic uplift of 0.34 mm/year. From Peltier and Fairbanks (2006).
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relative contributions of the various ice sheets. However, although the correlation between ice and ocean volumes is incontrovertible, the causal link is commonly obscured. Local effects that can obscure the true picture include tectonics, isostatic and hydroisostatic responses, and equatorial ocean siphoning (Mitrovica & Peltier, 1991). The wide regional variation in geophysical processes that affect local relative sea levels (RSLs) implies that sea-level curves are of regional significance only and precludes their use as direct indicators of either ice volume or mean sea-level change. A comparison between interpreted sea-level curves and data from different regions of the planet helps in understanding the interplay of climatic, oceanographic, and geophysical processes invoked to explain relative sea-level positions, in refining the parameters constraining the rheology of the Earth and aspects of the history of past ice sheets, thus providing a useful constraint on geophysical models. Signals of relative sea-level change are not uniformly distributed and are a function not only of the change in ice volume but also of the planet’s rheology through glacial isostatic adjustments (GIA), the changing gravitational potential of the ice sheets due to ice-sheet unloading and the subsequent redistribution of water masses in the global ocean, as well as a combination of local processes (Lambeck, 1993; Lambeck et al., 2006; Lambeck, Purcell, Johnston, Nakada, & Yokoyama, 2003; Milne et al., 2009; Milne & Mitrovica, 2008; Peltier, 1994; Yokoyama, Esat, & Lambeck, 2001a,b). A number of attempts have been made to model both global hydroisostatic adjustments (Bassett, Milne, Bentley, & Huybrechts, 2007; Bassett, Milne, Mitrovica, & Clark, 2005; Clark, Mitrovica, Milne, & Tamisiea, 2002; Lambeck, 1993; Peltier, 1994; Peltier, 1999) and equatorial ocean siphoning (Mitrovica & Milne, 2002; Mitrovica & Peltier, 1991), in order to simulate the lithospheric response to particular deglaciation histories and predict the general shape of local sea-level curves. However, aspects of these models remain controversial. Geophysical models show that global hydroisostatic adjustment provides the most geographically widespread mechanism to explain local relative sea-level histories (Bassett et al., 2005, 2007; Clark et al., 2002; Milne & Mitrovica, 2008; Stirling, Esat, Lambeck, & McCulloch, 1998). They require to accurately record sea-level changes on a regional scale, at various latitudes, in different tectonic settings, and at variable distances from former glaciated regions (“near-field” vs “far-field” of Peltier (1991) and Mitrovica and Peltier (1991)). At sites distant from former ice sheets (far-field sites), like in tropical coral reefs, the influence of glacio-isostatic rebound is minimized, and sea-level data are therefore more useful in constraining the total volume of land-based ice by using geophysical/ inverse modeling techniques, as well as in fingerprinting the source of meltwater contributions (Clark et al., 2002; Mix, Bard, & Schneider, 2001). In contrast, sea-level data from sites close to past ice sheets will provide crucial information regarding the melting history of each drainage basin and complement results from floating ice platforms. Ocean drilling is therefore uniquely positioned to obtain records of sea-level change at a range of latitudes, in different tectonic and sedimentary settings, and at variable distances from former glaciated regions.
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The processes leading to the collapse of past ice sheets and the timing and the volume of meltwater released under varying thermal regimes can be better constrained by studying the geologic record of Quaternary glacial–interglacial transitions known as terminations (e.g., the last and penultimate deglaciations, respectively ∼23 and ∼130 kyr BP). The rapid reduction of the global ice budget during Quaternary glacial–interglacial transitions also affected atmospheric and oceanic circulation through the rapid decrease in ice topography and the large increase in freshwater flux to the ocean. The study of the geologic record of terminations can therefore provide the opportunity to better understand the processes associated with ice sheet instability. Reconstruction of rates and magnitudes of sea-level rise during several terminations, which can only be recovered by scientific ocean drilling, will provide constraints for modeling ice sheet dynamics, clarifying the mechanisms of catastrophic ice sheet collapses, and determining the timing and the volume of meltwater released under varying thermal regimes. The Last Deglaciation (23–6 kyr BP; Figure 3.6.1) is generally seen as a potential recent analog for the environmental changes that our planet may face in the near future as a consequence of ocean thermal expansion and the melting of polar ice sheets related to a warming Earth. The reconstruction of the magnitude of eustatic changes during the last glacial period may help in constraining the volumes of ice that had accumulated on the continents.
3.6.2 CORAL REEFS: ARCHIVES OF PAST SEA-LEVEL AND ENVIRONMENTAL CHANGES Carbonate sediments are excellent sea-level markers and contain unique and important components of the records of sea-level timing, amplitude, and stratigraphic response. The relationship of these systems to the carbon cycle allows direct correlation of climatic and eustatic signals. Multiple dating techniques are available for carbonates (including 14C, U/Th, 87/86Sr, U/Pb, biostratigraphy, and magnetostratigraphy), thus enabling the examination of a wide range of frequencies and amplitudes of sea-level change, from millennial scale to tens of millions of years. While continental margin transects have the advantage that their stratigraphic architectures are well constrained by seismic data (Fulthorpe et al., 2008), coral reef systems provide the most reliable geological estimates of RSL as reef biological communities live in a sufficiently narrow or specific depth range to be useful as absolute sea-level indicators. The accurate dating of tropical reef corals by mass spectrometry is of prime importance to clarify the mechanisms that drive glacial–interglacial cycles during Quaternary times, to attempt to resolve the rates of millennial-scale changes in sea level, and to constrain geophysical models. Tropical coral reefs are also highly sensitive to variations in water chemistry and physical factors, and are valuable recorders of past climatic and environmental changes. Highresolution records of past global changes (especially changes in sea surface
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temperatures—SSTs and sea surface salinities—SSSs) are stored in the geochemical and physical parameters of coral skeletons and reef sequences and can be used to examine ocean/atmosphere variability and interactions. Changes in other environmental parameters such as light conditions, water energy, and nutrient levels are usually reflected in variations in the composition of reef communities, as reef-dwelling organisms are sensitive to subtle ecological changes affecting their environment. This explains why coral reefs now play a pivotal role in Quaternary paleoclimatic reconstructions. After Broecker et al. (1968), most coral reef records have concerned sealevel highstands corresponding to the Last Interglacial period approximately 125 kyr BP, and/or to the penultimate Interglacial (isotopic stage 7) from coral reef terraces exposed on the Huon Peninsula, Papua New Guinea (Bloom, Broecker, Chappell, Matthews, & Mesolella, 1974; Chappell, 1974, 2002; Chappell & Veeh, 1978; Chappell et al., 1996; Esat & Yokoyama, 2006; Stein et al., 1993), Barbados (Bard, Hamelin, & Fairbanks, 1990; Edwards, Chen, & Wasserburg, 1987; Gallup, Edwards, & Johnson, 1994; Mesolella, Matthews, Broecker, & Thurber, 1969; Potter & Lambeck, 2004), Sumba (Bard et al., 1996; Pirazzoli et al., 1993), the Red Sea (Dullo, 1990; Gvirtzman & Friedman, 1977; Strasser, Strohmenger, Davaud, & Bach, 1992), and Mexico (Blanchon, Eisenhauer, Fietzke, & Liebetrau, 2009). These generally coincide with major sea-level highstands (i.e., interglacial periods) predicted by the astronomical theory of climate change (Milankovitch, 1941). However, most of these studies concerned uplifted and presently emerged parts of reefs and reef terraces in active subduction zones where relative sea-level records may be biased by variations in rates of tectonic uplift and/or abrupt coseismic vertical motions. Because the amplitude of Quaternary sea-level changes was in the order of 120 m, the relevant reef and sediment archives, especially recording the glacial stages and the glacial–interglacial transitions, are mostly recorded on modern fore-reef slopes where they have been barely investigated by dredging (e.g., Cabioch et al., 2008; Camoin et al., 2006; Rougerie, Wauthy, & Rancher, 1992) and submersible sampling (e.g., Brachert, 1994; Brachert & Dullo, 1991, 1994; Dullo et al., 1998; Grammer et al., 1993; James & Ginsburg, 1979; Land & Moore, 1980; Macintyre et al., 1991; Webster, Wallace et al., 2004; Webster, Clague et al., 2004). These data are typically fragmentary but have brought to light valuable information regarding the interpretation of morphological features, both accretionary (e.g., terraces, relict reefs) and erosional (e.g., cliffs, notches) in relation to sea-level changes. The knowledge regarding the coral reef records of glacio-eustatic sea level has been improved by the development of drilling capabilities and radiometric dating techniques over the last 30 years. However, mostly highstand units were recorded in vertical reef drilling. Furthermore, in most cases, U/Th chronology was limited due to the scarcity of datable material, reflecting diagenetic alteration and postdepositional migration of U and Th isotopes. The scarcity of coral reef sea-level records and related data therefore challenges our ability to unravel
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the rate and timing of the Quaternary sea-level changes, as well as the nature of the coeval climate and environmental changes. Vertically, deeply cored reef sequences were recovered from barrier reefs located on continental margins, e.g., on the Australian Great Barrier Reef (e.g., Braithwaite & Montaggioni, 2009; Braithwaite et al., 2004; Richards & Hill, 1942; Webster & Davies, 2003), in New Caledonia (Coudray, 1976; Montaggioni et al., 2011), and in Belize (Gischler & Hudson, 2004; Gischler, Lomando, Hudson, & Holmes, 2000; Gischler, Ginsburg, Herrlez, & Prasad, 2010; Purdy, Gischler, & Lomando, 2003). Limestone columns beneath mid-oceanic atolls contain excellent records of past sea-level change, as the thermal subsidence due to gradual cooling of the oceanic lithosphere is the primary driving component of atoll subsidence and tends toward linearity with time (e.g., Detrick & Crough, 1978; Parsons & Sclater, 1977). Accordingly, mid-oceanic atolls have frequently been referred to as “dipsticks” (e.g., Wheeler & Aharon, 1991). Carbonate sequences of up to a few hundreds of meters, including both sea-level highstands and lowstands, were extracted from a number of atolls (e.g., Funafuti: Bonney, 1904; Cullis, 1904; Ohde et al., 2002; Bikini: Johnson, Todd, Post, Cole, & Wells, 1954; Enewetak: Ladd & Schlanger, 1960; Tracey & Ladd, 1974; Ludwig, Halley, Simmons, & Peterman, 1988; Quinn & Matthews, 1990; Quinn, 1991). However, like continental margins, there have been few drilling opportunities to document a well-defined chronology of sea-level highstand and lowstand reef units. The exception concerns Moruroa, French Polynesia, where highstand (Holocene, stages 5, 7, and 9) and lowstand (stages 2, 4, and 8) reef units were documented and accurately dated based in deviated 300-m long drill holes (Braithwaite & Camoin, 2011; Camoin, Ebren, Eisenhauer, Bard, & Faure, 2001). The study of coral reef records of the last deglacial events are of prime importance to constrain the timing and amplitude of rapid sea-level changes and to unravel the reef response to dramatic environmental perturbations. Before the Integrated Ocean Drilling Program (IODP) expeditions 310 and 325, only four accurately dated reef sequences that have been attributed to the times reflecting the Holocene-Pleistocene boundary were investigated by drilling, i.e., Barbados (26–7 kyr BP; Fairbanks, 1989; Bard et al., 1990; Fairbanks et al., 2005; Peltier & Fairbanks, 2006), Papua New Guinea (13–6 kyr BP; Chappell & Polach, 1991; Edwards et al., 1993), onshore Tahiti (13.85–2.38 kyr BP; Bard et al., 1996, 2010), and Vanuatu (23–6 kyr BP; Cabioch et al., 2003). Additional fragmentary information concerning the 9–20 kyr BP time span was recorded in Florida (Locker, Hine, Tedesco, & Shinn, 1996), Moruroa (Camoin et al., 2001), Papua New Guinea (Webster, Wallace et al., 2004), Hawaii (Webster, Clague et al., 2004), and the Marquesas Islands (Cabioch et al., 2008). However, uncertainties concerning the general pattern of the last deglacial sea-level rise remain because the apparent sea-level record may not be free of tectonic or isostatic complications. Three of the four major coral reef records of the last deglacial sea-level rise (Barbados, Papua New Guinea, and Vanuatu) are located in active subduction zones
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where tectonic movements can be large and discontinuous. The reconstructed sea levels may be therefore biased by variations in the rate of tectonic uplift and/or abrupt coseismic vertical motions. Also, Barbados is under the influence of GIA because of the waxing and waning of the North American ice sheet (Lambeck et al., 2002; Milne et al., 2009). Hence, there is a clear need to study past sea-level changes in tectonically stable regions or in areas where vertical crustal deformation is slow and/or regular, located far away from former ice-covered regions (far-field). Furthermore, the abrupt and significant environmental changes that accompanied the deglacial sea-level rise have been barely investigated in these studies, so the accurate reconstruction of the event was obscured. The only coral reef record that encompasses the whole last deglacial period was that of Barbados which suggested that the global sea-level rise, resulting from melting glaciers following the Last Glacial Maximum (LGM), did not occur uniformly, but was characterized by several centuries of extremely rapid sealevel rise of about 20 m (40 mm/year on average; Fairbanks, 1989; Bard et al., 1990; Fairbanks et al., 2005; Peltier & Fairbanks, 2006), at a time when there was 70% more grounded ice on Earth. These short-term events, thought to be related to massive and rapid discharges of freshwater from continental ice sheets and referred to as meltwater pulses (MWP-1A and MWP-1B, 14.08–13.61 kyr BP and 11.4–11.1 kyr BP, respectively; Figure 3.6.1), probably disturbed oceanic thermohaline circulation and global climate during the last deglacial period (Manabe & Stouffer, 1995; Weaver, Saenko, Clark, & Mitrovica, 2003). Their understanding is of utmost importance when considering the potential collapse of large ice sheets in response to recent climate change. However, the exact timing, origin (Northern Hemisphere ice sheets—NHIS vs Antarctic ice sheet—AIS; see discussion in Deschamps et al. (2012) and Gregoire, Payne, and Valdes (2012)), and consequences of these ice-sheet melting episodes were unclear and have been the subject of a considerable debate (Weaver et al., 2003; Stanford et al., 2006; see also; Deschamps et al., 2012). GIA models disagree on the hemispherical origin of the MWP-1A (Clark et al., 2002; Tarasov, Dyke, Neal, & Peltier, 2012). The duration and amplitude of the maximum lowstand during the LGM (Fleming et al., 1998; Yokoyama et al., 2001a,b; Yokoyama, Esat, Lambeck, & Fifield, 2000; Cutler et al., 2003; Peltier & Fairbanks, 2006), and the timing and the nature of the events following the LGM (Clark, McCabe, Mix, & Weaver, 2004; De Deckker & Yokoyama, 2009; Hanebuth, Stattegger, & Bojanowski, 2009; Yokoyama et al., 2001a,b) are additional controversial topics.
3.6.3 THE LAST DEGLACIAL SEA-LEVEL RISE IN THE SOUTH PACIFIC The IODP proposal 519 (Camoin, Bard, Hamelin, & Davies, 2002) aimed to reconstruct the last deglacial events by: (1) establishing the course of the last deglacial sea-level rise, (2) analyzing the reef response to sea-level and coeval environmental changes, and (3) defining the climatic variability during that
402 Earth and Life Processes Discovered from Subseafloor Environments
period. Regarding the course of the last deglacial sea-level rise, the objectives were specifically to: (1) establish the minimum sea level during the LGM, (2) assess the validity, the timing, and amplitude of meltwater pulses and thereby identify the exact sources of the ice responsible for these extremely rapid sealevel rises, and (3) test predictions based on different ice and rheological models. The two drilling areas, Tahiti and the Australian Great Barrier Reef, were selected based on their tectonic setting and their location at a considerable distance from the main former ice sheets (“far-field” site), to minimize the potential tectonic and hydrostatic parameters in the reconstruction of last deglacial sea-level changes. The effects of hydroisostatic processes reflect the geodynamic context: for small islands, the addition of meltwater produces a small differential response between the island and the seafloor, whereas the meltwater load produces significant differential vertical movement between larger islands or continental margins and the seafloor (Lambeck, 1993). There was, therefore, a need to establish the relative magnitudes of hydroisostatic effects at two ideal sites located at a considerable distance from the major former ice sheets, one on an oceanic island (i.e., Tahiti) and another on a continental margin (i.e., the Australian Great Barrier Reef). Furthermore, these sites are located far away from glaciated regions (“farfield”) and can therefore provide basic information regarding the melting history of continental ice sheets and the rheological structure of Earth. The expeditions linked to IODP Proposal 519, Expedition 310 “Tahiti Sea Level” (2005; Camoin, Iryu, McInroy, & The Expedition 310 Scientists, 2007a,b) and the IODP Expedition 325 “Great Barrier Reef Environmental Changes” (2010; Webster, Yokoyama, Cotterill, & The Expedition 325 Scientists, 2011; Yokoyama et al., 2011) aimed to provide the most comprehensive deglaciation curves from tectonically stable regions by conducting offshore drilling of fossil coral reefs now preserved at 40–130 m below present sea level. They were the two first expeditions of the successive drilling programs (Deep Sea Drilling Program—DSDP; Ocean Drilling Program—ODP; and Integrated Ocean Drilling Program—IODP) to drill deglacial reefs.
3.6.4 EXPEDITION 310 “TAHITI SEA LEVEL” 3.6.4.1 Introduction Tahiti is located in French Polynesia at 17°50’S and 149°20’W, in the central tropical South Pacific and belongs to the Society Archipelago which corresponds to a volcanic linear chain exhibiting an NW–SE general direction and which formed during the last 5 my as the result of the WNW-ward motion of the Pacific Plate over the Society Hotspot. Tahiti is a high volcanic intraplate island (2241 m maximum altitude) that was formed within the last 1.5 my and now lies near the southeastern end of the chain (Hildenbrand, Gillot, & Le Roy, 2004; Le Roy, 1994). Volcanic activity on this island ceased approximately 200 kyrs ago and the currently active volcanic center lies approximately 50 km southeast of
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Tahiti on the flanks of Mehetia Island and surrounding seamounts. The volcanic complexes of Tahiti are composed primarily of porphyritic basaltic lavas with alkaline affinities. Toward the end of the main volcanic phase on Tahiti (i.e., at 650–850 ka), the northern and southern flanks of the volcanic edifice collapsed catastrophically and spewed thousands of cubic meters of sediment into the surrounding sea (Hildenbrandt et al., 2004). Today, the island is heavily eroded and dissected by deeply incised radial valleys resulting from its exposure to persistent rainfall punctuated by strong storms. The subsidence rates of the island were previously estimated to range from 0.15 to 0.4 mm/year by Le Roy (1994) and Montaggioni (1988), respectively. An average subsidence rate of 0.25 mm/year has been deduced from the ages of the subaerial lavas underlying the Pleistocene reef sequence in the Papeete drill cores (Bard et al. 1996). Data obtained on pre-LGM Tahiti corals are consistent with this estimate of 0.25 mm/year. Two corals collected at 147 meters below sea level (mbsl) with U-Th ages of 153 kyr BP (MIS6) indicate an upper limit of 0.4 mm/year for the subsidence of the island, assuming a MIS6 sea-level lowstand of 90%, Inwood, Brewer, Braaksma, & Pezard, 2008) and quality were retrieved and, combined with the high-resolution downhole measurement data, correspond therefore to unique archives to resolve in unprecedented detail the reef response to last deglacial sea-level and coeval environmental changes. During the operations, the opportunity was taken to drill deeper beneath the postglacial reef sequence into older reef units, principally to ensure that the entire postglacial sequence was recovered but also to provide exciting new data on past sea levels and reef development around the time of the penultimate deglaciation (i.e., Termination II) (e.g., Fujita, Omori, Yokoyama, Sakai, & Iryu, 2010; Iryu et al., 2010; Ménabréaz, Thouveny, Camoin, & Lund, 2010; Thomas et al., 2009). The set of borehole geophysical instruments deployed was constrained by the scientific objectives and the geological setting of the expedition. A suite of downhole geophysical methods was chosen to obtain high-resolution images of the borehole wall (OBI40 and ABI40 televiewer tools), to characterize the fluid nature in the borehole (IDRONAUT tool), to measure borehole size (CAL tool), and to measure or derive petrophysical and geochemical properties of the reef units such as porosity, electrical resistivity (DIL 45 tool), acoustic velocities (SONIC tool), and natural gamma radioactivity (ASGR tool). A total of 10 boreholes were prepared for downhole geophysical measurements which were performed under open borehole conditions (no casing) with the exception of a few of spectral gamma-ray logs. Nearly complete downhole coverage of the postglacial reef sequence has been obtained from 72 to 122 mbsl and from 41.65 to 102 mbsl at the Tiarei sites and at the Maraa sites, respectively. Partial downhole coverage of the underlying older Pleistocene carbonate sequence has been acquired at those sites. The Tahiti drill cores were also analyzed for evidence of modern microbial activity in the subsurface of the fore-reef slopes. Onboard adenosine triphosphate activity measurements have shown a certain degree of microbial activity directly attached to rock surfaces; cultivation and microscopic observations were also carried out onboard.
3.6.4.3 Scientific Results A first reconstruction of sea-level rise and reef development encompassing the last 13.92 kyrs was based on the study of an expanded (85.5–92.5 m thick), continuous, reef sequence recovered in a series of vertical (P6 and P7) and inclined
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(P8, P9, and P10; from 30° to 33° by reference to the vertical) drill holes carried out in 1995 through the barrier reef tract off Papeete (Bard et al., 1996, 2010; Cabioch, Camoin, & Montaggioni, 1999; Camoin, Gautret, Montaggioni, & Cabioch, 1999; Montaggioni et al., 1997). The record was continuous from 13.9 kyr BP to present, but did not reach the critical MWP-1A period. The first evidence of reef growth during a period encompassing the MWP-1A came from material dredged on the modern foreslopes (15 kyr BP in situ coral, Camoin et al., 2006). A specific target of the IODP Expedition 310 was therefore the extension of the previous Tahiti sea-level record to cover earlier portions of the last deglacial sea-level rise. The IODP Expedition 310 “Tahiti Sea Level” (Camoin et al., 2007a,b) has provided a very accurate and continuous reef record of the last and penultimate deglaciations and brought a wealth of new information in various scientific fields.
3.6.4.3.1 Composition of the Last Deglacial Reef Sequence The drilled coral reef systems around Tahiti are composed of two major chronological and lithological sequences which are attributed to the last deglaciation and to older Pleistocene time windows (Camoin et al., 2007a,b). The contact between those sequences is characterized by the occurrence of an irregular unconformity caused by the diagenetic alteration and karstification of the older Pleistocene sequence during sea-level lowstand(s). It ranges in depth from ∼122 mbsl (Tiarei outer ridge, deep Maraa sites, and Faaa) to 94 mbsl on the Tiarei inner ridge, and 85 mbsl at shallow Maraa sites. The chronological and sedimentological data of the older Pleistocene reef sequences have been detailed in Thomas et al. (2009), Iryu et al. (2010), Fujita et al. (2010), and Ménabréaz et al. (2010). At all drill sites, the last deglacial reef sequence is mostly composed of reef frameworks comprising three major components—corals, algae, and microbialites—whose proportions vary largely throughout the last deglacial reef sequence (Figures 3.6.3 and 3.6.4). Two major biological communities have been described (Camoin et al., 2007a,b; Seard et al., 2011; Camoin et al., 2012): 1. The coralgal communities include seven distinctive assemblages characterized by various growth forms that form the initial frameworks. The dominant coral morphologies (branching, robust branching, massive, tabular, foliaceous, and encrusting) and the abundance of associated builders and encrusters determine distinctive frameworks displaying a wide range of internal structures, from loose to dense frameworks (Figure 3.6.3). The coral assemblages are described later in this section. 2. Microbialites represent a major structural and volumetric component of the recovered frameworks in which they may locally form up to 80% of the rocks. The microbial communities developed in primary cavities of the coralgal
408 Earth and Life Processes Discovered from Subseafloor Environments
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FIGURE 3.6.3 Core slabs displaying coralgal assemblages. (A). Robust-branching Pocillopora— encrusting/massive Montipora assemblage (PM) showing a highly bioeroded Pocillopora in growth position encrusted at its top by an encrusting Montipora. Sample 24A15R 1W 19-35, depth ∼118.6 m.
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frameworks, where they heavily encrusted the coralgal assemblages to form microbialite crusts ranging in thickness from a few centimeters to 20 cm. The microbialite crusts display a wide range of growth forms: laminated crusts, digitate microbialites, and structureless to massive micritic masses (Seard et al., 2011) (Figure 3.6.4). The most widespread microbialite development has been reported in coral frameworks dominated by branching, thin encrusting, tabular and robust branching corals (i.e., PPM, PP, tA, and rbA coral assemblages; see below) which built open frameworks typified by high (i.e., more than 50%) initial porosity values (Seard et al., 2011). The lipid biomarkers and their isotopic patterns (MAGEs and branched fatty acids: 10-Me-C16:0 and iso- and anteiso-C15:0 and -C17:0; Heindel et al., 2012; Heindel, Birgel, Peckmann, Kuhnert, & Westphal, 2010. ) indicate that the formation of microbialites was related to the activity of bacterial communities dominated by sulfate-reducing bacteria, thus confirming previous interpretations (Camoin et al., 1999). An accurate chronology has been obtained through the C14-AMS dating of numerous triplets of contiguous corals, coralline algal crusts, and microbialites. It was demonstrated that the microbialite crusts developed a few hundred years (i.e., approximately 100–500 years) after the coralgal communities in cryptic cavities, 1.5–6 m below the living reef surface, as a “filling front” which shortly followed the overall accretion of the coralgal frameworks during the last deglacial sea-level rise (Seard et al., 2011). This implies that there was no direct competition between living corals and microbialites. In primary cavities of the reef frameworks, microbialites are locally associated or interlayered with skeletal limestone; loose skeletal sediments (rubble, sand, and silt) rich in fragments of corals, coralline, and green algae (Halimeda); and, to a less extent, echinoids, molluscs, and foraminifers (mostly Amphistegina and Heterostegina). The amounts of volcaniclastic sediments (e.g., silt- to cobble-sized lithic volcanic clasts, crystal fragments, clays) are highly variable, from mere sand and silt impurities in the carbonate rock units to minor components (