Workshop Report - Ridge 2000 Program

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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
Page 2 and 3: The Mid-Oceanic Ridge A Dynamic G
Page 4 and 5: OCEAN STUDIES BOARD WALTER H. MUNK,
Page 6 and 7: PREFACE Recent discoveries of the w
Page 8 and 9: o Regional Scale: selected subsets
Page 10 and 11: 1 INTRODUCTION The global mid-ocean
Page 12 and 13: papers were compiled, printed, and
Page 14 and 15: 2 STATEMENT OF GOALS AND OBJECTIVES
Page 16 and 17: experience from land volcanic and m
Page 18 and 19: solid understanding of both the bio
Page 20 and 21: NEXT STEPS TOWARD A RIDGE INITIATIV
Page 22 and 23: 4 REPORTS OF THE WORKING GROUPS INT
Page 24 and 25: Critical Investigations The specifi
Page 26 and 27: Seismic refraction methods provide
Page 28 and 29: New Instrument and Laboratory Capab
Page 30 and 31: GROUP 2: GEOMETRY AND DYNAMICS OF M
Page 32 and 33: FORMATION OF OCEAN CRUST AT SPREADI
Page 34 and 35: 3. Regional Surveys. The third comp
Page 36 and 37: provide efficient and economically
Page 38 and 39: 3. Adaptation of tomographic invers
Page 40 and 41: Consequently, the sin;J1e most impo
Page 42 and 43: Thermal stresses have been suggeste
Page 44 and 45: electromagnetic fields must be meas
Page 46 and 47: capability should include at least
Page 48 and 49: In order to understand subseafloor
Page 50 and 51: fossil hydrothermal systems in ophi
Page 54 and 55: GROUP 5: BIOLOGY OF HYDROTHERMAL SY
Page 56 and 57: There are several key questions abo
Page 58 and 59: Dispersal of Organisms What are the
Page 60 and 61: Strategy Biological studies will em
Page 62 and 63: GROUP 6: WATER COLUMN DYNAMICS AND
Page 64 and 65: On the ridge segment scale, detaile
Page 66 and 67: standard transect sampling and Lagr
Page 68 and 69: APPENDIX I The Mid-Oceanic Ridge: A
Page 70 and 71: Forsyth, Donald Department of Geolo
Page 72 and 73: Lonsdale. Peter Scripps Institution
Page 74 and 75: Reeve, Michael National Science Fou
Page 76: Tunnicliffe, Verena University of V

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