OCEAN MARGINS

A Proposal to the European Science Foundation for a Network in the Life and Environmental Sciences

ABSTRACT

Ocean margins are features on a global scale that mark the transition between continental and oceanic crust. They are the product of predominantly vertical (i.e. subsidence and uplift) rather than horizontal movements. They include sites of some of the largest accumulations of sediments on the Earth's surface and are among the best indicators that we have of climatic, sediment flux and, sea-level changes in the past. Ocean margins are prone to large-scale slope failures and some are seismically active.

The nations of northwest Europe share one of the longest margin systems in the world. Yet, no one nation currently has access to all the resources and technology now required to determine the physical, chemical and biological processes that are occurring at ocean margins.

The purpose of this proposal is to develop a "network" for a new European-led inter-disciplinary and multi-national programme in ocean margins. Such a network is timely. The international scientific community has already identified the deep structure, sedimentary processes and fluid flow at ocean margins as high priority questions that need to be addressed in the immediate future. Furthermore, the hydrocarbons industry regards ocean margins as one of the few remaining exploration frontiers for the production of oil and gas.

We believe that a ESF supported network which examines common research objectives, discusses and implements the sharing of facilities within Europe, involves industry throughout its development, and collaborates with existing international programmes such as USA "MARGINS" will lead to important new advances in our understanding of ocean margins.

A. Background

Ocean margins are created by one of the fundamental Earth processes; namely the rifting and break-up of continental crust to form new ocean basins. Ocean margins comprise of some of the largest accumulations of sedimentary rocks on the Earth's surface and are among the best recorders that we have of the way that lithosphere responds to extensional, compressional and strike-slip tectonic forces, sea-level changes, and the transport of sediments from the continental interiors, to the coastal zone and into the deep sea. The countries of Europe share one of the longest ocean margin systems in the world. Extending from offshore Norway in the north, to southern Portugal and Spain in the south, and the Mediterranean Sea in the east, Europe has a variety of margin-types. These include rifted margins with abundant magmatism and thin sediments (e.g. Norway) and margins with little or no magmatism and thick sediments (e.g. SW approaches to UK and France). They also include examples of inactive transform and active margins. While differences in the amount of magmatism and sediments explain the diversity of present-day ocean margins, they obscure our understanding of the physical and chemical processes that are associated with the break-up of continents and the formation of new ocean basins.

During the past few years, there has been renewed interest by the scientific community in the processes that are occurring at ocean margins. The interactive nature and complexity of these processes has been recognised as has the need for interdisciplinary and multi-national collaborative studies to address them. Furthermore, societal interest in ocean margins has increased. Some margins are the habitat for major reserves of oil and gas. Others have been the site of earthquakes which in some cases have ruptured through the entire crust and triggered large-scale failures on the continental shelf and slope. Since a large percentage of the world's population lives within a short distance of the coastal zone, ocean margins constitute major hazards.

B. Principal Scientific Themes

A number of workshops on ocean margins have been held recently in different countries (e.g. USA, France, UK) from which the following three research "themes" have emerged:

1 : Deep structure, rifting processes and structural variability

Recent studies have improved our knowledge of the dynamics of rifting and the physical and chemical processes that operate in ocean margins. However, we still lack an understanding of how they evolve through time and space. This is partially due to the large range in the length and time scales that describe the processes that operate at margins.

Specific objectives of the deep structure research include the dynamics of rifting; the mechanisms of magma generation and emplacement; the interaction of rheology, strain rate, crustal flexure and faulting; the nature of the continent-ocean transition; and thermal and mechanical structure of rifted continental lithosphere. Subsequent to rifting, the evolution of ocean margins is dominated by vertical movements. Key questions here concern the heat transfer from the underlying lithosphere into the sedimentary cover; the role of rift flank uplifts in controlling the sediment supply; and deformation events including those expressed by seismicity. For many of these issues, the study of conjugate rifted margin pairs including the development of new quantitative models for their evolution is crucial. Conjugate margins typically lack symmetry and so the study of an individual margin therefore provides only partial evidence for its origin and evolution.

In Europe, the problem of imaging the deep structure of ocean margins is complicated by the difficulty that individual nations have in gaining access to the technology that is required. We know, for example, that volcanic sill emplacement and salt migration obscure our understanding of the deep structure of some ocean margins. New technologies will enable us to address this problem. Data acquisition at sea, however, is still a costly and complex operation. Nonetheless, the utilisation of the expertise that already exists in Europe, both within academia and industry, should provide the necessary platform with which to undertake these studies in the future.

2. Sedimentary Processes and Products

In general, there is little currently known about the sedimentary processes that have shaped ocean margins through time. Multi-disciplinary studies need to be developed that analyse this problem as a whole, since there is a continuum, from sediment transport by rivers, to coastline evolution, to shelf deposition and to deep-water sedimentation. Furthermore, ocean margins are mechanically coupled systems such that certain "feedbacks" exist across the transition. Subsidence, for example, due to the accumulation of sediment offshore maybe accompanied by uplift onshore. These isostatically induced uplifts have important consequences on the rates of erosion onshore and, in turn, on the supply of sediments to the deep-sea.

Fundamental questions concern controls (i.e. tectonics, sea-level fluctuations, earthquake triggering, fluid flow) of large-scale slope, down-slope and along-slope sediment transport. This area of research is relevant to the architecture of deep-sea fans, to some coastline slides, to the quantitative modelling of sedimentary basins and hazard studies, particularly to submarine cable laying and oil rig deployment.

High resolution imaging of the sea-floor (e.g. swath bathymetry, deep-towed side-scan sonar) combined with sub-surface sampling (e.g. giant piston coring and deep drilling) are required to identify fine-scale sedimentary architecture and to characterise slope failures and sedimentary paths from the shelf, across the slope and rise, to the deep-sea. Although there have been several attempts through the Ocean Drilling Programme to drill selected 'transects' of margins, including European margins, systematic bathymetric mapping and particularly sonar imaging coverage is still only partial.

3. Sub-Sea Floor Fluid Circulation

A major result of recent studies at active margins has been the discovery of significant evidence of sub-seafloor fluid flow. In contrast, there have been few equivalent investigations of the low temperature fluid flow systems in rifted and transfrom margins. Fluids have long been recognised to play an important role in diagenesis. They may be a significant contributor of methane and other compounds which may produce local or regional anomalies in the non-anthropogenic trace components of sea water. In shallow areas, these compounds may enter the atmosphere, in turn influencing the pattern of global climate. Gas hydrate layers in the sedimentary column, considering their potentially wide distributions, represent huge natural concentrations of methane and in addition can act as traps for upward migrating oil and gas.

Fundamental questions to be addressed in this research theme include the distribution and intensity of directed and focused flow, fluid compositions, especially hydrocarbon components from the fermentation of organic matter, the long term effects of sub-sea floor circulation on sediment diagenesis, and the pore pressure, porosity and stability of large sediment masses.

In order to address these questions, we need to identify the areas of greatest outflow in ocean margins, a task which can be accomplished using high-resolution geophysical and geological techniques as well as visual observations. A promising new technique is to determine the porosity field using high resolution multchannel seismic data processed in the depth domain.

A strategy to identify areas of most rapid flow and sample these fluids already exists in active margins where the strong outpouring of pore fluids supports exotic deep water biological communities. Although not as well explored as active margins, there are indications of cold-water seep communities (e.g. "Hovland reefs") in rifted margin settings offshore the UK and Ireland and, for example, in the Gulf of Mexico. Little is known, however, about the location of these seeps or about fluxes, plumbing geometry and time scales of fluid migration. This information is an important ingredient to first-order models of fluid flow patterns that exist in well sedimented ocean margins and how tectonic processes such as faulting, large-scale slope failure, and basement geometry may modify them.

C Why a network ?

We believe that this is an opportune time for enhanced co-operation among European scientists who study ocean margins and that a network is necessary to ensure that Europe remains at the leading edge of this important research area. A network would help bring the ocean margins community in Europe together and "kick-start" future common actions. Ocean margins are unique in the Earth Sciences in the scope of their subject, the range of inter-disciplinary interests, the considerable panoply of tools required and, the opportunities that they present for collaboration with industry.

1. Scope of the research

Ocean margins show a wide diversity in their structural setting. This diversity is clearly seen in Europe, where examples of rifted (volcanic and amagmatic), transform and, active types of margins are found. Despite this diversity, certain processes such as tectonic subsidence and uplift, large-scale slope failure and mass wasting and, fluid flow appear to be common to all these types of margins. A network would have as one of its principal aims the development of a programme that was focused on certain "targets" areas that best demonstrated the processes that are occurring at ocean margins. Because North Atlantic includes some of the best examples that we have of volcanic margins with little or no sediment, it is likely that European margins will be included as such target areas. However, there may be some processes that are best studied at margins in other oceans (South Atlantic, Indian), especially conjugate margin pairs.

2. Interdisciplinary studies

Many of the scientific questions at ocean margins are inter-linked. The deep structure, for example, is closely linked to the sedimentary history. Fluid flow patterns in ocean margins will, in all likelihood, depend on both the deep structure and the sedimentary history. Ocean margin studies can therefore be expected to impact on a wide range of disciplines, including marine geology and geophysics, geochemistry, structural geology, geomorphology and marine biology. A network would work to co-ordinate ocean margin studies

3. Ships and Technology

Modern exploration of the oceans requires a wide range of facilities, including ships, submersibles, remotely operated vehicles, multi-channel seismic systems, arrays of ocean-bottom seismometers, high-resolution side-scan sonar, swath bathymetry, drilling and sampling tools. Strengths in these areas are unevenly distributed among the various countries of Europe and there is room for more combination and exchange of resources through, for example, bilateral agreements or European Union support. A network would provide the means by which this might be achieved.

4. Industry

The hydrocarbons industry is moving its activities into ever deeper water. As a result, they have increased their interest in ocean margins. Specific questions that they would like resolved concern the location the continent-ocean boundary, the thermal evolution, the role of slope failures, and the correlation of seismic reflectors from the shelf to the deep-sea. Industry is particularly interested in the development of predictive models that can be applied to ocean margins. There have been a number of examples in the last decade where they have adopted such models (the "stretching model" for example) and incorporated them into their research strategy. They have also begun to adopt some of the exploration methods that have been developed for scientific studies, such as the use of wide-angle seismic surveys and ocean bottom sensors. Conversely, there are areas in which industry facilities are far superior to those currently available to the scientific community; notably in the field of 3-D seismic reflection, as well as drilling and coring. It would therefore be mutually advantageous if existing links between the industrial and scientific activities on ocean margins could be extended and developed. This could be facilitated by a network, especially if industry were to be involved in such a network from the beginning.

5. Training

Ocean margins research involves observations, through data processing, to the construction of analytical and numerical models to explain the data. It is a highly technical subject that involves "state of the art" tools and techniques (marine instrumentation, image processing and predictive modelling, for example) which will require the skills of a new generation of young European scientists. A network would provide support and encouragement to the young scientists of Europe who are already involved in the complexities of survey work at sea, the manipulation of large data sets, and the construction of analytical and numerical models of geological processes.

6. The international scene

A European-led margins network is especially timely in view of the large international programmes and major national programmes of the USA, and other countries that already exist in ocean margins research. Links with the recently formed USA MARGINS programme, with its current emphasis on active processes, is an important example. Such links would be best made through a network, rather than through individual scientists, institutions and nations as it is at present.

A European-led initiative in ocean margins, which begins as a network, could liase with the USA MARGINS programme and any other national efforts, such as the Ocean Drilling programme and with international unions such as IUGS and IUGG. Furthermore, a network would enable a a co-ordinated European response to be made to "Inter-Margins" which is an international initiative that is presently under discussion at the USA National Science Foundation as a margins counterpart of "Inter-Ridge".

D Network Activities and Tasks

The network will have as its overall aim the development of a new European-led initiative in the study of ocean margins. The study will be carried out through collaboration between individual scientists, institutions and nations in Europe. The network will seek to improve contacts and general co-ordination in ocean margin research at the European level and to work to develop a new programme in ocean margin research that uses this collaboration to develop selected "targets" for study.

Specific activities and tasks will include :

1. To obtain an overview of research activities and of sea-going and and laboratory facilities in Europe, to formulate high priority scientific problems and the specific types of experiments at sea that are needed, and to consider target areas for integrated studies.

2. To define a co-ordinated European-led initiative in ocean margins and, in liaison with ESF, the EU and national institutions, to examine ways that the initiative may be organised as a consortium or ESF programme, for example.

3 To bring together all interested parties to discuss a multi-disciplinary approach, to define key targets and, to discuss the technology that will be required for the installation and upgrading of existing large-scale facilities that are relevant to margin studies.

4 To develop - at an early stage - a close co-operation and involvement with industry. To achieve this, we envisage joint academia-industry workshops, from which mixed working groups would be formed to formulate the elements of a future programme.

5. To act as a forum for information and exchange of ideas and access to techniques within Europe and to international programmes by the installation of a web site. The site will include a internet-accessible database which will provide information about on-going research activities on margins in Europe. This will include summaries of proposed or scheduled scientific cruises, information about available facilities in network institutions and links to other margins-related activities and programs in Europe. The network will use the opportunity of major scientific meetings like the biannual EUG (European Union of Geosciences) and EGS (European Geophysical Society) meetings to inform the geoscience community about its activities. This will be done through seminars and special sessions dedicated to margins-related research.

We plan for the network to start in Spring, 1999 and to run for a period of 2 years. This would allow sufficient time, we believe, to develop a new programme in ocean margins. In particular, the timing would permit the submission of a joint interdisciplinary proposal to EC-FP5 framework, for which calls are expected during 1999 and 2000. In the event that EC-FP5 framework is unable to support the deep structure objectives of ocean margins, the timing will allow the network to pursue other possible sources of support within the EU, with the various national funding agencies and with the wider industry community.

F Co-ordination committee and budget

The activities of the network in ocean margins will be carried out by a "co-ordination" committee who will comprise of some of the leading authorities in ocean margins in Europe. Our main criteria in selecting the committee is that it be both multi-disciplinary and multi-national. Since one of the objectives of the network will be to develop a programme, the committee will comprise of a "core" of expertise in the conduct of large-scale marine geological and geophysical experiments at sea. This core will be supplemented by expertise in other aspects of ocean margin research such as structural geology, fluid flow and, numerical and experimental modelling. Where necessary, expertise in other subjects such as igneous petrology, geochemistry, geomorphology and marine biology will be co-opted to working groups within the network. In order that the network is able to involve industry from the earliest stages ( i.e. before a programme is developed ), we propose that two persons from industry be appointed as observers to the committee. Finally, we plan for two additional observers : one who will represent ESF and the other the USA MARGINS programme.

The steering committee will comprise :

A. B. Watts - Chairman

O. Eldholm (Norway) M. Canals (Spain) J. Henriet (Belguim) J. Hopper (Denmark) A. Ribbeiro (Portugal) J-C Sibuet (France) M. Torne (Spain) R. Von Huene (Germany) R. Whitmarsh (UK)

Observers :

Industry representatives (2) USA MARGINS committee ESF