InterRidge Initial Science Plan
The first decade of InterRidge (1992- 2003) saw the building of a strong international community which began to address problems of ridge research which could only be tackled as an international effort. This community was guided by the Intitial Science Plan, set out below. As of 2021 the Third Decadal Plan is in effect.
Mid-oceanic ridges are the primary site of volcanic activity on the planet and the primary site of creation of new crust. They exert a major influence on the evolution of the solid earth, affect the composition of the ocean waters and support unique forms of life. Yet, because they lie beneath the sea and originate in mantle processes deep within the earth, they are poorly understood.
InterRidge is an initiative concerned with all aspects of ridge research. It supports and develops programmes that are of major scientific interest, interdisciplinary, globally or thematically defined, and, most importantly, require or will benefit from international discussion, planning and implementation.
InterRidge aims to develop scientific, technical and logistical co-operation among nations and to strengthen international foundations for innovative research into the early part of the twenty first century.
InterRidge is defined as a decadal programme divided into three phases:
Phase 1 (1992-1994), devoted to improving co-ordination of on-going independent national and international (principally bi- and tri-lateral) activities, encouraging exchange and communication through the facilitation of international symposia and workshops, and planning specific future InterRidge actions;
Phase 2 (1995-1997), involving in-depth studies of temporal variability and broadened spatial characterisation, in the form of major interdisciplinary field efforts conceived and co-ordinated by InterRidge, and development of a database information catalogue accessible to the international ridge sciences community via the Internet;
Phase 3 (1997-2003), including continued mapping and sampling coverage of the global ridge system, intensive development and deployment of seafloor instrumentation, and an international symposium to consider progress and future directions.
II. PRINCIPAL SCIENTIFIC THEMES
The scientific purpose of InterRidge is to discover and quantify the inter-relationships among the various manifestations of the ridge system and to integrate growing understanding of ridge dynamics with knowledge about the functioning of the earth as a whole.
These goals concern many subjects, from seismology to bacteriology, and a variety of approaches at many different scales. Research objectives are subject to periodic review and re-orientation. Principal InterRidge activities are grouped under three major themes, or Integrated Projects, as defined at the General InterRidge Meeting in York in March 1992. These are: Global ridge systematics, Meso-scale ridge processes, and Active ridge processes. Their objectives are to:
Acquire a balanced set of global-scale data on the entire mid-ocean ridge system, which implies notably a concerted effort of exploration in high latitudes where data are extremely sparse.Observe, measure and monitor active processes at individual ridge sites in order to begin to quantify the fluxes of mass and energy involved and their biological consequences.Investigate the interplay of mantle processes at temporal and spatial scales that bridge the gap between the global perspective and fine-scale studies of active processes. These “meso-scale” studies focus on magmatic and tectonic patterns as well as on fluxes, and include a specific effort on ridges in marginal (back-arc) basins.Understand the evolution, reproduction strategies and dispersion paths of hydrothermal vent biota and determine their relevance to and interaction with physical, chemical, and geological processes at the ridge-crest.
In addition to the three principal themes, InterRidge is concerned with research which, although carried out under other programmes, is highly relevant to achieving overall InterRidge aims. Strengthening interaction with the Ocean Drilling Program, for example, is a priority. Similarly, research areas such as whole-mantle seismic tomography, satellite altimetry, and certain theoretical and experimental studies are of vital interest to the development of ridge science.
1. Global ridge systematics
The formation and early aging of oceanic lithosphere couple the deep earth and surface environments through mantle upwelling and other complex processes, some of which can be approached only from a planetary perspective. The purpose of the global programme is the characterization of mid-ocean ridges necessary to investigate broad-scale aspects of geologic, hydrothermal, geodynamic, petrologic and biologic processes active near spreading centers. There are two major scientific aspects of ridges that require data from a global spectrum of locations. First, ocean crust formation is a multi-dimensional problem, as is clear from the variations that occur even at constant spreading rate. Second, there are problems that are global in scale, and have wavelengths longer than any regional study can encompass. There are too few of these long-wavelength features to be investigated statistically. Their description alone requires surveys of large portions of the ridge system. In addition, there is inherent value in the exploration of unknown terrain: every ridge that has been investigated thus far has yielded surprises that did not conform to our preconceptions; until we begin to see broad-scale duplication of ridge properties, exploration remains necessary simply to know the variability and the global systematics that must be explained by quantitative models.
Objectives of the global reconnaissance project are to:
define the general spatial characteristics of the global ridge system;
understand the origin, evolution and inter-relationships of broad, ocean-scale patterns of variation in structure, rock composition, volcanism, hydrothermalism, and biological activity (taxonomy, physiology, genetics);
relate these characteristics to the deeper processes of the earth system;
Targets are the ridge south of 40S, the Indian Ocean, and the Arctic Ocean which are practically unmapped using modern methods, and very sparsely sampled.
2. Meso-scale investigations
Certain critical spatial and temporal information is, for practical purposes, available only at scales encompassing along-axis distances ranging from the length of a single segment (a few tens of kilometres) to several hundred kilometres, and extending tens to hundreds of kilometres off-axis. These studies have as their goals (a) identification of key variables controlling magmatic, hydrothermal and tectonic processes and (b) development of quantitative, testable models of ridge crest accretion.
The three main areas of research at the meso-scale are :
interplay between tectonic and magmatic processes and relationships to ridge segmentation;
crustal accretion in marginal basin (back-arc) settings;
segment-scale variations in fluxes.
Recent observations indicate that spreading is a truly three-dimensional process. However, the origin of its fundamental segmentation is still poorly understood. It appears to arise from the complex interplay between magmatism and tectonism, which may be related to the pattern of mantle upwelling beneath the ridge axis. In order to quantify the factors that control ridge segmentation, it will be necessary to determine the variation in morphology, crustal structure and petrology along axis at the scale of a few hundred kilometers (~3 segments) and off-axis out to crust of several million years age at a variety of ridges with different spreading rates, magma supply histories, segmentation geometries and proximity to hotspots. These observations will need to be closely integrated with detailed three-dimensional thermo-mechanical and petrologic modelling of the spreading process.
The presence of a subducted slab beneath back-arc spreading centers affects the mantle circulation and thermal flux, introduces volatile and other elements into the mantle source, and sometimes adds deeply-sourced arc magmas to the shallow mantle decompression melts. The geographic isolation of back-arc basins from mid-ocean ridges is an important variable in biological evolution, diversity, and ecology. The arc ridges that bound back-arc basins provide covering sediments and physical barriers that modify fluid circulation in the crust and ocean. The different composition of back-arc versus mid-ocean ridge crust and sediments profoundly affects all aspects of the hydrothermal systems: depth and temperature of the magma chamber, fluid and precipitate geochemistry, rock physical properties, and hence fluid-rock interactions. Most ophiolites and volcanogenic massive sulfide (VMS) deposits have geochemical signatures different from crust and hydrothermal deposits formed at mid-ocean ridges, but similar to those formed in back-arc basins.
The goal of the segment-scale fluxes topic is to quantify the magnitudes and spatial variability of all of the fluxes – magmatic, hydrothermal (heat, water, and chemicals), and biological – occurring within a volume extending for one to a few segments along strike; a few tens of kilometers across strike; and from the uppermost mantle to a height in the water column above the influence of hydrothermal plumes.
Meso-scale studies provide a vital link between global and the site-specific investigations of active processes (see below) and provide the essential context within which research on the latter can be intelligently focused. InterRidge will stress the concentration of efforts to (a) define variability along extensive, key portions of the ridge with similar spreading rates and (b) obtain integrated data sets from end-member, and other selected areas.
3. Observing and quantifying active ridge processes
The global oceanic ridge system is the locus of massive energy flux from the interior of the planet to its near-surface environment. Identifying the geophysical, geochemical and biological consequences of this energy output is a major focus of modern ridge-crest research efforts. Temporal patterns and energy pathways within any portion of the system are of major interest in defining the interplay among the myriad processes operative along the planetary rift system. Temporal scales of important activity range from seconds to millions of years, and spatial scales from microns to global in size. Large and small submarine volcanic eruptions, massive and microearthquake activity, extended and local hydrothermal exchange between oceanic crust and seawater, and all levels of chemosynthetically-based life processes are integral components of ridge-crest systematics.
As in all volcanic systems, ridge-crest activity is episodic on time and spatial scales that are not readily observable. A major problem to be addressed by InterRidge is the issue of the balance between highly transient and more steady-state processes at the ridge crest.
Central to the objective of quantifying active physical, chemical and biological processes is the aim of establishing long-term seafloor monitoring systems. An essential prerequisite for any system is the development of testable models and their refinement by iteration with field observations. Observing and measuring various phenomena when the ridge is most active is an associated aspect of the overall task, as is the approach of revisiting parts of the ridge to test for recent changes.
III. CONTRIBUTION TO INTERNATIONAL RIDGE RESEARCH
InterRidge has no budget for funding data collection or analysis. Instead, its contribution to international ridge research is to facilitate and coordinate. This can operate at effectively three levels:
Development of research that can only be carried out effectively at the international level, either because it requires a level of resources (e.g. large numbers of instruments, or massive facilities such as a drilling ship) that are not available to single or small groups of countries, or because it requires coordination at an international level (e.g. for rapid response to transient events);Coordination of work that could be carried out by individual investigators, national programmes or small groups of countries, but which would achieve significant added value by being part of a coordinated programme (e.g. by being being carried out at a common site);Advancement of the ongoing work of individuals, national and international groups by providing information and data-exchange services.
InterRidge can achieve these objectives by:
bringing the expertise of the international ridge research community together to identify priority issues, define questions and focus interests both geographically and thematically;
facilitating the exchange of ideas and planning, e.g. by convening international meetings and workshops;
expressing the consensus of the international community in a unified voice to national funding agencies and other international programmes providing services to the community;
assisting in defining and coordinating field programmes and experiments;
providing current information about research activities, especially sea-going operations, by publication of workshop reports and a semi-annual newsletter;
helping to improve procedures for data management, exchange, synthesis and preservation;
create an information data base (track lines, sample locations, ultimately geochemical analyses, geophysical syntheses…);
encourage participation of smaller oceanographic countries and individual scientists from non-sea-going countries;
providing an international electronic directory of InterRidge researchers.
IV. PROGRESS TO DATE AND PLANNING FOR THE FUTURE
During Phase 1 of the InterRidge Program, significant progress has been made towards achieving both Global and Meso-Scale project objectives, and especially in working towards the geographic and thematic focus necessary for an effective programme. The Active Processes project has been slower starting, partly because it was seen as building on the early decisions of the Global and Meso-Scale projects and then progressing in parallel with them. As originally envisaged in the InterRidge Initial Program Plan, much of this work has involved the planning of activities for Phase 2 and beyond. This has largely been acieved through a series of InterRidge workshops, all of which have been open to the general scientific community.
1. Global Studies
During Phase 1 of the Global project the following progress has been made:
two workshops were held to determine science priorities and the levels of existing and necessary data, and led to coordination of international and interdisciplinary efforts focussing initially in the Indian Ocean;
participants in these meeting recommended an annual Indian Ocean Meeting be convened by InterRidge to ensure proper dissemination of information and data;
an “Indian Ocean Column” has been made a permanent feature of the InterRidge News to further facilitate exchange of information concerning research activities in the Indian Ocean;
a science and planning meeting focusing on the Arctic Ridges has been organized and will be convened in November 1994.
The prime focuses of the Global theme during Phase 2 of the Program Plan (1995-1997) are:
the establishment of a global multibeam bathymetric database by linking distributed databases via the World Wide Web (a start is already being made in November 1994);
coordinated reconnaissance mapping and sampling of a complete super-segment, the Southwest Indian Ridge from the Bouvet Triple Junction to the Rodrigues Triple Junction (first cruises scheduled for early 1995);
coordination of planning efforts for mapping and sampling of the Arctic Ridges.
2. Meso-Scale Studies
During Phase 1 of the Meso-Scale project the following progress has been made:
the principal scientific issues involved in investigation of second-order segmentation of the mid-ocean ridges in terms of magmatic and tectonic processes and mass, energy and chemical fluxes were identified at a science meeting entitled
Segmentation and Fluxes at Mid-Ocean Ridges: A Symposium and Workshops, held in September 1993;
a follow-up planning meeting entitled 4-D Architecture of the Oceanic Lithosphere was convened in September 1994 to discuss experiment design and site locations for an international project to investigate magmatic, tectonic and hydrothermal processes at a second-order segment;
Back-Arc Basin Studies: A Workshop was convened in 1993 to identify the principal scientific issues and coordinate research efforts in the study of back-arc basin spreading;
InterRidge was instrumental in creating a new SCOR Working Group 99: “Linked Mass and Energy Fluxes at Ridge Crests”;
In response to an invitation from JOIDES, InterRidge has made a submission to the revision of the ODP Long Range Plan.
The prime focuses of the Meso-scale theme for the timescale 1995-1999 are:
an integrated study of a fast spreading segment (Hess Deep);
an integrated study of a slow spreading segment (Mid-Atlantic Ridge, shortlist decided);Ocean Drilling experiments integrated with both the above and at Atlantis II FZ, SWIR;
petrological database of Back-arc Basins on World Wide Web;
segment-scale experiment to measure integrated fluxes at Mid-Atlantic Ridge.
3. Active Processes
InterRidge efforts under the Active Processes theme will be developed under two main initiatives:
development of a ridge observing and monitoring capability, including long-term observatories;
detection of transient ridge-crest seismic, volcanic and hydrothermal events and logistical response to them through a strategy of international collaboration.
A workshop Event Detection and Response and A Ridge-Crest Observatory to further define this part of the programme was convened in Paris in January 1995.
This short paper can give only a brief overview of the scientific objectives of InterRidge and their justification. The science plan has been progressively refined by the various workshops described above, the reports of which are generally available and contain much more detail on the detailed scientific background, aims and objectives, and implementation plans for the various parts of the programme.