Workshop Report - Ridge 2000 Program

The Mid-Oceanic Ridge 

A Dynamic Global System 

Ocean Studies Board 

Commission on Physical Sciences, 

Mathematics, and Resources 

National Research Council 

National Academy Press 

Washington, D.C. 1988

NOTICE: The project that is the subject of this report was approved by the 

Governing Board of the National Research Council, whose members are drawn 

from the councils of the National Academy of Sciences. the National Academy 

of Engineering and the Institute of Medicine. The members of the committee 

responsible for the report were chosen for their special competences and with 

regard for appropriate balance. 

This report has been reviewed by a group other than the authors according 

to procedures approved by a Report Review Committee consisting of members of 

the National Academy of Sciences. the ,National Academy of Engineering. and the 

Institute of Medicine. 

The National Academy of Sciences is a private. nonprofit self-perpetuating 

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research. dedicated to the furtherance of science and technology and to their 

use for the general welfare. Upon the authority of the charter granted to it 

by the Congress in 1863. the Academy has a mandate that requires it to advise 

the federal government on scientific and technical matters. Dr. Frank Press is 

president of the National Academy of Sciences. 

The National Academy of Engineering was established in 19611. under the 

charter of the National Academy of Sciences. as a parallel organization of 

outstanding engineers. It is autonomous in its administration and in the 

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responsibility for advising the federal government: The National Academy of 

Engineering also sponsors engineering programs aimed at meeting national needs, 

encourages education and research, and recognizes the superior achievements of 

engineers. Dr. Robert M. White is president of the National Academy of 

Engineering. 

The Institute of Medicine was established in 1970 by the National Academy 

of Sciences to secure the services of eminent members of appropriate 

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the public. The Institute acts under the responsibility given to the National 

Academy of Sciences by its congressional charter to be an adviser to the 

federal government and, upon its own initiative, to identify issues of medical 

care. research. and education. Dr. Samuel O. Thier is president of the 

Institute of Medicine. 

The National Research Council was organized by the National Academy of 

Sciences in 1916 to associate the broad community of science and technology 

with the Academy's purposes of furthering knowledge and advising the federal 

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providing services to the government. the public. and the scientific and 

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and the Institute of Medicine. Dr. Frank Press and Dr. Robert M. White are 

chairman and vice chairman. respectively. of the National Research Council. 

Support for this project was provided by the National Science Foundation. 

Office of Naval Research. National Oceanic and Atmospheric Administration. and 

the U. S. Geological Survey. 

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OCEAN STUDIES BOARD 

WALTER H. MUNK, Scripps Institution of Oceanography, Chairman 

D. JAMES BAKER, JR .. Joint Oceanographic Institutions, Inc. 

PETER BREWER, Woods Hole Oceanographic Institution 

JOHN M. EDMOND, Massachusetts Institute of Technology 

EDWARD A. FRIEMAN, Scripps Institution of Oceanography 

MICHAEL GLANTZ. National Center for Atmospheric Research 

MICHAEL C. GREGG, University of Washington 

JOHN IMBRIE, Brown University 

REUBEN LASKER, National Oceanic & Atmospheric Administration 

JAMES J. McCARTHY, Harvard University 

DENNIS A. POWERS, Johns Hopkins University 

C. BARRY RALEIGH, Columbia University 

DAVID A. ROSS, Woods Hole Oceanographic Institution 

JOHN G. SCLATER, University of Texas at Austin 

JOHN H. STEELE, Woods Hole Oceanographic Institution 

MARY TYLER, Versar, Inc. 

CARL I. WUNSCH, Massachusetts Institute of Technology 

MARY HOPE KATSOUROS, Senior Staff Officer 

JUDITH MARSHALL, Staff Assistant 

iii

COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND RESOURCES 

NORMAN HACKERMAN, Robert A. Welch Foundation 

GEORGE F. CARRIER, Harvard University 

DEAN E. EASTMAN, IBM T. J. Watson Research Center 

MARYE ANNE FOX, University of Texas 

GERHART FRIEDLANDER, Brookhaven National Laboratory 

LAWRENCE W. FUNKHOUSER, Chevron Corporation 

PHILIP A. GRIFFITHS, Duke University 

J. ROSS MACDONALD, University of North Carolina at Chapel Hill 

CHARLES J. MANKIN, University of Oklahoma 

PERRY L. McCARTY, Stanford University 

JACK E. OLIVER, Cornell University 

JEREMIAH P. OSTRI KER, Princeton University 

WILLIAM D. PHILLIPS, Mallinckrodt, Inc. 

DEN IS J. PRAGER, MacArthur Foundation 

DAVID M. RAUP, University of Chicago 

RICHARD J. REED, University of Washington 

ROBERT E. SIEVERS, University of Colorado 

LARRY L. SMARR, University of Illinois 

EDWARD C. STONE, JR., California Institute of Technology 

KARL K. TUREKIAN, Yale University 

GEORGE W. WETHERILL, Carnegie Institution of Washington 

IRVING WLADAWSKY-BERGER, IBM Corporation 

RAPHAEL G. KASPER, Executive Director 

LAWRENCE E. McCRAY, Associate Executive Director 

iv

PREFACE 

Recent discoveries of the widespread nature of volcanicallydriven 

submarine hot springs and their attendant chemosynthetically-based 

animal communities underscore the fact that the 

seafloor/ridge crest environment represents one of the current 

frontiers in the exploration and understanding of our planet. 

The global spreading center network may be viewed as a single 

system of focused energy flow from the earth's interior to the 

lithosphere, hydrosphere, and biosphere. Viewed in this manner 

it becomes evident that the processes involved in generation of 

oceanic lithosphere are strongly interconnected and that an 

interdisciplinary approach will be necessary to achieve major 

strides in our understanding of the role lithosphere genesis 

plays in planetary evolution. 

Major technical advancements in seafloor imaging capability 

and recent developments in understanding relevant ridge cre.st 

processes have suggested to a number of scientists that it was 

timely to hold structured discussions of the problems and 

benefits of making comprehensive, in-depth observations and 

measurements of this global system. Further, the active nature 

of the planetary ridge system combined with the vastly improved 

capacity for spatial resolution of features on and beneath the 

seafloor has led researchers to begin examining the potential 

for making a wide variety of integrated time-series measurements 

on processes related to lithosphere genesis. 

In response to these exciting developments, the Ocean 

Studies Board of the National Research Council agreed to host a 

workshop on liThe Mid-Ocean Ridge: A Dynamic Global System." 

The report that follows presents the results of that workshop, 

which was held from April 6 through 10, 1987, at Salishan Lodge, 

Gleneden Beach, Oregon. More than 80 individuals representing 

six countries and a wide range of expertise participated in the 

workshop. Six working groups, organized around the principal 

themes identified by the steering committee, were suggested 

during the preparation phase with the recognition that exchange 

between related groups would be necessary and useful. The 

participants in each group and its focus were as follows. 

o Group 1: "Mantle Dynamics: Magma Generation and 

Delivery." Donald Forsyth and Jack Whitehead, Co-Chairmen; 

Roger Buck, Charles Cox, Roger Denlinger, Henry Dick, 

Michael Gurnis, Adolphe Nicolas, John Orcutt, 

Jason Phipps Morgan, and Sean Solomon. 

v

o Group 2: "Geometry and Dynamics of Magma Chambers." 

Robert Detrick and Charles Langmuir, Co-Chairmen; Wilfrid Bryan, 

Charles Cox. Karl Gronvold, John Malpas, Stewart McCallum, 

Janet Morton. Adolphe Nicolas, Michael Purdy, Kristin Rohr, and 

John Sinton. 

o Group 3: "Ridge Crest Segmentation, Tectonic Cycles 

and Lithosphere Evolution." Rodey Batiza and Paul J. Fox, 

Co-Chairmen; Jean Francheteau, William Haxby, Jeffrey Karson. 

Clive Lister, Peter Lonsdale. Kenneth MacDonald, Bruce Malfait, 

John Mutter, Ned Ostenso, Marc Parmentier, Jason Phipps Morgan, 

Hans Schouten, Roger Searle, Jean-Christophe Sempere, 

Fred Spiess, and Robert Tyee. 

o Group ll: "Subseafloor Hydrothermal Processes." 

Johnson Cann and John Edmond, Co-Chairmen; Alan Chave, 

John Delaney, Dave Janecky, Marc Langseth, Robert Lowell, 

Russ McDuff. Peter Rona, William Seyfried, Wayne Shanks, 

Norman Sleep, Geoffrey Thompson, and Richard von Herzen. 

o Group 5: "Biology of Hydrothermal Systems." 

Jim Childress and George Somero. Co-Chairmen; John Baross, 

Daniel Desbruyeres, Fredrick Grassle, Eric Hartwig, 

Robert Hessler, Holger Jannasch, Richard Lutz, Michael Reeve, 

Gary Taghon, and Philip Taylor. 

o Group 6: "Water Column Dynamics and Sedimentation 

Processes." John Lupton and Jack Dymond, Co-Chairmen; 

Edward Baker, Edward Bernard, Robert Collier, Stephen Hammond, 

Gary Klinkhammer, Michael Mottl, David Ross, and 

Richard Thompson. 

Despite the fact that fields of scientific inquiry among the 

participants varied from mantle dynamics to cell biology, a 

remarkable level of consensus regarding overall focus and 

general approaches to the dynamic processes involved in ocean 

lithosphere genesis emerged in the working group reports. The 

unifying goal of the RIDGE initiative (Ridge Interdisciplinary 

Global Experiments) is to understand the physical, chemical, and 

biological causes and consequences of mass and energy transfer 

within the global ridge system through time and space. Each 

group identified at least three scales of inquiry necessary to 

achieve this overall goal as well as its own specific 

objectives. 

o Global Scale: a significant proportion of the global 

rift system must be characterized sufficiently well to establish 

what is representative and what the range of natural variation 

is at the planetary level. 

vi

o Regional Scale: selected subsets of the rift system 

must be thoroughly documented at scales of hundreds of kilometers 

both along and across strike to provide comprehensive 

and comparable data sets required to evaluate the reasons for 

their similarities and the differences. 

o Local Scale: a small number of sites should be chosen 

for focused long-term efforts directed at documentation of the 

temporal variation in a broad range of ridge crest-related 

processes. 

Workshop participants made no attempt to design more 

specific experimental approaches to the objectives, but it was 

generally recognized that an interdisciplinary program of ridge 

crest experiments was feasible, worthwhile, and timely. Discussion 

of the overall goal, specific working group objectives, and 

recommendations for next steps in planning such a program are 

discussed in the report. 

Financial support for the workshop was provided by the 

National Science Foundation, the Office of Naval Research. the 

National Oceanic and Atmospheric Administration, and the U.S. 

Geological Survey. Stephen Hammond of NOAA, Janet Morton of 

the USGS, and David Ross of WHOI and OSS served as scientific 

liaison members to the Steering Committee and contributed 

substantially to the preparation of the workshop and editorial 

revision of the report. We deeply appreciate the special 

efforts of Alan Chave and David Janecky before, during, and 

after the workshop in helping to organize the program and 

present the final product. 

John R. Delaney 

Steering Committee Chairman 

vii

CONTENTS 

1 INTRODUCTION 

1 

2 STATEMENT OF GOALS AND OBJECTIVES 

5 

3 NEXT STEPS TOWARD A RIDGE INITIATIVE 

11 

4 REPORTS OF THE WORKING GROUPS 

13 

Introduction, 13 

Group 1 - Mantle Dynamics: 

Group 2 

Group 3 - 

Group 4 

Group 5 

Group 6 

Magma Generation and 

Delivery, 14 

Geometry and Dynamics of Magma Chambers, 21 

Ridge Crest Segmentation, Tectonic Cycles, 

and Lithosphere Evolution, 30 

Subseafloor Hydrothermal Processes, 38 

Biology of Hydrothermal Systems, 45 

Water Column Dynamics and Sediment 

Processes, 53 

APPENDIXES 

59 

I List of Participants, 59 

II Background Papers 

ix

1 

INTRODUCTION 

The global mid-ocean ridge is perhaps the most striking 

single feature on the solid surface of our planet. Sections of 

the ridge extend along the floors of all the world's oceans to a 

length in excess of 50,000 km. The mid-ocean ridge dominates 

the Earth's volcanic flux and creates an average of 20 km 3 of 

new oceanic crust every year. The processes of generation and 

cooling of oceanic lithosphere contribute two thirds of the heat 

lost annually from the Earth's interior. One third of the heat 

flux in oceanic lithosphere is carried by the circulation of 

seawater through fractures in hot oceanic crust. This 

hydrothermal circulation facilitates a major chemical exchange 

between seawater and oceanic crustal rocks that acts as an 

important regulator of the chemistry of the oceans and of the 

volatile content of the Earth's interior. The most stunning 

manifestations of this circulation are the high-temperature 

hydrothermal vents along the ridge axis. Major vent fields 

provide the energy and nutrients for the support of diverse 

communities of organisms sustained by a unique food chain based 

on chemosynthetic bacteria. Not only are these organisms 

profoundly influenced by such hydrothermal circulation, but the 

vent communities in turn have a marked impact on the physical 

and chemical environments they inhabit. These types of 

interactions point to an essential interconnection on a wide 

variety of temporal and spatial scales among the biological and 

physical processes operative along the ocean ridge system. 

The last major report of the National Research Council on 

the scientific objectives for study of the mid-ocean ridge was 

Understanding the Mid-Atlantic Ridge, published under the 

auspices of the Ocean Affairs Board in 1972. That report had a 

major impact on subsequent programs in mid-ocean ridge science. 

Most notable was Project FAMOUS I French-American Mid-Ocean 

Undersea StudyL which initiated the use of manned submersibles 

to conduct geological studies of the mid-ocean ridge median 

valley. 

The 15 years since the publication of that report. however, 

have seen many new discoveries of ridge phenomena and the 

development of a number of sophisticated technological tools for 

1

detailed investigation of the seafloor and the subsurface 

crust. High temperature hydrothermal vents. for instance. were 

discussed only as theoretical possibilities before their 

discovery in the Pacific in the late 1970s. Such vent fields 

and their associated biological communities were not observed on 

slow spreading ridge crests until 1985. High resolution swath 

mapping and side-scan sonar imaging have only recently begun to 

yield a rich return of information on the detailed morphology 

and structure of ridge systems. including such discoveries as 

the existence of overlapping spreading centers and major 

along-strike variations in volcanic and tectonic processes. 

Multi-channel seismic imaging techniques have advanced to the 

stage where widespread mapping of the prominent reflector 

thought to mark the roof of the axial magma chamber has been 

initiated. The Global Positioning Satellite system promises to 

reduce ship navigational errors to a few tens of meters on a 

routine basis. permitting easy intercomparison of data sets and 

assured placement of instrumentation for experiments. 

Much of the promise of this new technology remains to be 

realized. Detailed sampling and mapping of the mid-ocean ridge. 

for instance. has been confined to date only to a small fraction 

of its total length. The range in diversity of volcanic and 

tectonic processes manifested along the ridge axis. as a consequence. 

has not yet been fully defined. More fundamentally. 

the complex and interlinked processes of magmatism. hydrothermal 

circulation. development of vent communities. and lithospheric 

evolution are only dimly understood. The dynamics of these 

processes have not yet been elucidated because of the lack of 

in situ observations of sufficient duration and diversity to 

determine the important interactions and time scales. 

For these reasons. the Ocean Studies Board convened a workshop 

on the mid-ocean ridge. The workshop participants were 

asked to summarize our current understanding of the processes of 

generation and evolution of oceanic lithosphere. to identify the 

primary objectives for ridge crest science in the next decade. 

and to outline a research program capable of meeting these 

objectives. The workshop proceedings presented here are the 

response to that charge. 

In organizing the workshop. the Steering Committee attempted 

to assure that a wide spectrum of views from the entire oceanographic 

community would be represented. More than 80 individuals 

representing physical. chemical. and biological oceanography 

and marine geology and geophysics were invited to participate. 

The list of participants is included in Appendix I. 

Before the workshop. a number of participants were asked to 

prepare papers on the state of our understanding of the 

principal dynamical processes occurring at the mid-ocean ridge. 

with an emphasis on the major scientific questions currently 

outstanding. Additional papers were solicited on promising 

techniques for addressing these questions. The background 

2

papers were compiled, printed, and bound prior to the workshop, 

where they served as a basis for discussion. Because of the 

importance of these papers to the deliberations, they are made 

available in Appendix II. 

The first. day of the workshop was devoted to open discussion, 

in a plenary session, of six principal scientific themes 

of the mid-ocean ridge system: 

1. mantle dynamics: magma generation and delivery; 

2. geometry and dynamics of magma chambers; 

3. ridge crest segmentation, tectonic cycles, and 

lithospheric evolution; 

4. subseafloor hydrothermal processes; 

5. biology of hydrothermal systems; and 

6. water column dynamics and sediment processes near 

hydrothermal vents. 

The discussions were initiated by 10- to 15-minute 

commentaries, which drew on, but did not repeat, the content 

of the position papers. Discussion, often heated, of the major 

issues followed each presentation. By the end of the day all 

participants had been exposed to the major scientific issues 

held to be of greatest importance to each of the disciplinary 

groups. 

On the second and third days, smaller working groups met to 

discuss each of the principal scientific themes. Each working 

group was asked to determine the single most important 

scientific objective within its respective theme and to define 

the processes that must be studied and the approach that must be 

taken to achieve that objective. While many of the working 

groups began their discussions along narrow problematic or 

disciplinary lines, it became clear to all participants that the 

operative processes are strongly interconnected and that a 

multidisciplinary attack will be necessary to achieve major 

advances in understanding. 

On the final day, the workshop participants agreed on a set 

of primary scientific objectives for the future study of the 

global mid-ocean ridge system. They further agreed that these 

objectives could be met in the next decade by a coordinated 

program of exploration and experiment, and that planning for 

such an effort. to be name RIDGE (Ridge Interdisciplinary Global 

Experiments), should proceed. It was evident that resources 

from a variety of federal agencies will be required to support 

the RIDGE program. It was further recommended that this program 

be international in scope, a view endorsed by representatives 

from the United Kingdom, France, Japan, Canada, and Iceland 

present among the workshop participants. 

These proceedings reflect views expressed by workshop participants, 

and the overall goal and specific objectives as 

3

stated in Chapter 2 represent a consensus reached by the workshop 

as a group and not necessarily those of the members of the 

Ocean Studies Board. The suggested next steps in the development 

of RIDGE are outlined in Chapter 3. Chapter 4 includes the 

full reports of the six working groups.

2 

STATEMENT OF GOALS AND OBJECTIVES 

Activity along the global mid-ocean ridge involves complex 

interactions among a number of processes. Decompressional 

melting of the Earth's mantle delivers molten rock to ridge-axis 

magma chambers. Volcanic eruption and hydrothermal circulation 

cool and solidify the magma, forming new oceanic lithosphere. 

Temporal and spatial variations in these processes along the 

ridge axis contribute to distinctly segmented patterns of 

fracturing in the newly accreted lithosphere. Circulating 

seawater guided by the fractures extracts heat from the magma 

chamber, exchanges chemically with the oceanic crust and upper 

mantle, and supports seafloor hotspring activity of widely 

varying intensity. Chemosynthetically-based biological 

communities thrive on the hydrothermally induced nutrient 

fluxes. Geothermally driven water column plumes disperse heat. 

chemical species, and biota from the vents into the overlying 

oceans and adjacent sediments. 

The interactions among these major processes allow the 

global spreading center network to be viewed as a single complex 

and dynamic system of focused energy flow from the Earth's interior 

to the lithosphere, hydrosphere, and biosphere. Workshop 

participants agreed that the unifying goal of the RIDGE initiative 

is to understand the physical, chemical and biological 

causes and consequences of energy transfer within the global 

ridqe system through time and space. 

Workshop participants further agreed on six primary scientific 

objectives necessary to accomplish the broad goal of the 

RIDGE initiative: 

1. to understand the flow of the mantle, the generation of 

melt, and the transport of magmas beneath mid-ocean ridges; 

2. to understand the processes that transform magma into 

ocean crust; 

3. to understand the processes that control the segmentation 

and episodicity of lithosphere accretion; 

4. to understand the physical, chemical. and biological 

processes involved in the interactions between circulating 

seawater and the lithosphere; 

5

5. to determine the interactions of organisms with 

physical and chemical environments at mid-ocean ridges; and 

6. to determine the distribution and intensity of 

mid-ocean hydrothermal venting and the interaction of venting 

with the ocean environment. 

A brief development of the rationale and definition of 

each of these objectives follows. Further detail is provided 

in the respective working group reports, presented in full in 

Chapter 4. 

OBJECTIVE 1: To understand the flow of the mantle, the 

generation of melt. and the transport of magmas beneath 

mid-ocean ridges. 

Material in the Earth's mantle wells up beneath mid-ocean 

ridges in response to the spreading of the lithospheric plates. 

This upward flow is accompanied by pressure-release melting of 

mantle material. The detailed pattern of mantle flow and the 

depth extent and degree of melting, however, are poorly known. 

The physical and chemical processes that control melt segregation 

and the transport of magma to chambers at the base of, or 

within, the crust are also poorly understood. These processes 

control the structure of young oceanic lithosphere and the composition 

of the melt emplaced in crustal magma bodies. Spatial 

and temporal variations in these processes are strongly linked 

to mantle heterogeneity, to variations in crustal morphology 

and composition, and to segmentation of the ridge crest. 

Seismological and electromagnetic techniques are capable of 

determining the deep structure and anisotropy of the mantle 

beneath mid-ocean ridges with a spatial resolution sufficient 

to define the signature of large-scale flow and the distribution 

of melt within the mantle. Development of new technology 

will be necessary before the promise of these techniques can 

be realized. 

OBJECTIVE 2: To understand the processes that transform magma 

into ocean crust. 

The transformation of magma into oceanic crust at spreading 

centers has fundamental implications for the mechanisms of heat 

and material transport from deep within the Earth to the lithosphere, 

hydrosphere, and biosphere. Most models of ocean crust 

formation require the presence of a shallow molten zone, or 

magma chamber, in the crust beneath the spreading axis. Such 

magma chambers control the structure and composition of oceanic 

crust and provide the heat to drive hydrothermal systems. 

The important processes that transform mantle melt into 

oceanic crust and the role of crustal chambers are poorly 

understood. Owing to recent advances in technology and 

6

experience from land volcanic and magmatic systems, however, 

we can now address several critical problems. We can begin 

to determine the global distribution and physical properties 

of magma chambers at oceanic ridges and their temporal and 

spatial variability. Studies can be carried out of interrelationships 

among magmatism, tectonism, and hydrothermal 

activity. Internal dynamics of magma chambers are important 

factors that must be understood along with their effects on 

structure and composition of the crust and the transfer of heat 

from the magma chamber. Of vital concern are the physical and 

chemical processes occurring at the interface between the magma 

chamber and the overlying region of seawater circulation. 

OBJECTIVE 3: To understand the processes that control the 

segmentation and episodicity of lithospheric accretion. 

Use of new technology such as satellites, swath-mapping, and 

side looking sonar has revealed that the global rift system is 

segmented and that the pattern of segmentation varies temporally 

and spatially. The ocean crust and lithosphere are generated in 

a patchwork fashion by individual ridge segments that interact 

dynamically at their borders with other segments. The thickness 

and thermomechanical properties of the young ocean lithosphere 

are determined by interactions among volcanic and tectonic 

processes along individual segments, and this episodic or cyclic 

interplay can vary both temporally and spatially. Segmentation 

and episodic accretion are reflections of the interaction between 

upwelling mantle flow and the young lithosphere this flow 

engenders. The interplay is moderated and affected by melting, 

melt migration, and volcanism. Consequently, processes of melt 

formation, segregation, and ascent to magma chambers also displaya 

segmented pattern and temporal variability. Likewise, 

segmentation-scale diversity may arise in the style and 

distribution of hydrothermal venting, mid-water plumes and 

vent-related fauna. It is essential to understand the physical 

processes controlling segmentation, its temporal and spatial 

variation, and the processes causing episodic accretion along 

individual segments and their boundary zones. The individual 

processes of melt migration and eruption, faulting, fissuring, 

and stretching must also be better understood so that their 

possible interactions can be interpreted. 

OBJECTIVE 4: To understand the physical, chemical, and 

biological processes involved in the interactions between 

circulating seawater and the lithosphere. 

Hydrothermal systems at mid-ocean ridge crests transfer 

much of the heat from the Earth's interior to its surface. 

Hydrothermally-induced chemical exchanges between the oceans 

and underlying crust are pivotal in influencing. the chemical 

mass balances that affect the composition of the oceans and 

7

control the genesis of many types of seafloor ore deposits that 

are analogous to those found on land. Ridge crest venting of 

seawater provides the ultimate energy source to support unique 

chemosynthetic biological communities on mid-ocean spreading 

centers. Interactions with circulating seawater strongly affect 

the geometry and external dynamics of axial magma chambers, 

resulting in some of the topographic and morphological variability 

seen on ridge segments. The injection of vent water into 

the ocean by hydrothermal activity has implications for ciculation 

patterns. A detailed understanding of the individual 

physical and chemical processes that constitute a hydrothermal 

system will provide insight into many problems in biological, 

chemical, geological. and physical oceanography. While current 

research on seafloor hydrothermal circulation has begun to 

address a few of these problems, new approaches and a more 

focused effort will be required to achieve an interdisciplinary 

view. 

Four broad areas about which future hydrothermal system 

research might center can be outlined. First. the physical 

mechanisms of heat transfer from magma chambers or hot rock 

into hydrothermal systems must be identified. Second, the 

geometry of hydrothermal plumbing and the permeability structure 

of the crust must be delineated. Third, information must 

be gathered about the temporal variability of hydrothermal 

systems. Finally, the spatial variability and tectonic associations 

of hydrothermal systems must be more clearly defined. 

All of these objectives involve a mixture of basic exploratory 

research with more focused, detailed investigations using new 

technologies and imaginative approaches. 

OBJECTIVE 5: To determine the interactions of organisms with 

physical and chemical environments at mid-ocean ridges. 

The discovery and subsequent studies of unique biological 

communities associated with hydrothermal vents along the midocean 

ridge system have altered drastically many traditional 

views of biological processes and adaptations on this planet. 

In these hydrothermal environments, the energy source is chemical 

rather than solar, with chemosynthetic bacteria rather 

than photosynthetic plants at the base of the food chain. 

Many of the dominant animals at the vents have incorporated 

these bacteria within their tissues, resulting in unusual 

symbiotic adaptations that are now proving to be far more 

widespread throughout the entire Earth's biosphere than 

originally imagined. Some bacteria in these environments 

survive temperatures well above the range once thought 

tolerable for living organisms, and continuing studies of 

such microbial adaptations will be of fundamental importance 

to our understanding of the basic structure of living matter. 

Further definition of the extent to which chemosynthetic bacteria 

affect the chemistry of vent fluids is essential to a 

8

solid understanding of both the biology and geochemistry of 

these systems. 

The great spatial and temporal variability in environmental 

parameters at hydrothermal vents stands in marked contrast to 

that usually encountered in the deep sea, and such conditions 

alter physiological. behavioral, reproductive, and dispersal 

requirements placed on the organisms. One of the most remarkable 

manifestations of this variability is a vent community 

strikingly different from the surrounding deep-sea fauna, often 

at high taxonomic levels. Detailed studies of mechanisms of 

dispersal. the role of geographic isolation in the evolution of 

vent communities, the spatial and successional special patterns 

at particular vents sites, and the time scale of vent activity 

along various ridge segments are critical to our understanding 

of the biological and geological consequences of such variability. 

Equally important are further studies of the responses 

and adaptations of these organisms to, and their impacts on, 

these hydrothermal systems on time scales ranging from seconds 

to eras and spatial scales ranging from millimeters to global. 

OBJECTIVE 6: To determine the distribution and intensity of 

mid-ocean hydrothermal venting and the interaction of venting 

with the ocean environment. 

Hydrothermal plumes which issue from seafloor vents link 

the oceanic lithosphere, hydrosphere, and biosphere through 

a complex series of physical, chemical, and biological interactions. 

Plumes disperse heat and chemical species from 

newly-formed ocean crust, thereby modifying the composition 

of seawater and the underlying sediments on a global scale. 

Plumes influence the distribution of deep sea biota remote 

from the vents by providing energy, nutrients, and dispersal 

mechanisms. Hydrothermal plumes can be direct indicators of 

abyssal currents; however, the flux of buoyant water from 

hydrothermal vents also promotes vertical mixing and may even 

contribute to deep ocean circulation. Although many early 

studies used the plume as an exploration tool for locating new 

hydrothermal vents, recent work has shown that the plume can 

address fundamental questions regarding the magnitude and scale 

of hydrothermal venting. 

The character of the plume is determined both by crustal 

processes and by the oceanic environment. Changes in the plume 

can reflect events with diverse spatial and temporal scales, 

such as magma chamber evolution, changes in the subsurface 

hydrothermal plumbing, and shifting bottom currents. To understand 

these complex interactions, we must study hydrothermal 

plumes over a wide range of scales in time and space: from the 

scale of the individual vent plume fluctuating over a period of 

seconds, up to the 1000-km scale of the large ocean-basin plumes 

estimated to contain the integrated output from 100 years of 

9

hydrothermal venting. An important new research direction is to 

move from the realm of general observations to the quantification 

of rates and processes in hydrothermal plumes. a goal that 

can best be achieved via the cooperative. multidisciplinary 

approach suggested in these proceedings. 

In summary. workshop participants recognized that significant 

strides in understanding any particular aspect of the midocean 

ridge system will require focused efforts at integration 

with related processes. Ridge subsystems commonly studied by 

individual researchers are not separable from the system cjs a 

whole. All working groups identified scales of inquiry that 

range over several orders of magnitude in time and space. 

Current technologies are relatively well developed for 

establishing that spatial variations within the system. but 

observations of temporal change will be challenging to obtain. 

Global-scale reconnaisance surveys can set the context for more 

focused regional studies in which coordinated experiments 

involving a range of long-term measurements can be implemented. 

A common requirement of many of the recommended studies is a 

need for accurate age information on time scales between a 

decade and a million years. Innovative approaches to dating of 

hydrothermal fluids. rocks. and biological materials will be 

necessary to meet this requirement. 

10

NEXT STEPS TOWARD A RIDGE INITIATIVE 

3 

The workshop participants were unanimous in their agreement 

that a major interdisciplinary investigation of the mid-ocean 

ridge system would be both feasible and of outstanding scientific 

merit. It was further recommended that the initial planning 

steps for such an initiative should be taken during the coming 

year. 

The next steps necessary for the development of a RIDGE initiative 

as identified by the workshop steering committee are as 

follows: 

1. Distribute the workshop report and solicit comments. 

This report is being widely circulated within the U.S. scientific 

community to provide potentially interested participants with 

the background and recommendations of the workshop. It is to be 

stressed that this report is not a scientific plan. It consists 

of the opinions and ideas of workshop participants. Recipients 

of this report are asked to provide their own answers to the 

questions addressed by the workshop participants and to comment 

on the results. These responses will be incorporated in the 

development of the program plan. 

2. Form a RIDGE Steering Committee. The Committee should 

provide oversight for early planning and advise appropriate 

U. S. funding agencies on program implementation. 

3. Establish RIDGE working groups. It is planned that 

these working groups will assist in the formulation of the 

program and will consider aspects critical to further planning. 

It is suggested that the working groups focus on the following 

topics: 

a. Mapping and sampling, 

b. Advanced measurement, and 

c. Theory and laboratory experimentation. 

4. Initiate an annual summer RIDGE forum for the purpose 

of encouraging scientific exchange. evaluating program progress 

and reviewing scientific objectives. This forum would be open 

to interested participants. 

11

5. Explore possibilities for establishment of an international 

component for RIDGE. 

6. Host planning workshops on technical topics as necessary 

to develop a detailed scientific plan. 

7. Draft a scientific plan for RIDGE. Because of the many 

technical and scientific uncertainties bearing on program design, 

the initial plan will be preliminary and will be modified 

as required over a period of several years. The plan will take 

into account all comments, criticisms, and suggestions provided 

in response to the workshop report. 

12

4 

REPORTS OF THE WORKING GROUPS 

INTRODUCTION 

The following six reports, written during the workshop, 

present the deliberations of the working groups. Each working 

group focused on one of the six scientific themes of the 

mid-ocean ridge system. The working group members were asked to 

consider the following questions: 

1. What is the single most important scientific objective 

within this theme? 

2. What are the critical problems (primary and secondary) 

that must be solved in order to achieve this objective? 

3. What are the specific physical processes that 

studied in order to understand the critical problems? 

be listed in priority order? 

need to be 

Can they 

4. What data ought to be collected, and what is it 

realistic to expect in the future? 

5. What laboratory, theoretical, and numerical developments 

are needed now and what capabilities should be developed? 

6. What measurement capabilities are needed? 

capabilities exist, or can they be developed during 

decade? 

Do these 

the coming 

7. What is the strategy for proceeding? What studies must 

be simultaneous? What needs to be done now for planning? 

8. What cross-disciplinary coordination needs to be 

planned? 

13

GROUP 1: 

MANTLE DYNAMICS: MAGMA GENERATION AND DELIVERY 

Members: 

Donald Forsyth. Co-Chairman 

John Whitehead. Co-Chairman 

Roger Buck. Charles Cox. Roger Denlinger. Henry Dick. 

Michael Gurnis. Adolphe Nicolas. John Orcutt. 

Jason Phipps Morgan. and Sean Solomon 

Scientific Rationale 

Pressure-release melting of upwelling mantle beneath a 

spreading center is the primary process by which magma is 

generated. The depth and degree of partial melting beneath the 

ridge is controlled by the rate of upwelling and the composition 

and temperature of the mantle. The spatial and temporal 

distribution of melting thus reflects the dynamics of mantle 

flow. Although some constraints on the pressure and temperature 

conditions of melt formation are provided by petrological 

studies. the physical processes which control magma generation 

and delivery. and their chemical consequences. are poorly 

understood. 

The primary scientific objective in the study of mantle 

dynamics at spreading centers is to understand the flow of the 

mantle. the generation of melt. and the transport of magmas 

beneath ridge systems. Separation of melt from residual mantle 

will control the redistribution and chemical stratification of 

mantle materials. the structure of young oceanic plates. the 

rate and geometry of melt delivery to the base of the crust. and 

the composition of parental melts emplaced in crustal magma 

bodies. Understanding these mechanisms is important for a broad 

range of topics. including the nature of mantle heterogeneity. 

the spatial and temporal variations in crustal morphology. 

structure. and composition. and segmentation of the ridge crest. 

Investigation of this problem can be separated into two 

questions: (1) what is the pattern of mantle flow and melt 

generation beneath a spreading center? and (2) how does melt 

segregate from the mantle and migrate to the base of the crust? 

The answers to these questions will require coordinated. 

interdisciplinary observational. laboratory. and theoretical 

efforts. In addition. understanding of the behavior of the 

upper mantle revealed by ophiolite studies is of great 

importance. 

14

Critical Investigations 

The specific physical and chemical characteristics and 

processes which must be studied in order to answer these two 

questions include: 

1. Orientation of Upper Mantle Crystal F"bric. Olivine 

crystals are strongly anisotropic in their elastic properties 

and preferentially aligned by shear flow deformation. Thus, 

spatial distribution of seismic velocity anisotropy can 

constrain flow directions. 

2. Three-dimensional Distribution of Melt within the 

Mantle. The geometry of melt distribution will help constrain 

the conditions of melt formation and pathways of melt migration. 

3. Distribution of Temperatures within the Mantle. 

Lateral variations in temperature reflect spatial variations in 

hydrothermal circulation, flow of mantle materials, and melt 

formation and transport. 

4. Compositional Variability within the Mantle. Variations 

in composition of upwelling mantle dictate the volume and 

chemistry of melt. Variations in composition of the residual 

mantle are introduced by the melt extraction process. 

5. Physics and Chemistry of Melting within an Open System. 

Nearly all laboratory and thermodynamics studies to date are 

based on the assumption of a closed system, which is not valid 

in the mantle because of differential movement of melt and 

mantle materials. 

6. Physical Properties of Crystal-melt Aggregates. Interpretation 

of seismological, electromagnetic, and rheological 

phenomena requires more complete knowledge of the physical 

characteristics of rock-melt mixtures. 

7. Physical Mechanisms for Melt Migration and Segregation 

in a Deforming Crystalline Matrix. Whether melt moves from the 

generation site to the surface by way of porous flow, diapirism. 

or dike propagation will be critical to the delivery rate of 

melt and the degree of mixing and chemical modification which 

occurs during ascent. 

8. Variations in Crustal Structure, Morphology. and 

Composition. These variations. in the form of thickened crust. 

seamounts. or changes in composition, provide our only record 

of long-term changes in the spatial and temporal distribution 

of the melting and melt transport processes. 

15

9. Early Evolution of Oceanic lithosphere. Growth and 

deformation of the oceanic lithosphere affects the development 

of ridge axis morphology, the migration of melt, and the pattern 

of mantle flow. 

Approaches 

Successful investigation of these phenomena requires a 

combination of field, laboratory, and theoretical studies. 

Field Studies 

1. Seismological Studies. Seismic waves are fundamental 

means of sampling the Earth's interior. Different modes of wave 

propagation sample the Earth in distinct and complementary ways. 

Active (man-made) seismic sources have the advantages of control 

over the location and timing of the source, but are limited in 

size, and therefore depth of penetration. With year-long 

observation times, teleseismic (natural) sources probably 

provide the best tool for directly sampling the deeper structure 

where melting occurs. 

Passive seismic tomography can be used to determine the 

three-dimensional seismic velocity structure of the upper mantle 

and holds the potential for measuring directly the flow-aligned 

fabric of the mantle, distribution of zones of partial melting, 

and variation in the lithosphere structure associated with its 

early evolution. Tomographic experiments require long-term 

deployment of a large number (-100) of Ocean Bottom Seismometers 

(OBS's) in a grid to record arrival times and waveforms of body 

waves from distant earthquakes. With sufficient data from a 

variety of distances and azimuths, the travel time or waveform 

data can be inverted to recover the seismic velocity structure 

with a horizontal resolution comparable to the instrument 

spacing and a vertical resolution that will depend on the 

distance range of the sources. 

Surface wave methods detect the dispersion of teleseismic 

surface waves in the period range that is sensitive to structure 

of the upper 200 km of mantle. Velocity variations as a 

function of period indicate variations in average shear 

velocity, which is sensitive to temperature, composition, and 

the presence of melt. Measurement of both Love and Rayleigh 

waves, which have different polarizations, and. azimuthal 

variations in velocity yield information on anisotropy and 

crystal alignment with flow fields. This method requires 

deployment of eight to ten long-period seismometers over a 

region of several hundred kilometers square for periods of about 

a year, in order to ensure monitoring of an adequate number of 

teleseismic events. Another related technique is to measure the 

response to loading of the seafloor by long wavelength water 

gravity waves. 

16

Seismic refraction methods provide information on crustal 

structure, which can be used to investigate variations rn 

crustal thickness and composition and their relationship to 

seafloor morphology. In addition, anisotropy in the shallow 

upper mantle can be mapped with this method and compared with 

observations in ophiolite ultramafic sections. 

Multichannel seismic reflection techniques can map crustal 

thickness and provide greater resolution of crustal structure 

than other methods. Deeper, sub-horizontal, strongly reflective 

layers associated with interfaces between unmelted and melted 

mantle regions, if presenL may also be detected with this 

technique. 

Earthguake studies involve deployment of a network of OSS's 

on a ridge segment located near a seismically active region 

(e.g., a large fracture zone or subduction zone). Regional 

earthquakes yield a number of seismic phases sensitive to upper 

mantle structure that are not strongly excited in experiments 

with artificial sources and not detectable at teleseismic 

distances. In addition, the maximum depth of local seismic 

activity (microearthquakes) provides a key constraint on 

lithospheric thermal structure. 

2. Electromagnetic Techniques. The electrical conductivity 

of ultramafic rocks increases rapidly with temperature and 

dramatically increases when connected melt is present. Electromagnetic 

techniques can map the conductivity and anisotropy of 

conductivity within the mantle and will be a valuable tool in 

assessing the temperature, melt content and directional properties 

of the partial melt fabric within the mantle. Magnetotelluric 

sounding, which uses naturally-occurring magnetic 

fluctuations generated in and above the earth's atmosphere, may 

be effective in detecting extensive bodies of partial melt to 

depths greater than 100 km, but it is limited to detecting 

regions with conductivities comparable to that of the overlying 

ocean. Active source techniques can be used to detect variations 

in much more resistive materials to depths of 10-30 km. 

3. Rock Sampling. Systematic sampling of basalts and 

peridotites emplaced at selected spreading center segments and 

fracture zones can help to constrain the spatial and temporal 

variability of the melting process and efficiency of melt 

extraction in the upper mantle. Compositional variations in 

seafloor basalts reflect the integrated history of magmatic 

processes beneath a ridge axis and thus allow inferences to be 

made about melt generation and transport at depth. Correlation 

of these variations with crustal structure variations indicate 

spatial changes in these processes. Laboratory analysis of 

petrofabric characteristics of peridotites, as well as chemical 

variations in the peridotites, will indicate the degree of 

melting, the amount of trapped melt and its distribution, and 

the crystal fabric left after melting and melt extraction. The 

inter-relationships among major, trace, and isotopic element 

variations in basalts and spatially associated peridotites will 

also help to constrain these processes. 

17

4. Regional Surveys. Variations in crustal thickness, 

which may indicate variations in magma supply from the mantle, 

are most efficiently mapped over large regions by combined 

gravity and bathymetric surveys. In addition, gravity 

measurements may provide some constraints on the thermal 

structure of the mantle. Surveys may indicate the presence of 

small-scale secondary convection which could influence the 

melting process. Of particular importance is a determination of 

the distribution of off-axis volcanism that may reflect spatial 

variations in melt production in the vicinity of the ridge. 

Laboratory Experiments 

1. High Temperature/Pressure Experiments on Mantle 

Materials. Experimental determination of the physical and 

chemical behavior of mantle materials and melt-rock aggregates 

over the range of relevant temperature (800-1400 0 C), pressure 

(1-30 kbar), and strain rate conditions is critical to meaningful 

interpretation of data obtained by field studies, as well as 

to the parameterization of models which simulate components of 

the upper mantle flow/melt regime beneath spreading centers. 

Needed studies include characterization of: equilibrium and 

non-equilibrium chemical interactions between melt and rock; 

physical properties such as seismic velocities, electrical 

conductivity, and rheology (particularly at low deviatoric 

stress); and, the distribution of melt in, and permeability 

of. partially molten peridotite. 

2. Laboratory and Numerical Fluid Dynamic Experiments. 

Laboratory and numerical fluid mechanics experiments on idealized 

and analogue mantle systems result in testable predictions 

about the behavior of the system they describe, directly 

stimulate the design of field experiments, and show how the 

integrated system might work. Laboratory experiments can give 

direct information about fluid instabilities, episodicity of 

transport phenomena, and complicated flows that are beyond the 

range of present calculations. Numerical experiments, which can 

involve more realistic geometries than laboratory analogues and 

yield extensive quantitative predictions, can be developed in 

three dimensions with supercomputers. Future experiments can 

investigate: episodicity in melt and transport phenomena, 

diapirism; flow with large variations in temperature, pressure 

and temperature-dependent viscosity; two-phase flow including 

compaction; coupling between two-phase flow and sub-solidus 

thermal convection; and, interaction of mantle flow with the 

lithosphere. 

3. Numerical Modeling of Wave Propagation. Tomographic and 

electromagnetic experiments require development of numerical 

simulations of seismic and electromagnetic wave propagation in 

three-dimensional, inhomogeneous, anisotropic media. 

18

New Instrument and Laboratory Capabilities Required 

While many of the studies proposed can utilize existing 

tools and techniques, there are four facilities which require 

development: 

1. Long-lived, Broad-band Ocean Bottom Seismomet.ers. The 

tomographic studies require on the order of 100 OBS's that can 

remain on the seafloor for periods of a year or more and can 

respond to a wide range of frequencies. A similar number of 

comparable instruments are needed for surface wave and eart.hquake 

studies. These instruments do not presently exist.. and 

a development program should be initiated as soon as possible. 

2. Off-axis Basement Sampling. Rapid alteration and burial 

of rock surfaces as oceanic crust moves away from the ridge 

crest limits accessibility to off-axis basalts and peridotites. 

A tool such as a portable rock coring device is required which 

can rapidly and inexpensively obtain rock samples from the 

seafloor. Important attributes of this device are the capabilities 

of obtaining cores of 1 to 10 m length and real-time site 

evaluation through the use of video cameras and sub-bottom 

profilers. 

3. Instrumentation for Low Deviatoric Stress, High Temperature, 

High Pressure Experimentation. Current experiments are 

performed at high deviatoric stress for short time periods. To 

better simulate mantle conditions, a capability for long duration, 

low deviatoric stress experiments at high temperatures and 

pressures is required. It would be desirable if such a facility 

could accommodate experiments with partially molten materials. 

4. Shiptime. The time involved with deployment, surveying, 

and maintaining equipment utilized in these experiments requires 

on the order of 8 months of shiptime each year for at least a 

decade. 

5. Aerogravity Capabilities. If the capabilities for 

swathmapping tools for high resolution bathymetry are extended 

to ship-track spacings of 10 km or more. then traditional surface 

ship sampling of magnetics and gravity will not be obtained 

at sufficiently dense spacings to map crustal structure. Therefore, 

reliable aerial gravity techniques must be developed which 

can be used in conjunction with high resolution navigational 

techniques such as CPS. 

Planning Considerations 

Development of new instruments requires several years before 

they will be routinely operational and must therefore be 

initiated at once. These include the OBS's, which need to be 

designed and tested and require development of sophisticated 

19

telemetering capabilities, and the high temperature/pressure 

apparatus. Rock coring devices are presently being designed, 

and merely lack the funding for prototype fabrication and 

testing. 

There are few limitations on the actual implementation of 

the field programs, once the equipment items are available. The 

requirements of the seismic tomography experiments, which 

include the distribution of natural teleseismic sources at a 

wide range of distances and azimuths from the study area, seem 

to be the major constraint in site selection. For each of the 

studies, it would be ideal to examine the behavior of the 

upwelling/melting processes as a function of the major tectonic 

variables, such as spreading rate. In most cases, the various 

field studies can be combined and integrated for the same 

region. 

Coordination With Other Research Programs 

The mechanisms of melt production and heat transport beneath 

a spreading center provide the fundamental regulation of all 

other processes associated with oceanic crust accretion, 

lithosphere evolution, and hydrothermal circulation. As such, 

there are obvious linkages between these studies and those aimed 

at the larger time-scale and spatial-scale phenomena associated 

with these particular processes. In particular, tectonic cycles 

and along-axis variations in crustal accretion processes may be 

directly controlled by magma delivery. The scales of inquiry 

necessary for mantle dynamics make it possible to coordinate 

with the regional and global scale mapping and sampling studies 

necessary to look at shallower processes. In addition, many of 

the experimental observations and laboratory models required for 

investigation of these studies are closely related to those 

necessary for understanding magma chamber dynamics. Although 

the scale of inquiry is much larger, most of the instrumentation 

necessary for these studies has direct application to the other 

areas of investigation at smaller scales. Finally, the 

information being obtained by study of analogue systems, such as 

ophiolites, and by the ODP operations are highly complementary 

to the objectives of this program. 

20

GROUP 2: 

GEOMETRY AND DYNAMICS OF MAGMA CHAMBERS 

Members: 

Robert Detrick, Co-Chairman 

Charles Langmuir, Co-Chairman 

Wilfred Bryan, Charles Cox, Karl Gronvold, 

John Malpas, Stewart McCallum, Janet Morton, 

Adolphe Nicolas, Michael Purdy, Kristin Rohr, 

John Sinton 

Primary Motivation and Goals 

Sixty percent of the earth's surface is created at ocean 

ridges, as magmas generated within the mantle are cooled at the 

boundary layer between the mantle and the ocean. The way in 

which magmas are transformed into oceanic crust at spreading 

centers has important implications for the mechanisms of heat 

and material transport from deep within the earth to the 

lithosphere, hydrosphere and biosphere. This transfer process 

through time has been one of the major ways the earth's 

temperature has been controlled and has played a pivotal role in 

the creation of continents and the control of the composition of 

seawater. Despite the significance of this process for the 

whole earth system, it is poorly understood. On land, processes 

associated with the injection of magma into the crust can be 

continuously monitored at volcano observatories. In contrast. 

although the amount of material emplaced at ocean ridges exceeds 

by orders of magnitude that erupted on land, we are not even 

sure what an ocean ridge volcano actually is: we do not know 

its size, the timing and quantity of lava in individual 

eruptions, the number of volcanic edifices fed by the same magma 

chamber, or how the ocean crust is actually created through the 

processes of magma solidification. A primary objective of 

further study of the mid-ocean ridge is to understand the 

processes that transform magma into ocean crust. 

Most models of crustal accretion require the presence of a 

molten zone, or magma chamber, in the crust beneath the axis. 

In these magma chambers, magmas derived from the upper mantle 

differentiate to create the lower ocean crust before they erupt 

on the sea floor. Magma chambers are also the heat engines that 

drive hydrothermal circulation with its metallogenic and 

biological conseqences. They directly control the igneous 

structure and composition of oceanic crust. In addition, their 

variations in time and space provide important constraints on 

magma transport from the upper mantle and on the nature and 

distribution of hydrothermal activity. 

21

Research over the past few years has provided a definition 

of how small parts of the system work. However. major advances 

in geophysical and geochemical techniques now allow us to 

envision a coordinated. long-term program on a global scale 

which will provide an integrated understanding of the processes 

of crustal accretion. 

Critical Problems 

In order to understand the processes that transform mantle 

melt into oceanic crust and the role of crustal magma chambers. 

there are eight critical problems that must be addressed: 

1. What is the global distribution of magma chambers along 

oceanic ridges. and how does this distribution correlate with 

tectonic segmentation. spreading rate. and mantle temperature? 

2. What are the variations in the size. shape and physical 

properties of ridge crest magma chambers? 

3. What are the internal dynamics of magma chambers? 

4. How are the magma chambers cooled? 

5. What is the spacing of input of magma from the mantle 

and output through eruption at the seafloor? 

6. What is the temporal variability of magmatic processes? 

7. What are the relationships among magmatism. tectonism 

and hydrothermal activity? 

8. Is the ophiolite model a valid structural analogue for 

oceanic crust? 

In order to address these problems several different 

physical processes must be studied Isee Figure 1): 

Magma formation and transport affects the composition of the 

mantle melt and the temporal and spatial supply of magma to the 

crust. 

Magma differentiation and crystallization modifies the 

magmas delivered from the upper mantle before they solidify to 

form oceanic crust. 

Hydrothermal circulation and conductive cooling transfer 

heat out of the magma chamber and control its crystallization 

history. 

Volcanism delivers magma and heat to the sea floor. 

Tectonism causes faulting and fissuring that control the 

morphology of the spreading center and the locus and style of 

volcanism. 

22

FORMATION OF OCEAN CRUST 

AT SPREADING CENTER 

VOLCANISM 

HYDROTHERMAL ISM 

TECTON ISM 

\~.......I'-----"--/ 

DIFFERENTIATION 

AND 

CRYSTALLIZATION 

MAGMA FORMATION 

AND TRANSPORT 

FIGURE 1 

23

Strategies For Solving The Critical Problems 

We envision a strategy with four major components. 

1. Global Reconnaissance. The first component would 

include reconnaissance studies of substantial lengths of the 

mid-ocean ridge system in order to obtain a measure of the world 

wide variability of ocean ridge morphologic, structural and 

chemical characteristics. The reonnaissance would include 

bathymetric surveys over a distance of approximately 1000 km 

continuously along the strike of the ridge, with a swath width 

of several times the active accretion zone; multichannel seismiC 

(MCS) surveys along the axis to define the lateral continuity 

and width of the axial low velocity zone and any variations in 

seismically estimated crustal thickness; petrological sampling 

with approximately one station for every 10 to 20 km of ridge 

length, in order to determine the regional geochemical signature 

and to explore quantitative relationships among petrology, 

bathymetry, and the MCS axial reflector, and continuous 

surveying of along-axis water column temperature and chemical 

anomalies, in order to determine the distribution of 

hydrothermal activity. Such reconnaissance surveys should cover 

ridges which vary in their spreading rate, in their tectonic 

style (i .e., fracture zone spacing, presence or absence of rift 

valley, back-arc settings L and in the ambient mantle 

temperature (i.e., hot spots such as Ic.:land and cold spots such 

as the Australian!Antarctic Discordance). Approximately ten 

such surveys will be necessary to obtain adequate global 

coverage. These surveys will lead to coverage of about 

20 percent of the entire system of ocean ridges. They will 

determine the global distribution of magma chambers and provide 

the data necessary to develop quantitative relationships among 

spreading rate, gross tectonic fabric, magma chambers and 

geochemistry. 

2. Eruption Detection. The second component stems from 

the recognition that the ocean ridge volcano observatory should 

be located in an area of active volcanism. To find such a 

location we need to know the periodicity in space and time of 

volcanic eruptions on the sea floor, and the relationship of 

such eruptions to hydrothermal activity. There is at the moment 

no such information for submarine ocean ridges. Calculation of 

magma production rates and analogy with terrestrial volcanos 

suggests we should be able to find an active volcanic area which 

would remain active on the time scale of a decade. To find such 

a location, however, requires effective eruption monitoring. 

Two approaches could be explored: (a) long term monitoring of 

hydrothermal plumes and (b) acoustic monitoring. In addition to 

locating active ridge segments, such monitoring will provide 

data concerning regional eruption frequency and spatial 

systematics. 

24

3. Regional Surveys. The third component is more intensive 

mapping and sampling of smaller (300 km) areas within the 

reconnaissance surveys. About five such areas should be 

selected. A critical addition in these smaller areas would be 

the extension of mapping and sampling to older crust extending 

approximately 150 km to either side of the ridge axis. In these 

areas, there would be higher resolution bathymetry, multichannel 

seismics and sampling, with the addition of side scan sonar, 

electromagnetic surveys, and airborne gravity and magnetics. 

Certain areas within these regions would also be the sites of 

seismic refraction experiments, and observations and sampling by 

a deep-tow package, submersible or remotely operated vehicle 

(ROV). One spreading cell in the region should have continuous 

along-axis photo coverage of the accretion zone. More intensive 

eruption monitoring should take place at promising locations 

within the regional area. Studies on the regional scale will 

begin to address the size, shape, physical properties and 

temporal variability of magma chambers and eruptive units, and 

will provide more detailed relationships between magmatism and 

tectonics. 

4. Seafloor Volcano Observatory. The final component is 

the establishment of a long term ocean ridge volcano observatory 

along an active portion of a spreading center. The scale of 

this observatory should be that of a spreading center cell, or 

a length of about 50 km. Realistically, one such observatory 

could be well established by the end of a decade of study. The 

observatory would be completely mapped and heavily instrumented. 

Mapping should include complete photo coverage; identification, 

sampling and analysis of individual lava flows; and detailed 

maps of faults, fissures, gravity, magnetics and bathymetry. 

All these aspects should be monitored for changes through time. 

Instruments should include strain and tilt meters, geodetic 

measurements, continuous gravity and magnetic monitoring, 

permanent seismic stations, and hydrothermal monitoring. In 

addition, there should be three-dimensional structural 

information gained by 3-D multichannel seismic surveys, seismic 

tomography, and electromagnetic measurements. The observatory 

would also be a prime candidate for crustal drilling. It is the 

key ingredient to understanding how ocean ridge volcanoes 

actually work. 

Although the establishment of the volcano observatory would 

be towards the end of the decade-long program, all other 

components of the program could proceed in parallel. The Juan 

de Fuca Ridge and the East Pacific Rise between 90 and 130N 

have had their reconnaissance survey, and funded programs consistent 

with the regional 300-km scale of study are underway. 

Thus, more intensive efforts in these areas could proceed at the 

same time as reconnaissance programs at other locations. 

Development of instruments for the volcano observatory and 

eruption monitoring should also begin immediately. 

25

Related Studies 

In addition to these strategies which relate directly to the 

active ocean ridge system, there are two other areas of study 

which should provide important constraints which cannot be 

obtained in any other way. The first involves the study of 

ophiolites, which may be appropriate structural analogues for 

ocean crust and uppermost mantle, and are exposed in ways that 

never occur in the oceans, providing a unique three dimensional 

perspective. Detailed structural and geochemical investigations 

of these bodies can provide important constraints on the nature 

and scale of melt segregation processes in the uppermost 

mantle, on the size and internal dynamics of magma chambers, and 

on the critical interface between crustal magma bodies and 

circulating water systems. 

The second important objective is at least one deep crustal 

drill hole which extends all the way to the mantle. To date, 

the principal stratigraphic units in the ocean crust have been 

defined on the basis of characteristic velocities of transmitted 

seismic waves. Each of these layers is assumed to be composed 

of rock which has a seismic velocity similar to that of the 

layer, and analogous to the layers observed in ophiolites. But 

the bulk seismic properties of a rock may be very different from 

that of individual samples, since the bulk properties integrate 

the effect of cracks, veins and zones of alteration. Thus the 

assumption that ophiolites accurately represent the stratigraphy 

and composition of ocean crust has yet to be tested by actual 

observation and sampling of a deep section of ocean crust. Such 

a hole also is essential to provide "ground truth" against which 

we may test the correspondence between actual observed 

lithologic boundaries and the boundaries obtained by 

conventional seismic surveys in the vicinity of the hole. 

Continuous core sampling through layer 3 gabbro can also 

provide much mineralogical and geochemical information on the 

nature and rates of crystallization within a crustal magma 

chamber, and is the only way we can determine the bulk 

composition of the ocean crust. Also, the presumed connection 

between fractionated basalts I in layer 2) and crystallization 

processes in the chamber can be tested. Finally, if the hole 

does successfully penetrate the underlying mantle peridotite, we 

would for the first time have a coherent set of samples with 

which to trace the evolution of a melt from its origin as a 

mantle partial melt, through the deep crustal accretion zone, to 

its extrusion on the seafloor. 

1. 

out full 

imaging 

Data To Be Collected 

Morphology and Sampling. It will be necessary to carry 

coverage bathymetric mapping and side scan sonar 

at a wide range of resolutions, from the regional, to 

26

provide efficient and economically feasible coverage of 

thousands of kilometers of rise crest. to the highly detailed 

(on the scale of meters) to produce the "base map" for long term 

observatory-type studies. Rock sampling strategies will vary 

from reconnaissance dredging to the use of submersibles and ROVs 

to recover samples on the scale of individual flows. Shipboard 

rock analyses will be needed to permit rapid response to sample 

data acquired during mapping of active volcanic features, and to 

allow real-time optimisation of regional reconnaissance 

surveys. The need to construct precise and complete geologic 

maps will require large area photographic coverage using either 

deep tow vehicles or submersibles, as well as high resolution 

side-scan sonar systems. The necessary photographic 

capabilities exist within the community in the form of various 

deep-tow still or video camera systems and submersibles. The 

tools for mapping the morphology, e.g" SEABEAM, SEAMARC I and 

II, and GLORIA, are available, but improvements in resolution 

and swath width capabilities would be extremely beneficial to 

this program. Sampling techniques require development to 

provide a compromise between the detail and expense of manned 

submersibles and the blind approach of conventional dredging. 

Again ROV's may be the solution here, but wire-line rock drills 

may be required for effective off-axis operation. Rock dating 

in the age range 0 to 1 Myr may well be needed to define the 

sequence of volcanic and tectonic events associated with near 

surface magma injection and eruption. Possible techniques 

include thermoluminescence, U-Th disequilibrium, 14C dating 

of hard parts of vent fauna, and secular variation of the 

magnetic field. 

2. .Structural Measurements. Four approaches are needed to 

map the structure of the uppermost 5 to 10 km beneath the rise 

crest. 

Seismic Methods: Two techniques will be applicable. Multichannel 

seismic (MCS) reflection profiling provides the capability 

to map boundaries within the igneous crust and to image the 

axial magma chamber. The MCS capability I perhaps with shipboard 

processing capability) allows the regional mapping of the rise 

crest to detect the presence or absence of the axial magma 

chamber (AMC) reflector as well as high spatial resolution of 

the AMC when used in tight grid surveys. Seismic tomography 

experiments using networks of ocean bottom instruments and both 

earthquake and explosive sources will give images of the lateral 

velocity variations in three dimensions and define the size and 

shape of the AMC as well as providing constraints on its 

internal structure. As far as is possible, detailed MCS surveys 

and tomography experiments should be coordinated and integrated 

efforts. 

27

Electromagnetic Methods: Because of the huge changes in 

conductivity that occur in hot rock when there are small 

percentages of melt or water, electromagnetic methods hold 

considerable promise for the location and definition of both 

the AMC and regions of partial melt and the orientation of 

dike swarms relative to the underlying ridge axis. Both 

active electromagnetic measurements using deep-towed sources 

and passive magnetotelluric experiments will be necessary. 

Magnetics and Gravity: Maps of the magnetic and gravity 

field on a regional scale are needed, perhaps from the air, if 

adequate navigational capability is available and aerogravimeters 

are developed. Deep-tow magnetic surveys for high 

resolution mapping of the magnetic fabric of the shallow crust 

will also be necessary. 

3. Monitoring of Active Processes. Measurements of the 

total heat flux will be required and this may require both 

monitoring of active venting and the mapping of temperature 

anomalies within plumes on a regional scale. The capability 

must be developed to recognize and approximately locate active 

eruptive episodes (perhaps by acoustic or plume detection 

methods) . At appropriate sites long term (several year) seismic 

monitoring using large networks of ocean bottom seismometers 

will be necessary to define both the scale and timing of magma 

movement at shallow depths and the accompanying faulting. 

Geodetic measurements are crucial to detailed definition of the 

AMC inflation-deflation-rifting processes as are tilt and strain 

measurements. Sea floor gravity and magnetics measurements 

through time at specific localities will provide information on 

the cooling history of lava flows. These efforts require 

substantial new instrument development. in addition to adaption 

and refinement of instrumentation that is presently in use on 

subaerial volcanos. All these long-term monitoring experiments 

require development of large volume data storage capabilities, 

with perhaps the provision for real time data transmission. 

Drill holes will provide sites for downhole monitoring and 

measurement experiments. The utility of these holes will be 

greatly enhanced if techniques are devised for simple wire-line 

re-entry from conventional research vessels. 

Needed Laboratory, Theoretical and Numerical Experiments 

1. Studies of experimental phase equilibria at pressures 

of 2 to 10 kbars; mantle melting experiments up to pressures of 

40 kbar. 

2. Laboratory measurements of physical properties (seismic 

velocity, density, viscosity, electrical conductivity) for rocks 

at high temperatures, partial melts, and magma. 

28

3. Adaptation of tomographic inversion techniques to 

include amplitude information. Improved numerical techniques 

for seismic processing and modeling in laterally heterogeneous 

media. 

4. Development of numerical modeling methods to calculate 

the evolution of the chemistry of magmas. 

5. Careful inter-laboratory calibration of geochemical and 

petrologic data. 

6. Experimental and theoretical studies of fluid dynamics 

with reference to ma~ma chamber processes are required for the 

development and verification of models suggested by field. 

petrologic and geophysical evidence. 

7. Development of standard data formats to facilitate data 

exchange and the establishment of a global data repository. 

Interdisciplinary Implications 

A program of the magnitude outlined here will generate a 

very large data set in a variety of fields. Individually. the 

procedures outlined above will answer many of the critical 

questions concerning the transformation of magma into ocean 

crust. Theoretical modeling. constrained by the observations. 

is an important component of the study. and will address 

especially the question of internal dynamics of magma chambers. 

These diverse observations and theoretical studies must be 

synthesized to arrive at a model or series of models for the 

transformation of mantle melt into oceanic crust. Magmatic 

processes occurring at the crustal level are closely coupled to 

other first order processes at the oceanic ridge system. The 

nature of the processes occurring at the interface between the 

magma chamber and the overlying region of seawater circulation 

are presently poorly known. but are of particular importance to 

understanding the magmatic and hydrothermal systems. The 

knowledge gained concerning the spatial and temporal supply of 

magma to the crust and the geometry and structure of the 

hydrothermal plumbing system will help constrain these models of 

the magmatic system. Hydrothermal systems have the potential to 

generate ore deposits. support diverse biologic communities and 

affect global ocean chemistry. Since some type of magmatic heat 

source is the driving mechanism for hydrothermal systems. our 

increased understanding of this magmatic system will help answer 

critical problems in these other areas. Intense monitoring of 

subaerial volcanos over the past 2 to 3 decades has provided a 

clear understanding of these volcanic processes at a few places 

on land. The technology now exists to apply similar monitoring 

and mapping techniques to the oceanic ridge system and achieve 

an understanding of the fundamental magmatic and thermal 

processes occurring at the largest volcanic and hydrothermal 

system on the planet. 

29

GROUP 3: 

RIDGE CREST SEGMENTATION, TECTONIC CYCLES 

AND LITHOSPHERE EVOLUTION 

Members: 

Rodey Batiza, Co-Chairman 

Jeff Fox, Co-Chairman 

Jean Francheteau, William Haxby, Jeffrey Karson, 

Clive Lister, Peter Lonsdale, Kenneth MacDonald, 

Bruce Malfait. John Mutter, Ned Ostenso, 

Marc Parmentier, Jason Phipps Morgan, Hans Schouten, 

Roger Searle, Jean Sempere, Fred Spiess, Robert Tyce 

Introduction 

The ocean lithosphere, which covers about 60% of our planet, 

is created mostly at mid-ocean ridges and associated spreading 

centers. Knowing the structure and composition of this 

lithosphere is fundamental to a full understanding of the ocean 

basins, and ultimately to our understanding of planetary geology 

as a whole. The oceanic lithosphere is the solid flour of the 

ocean basins; it defines their shapes, and thus provides a major 

control on the distribution of seafloor sediments, ocean 

currents, and biological organisms and communities. Processes 

operating at the ridge axis emplace much of the mineral wealth 

of the world's oceans, and provide a major source and sink of 

dissolved elements in the oceans. The mid-ocean ridges comprise 

a major proportion of the active plate boundaries of the world, 

so understanding the dynamic processes of the ridges is a vital 

contribution to understanding global geology. And ultimately, 

the lithosphere that was created at the ridge axis interacts 

with and may even become accreted to the continents at 

subduction zones and volcanic areas. 

Over the past ten to fifteen years, many detailed, localized 

studies have been made at various parts of the mid-ocean ridge 

axis, using a variety of steadily improving technologies. These 

studies have shown that the ridge is far from uniform, and often 

varies surprisingly rapidly in both space and time and displays 

a distinct segmentation. We have begun to realize that a full 

understanding of the ridge, and of the underlying mantle 

processes that give rise to it. will depend on extending our 

studies from very local areas to fully regional and even global 

scales, while continuing to examine critical processes in great 

detail locally. In parallel with the development of this new 

awareness of the nature of the scientific problem, we have seen 

the development of wide-swath seafloor imaging devices that can 

be routinely deployed to survey whole regions of the seafloor 

quite rapidly. With the advent of these advances in scientific 

awareness and technology, it is therefore very timely to make a 

renewed, concerted, and vigorous thrust towards understanding 

the lithosphere dynamics of mid-ocean ridges. 

30

Consequently, the sin;J1e most important objective within 

this theme is to understan the processes that control the 

segmentation and episodicity of lithosphere accretion. Within 

our overall objective we recognize three major sets of problems: 

1. the nature, generation and evolution of ridge 

segmentation; 

2. the determination and explanation of the physical 

processes that operate along and between individual ridge 

segments; and, 

3. the early thermo-mechanical evolution of the oceanic 

lithosphere. 

1. The Nature, Generation and Evolution of Ridge Segmentation. 

Recently there has been a watershed of new ideas 

concerning the processes which control the accretion of oceanic 

crust and lithosphere at mid-ocean ridges. One important 

insight is that along-strike and temporal variations in tectonic 

and magmatic activity are at least as important as the 

well-documented variations in structure perpendicular to strike 

(i.e.. aging and deepening of the lithosphere). The rise axis 

undulates up and down hundreds of meters along strike, the deep 

regions of the rise occurring at transform faults and other 

ridge axis discontinuities such as the recently discovered 

overlapping spreading centers and "zero-offset" transform 

faults. Those discontinuities define a tectonic and volcanic 

segmentation of the ridge axis on the order of tens to several 

hundred kilometers which appears to be a global phenomenon. 

Segmentation defines a three-dimensional rather than 

two-dimensional process of volcanism, tectonism, and crustal 

accretion, systematically spaced along the present plate 

boundary. As this process has been discovered only recently, 

there are a number of outstanding questions. 

For example, what are the causes of ridge crest segmentation 

and how do the segments evolve in time and space? Is segmentation 

related to melting anomalies in the upper mantle which 

deliver basaltic magma to the ridge? Do the mid-sections of the 

segments overlie zones of high melt flux, while the ends of the 

segments represent null points of magma replenishment? What is 

the relationship between the axial magma chamber and 

segmentation? Do thermoelastic stresses in the lithosphere also 

contribute to segmentation of the ridge due to lateral thermal 

contraction of the plate as it cools? Are accretionary 

processes at spreading segments which terminate against major 

transform faults conditioned by these boundaries and thus more 

stable? Are other kinds of discontinuities the consequence of 

waxing and waning phases of melt generation? Do these phases 

migrate laterally? How stable are the segments with small 

offsets and does their persistence and/or temporal variability 

relate to upper mantle processes? What is the response of the 

architecture and segmentation of the ridge axis to changes in 

plate motion? 

31

2. Characterization of Individual Segments and their 

Boundaries. Once the characteristics of segmentation are known 

in detail, it will be of great interest to determine the spatial 

and temporal stability of the segment. This includes possible 

cyclic or episodic interplay among volcanic and tectonic 

processes within a single segment as well as the dynamic 

interaction between individual segments focused at their 

boundaries. The nature of the lithosphere created by individual 

segments may vary along the strike of the segment and with time 

in a periodic or episodic manner as suggested by the diverse 

morphologies and petrologic characteristics of individual 

segments. Individual processes that must be understood are the 

nature of faulting and fissuring, the depth of the brittle to 

ductile transition, and the thermo-mechanical and stress 

characteristics of young lithosphere. In addition, it is 

necessary to better understand processes of magma generation, 

ascent, storage, eruption and intrusion and how these interact 

with tectonic processes within a segment. Are the deeper 

processes that control magma generation and spreading coherent 

over distances larger than a single segment- or do segments 

behave independently? If so, is this primarily due to the 

interaction of the upper mantle with the young and evolving 

lithosphere, or the termporal and spatial variability of upper 

mantle processes? 

3. Thermal and Mechanical Processes Affecting the 

Evolution of Oceanic Lithosphere. The oceanic lithosphere is 

defined as the cool, mechanically strong boundary layer that 

overlies weaker ductile mantle. A thorough understanding of the 

spreading process requires knowledge of the mechanisms affecting 

the creation and subsequent evolution of the lithosphere. It is 

first necessary to understand the cooling processes, including 

hydrothermal convection and thermal conduction, that cause the 

lithosphere to form and thicken. Simultaneously, distributed 

horizontal extension or stretching will thin the lithosphere. 

These processes will be interrelated: for example, the 

stretching process will create faults and fissures that will 

allow seawater to penetrate the crust and mantle. The 

importance of these processes emphasizes the need to understand 

the temporal and spatial distribution, both along and across 

strike, of faulting and extensional deformation. 

Deformation of the lithosphere will be controlled by the 

mechanical properties of the rock comprising it and the forces 

or stresses acting upon it. Stresses within the lithosphere 

will result from differential contraction due to cooling, normal 

and shear stresses exerted at the base of the lithosphere by 

mantle flow and melt segregation processes, forces due to ridge 

axis topography, and forces transmitted to the ridge axis 

through the lithospheric stress guide. One important objective 

of mid-ocean ridge studies is to understand the relative 

importance of these various forces in controlling deformation at 

the ridge axis. 

32

Thermal stresses have been suggested as a mechanism controlling 

ridge segmentation and may also generate permeability that 

promotes hydrothermal cooling. Shear stresses at the base of 

the lithosphere due to mantle flow may control the distribution 

of horizontal extension or necking and associated differential 

vertical movements of the seafloor. A better understanding of 

the temporal and spatial distribution of extension will help 

clarify the relative roles of tectonic and magmatic processes in 

producing pervasive ridge-parallel linear abyssal hill topography, 

and will provide a clearer idea of how episodic movement 

at a ridge axis is converted to continuous motion of the plate. 

Horizontal forces arising from ridge axis topography have been 

suggested as a mechanism controlling ridge segment stability and 

propagation. Temporal evolution of ridge segment geometries is 

also thought to be influenced by changes in plate boundary 

forces transmitted to the ridge axis through the lithosphere. 

Stresses generated during spreading on one segment and 

transmitted through the lithosphere may control the next 

spreading episode on an adjacent ridge segment. 

Data Collection 

Because of the wide variety of time and space scales over 

which the processes of interest operate, we see a need to carry 

out field studies at similarly appropriate scales. These will 

range from global scale, utilizing for example satellite data 

and worldwide syntheses of surface data, through the vitally 

important. newly recognized dimension of regional scales, to the 

more traditional scale of localized, highly detailed studies. 

It will. be important at all scales to insure that observations 

and samples are carried out in a sufficiently regular and 

closely-spaced fashion, and in particular that the sampling of 

periodic phenomena is complete and un-aliased. 

1. Global-scale Studies. There is a need for a global 

perspective on the lithosphere generation process, of the sort 

that can be acquired only by a complete inventory and systematic 

description of all active sites of ocean-crust accretion. 

Satellite observations can provide a data set with uniform 

coverage and accuracy, but at present of only low resolution. 

New shipboard observations are required to provide sufficient 

resolution for definition of the significant classes of 

accreting plate boundaries, fine-scale delineation of the plan 

pattern of their axes, and description of along-strike variations 

of such basic properties as depth, sediment thickness, and 

amount of hydrothermal discharge. Accordingly, we believe it is 

essential to accurately map the location of spreading axes on a 

global basis. We propose that a feasible program would consist 

of wide swath sonar and bathymetric imaging on a single 

longitudinal pass plus a seismic profile where appropriate, 

combined with regularly spaced geological sampling, photography 

and CTD measurements. 

33

2. Regional Surveys. Regional surveys should encompass 

several spreading segments and extend to at least 5 m. y. old 

crust. To characterize the physiography, full multibeam 

bathymetry and side-scan sonar coverage should be obtained, in 

conjunction with the acquisition of ship and airborne gravity 

and magnetic measurements (with a nominal spacing of not more 

than 5 km). These surveys should be followed or accompanied by 

the acquisition of marine seismic data, including multichannel 

seismic imaging along the ridge crest and along critical 

isochrons on the ridge flanks out to the 5 m. y. isochrons. 

Flow-line crossings should be conducted along several transects 

within each segment - adjacent to segment boundaries, across the 

center of a segment, and in I laces dominated by tectonism or 

volcanism. A suite of seismic refraction experiments should be 

conducted at several locations to define the deep structure of 

the ridge axis and of young oceanic lithosphere. These should 

be done at critical isochrons surveyed by reflection profiling. 

Microearthquake studies using arrays of on-bottom instruments 

should be made to describe the tectonics within the area of the 

seismic refraction experiments. The initial morphologic surveys 

will be used to guide systematic basement sampling on and 

off-axis, in conjunction with near-bottom photography, and other 

relevant in situ geophysical measurements. 

3. Detailed Local Studies. Detailed studies will be 

necessary at both the centers and the edges of spreading segments 

and may be separated into two groups: (1) studies that 

define the present architecture of the lithosphere and 

(2) studies that measure ongoing processes. 

The first group of studies requires geological mapping of 

the surface of the seafloor as well as investigations of the 

crust and mantle at depth. The geological mapping must be 

constrained by high resolution bathymetric and side scan sonar 

mapping base and include the areal extent of outcropping 

basement and surficial units, the locations and orientations of 

faults, fissures, ductile deformation features and any movement 

indicators on them, and active hydrothermal systems. Direct 

outcrop sampling is necessary for geochemical studies and 

oriented samples are essential for structural and magnetic 

studies. Detailed sampling and mapping of fault scarps could 

yield data on the volcanic and possibly plutonic stratigraphy of 

the crust. the crack structure and history of subsurface rocks, 

the alteration history of the crust, and the deep structure of 

hydrothermal systems. Developing a three-dimensional picture of 

the lithosphere is an integral part of these studies and it is 

likely that the most important data will come from direct 

sampling by deep drilling (kilometers depth) and shallower holes 

Ieven a few meters). Downhole logging and other experiments are 

needed to define the physical properties of rocks at depth. 

Correlations between physical properties and geophysical interfaces 

mapped from the regional surveys could produce a quantum 

leap in interpreting seismic structure. Gravity, magnetic and 

34

electromagnetic fields must be measured directly on the seafloor 

or in boreholes. 

The second class of data that must be collected is related 

to defining dynamic processes that can constrain modes of 

crustal deformation. These studies are more difficult to do 

because they require measurements over relatively long periods 

of time (years) mostly with devices that have not been previously 

used. These include measurements of strain and elevation 

changes in actively deforming areas with geodetic surveys and 

possibly strain meters and tilt meters, as well as long-term 

electromagnetic field measurements. Detailed locations and 

focal mechanisms for microearthquakes are needed to define fault 

geometry and kinematics in the brittle crust. These would be 

especially useful in conjunction with surface mapping and 

borehole monitoring. 

Laboratory, Theoretical, and Numerical Developments 

Important laboratory measurements that influence our understanding 

of mid-ocean ridge processes include both mechanical 

and electrical properties of rocks. We need a better 

understanding of the ductile strength or viscosity of crust and 

mantle rock particularly as a function of temperature, composition 

and degree of partial melting. Knowing the frictional 

resistance to sliding on existing faults and the critical stress 

intensity factor required to create new faults is essential for 

determining the brittle strength of the lithosphere. Elastic 

wave velocities, especially their dependence on temperature, 

degree of partial melting, and composition are important to 

interpreting the seismic velocity structure of ridge segments. 

Electrical properties, particularly the conductivity, will be 

needed to interpret electromagnetic observations. Laboratory 

studies will also be required for chemical and isotopic analysis 

and to develop new dating techniques, particularly ones which 

allow us to establish ages in the range of 0 to 10 years. 

Theoretical modelling studies and physical experiments allow 

us to examine simple physical systems or processes that may be 

important at ridge segments. Physical experiments include wax 

models, convection experiments, and porous flow/compaction 

experiments. Theoretical studies include convective and necking 

instability, crack propagation and fault growth. These ongoing 

types of studies will continue to provide new physical insight 

and understanding. Large-scale numerical experiments made 

possible by new developments in computer technology will allow 

us to theoretically model the interaction of individual 

processes. 

Seismic tomographic methodologies should be advanced to 

include amplitude effects. Multichannel seismic imaging of the 

subsurface requires major developments to account for scattering 

35

and rough topography. We further require the development of 

forward numerical modelling and inverse methods appropriate when 

the heterogeneities are on the order of seismic wavelengths of 

200 to 500 m, and that also account for the effects of surface 

and volume scattering, attenuation, and anisotropy at these 

scales. The integrated analysis of swath mapping, acoustic 

imaging, multichannel profiling, and aero-gravity and magnetics 

data will require the development of an interactive computer 

imaging and data analysis capacity. 

Marine Data Acquisition 

Our ability to initiate the measurement and sampling 

programs discussed above rests on the fact that new techniques, 

some brought into play only recently, are available to gather 

many of the types of data we need. These include multibeam echo 

sounding systems, acoustic and optical imaging techniques, ocean 

bottom seismographs, magnetometers, shipboard and airborne 

gravimeters and methods for controlled sampling of loose rock. 

The rates of coverage and the resolution of existing versions of 

these systems, while adequate for some purposes, leave much room 

for improvements and specific ideas exist as to how such 

improvements could be made. Beyond these existing instrument 

types there are new concepts emerging that could contribute 

substantially to our understanding of the generation and 

evolution of the lithosphere, and that could be available within 

the next few years. These include devices for obtaining 

oriented, fresh rock samples from selected outcrops; systems for 

measuring strain, tilt and elevation changes; and high 

resolution on-bottom gravimeters. 

Two challenging areas for the future lie in implementing an 

ability to locate and react rapidly to the occurrence of 

transient events {volcanic eruptions, earthquakes}; and in 

developing means for using deep drill holes after departure of 

the drilling ship. Under-way monitoring of hydrothermal venting 

would allow us to detect hydrothermal activity while conducting 

large-scale surveys. 

In addition to the measurement instruments required for 

particular types of data acquisition, there are several recent 

supporting technological advances that will enhance our ability 

to carry out sea foor tasks effectively. Fiber optic cables, 

remote operated cable connected and autonomous vehicles, 

improved computing and recording capacity for shipboard and sea 

floor data handling, and continuous high-accuracy satellite 

navigation will all help open new opportunities. 

Finally, it is clear that this program embodies significant 

ship requirements supporting a wide range of capability. For 

global and regional surveys we will need the use of a ship with 

well integrated survey capabilities for extensive periods. This 

36

capability should include at least swath bathymetry, acoustic 

imagery, and multichannel seismics. Ship support for handling 

seafloor work vehicles, remotely controlled sampling systems, 

bottom landers, and autonomous vehicles will also be required, 

and might well involve a second ship. 

Strategy 

Simultaneous efforts are deemed important on all scales. 

Development of an integrated survey capability should begin 

immediately followed by initiation of a global survey effort 

building upon existing data sets. This will be important in 

order to identify secondary regional sites. Primary regional 

site surveys should be identified and undertaken simultaneously, 

based on expansion of existing regional coverage in selected 

sites. Within these primary regional sites, initial detailed 

sites should be selected for development and deployment of 

needed capabilities as soon as they become available. Secondary 

regional and detailed sites should be identified from global and 

regional survey data. 

Planning these extensive survey efforts will require 

compilation and analysis of existing data sets. International 

and institutional collaboration should be fostered at all levels 

to insure that all possible data can be included. Plans for 

integration of new and existing data sets will also be required, 

along with consideration of standard format for data collection 

and exchange. 

Coordination 

Spatial and temporal measurements of ridge crest processes 

can contribute to our understanding of evolution of the lithosphere. 

Coordination of programs of data acquisition will be 

essential to maximizing the integration of data sets as well as 

overall coverage. Survey planning should include consideration 

of geological. geophysical, biological, and physical oceanographic 

requirements so that studies at selected sites will 

address the broadest range of objectives. 

Global and regional surveys should include techniques for 

detecting hydrothermal plumes, and for water and seafloor 

sampling capabilities so that survey work can be interrupted for 

more detailed study in the event of a major discovery. Detailed 

surveys will involve surface and bottom stations as well as 

underway survey work with various simultaneous efforts being not 

only possible but desirable. Here simultaneous measurements of 

seismic, stress-strain, and vent activity can teach us much 

about ridge crest processes. 

37

GROUP 4: 

SUBSEAFLOOR HYDROTHERMAL PROCESSES 

Members: 

Johnson Cann. Co-Chairman 

John Edmond. Co-Chairman 

Alan Chave. John Delaney. David Janecky. 

Marc Langseth. Robert Lowell. Russell McDuff. 

Peter Rona. William Seyfried. Wayne Shanks. 

Norman Sleep. Geoffrey Thompson. Richard von Herzen 

Motivation and Goals 

Seafloor hydrothermal systems are a central component of a 

dynamic process that transfers energy and mass through the crust 

of the earth. Chemical and thermal exchanges between the ocean 

and the oceanic crust in hydrothermal systems play a major role 

in the cooling of the earth. the genesis of many types of ore 

deposits. control of geochemical mass balances that influence 

the composition of the oceans. and the ecology of associated 

chemosynthetic animal communities. An order of magnitude 

estimate of the flow rate of seawater shows that the entire 

ocean is cycled through the oceanic crust every few million 

years. equivalent to a flow rate of several million gallons per 

second. The thermal power output of this system is about 10 

million megawatts. Previous and current research on seafloor 

hydrothermal systems has begun to address the complexity of the 

physical. chemical. and biological components involved in the 

interactions between circulating seawater and the lithosphere. 

New approaches are required to understand the physics and 

chemistry of t.he individual processes which produce t.emporal and 

spatial variability of hydrothermal circulation. and the 

geological products of rock-water interactions. 

Rocks and sediments which make up the seafloor are permeable. 

allowing wat.er to penetrate t.hrough t.he seafloor and into 

the oceanic lithosphere. The downwelling seawater is heated 

when it. flows near the magmat.ic sources which drive hydrothermal 

circulation. The most prominent locus of magmatic activity is 

the ridge system which extends through all the ocean basins. In 

addition. magmatic activity is associated with volcanic centers. 

Research into hydrothermal flow complements the investigations 

of magmatic systems proposed by Working Groups 1 and 2 and will 

reveal the intertwined dynamics of the magma-hydrothermal system. 

In fact. it is likely that hydrothermal activity strongly 

affects the depth and geometry of crustal magma chambers on 

mid-ocean ridges. A primary objective in the future study of 

the global mid-ocean ridge system is to understand the physical. 

chemical. and biological processes involved in the interactions 

between circulating seawater and the lithosphere. 

38

In order to understand subseafloor hydrothermal systems, 

energy transfer processes between the oceanic mantle and the 

seafloor must be defined. Because the individual components of 

hydrothermal systems are intimately connected to both 

deep-seated and near-surface processes, the critical problems 

cannot be easily separated or prioritized. Rather, a number of 

first order problems must be identified and addressed in a 

cohesive manner. The problems can be viewed as fundamental and 

inter-related, and work proposed below reflects our considerable 

ignorance concerning details of how hydrothermal systems 

operate. 

We have identified four primary areas about which future 

research might center. 

1. . Heat Transfer into Hydrothermal Systems. Does heat 

flow by conduction through the roof of a crustal magma chamber, 

or by propagation of cracks into hot rock? How closely coupled 

is magmatic and hydrothermal activity? How does the 

hydrothermal system respond to lava eruption, dike injection, or 

magma chamber replenishment events? 

2. The Hydrothermal Plumbing System. To what depth does 

hydrothermal circulation extend? What is the nature of the 

sub-surface permeability structure, and the scale and distribution 

of fracture networks? How is the plumbing system affected 

by chemical reactions and biological processes? 

3. Temporal Variability. What is the correlation between 

temporal variations in temperature, flow rate, and chemical 

composition of venting fluids? Does the variability reflect 

changes in the permeability structure and if so are the changes 

associated with chemical, biological or tectonic processes? 

Does the variability reflect changes in heat input? 

4. Spatial Variability. How do differences in mass flow 

rate, temperature, and chemical composition relate to differences 

in the magmatic and tectonic environment? To what extent 

might these differences reflect the transiency of the systems? 

Beneath these four first order problems lie a number of 

closely connected, secondary questions. Subsidiary in this 

context does not refer to relative geological and/or economic 

importance, but encompasses a relationship to the more 

fundamental questions listed above. These include: 

o What are the relationships between the components of 

mass flow in hydrothermal systems, including possible direct 

magmatic contributions to global geochemical cycles? 

o What is the nature of the chemical reactions between 

hydrothermal fluids and sediments? 

39

o What are the physical differences and relationships 

between high and low temperature hydrothermal systems? Onand 

off-axis systems? Bare and sedimented ridge systems? 

o What are the physical and chemical controls on the 

distribution and characteristics of sulfide mineral deposits? 

o What is the biological contribution to surface and 

subsurface chemical reactions? 

o What determines whether there is diffuse or organized 

(i.e.• black smoker) discharge? 

Background 

Background information on seafloor hydrothermal systems 

pertinent to the processes program is contained in the position 

papers by Cann and Edmond. and others. in Appendix II. The 

most important points are highlighted here for reference. but 

the pertinent papers should be consulted for details. 

1. Hydrothermal circulation is pervasive both on and off 

of mid-ocean ridge systems throughout the world oceans. as 

revealed by heat flow and temperature data. 

2. Alteration products from hydrothermal activity are 

widespread in seafloor rocks and their ophiolite analogs. 

3. luid chemistry for high temperature vents (up to 

400 0 C) has given information about the results of the 

alteration process anq the geometry of the systems. 

4. Laboratory experiments and theoretical modeling have 

constrained mechanisms of the alteration process. 

Approaches 

Several kinds of field data need to be obtained to elucidate 

the most important chemical and physical processes associated 

with hydrothermal systems. 

1. Detailed geological maps based on 3-D imaging 

techniques must be compiled with a spatial resolution of less 

than 1 m. and sampling of individual vent systems relating local 

geology to biological assemblages needs to be conducted with a 

similar accuracy. These must be coupled with precision dating 

of lava flows. hydrothermal products. vent fluids. biological 

communities. and other features. Analyses of ancient sediments 

and altered igneous rocks for paleochemical tracers to define 

the nature of hydrothermal activity through time should also be 

obtained. The results of related geological investigations of 

40

fossil hydrothermal systems in ophiolites and in other terrains 

must be integrated with seafloor studies. 

2. Geophysical data related to the subseafloor geometry 

and structure of porosity and permeability are essential. These 

data include seismic imaging, controlled source electromagnetic 

sounding, static magnetic properties of rocks. and density 

contrasts using seafloor and borehole gravimeters, all with 

instruments developed for high resolution. 

3. Heat flow, pore pressure, thermo-physical property. and 

chemical concentration gradient data in sediments associated 

with sediment-hosted hydrothermal systems must be collected. 

4. Measurements of vent flow parameters covering the full 

range from diffusive to jet-like flow are needed. The required 

observations include direct. non-intrusive measurements of fluid 

flow rates and fluxes, accurate and representative temperature 

data, and subseafloor pore lJressure and chemical concentration 

gradient data. Determinations of mixing rates at the sea floor 

and in sub-bottom regions, compositions of the different parts. 

and fluxes of chemical species are also important. Measurements 

of the total heat output of the entire exhalative zone of axial 

hydrothermal systems over time should be combined with 

observations of the acoustic and seismic signatures of active 

vents. 

5. The chemical composition of reactants and products. 

such as fluid components. hydrothermal precipitates, and altered 

rocks need to be measured. Inorganic. organic and isotopic 

analyses of these components must be integrated with these data. 

6. Measurements should be collected below the seafloor, 

including within ODP drill holes, of in situ physical parameters 

and chemical properties. These include standard and innovative 

wireline logs, geophysical experiments and geochemical 

measurements of many different kinds. Geophysical experiments 

may be required between boreholes. New, high temperature 

instruments are clearly necessary. 

7. These types of data must be combined with geophysical 

and petrological measurements of magma chamber properties, as 

well as geochemical and physical oceanographic measurements of 

surface plumes, to provide a coherent. large-scale picture of 

the entire seafloor hydrothermal system. 

In conjunction with field programs, laboratory. theoretical. 

and numerical developments must focus on specific geologic, 

geochemical and geophysical processes to constrain subseafloor 

water-rock interactions. 

41

o Laboratory experiments must test and generate thermodynamic 

and kinetic data for mineral reactions at elevated 

temperatures, pressures, and for varying salinity (0.5 to 2 

times that of seawater). Near-supercritical conditions should 

be emphasized. These experiments must address such issues as 

aqueous speciation (inorganic and organic), solid-solution 

relations for key alteration phases such as feldspar, chlorite, 

and epidote, and fluid-mineral trace element distributions. 

Analytical techniques must be developed to obtain more accurate 

measurements of trace element and isotopic systematics of 

hydrothermal alteration products. Ion and proton microprobe 

techniques are expected to be especially useful. 

o Numerical techniques and supporting data are required 

to permit the modeling in three dimensions of fluid flow in 

inhomogeneous ocean crustal rocks. Explicit account must be 

made of the temporal and spatial distributions of primary and 

secondary permeability (on macro to micro scales) and 

pressure-volume-temperature composition properties of fluids. 

The effect of different and variable heat transfer mechanisms 

must also be included. 

o Physical and chemical models of subseafloor hydrothermal 

processes must be coupled to include the interconnectedness 

of chemical and physical controls on fluid 

circulation. 

o Techniques must be developed to permit dating of 

fluids, igneous materials, and hydrothermal products. These 

techniques must make use of absolute and relative dating schemes 

and permit timing of events on scales of 1 to 1.000,000 years. 

Many of the measurement capabilities required to characterize 

seafloor hydrothermal systems need to be improved and 

refined. 

o Precise and routine positioning on the seafloor is 

essential for establishing spatial and temporal relationships. 

o Instruments for geophysical measurements and experiments, 

including seismic, controlled source electromagnetic, 

and passive acoustic, need to be optimized for characterizing 

the relevant spatial scales. The high data rates involved 

require rapid incorporation of evolving technologies for 

instrument control and data storage. Accurate and innovative 

permeability measurements in crustal rocks and sediments are 

also essential. Remotely operated vehicles (ROV's) should 

be developed into powerful tools for mapping, sampling, and 

experimental servicing. 

o Improved water sampling equipment is needed for use at 

high temperature vents and in boreholes. These need to be 

42

instrumented to record the environmental conditions during 

sampling. Contamination of samples with seawater, even from the 

small sampler dead volumes, presently precludes a number of key 

measurements. Chemical sensors and procedures for making 

in situ measurements need to be developed, both for documenting 

temporal variability of active vents and to provide data free of 

artifacts introduced by continued reaction within discrete 

samplers. 

Strategy 

We advocate a balanced, three-pronged, simultaneous approach 

in the fi rst stages: 

1. Exploration, a continued search for new and varied 

hydrothermal systems in a wide suite of geological environments, 

including island arc and back-arc terrains. 

2. Development of new sampling tools, chemical sensors and 

laboratory measurement techniques needed for the investigation 

of diverse physical and chemical processes, together with 

improvements in forward modeling and inversion techniques. New 

tool development should include both deep and shallow drilling 

capabilities for a high temperature environment. 

3. Initial deployment of instrumentation to make temporal 

measurements at specific vents and characterize the principal 

processes. These are essential as a guide in organizing future 

experiments, and devising new sensor technologies and 

approaches. 

We are in the initial stages of exploration for active 

hydrothermal systems, and already have discovered several major 

seafloor sulfide deposits. We predict that additional exploration 

will lead to near-term discovery of seafloor hydrothermal 

systems of unprecedented size and intensity, which would not 

only produce mineral deposits of potentially economic proportions, 

but would also yield major perturbations of the global 

geochemical cycle. Other discoveries are likely in back-arc, 

island arc, and seamount areas, where the systems will have very 

different characters from those of the open oceans. Many major 

fossil hydrothermal deposits are in sediment-dominated systems, 

and exploration in such areas may be especially interesting. 

In parallel with the program of exploration for new systems, 

testing of new instruments (chemical and physical sensors) and 

of instrumented packages for down-hole and/or long-term deployment 

must begin using submersibles, drillship time, ROVs, and 

limited-duration bottom moorings. ROVs (remotely operated 

vehicles) represent a particularly exciting prospect for undersea 

investigation of ridge crest hydrothermal systems. In the 

43

near future, it may be possible to design free swimming vehicles 

to conduct complex sampling and monitoring operations of hot 

spring emanations. Eventually, advanced robotics, artificial 

intelligence, and utilization of natural heat for power might 

lead to independent and long-term ocean bottom instrument 

packages. 

A later phase should include detailed studies of specific 

sites. We would anticipate that three sites should be chosen 

for initial study, identified as different based on our present 

knowledge of hydrothermal systems. We recommend that one of the 

sites should be a classic black-smoker, bare-rock site, with 

relatively small sulfide deposits, a second location should be 

selected on a sedimented ridge crest with more massive 

mineralization, and a third should include a low temperature 

hydrothermal system, possibly located off of the ridge axis. 

At these locations, intensive studies would include detailed 

geological mapping, determination of the temporal variability of 

the flow, testing of new instrumental configurations, and 

limited drilling. The contrasts between the sites will allow 

characterization of the fundamental differences between small 

(young?) and large (old?) bare rock systems, and between those 

and the sediment-hosted systems. 

Other kinds of targets can be envisaged, such as vents with 

salinity significantly above or below that of seawater, with 

unusually high or low temperature venting, back-arc or island 

arc terrains, unusually shallow water and deep water sites, and 

regions associated with seamount volcanos. 

As the exploration and initial seafloor experimentation 

phases, and subsequent long-term studies, develop and become 

more mature after the first few years, increased knowledge 

should enable the selection of one or more sites which have the 

most promise of augmenting our understanding of the sub-seafloor 

systems. At these sites, measurement and sampling should be 

done with the full array of techniques which are then available. 

Our goal is no less than the comprehensive description of how a 

sub-seafloor hydrothermal system is working, enabling us to 

estimate those characteristics which are most critical for 

determining the variability and similarity among all such 

systems. Only then can we make confident predictions of other 

systems not yet studied in detail or only partially 

characterized, and the extent to which they contribute to the 

overall heat and mass transfers on the entire mid-ocean ridge. 

44

GROUP 5: 

BIOLOGY OF HYDROTHERMAL SYSTEMS 

Members: 

James Childress, Co-Chairman 

George Somero, Co-Chairman 

John Baross, Daniel Desbruyeres, Fredrick Grassle, 

Eric Hartwig, Robert Hessler, Holger Jannasch, 

Richard Lutz, Michael Reeve, Gary Taghon, 

Philip Taylor 

Introduction 

Study of deep-sea hydrothermal vents has revealed several 

attributes that are extraordinary from a biological perspective. 

First, the energy source is geothermal rather than solar, with 

chemoautotrophic bacteria at the base of the food chain. 

Second, many of the animals have incorporated these bacteria as 

symbionts, resulting in unusual adaptations that are proving to 

be more widespread than we orginally imagined. Some of these 

adaptions enlarge our perceptions of biological possibilities on 

this planet. Third, some bacteria survive temperatures well 

above those we thought life could tolerate. This phenomenon is 

of fundamental importance to our understanding of the basic 

structure of living matter. Fourth, the great spatial and 

temporal variability in environmental parameters at vents stands 

in marked contrast to that usually encountered in the deep sea. 

These conditions alter the physiological. behavioral, reproductive, 

and dispersal requirements placed on the organisms. 

Finally, the vent fauna is largely different from the 

surrounding deep-sea fauna, often at high taxonomic levels. 

This dichotomy is puzzling, and its explanation will involve 

important aspects of ecological adaptation, population genetics 

and evolution. 

Given the strong dependence of biology on geochemical 

processes, vents provide a valuable "natural laboratory" to 

address, in detail, questions spanning levels of biological 

organization from individual cells to entire ecosystems. Our 

central objective is to determine the interactions of organisms 

with geological. chemical, and flow environments at mid-ocean 

ridges on time scales ranging from seconds to eras and spatial 

scales ranging from millimeters to global. The major components 

are elaborated in the following sections. 

45

Microbiology 

What is the qualitative and quantitative role of bacterial 

chemosynthesis for the biology of vent communities, and how do 

these bacteria affect the geochemistry of these systems? 

Chemosynthetic bacteria are the primary producers that 

support the complex animal communities found in all vent 

environments. Some of the associations between bacteria and 

animals have been identified, such as endosymbioses, while more 

loose associations involving meio- and macrofauna grazing are 

largely unknown. Sites of microbiological production and the 

sources of energy to sustain this activity in vent systems are 

complex and not yet adequately studied. The vent environments 

have markedly different chemical and physical characteristics: 

warm to super-heated waters, rock and smoker surfaces, 

sediments, water column including plumes, animals, and 

subcrustal areas. 

Microbiology must be considered within an interdisciplinary 

context that would (1) measure the rates of microbial growth and 

chemosynthetic activity associated with all vent environments 

and identify the complex interactions between microorganisms and 

the physical, chemical and geological properties in these 

environments, (2) identify the spatial and temporal variations 

in physiological characteristics and phylogenetic composition of 

unique vent microbial communities, (3) study the physiology of 

the diverse groups of aerobic and anaerobic bacterial isolates 

with emphasis on their catalytic roles in biogeochemical 

processes at various vent sites and assess the contribution of 

unusual thermophilic bacterial communities on these transformations, 

and (ll) develop the instrumentation for measurement of 

microbial activity in situ and apply molecular biological 

procedures to vent microbial communities. 

Physiology and Biochemistry of Vent Animals 

How do vent animals exploit chemosynthetic processes? 

Most of the large and dominant animals of the vent communities 

have incorporated into specialized tissues chemosynthetic 

bacteria (symbionts) which, like certain of the free-living 

bacteria discussed above, exploit the energy of reduced compounds 

which are contained in the vent water. In these highly 

developed symbioses, the host animal transports to the bacterial 

symbionts chemosynthetic substrates extracted from the vent 

waters; t.he bacteria ret.urn food mat.erials and building blocks 

t.o t.heir host. Underst.anding the physiology and biochemistry of 

t.hese symbioses is essential for interpreting the ecological and 

evolutionary patterns of marine communities and establishing 

linkages between the biology and the geochemistry of the vents. 

116

There are several key questions about these symbioses. One 

concerns the full spectrum of energy sources that these 

symbioses can exploit. Hydrogen sulfide is clearly a major 

energy source for some of the symbioses, but there is a strong 

possibililty that other reduced substances, e.g., methane 

(natural gas). hydrogen, manganese, iron, and ammonia, may be 

exploited as well. A second major question is how these energy 

sources are transported from the ambient water to the symbionts 

by the host. 

To investigate the exploitation of these energy resources, 

detailed studies of the chemistry of the vent waters bathing the 

animals must be paired with investigations of the physiological 

and biochemical properties of the intact symbioses as well as 

those of the separate bacterial and animal components. 

The life cycles of symbioses must be studied to learn how 

the animal selectively acquires the correct type of symbiont. 

and how the animal then regulates the culturing of the symbionts 

for its own benefit. How are bacterial numbers regulated? How 

does the animal control the release of nutrients from its 

symbionts? 

To achieve these goals, methodologies must be developed: 

(1) to allow maintenance and study of the organisms under 

conditions of temperature, pressure, and water chemistry that 

stimulate in situ conditions; (2) to permit the isolation, 

culturing,-and characterization of the sybmionts; and (3) to 

enable the determination of the nutrient exchanges between 

symbionts and hosts. These experimental questions must be 

applied to additional symbioses as they are discovered at ridge 

crests and at other sites where chemosynthetic food chains may 

exist. Likewise, these methods will allow precise studies of 

the impact of temporal and spatial variations in water chemistry 

on the functioning of the symbioses. 

How do animals survive in the toxic vent waters? 

In addition to serving as energy sources for chemosynthesis, 

certain of the reduced substances in the vent waters, notably 

hydrogen sulfide, are highly toxic. Thus, exploitation of these 

resources by symbiont-containing animals necessitates evolution 

of mechanisms for controlling their toxicity. Likewise, 

symbiont-free animals that take advantage of the vent milieu 

have solved the problems posed by toxic substances in the 

water. The ability to control the toxicity of sulfide may be 

the critical factor determining whether or not an animal can 

survive in and exploit the vent environment. The elucidation of 

the mechanisms used to detoxify sulfide and other poisonous 

substances in the vent waters will not only provide important 

i~sights into the biology of the vent organisms, but also will 

yield basic information on detoxification processes applicable 

to all animals, including humans. 

47

What are the interactions between vent animals and water 

chemistry? 

Critical to the understanding of the symbioses, indeed, to 

all facets of the vent biology program, is detailed study of the 

temporal and spatial variability in vent water chemistry. Using 

in situ analysis of water chemistry allows the description of 

the animals' chemical habitats as well as the animals' effects 

on that chemistry. A system for such analyses currently exists 

and is capable of analyzing a limited suite of substances 

(oxygen, sulfide, silicate) at time scales of minutes to hours. 

The full understanding of the interactions of water chemistry 

with organisms requires the development of in situ chemical 

analyzers capable of examining many more substances and working 

at both shorter (seconds) and longer (days and months) time 

scales. 

Population and Community Ecology 

How do vent populations and communities vary in response to 

the spatial mosaic and physical variations in the life of 

vents? Are there predictable spatial and successional species 

patterns? 

The answer to these questions requires an ability to plot 

faunal distributions throughout the duration of a vent. and to 

measure relevant physical parameters such as temperature, 

metabolic substrates or toxins, and water flux. Determination 

of the causes of these patterns will come from understanding of 

colonization processes, metabolic needs and limitations, growth, 

population dynamics, food webs, and other inter- and 

intra-specific relationships. 

The study of species interactions within a community 

involves sampling, continuous observation at single vents, and 

experimental manipulations such as chemical enrichments, 

redirection of flow, controlled anaerobic environments, and 

animal inclusions and exclusions. 

The central activity of temporal studies is repeated photographic 

surveys coupled with environmental assay and sampling of 

experimental sites. Improved techniques are necessary to 

conduct these activities. Most important is the ability to 

return to sites at regular intervals (about 1 year) to sample 

and experiment with minimal disturbance to the system. Image 

processing techniques developed for this application will 

greatly enhance photographic analysis. To maximize our 

understanding of the processes that lead to faunal change, this 

program must be joined to geological and chemical programs 

monitoring seismic events, subterranean precipitation, and 

variation in the chemistry and flux of vent waters. 

48

Dispersal of Organisms 

What are the biological and physical characteristics 

responsible for the dispersal and life histories of organisms at 

deep-sea hydrothermal vents? 

A concerted effort must be devoted to defining the range of 

reproductive strategies encountered among vent species and to 

obtaining a detailed understanding of the reproductive responses 

of vent organisms to environmental signals. Vent spacing, ridge 

segmentation, offset distances, and interposing land masses may 

provide barriers to gene exchange allowing chance events and 

local selection to influence the genetic composition of populations 

and species. The role of chance events and natural selection 

in the development of vent ecosystems will be understood 

through study of dispersal stages and genetic differentiation of 

populations. 

Vent chemistry and fluctuations in vent flow need to be 

related to life history features such as rate of growth, time to 

maturity, reproduction and mortality, and selective survival of 

post-settlement stages. The influence of hydrothermal plume 

dynamics andI or physical currents (mesoscale eddies, along-ridge 

transport, etc.) on the transport of various life history stages 

of vent organisms needs intense study, as does the distribution 

of such stages within both the water column and the benthic 

boundary layer. To address these problems it is paramount to 

know the duration of vent activity. 

Necessary sampling and analytical approaches include in situ 

chemical characterization of hydrothermal systems, measurements 

of rates of tissue accretion and skeletal deteriorationl 

dissolution, in situ organism manipulations, and efficient 

sampling of the plankton. In addition it is necessary to 

undertake physical oceanographic measurements, settlement and 

colonization substrate experiments, interpretative analyses of 

larval morphological features, studies of mitochondrial DNA, and 

gel electrophoretic studies. 

Speciation and Evolution 

What is the role of geographic isolation in the evolution of 

vent communities on ocean ridges? 

Evolution of vent communities is a reflection of long-term 

geological processes governing ridge and hydrothermal evolution. 

Linear spacing of vents and the isolation of entire ridge 

systems results in evolutionary processes on several spatial 

scales: separation of populations and species, evolution of one 

species into another, introduction of new species to the vent 

habitat. and co-evolution of the community members. 

49 .

Evolution can be examined by studies of on-going processes 

and by analysis of present patter~s in vie~ of hi~torical 

events. Extension of the populatIon genetIc studIes to 

comparisons on the species level will reveal taxonomic 

affinities. Smaller scales of evolution can be identified from 

community comparisons between separate segments of a ridge. 

Identification of major discontinuities in vent community 

composition along or among ridges should allow recognition of 

geographic centers of evolution. Fundamental geological 

differences among ridges, such as spreading rates, should be 

examined in terms of species diversity and adaptions in response 

to varying geochemical patterns. Communities in other deep-sea 

habitats dependent upon chemosynthetic energy are composed of 

different species; they may yield clues to the evolutionary 

origin of hydrothermal vent species. Analysis of fossil vent 

species in sulfides will give direct evidence of past 

evolutionary steps. Sedimented hydrothermal systems may 

preserve evidence for relationships between chemistry, bacteria, 

and animals. 

Specific data requirements include information from geology 

and geophysics on past ridge morphology and rifting history to 

identify times and methods of isolation. Parallel evolutionary 

adaptions to the vent habitat can be identified by comparisons 

of systematics and physiology. Traditional and genetic techniques 

should be employed in erection of animal phylogenies. A 

key technique to aid these studies is the refinement of 

mechanisms to identify the genetic differentiation in a variety 

of organisms. 

Plume Studies 

How do hydrothermal plumes contribute to the total biological 

productivity associated with vent and other benthic 

environments? 

Extensive plumes associated with hot vent systems represent 

the vertical and horizontal component of hydrothermally derived 

biologically important energy sources. These energy sources 

support a chemosynthesis based food chain, the significance of 

which is not known. The importance of plume systems as a source 

of chemosynthetically fixed carbon, and the fate of this organic 

carbon needs study. Species composition and feeding rates of 

zooplankton consuming plume bacteria and the role, if any, 

plumes have on the dispersal and nutrition of vent animal larvae 

are critical to understanding this system. 

50

Strategy 

Biological studies will emphasize four distinct scales of 

observation, sampling, and experimentation: (1) point scale of 

individual vents, (2) localized scale of vent fields, 

(3) regional scale of thousands of kilometers, and (4) global 

scale comparing regions. 

Required Techniques 

To achieve the listed objectives, the development and 

improvement of the following techniques are among the 

prerequisites: 

.!D. situ: (1) Instrumentation for chemical analyses of fluids 

on both instantaneous and long-term scales. (2) Instrumentation 

for measurement of microbial activity. (3) Measurements of 

animal growth rates and of soft and hard-part deterioration. 

(4) Organism manipulations for habitat alteration and colonization 

experiments. (5) A vehicle (remote or manned) available 

for, and capable of. repeated and non-disruptive visits to the 

same area. (6) Large- and small-scale photographic mapping. 

Laboratory: (1) Probes of the genetic make-up of organisms 

(ribosomal ribonucleic acid sequencing, isoenzyme assays, 

mitochondrial DNA comparisons, and DNA hybridization). 

(2) Equipment for maintenance of animals under simulated vent 

conditions. (3) Equipment for measurements of metabolism of 

microbes and animals under simulated vent conditions. 4. Image 

processing applied to deep-ocean photographs. 

Long-term: (1) Long-term bottom stations for continuous 

observations of specific sites. (2) Mechanisms for detecting 

biological markers in hydrothermal plumes. (3) Mechanisms for 

detecting subsurface life. 

Summary 

The chemosynthetically driven ecosystems of ridge crests can 

only be studied effectively if the physiologies, biochemistries, 

distributions, ecologies, and evolutionary histories of the 

microbial and animal species are linked to geochemical and 

geophysical processes. Basic understanding of the organismal 

adaptions enabling the tolerance and the exploitation of the 

vent waters, and comprehension of the way temporal and spatial 

variability in vent flow affect bacterial and animal life are 

the chief goals of the vent biology program. These goals can 

only be realized through complementary and collaborative programs 

in physical oceanography, geochemistry, and geophysics. 

Conversely, the success of these other, non-biological programs 

necessitates inputs from the biological studies, such as 

51

information concerning the effects of the organisms on water 

chemistry and the utility of biological observations as 

indicators of water chemistry, current regimes, and vent 

development. 

52

GROUP 6: 

WATER COLUMN DYNAMICS AND SEDIMENT PROCESSES 

Members: 

Jack Dymond, Co-Chairman 

John Lupton, Chairman 

Edward Baker, Edward Bernard, Robert Collier, 

Stephen Hammond, Gary Klinkhammer, Michael Mottl. 

David Ross, Richard Thompson 

Primary Objective 

To determine the distribution and intensity of mid-ocean 

hydrothermal venting and the interaction of venting with the 

ocean environment. 

Critical Problems 

1. To quantify the spatial and temporal variability in 

hydrothermal output along mid-ocean ridges. 

2. To quantify the effects of hydrothermal venting on the 

oceanic environment. 

Significant Characteristics and Processes of Venting 

1. Spatial Variability in Thermal and Chemical Output. 

The distribution of venting and flux of hydrothermal effluent 

are critical to modelling the ridge-ocean system. It is 

necessary to obtain this information on scales ranging from 

individual vent fields, to ridge segments, to oceanic basins. 

2. Temporal Variability in Hydrothermal Venting. Geophysical 

and geochemical evidence demonstrate that hydrothermal 

venting is variable over a wide range of time scales. These 

variations can be gradual or episodic. Temporal variations in 

venting contain important information about sub-seafloor processes. 

This variability must also be considered in designing 

plume sampling strategies. 

3. Global Scale Influence on Ocean Chemistry and Biology. 

The oceanic budgets of heat and mass are influenced by hydrothermal 

venting. The hydrothermal plumes provide energy, 

nutrients, and dispersal mechanisms for biological communities. 

53

4. Evolution of the Hydrothermal Plumes. The physical 

evolution of hydrothermal plumes depends on the interaction of 

the buoyancy and momentum flux of the plume with t.he local 

currents and density structure. These interactions determine 

the form of the hydrothermal plume. The chemical evolution 

includes transformations between dissolved constituents, fine 

advected particles and large settling particles. These 

transformations are mediated by organisms suspended in the 

hydrothermal plume. 

5. Low-temperature vs. High-temperature Venting. Although 

high~temperature, point-source venting is the most spectacular 

form of hydrothermal emission, it may not be the dominant source 

of heat and chemicals. The chemistry, biology and physics of 

low-temperature (diffuseI systems are different. The variety of 

venting types reflects a range of subsurface processes and 

produces distinct plume geometries and compositions. 

6. Off-axis Venting. Off-axis hydrothermal circulation is 

known to exist, but its role in mid-ocean ridge processes is 

uncertain. 

7. Plume-driven Oceanic Circulation. Heat and momentum 

injected by hydrothermal plumes may drive circulation in the 

deep ocean. The relevant flows range from local turbulent 

entrainment with vertical pumping to large-scale, quasigeostrophic 

buoyancy-driven circulation. 

8. Hydrothermal Effluents as Passive Tracers. Mapping the 

neutrally-buoyant effluent layer is a powerful tool for studying 

the physical processes of advection, mixing, and diffusion in 

the deep ocean. 

9. Sedimentary Records of Hydrothermal Activity. The 

sediments are the final repository for most of the materials 

injected at mid-ocean ridges. They contain a record of the 

variation of hydrothermal activity over geologic time scales. 

Depositional processes. bioturbation, and diagenesis determine 

the fidelity of this record. 

Observational Strategies 

Observational strategy is centered on three spatial scales: 

vent field (tens to hundreds of meters), ridge segment (100 to 

200 kmL and ocean basin (1000 kml. The level of temporal 

variability important in each case is proportional to the 

spatial scale. At the finest level. investigations will focus 

on submersible and surface ship determinations of 

vent-field-scale heat and mass flux by near-simultaneous 

measurements in the buoyant and neutrally buoyant plume. 

Variability on the scale of hours to months should be assessed 

by continuous monitoring of individual orifices and by moored 

sensors in the near-field plume. 

54

On the ridge segment scale, detailed plume mapping probably 

by sensors towed from surface ships will inventory the vent 

field distribution (both on and off axis ) for comparison to 

axial morphology, petrographic heterogeneity, geophysical 

variability, and faunal distributions. Techniques of flux 

determination developed by the detailed vent field studies will 

allow a reliable determination of the total segment - scale 

flux. Variability on an annual to decadal scale must be 

assessed by repeated surveys of selected segments, although the 

contribution of large but infrequent hydrothermal events should 

be continuously monitored by an appropriate distribution of 

moored sensors. Identification of such events will pinpoint 

fruitful locations for geological and geophysical studies. 

Basin scale studies have equal along and across-axis 

components and are central to the primary objective of 

determining the global effect of hydrothermal venting on the 

oceanic environment. Along-axis plume surveys, conducted 

simultaneously with geophysical surveys and calibrated by a few 

detailed segment-scale surveys, will provide a first-order 

estimate of the global magnitude and distribution of the 

hydrothermal flux. Across-axis surveys of the dispersing plume 

will establish the hydrothermal link to oceanic chemistry, 

mixing, and circulation. Complementary sediment studies provide 

the geologic history of venting. 

Data Collection and Measurement Capabilities 

We have identified four different scales in space and time 

over which data collection must occur. 

On the scale of an individual vent orifice or chimney, we 

require accurate measurements of the temperature and composition 

of the exiting hydrothermal fluids, both high and low temperature, 

including an estimate for the hydrothermal end-memberl s) 

feeding a vent field. These data are basic for characterizing 

the source of any hydrothermal plume. Measurements of mass and 

heat flux from individual high-temperature vents are also 

essential, along with video recordings of vent orifices to aid 

in quantifying the proportion of the total flux which occurs via 

hot, focused venting vs. cooler, diffuse venting. Technical 

improvements such as acoustic or electromagnetic flowmeters 

should be investigated for this application. 

On the scale of a vent field, on the order of 100 m x 100 m, 

we require detailed mapping of topography, geological and hydrothermal 

features, and physical and chemical parameters in the 

buoyant, rising plume( s) on a scale of a few meters to a few 

hundred meters. Fine-scale measurements of temperature, 

velocity. composition, and particle distribution are required 

because the rising plume is characterized by large gradients in 

space and time. Measurements on this scale should produce the 

55

most accurate estimates of heat and chemical flux from individual 

vent fields. They also are required for optimal placement 

of moorings designed to monitor variation in vent-field plumes 

with time. 

Vent-field monitoring is appropriate over time scales of 

weeks to months or longer, in order to measure possible 

variations in output resulting from subsurface processes. It 

should include thermistors, current meters, transmissometers, 

and chemical sensors. Sediment traps and novel remote sensors 

such as electromagnetic and acoustic doppler current meters, 

acoustic backscattering and tomography devices for measuring 

plume structure, and various chemical sensors would also be 

useful. 

Particles represent a major problem, both in characterizing 

their concentration and size distribution and in preventing 

their reaction with ambient water after sampling. .!.!:!. situ 

pumping and filtration as well as laser particle sizing should 

be developed or adapted to solve these problems. 

On the scale of one to several ridge segments, or about 

200 km along the axis, measurements have traditionally been made 

from surface ships. We recommend development of an apparatus 

for efficiently detecting and characterizing hydrothermal . 

plumes. The apparatus should be compatible with high-speed 

("'8 kts) geophysical surveys as well as with slower and more 

detailed vent-field surveys. It should at least measure 

temperature, conductivity, and light transmittance every 30 m 

over the lower 600 m of the water column and also higher, to 

detect both normal plumes and larger transient plumes as 

discovered in August 1986 on the S. Juan de Fuca Ridge. It 

could consist of an ROV, or of a towed fiber optic sensor array, 

with power supply and data processing equipment located on the 

ship rather than on the cable to reduce drag. The apparatus 

should be designed to accommodate additional chemical sensors as 

they become available. 

Monitoring from long-term moorings is also appropriate on 

the scale of a ridge segment. primarily to detect large 

intermittent, transient plumes such as that noted above, which 

had a diameter of 20 km. These moorings could detect a similar 

plume if spaced every 10 km. Once detected, it would be 

important to track such a plume, possibly with an instrumented, 

neutrally buoyant Lagrangrian drifter. 

The largest scale with which we are concerned is that of an 

ocean basin, equivalent to a 1000 km section of ridge axis. The 

apparatus described above, for characterizing plumes, used 

either alone or as part of a survey, should be capable of 

rapidly determining the presence or absence of plumes along the 

ridge axis over these distances. Off-axis advection and 

dispersal on the scale of an ocean basin can be evaluated using 

56

standard transect sampling and Lagrangian drifters. The 

development of Lagrangian drifters with in-situ chemical sensors 

would enhance our understanding of the long-term chemical 

evolution of hydrothermal emissions. . 

Laboratory, TheoreticaL and Numerical Modeling 

Laboratory, analytical and numerical simulation models provide 

valuable and instructive insight into ridge plume dynamics 

and variablity under controlled conditions. Such models will 

prove important to the interpretation of field observations and 

to the identification of key elements of plume dynamics. 

Refined plume models are needed to explain coalescing of 

multiple source vent fields and the effects of high frequency 

(tidal) cross-flow fluctuations on the spatial structure and 

temporal variability of plumes. Models will help predict the 

propagation, structural evolution and vorticity dynamics of 

episodic mesoscale plumes. Formed intermittently along 

mid-ocean ridges, these vent-like features are expected to 

display analogous behavior to warm and cold core eddies that 

proliferate within the upper ocean. Numerical simulation models 

are essential to our understanding of the general abyssal 

circulation and its interaction with mid-oceanic ridges. Such 

models are further needed to separate truly passive aspects of 

large scale plumes from active effects in which the plume 

induces modifications to the basin-scale background abyssal 

circulation. Models also should be applied to problems of 

particle-fluid transport within the heterogeneous media of vent 

fields. Modeling experiments are required for understanding the 

behavior of suspended particles and biological organisms within 

the circulation of oceanic plumes. This type of research is 

also essential for determining chemical process rates (such as 

metal and methane oxidation rates) within the plume environment 

and for providing estimates of the evolution and modification of 

advecting plumes. It is anticipated that many of the processes 

ubiquitous to hydrothermal vent sites can be accurately 

simulated through laboratory, analytical and numerical models. 

These models will help in the interpretation of observations 

within this convoluted oceanic regime and provide a basis for 

field experiments. 

Coordination with Other Investigations 

Plume studies are linked with other types of mid-ocean ridge 

investigations by commonalities in observational strategy and 

instrumentation. Improved cables and towed-sensors will 

facilitate simultaneous plume-mapping and geophysical surveys 

along ridge axes. The spacing and service requirements of seafloor 

instruments for both plume measurements and geophysical 

monitoring are comparable. Real-time detection of intense, 

episodic hydrothermal discharge may be helpful in locating foci 

of major crustal movements along ridge crests. Water column 

57

studie!; that coordinate plume measurements and biological 

sampling will advance our understanding of the ecological role 

of the plume in distributing organic matter, bacteria, and 

plankton away from the vent field. On the ocean-basin scale, 

plume tracer studies complement other global programs committed 

to understanding oceanic circulation (WOCE) and chemical fluxes 

(GOFS) • 

58

APPENDIX I 

The Mid-Oceanic Ridge: 

A Dynamic Global System 

Salishan Lodge, Gleneden Beach, Oregon 

6-10 April 1987 

Participant List 

Agnew, Duncan 

Scripps Institution of Oceanography 

University of California, San Diego 

IGPP A-025 

La Jolla, CA 92093 

Baross, John A. 

School of Oceanography WB-1O 

University of Washington 

Seattle, WA 98105 

Batiza, Rodey 

Department of Geological Sciences 

Northwestern University 

Locy Hall 

Evanston, IL 60201 

Bernard, Edward 

NOAA/PMEL 

7600 Sand Point Way, N.E" Bldg. 3 


Bryan, Wilfred B. 

Department of Geology and Geophysics 

Woods Hole Oceanographic Institution 

Woods Hole, MA 02543 

Buck, .Roger 

Lamont-Doherty Geological ObserVatory 

Oceanography Building 

Palisades, NY 10964 

Cann, Johnson R. 

Department of Geology 

University of Newcastle upon Tyne 

Newcastle upon Tyne, NE1 7RU 

United Kingdom 

Chave, Alan 

AT&T Bell Labs 

600 Mountain Ave" Room 1E-444 

Murray Hill, NJ 07974 

59

Childress, James 

Department of Biological Sciences 

University of California, Santa Barbara 

Santa Barbara, CA93105.· 

Collier, Robert 

College of Oceanography 

Oregon State University 

Corvallis, OR 97330 

Cox, Charles 



IGPP A-030 


Delaney, John 

School of Oceanography, WB-lO 



Denlinger, Roger 

U. S. Geological Survey 

c/o School of Oceanography WB-lO, 



Desbruyeres, Daniel 

IFREMER - Center de Brest 

B. P. 337 - 29273 BREST CEDEX 

France 

Detrick, Robert 

Graduate School of Oceanography 

University of Rhode Island 

Kingston, RI 02881 

Dick, Henry 




Dymond, Jack 

College of Oceanography 


Corvallis, OR 97330 

Edmond, John 

Department of Earth, Atmospheric, and 

Planetary Sciences 

Massachusetts Institute of Technology 

Cambridge, MA 02139 

60

Forsyth, Donald 


Brown University 

Providence, RI 02412 

Fox, P. Jeff 

Graduate School of Oceanography 


Naraganssett, RI 02882 

Francheteau, Jean 

Institut de Physique de Globe 

Lab de Geophysique Marine 

Univ. Pierre & Marie Curie 

2 Place Jussieu 

75230 Paris CEDEX 05 

France 

Fujimoto, Hiromo 

Ocean Research Institute 

University of Tokyo 

1-15-1, MinamidaL Nakano-Ku 

Tokyo, 164 Japan 

Grassle, Fredrick 



Gronvold, Karl 

Nordic Geological Institute 

University of Iceland 

101 Reykjavik 354 1 

Iceland 

Gurnis, Michael 

Seismology Lab 

California Institute of Technology 

Mail Code 252/21 

Pasadena, CA 91125 

Hammond, Stephen 

OSU Hatfield Marine Science Center 

Newport. OR 97365 

Hartwig, Eric 

Office of Naval Research 

800 N. Quincy Street, Code 112 

Arlington, VA 22217 

Haxby, William F. 


Lamont-Doherty Geological Observatory 


61

Hessler. Robert 


University of California. San Diego 

IGPP A-002 

La Jolla. CA 92093 

Hildebrand. John 


Institute for Marine Resources 


Janecky. David 

Los Alamos National Laboratory 

INC-7 MS J514 

Los Alamos. NM 87545 

Jannasch. Holger 


Woods Hole. MA 02543 

Karson. Jeffrey 


Duke University 

Old Chemistry Building 

Durham. NC 27706 

Katsouros. Ms. Mary Hope 



2101 Constitution Avenue. N.W. 

Washington. DC 20418 

Klinkhammer. Gary 

Department of Earth. Atmospheric. and 



Cambridge. MA 02139 

Langmuir. Charles 


Palisades. NY 10964 

Langseth. Marcus 


Palisades. NY 10964 

Lister. Clive 

School of Oceanography. WB-lO 


Seattle. WA 98195 

62

Lonsdale. Peter 



IGPP A-005 


Lowell. Robert 

National Science Foundation 

1800 G Street. NW. Room 606 


Lupton. John 

Marine Science Institute 

University of California. Santa Barbara 

Santa Barbara. CA 93106 

Lutz. Richard 

Biology Department 

Rutgers University 

New Brunswick. NJ 08900 

MacDonald. Kenneth C. 


University of California. Santa Barbara 

Santa Barbara. CA 93106 

Malfait. Bruce 


1800 G Street. NW. Room 605 


Malpas. John 

Memorial University of Newfoundland 

Marine Sciences Research Laboratory 

St. John's. Newfoundland 

Canada 

Marshall. Ms. Judith 



2101 Constitution Avenue. N.W. 


McCallum. I. Stewart 

Department of Geology AJ-20 



McDuff. Russell 

Department of Oceanography. WB-10 



63

Morton, Janet 

U. S. Geological Survey, MS 999 

345 Middlefield Road 

Menlo Park, CA 94025 

Mottl, Michael 

Hawaii Institute of Geophysics 

University of Hawaii 

2525 Correa Road 

Honolulu, HI 96822 

Mutter, John C. 



Nicolas, Adolphe 

Lab Tectonophysique 

Universite de Montpellier II 

Place Eugene Bataillon 

34060 Montpellier 

France 

Orcutt, John 



IGPP A-025 


Ostenso, Ned 

Director, National Sea Grant Program 

National Oceanic and Atmospheric Admin. 

Room 918, Building 5 

6010 Executive Blvd. 

Rockville, MD 20852 

Parmentier, E. Marc 


Brown University 

Box 1846 

Providence. RI 02912 

Phipps Morgan, Jason 

Department of Earth, Atmospheric, and 



Cambridge, MA 02139 

Purdy, G. M. 



64

Reeve, Michael 


1800 G Street, NW, Room 611 

Washington, DC 20550 

Rohr, Kristin 

Pacific Geoscience Centre 

P.O. Box 6000 

Sidney, British Columbia 

V8l 4B2 Canada 

Rona, Peter A. 

National Oceanic and Atmospheric Admin. 

4301 Rickenbacker Causeway 

Miami, Fl 33149 

Ross, David A. 

Chairman, Marine Geology and Geophysics 



Sandwell, David 

Institute for Geophysics 

University of Texas at Austin 

Austin, TX 78751 

Schouten, Hans 



Searle, Roger C. 

Institute of Oceanographic Sciences 

Wormley, Godalming 

Surrey GU8 5UB 

United Kingdom 

Sempere, Jean-Christophe 



Seyfried, William E" Jr. 


University of Minnesota 

Minneapolis, MN 55455 

Shanks, Wayne 

U. S. Geological Survey 

12201 Sunrise Valley Drive 

Reston, VA 22092 

65

Sinton. John 

Hawaii Institute of Geophysics 

University of Hawaii 

Honolulu. HI 96822 

Sleep. Norman 

Department of Geophysics 

Stanford University 

Stanford. CA 94305 

Solomon. Sean C. 

Department of Earth. Atmospheric. and 



54-522 

Cambridge. MA 02139 

Somero. George 

Marine Biology Research Division. A-002 



la Jolla. CA 92093 

Spiess. Fred 

Institute for Marine Resources. A-028 



la Jolla. CA 92093 

Stephen. Ralph A. 



Taghon. Gary 

Hatfield Marine Science Center 


Newport. OR 97365 

Taylor. Phillip 


1800 G Street. N. W. 


Thompson. Geoffrey 



Thomson. Richard E. 

Institute of Ocean Sciences 

P.O. Box 6000 

Sidney. British Columbia 

V8l 4B2 Canada 

66

Tunnicliffe, Verena 

University of Victoria 

Department of Biology 

Victoria, British Columbia 

V8W 2Y2 Canada 

Tyee, Robert 

School of Oceanography 


Kingston, RI 02882 

Von Herzen, Richard 



Whitehead, John A. 



67

Workshop Report - Ridge 2000 Program

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