The Phanerozoic Carbon Cycle: CO2 and O 2 Robert A. Berner OXFORD UNIVERSITY PRESS THE PHANEROZOIC CARBON CYCLE To Jacques Joseph Ebelmen, who had it all figured out 160 years ago and whose pioneering work on the long-term carbon cycle is virtually unknown THE PHANEROZOIC CARBON CYCLE: CO 2 AND O 2 Robert A. Berner 1 2004 3 Oxford New York Auckland Bangkok Buenos Aires Cape Town Chennai Dar es Salaam Delhi Hong Kong Istanbul Karachi Kolkata Kuala Lumpur Madrid Melbourne Mexico City Mumbai Nairobi São Paulo Shanghai Taipei Tokyo Toronto Copyright © 2004 by Oxford University Press, Inc. Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York 10016 www.oup.com Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Berner, Robert A., 1935– The phanerozoic carbon cycle : CO 2 and O 2 / Robert A. Berner. p. cm. Includes bibliographical references and index. ISBN 0-19-517333-3 1. Atmospheric carbon dioxide—Evolution. 2. Carbon cycle (Biogeochemistry) I. Title. QC879.8.B47 2004 577'.144—dc22 2003060954 987654321 Printed in the United States of America on acid-free paper 1 Preface There is much confusion attached to the term “carbon cycle.” It has been applied to different time scales ranging from hours in biological systems, to decades in future global warming, to millennia and hundreds of mil- lennia in climate history. Much neglected is the cycling of carbon over longer time scales, and the purpose of this book is to alleviate this situ- ation. What I call the “long-term carbon cycle” involves the exchange of carbon between rocks and the various reservoirs near the earth’s sur- face, the latter including the atmosphere, hydrosphere, biosphere, and soils. Exchange with the surface involves such processes as chemical weathering of silicate minerals, burial of organic matter in sediments, and volcanic degassing of CO 2 . I have spent much time worrying about such processes and feel that it is time to show how the long-term cycle works and how to use it in deducing factors affecting the evolution of atmospheric CO 2 and O 2 over the past 550 million years (Phanerozoic time). This is a new world to most people studying the “carbon cycle,” especially as it relates to future global warming. It is not generally real- ized that global warming due to the burning of fossil fuels is simply a large acceleration of one of the major processes of the long-term carbon cycle, the oxidative weathering of sedimentary organic matter. Descriptive discussion of the long-term carbon cycle is not enough. The other role of this book is to show how one can make quantitative estimates of rates of carbon flux between rocks and the earth’s surface and how these fluxes can be used to estimate past levels of atmospheric CO 2 and O 2 . In this way, I introduce the reader to a much needed multidisciplinary quantitative approach to earth history, which is some- times referred to as “earth system science.” I, and other workers, have published a number of papers on modeling of the long-term cycle, but there is no central place one can go to get the fundamentals of this cycle. This book is hopefully that place. I am indebted to the many discussions of the long-term cycle with earth scientists, which are too numerous to list here. However, discus- sions with Klaus Wallmann, David Beerling, Dana Royer, Tom Crowley, Steve Petsch, Derrill Kerrick, Ken Caldeira, Leo Hickey, Dick Holland, Bill Hay, Fred Mackenzie, Bette Otto-Bliesner, Betty Berner, John Hedges, John Hayes, Lee Kump, and Tony Lasaga at various times over the past 20 years have been unusually helpful. Several of these people will recognize their contribution to the GEOCARB modeling discussed in this book. Special acknowledgment goes to the late Bob Garrels, who introduced me to geochemical cycle modeling in general. Without his influence this book would never have been written. Also, the book would probably not have been written now if editor Cliff Mills, at the sugges- tion of Brian Skinner, hadn’t suggested doing so. vi Preface 1 Contents 1. Introduction 3 The Short-Term Carbon Cycle 3 The Long-Term Carbon Cycle 5 Modeling the Phanerozoic Carbon Cycle 9 2. Processes of the Long-Term Carbon Cycle: Chemical Weathering of Silicates 13 Mountain Uplift, Physical Erosion, and Weathering 13 Plants and Weathering 18 Atmospheric Greenhouse Effect and Weathering 25 Solar Radiation, Cosmic Rays, and Weathering 31 Continental Drift: Effect on Climate and Weathering 33 Lithology and Weathering 36 Submarine Weathering of Basalt 38 Summary 39 3. Processes of the Long-Term Carbon Cycle: Organic Matter and Carbonate Burial and Weathering 40 Organic Matter Burial in Sediments 41 Land Plant Evolution 48 Weathering of Organic Matter 50 Carbonate Weathering 52 Carbonate Deposition and Burial 54 Summary 56 viii Contents 4. Processes of the Long-Term Carbon Cycle: Degassing of Carbon Dioxide and Methane 58 Degassing Rate of CO 2 58 Metamorphic and Diagenetic CO 2 Degassing 64 Carbonate Deposition and Degassing 65 Methane Degassing 66 Summary 70 5. Atmospheric Carbon Dioxide over Phanerozoic Time 72 Long-Term Model Calculations 72 Perturbation Modeling 77 Model Results 78 Proxy Methods 87 Summary: CO 2 and Climate 98 6. Atmospheric O 2 over Phanerozoic Time 100 The Long-Term Sulfur Cycle and Atmospheric O 2 101 Model Calculations 103 Model Results 112 Independent Indicators of Phanerozoic O 2 115 Summary 123 References 125 Index 147 THE PHANEROZOIC CARBON CYCLE [...]... two cycles: the short-term cycle and the long-term cycle The Short-Term Carbon Cycle The carbon cycle, ” as most people understand it, is represented in figure 1.1 Carbon dioxide is taken up via photosynthesis by green plants on the continents or phytoplankton in the ocean On land carbon is transferred to soils by the dropping of leaves, root growth, and respiration, the death of plants, and the development... The cycle of carbon is essential to the maintenance of life, to climate, and to the composition of the atmosphere and oceans What is normally thought of as the carbon cycle is the transfer of carbon between the atmosphere, the oceans, and life This is not the subject of interest of this book To understand this apparently confusing statement, it is necessary to separate the carbon cycle into two cycles:... from the ground, oxidized by burning, and given off to the atmosphere as CO2 The Long-Term Carbon Cycle Over millions of years carbon still undergoes constant cycling and recycling via the short-term cycle, but added to this is a new set of processes affecting carbon This is the long-term carbon cycle, the subject of this book What distinguishes the long-term carbon cycle from the short-term cycle is the. .. from minerals to the oceans (Note that in reaction 1.6 there are two bicarbonate ions produced from calcium carbonate weathering and that one of them comes from the carbon contained within the carbonate mineral itself.) Modeling of the long-term cycle involves calculation of the rate of Ca and Mg silicate weathering, and this requires a knowledge of the rates of Ca and Mg carbonate weathering (Fwc in... CO2 (IPCC, 2001) Modeling the Phanerozoic Carbon Cycle Together the carbonate-silicate and organic long-term subcycles play the dominant role in controlling the levels of atmospheric CO2 and O2 over millions to billions of years In this book I show how these subcycles have operated only over the past 550 million years, the Phanerozoic eon The Phanerozoic is chosen because of the abundance of critical... aspects of the short-term cycle are components of the long-term Figure 1.2 The long-term carbon cycle (After Berner, 1999.) 6 The Phanerozoic Carbon Cycle Table 1.1 Masses of carbon involved in both the short-term (prehuman) and long-term carbon cycles compared with some fluxes in the long-term cycle Mass (1018 mol) Substance or flux Carbonate C in rocks Organic C in rocks Oceanic dissolved inorganic carbon. .. reconstructions, and relatively agreed-upon tectonic and climatic histories Such a situation is not available for the Precambrian The plethora of Phanerozoic geological, biological, and climatic data are extremely useful in trying to recreate the history of the carbon cycle This will be done in the present book The reader is referred to the books by Holland (1978, 1984) for discussion of the carbon cycle before the. .. Mg and Ca-Mg silicates and carbonates In this book the reaction will be referred to as the Ebelmen-Urey reaction Only the weathering of Ca and Mg silicates is important; weathering of Na and K silicates does not lead to loss of CO2 because these elements do not form common carbonate minerals in sediments (The CO2 consumed during Na and K silicate weathering is returned to the atmosphere during the. .. biota Land herbivores eat the plants, and carnivores eat the herbivores In the oceans the phytoplankton are eaten by zooplankton that are in turn eaten by larger and larger organisms The plants, plankton, and animals respire CO2 Upon death the plants and animals are decomposed by microorganisms with the ultimate production of CO2 Carbon dioxide is exchanged between 3 4 The Phanerozoic Carbon Cycle Figure... from the mass balance expression for bicarbonate (reactions 1.1, 1.2, and 1.6): Fwsi = Fbc – Fwc (1.13) Fbc – Fwc represents the carbonate that is formed only from the weathering of Ca and Mg silicates, as opposed to that formed from both Ca and Mg silicate and carbonate weathering (Fbc) Equation (1.13) illustrates the necessity of knowing the rate of carbonate weathering (Fwc) in calculating the rate . carbon cycle into two cycles: the short-term cycle and the long-term cycle. The Short-Term Carbon Cycle The carbon cycle, ” as most people understand it, is represented in figure 1.1. Carbon. Introduction 3 The Short-Term Carbon Cycle 3 The Long-Term Carbon Cycle 5 Modeling the Phanerozoic Carbon Cycle 9 2. Processes of the Long-Term Carbon Cycle: Chemical Weathering of Silicates 13 Mountain. recreate the history of the carbon cycle. This will be done in the present book. The reader is referred to the books by Holland (1978, 1984) for discussion of the carbon cycle before the Phanerozoic. All