412 



78 OCEANOGRAPHY IN THE NEXT DECADE 



erosion and transport, and estuarine and delta sedimentation. Coastal 

 processes are discussed elsewhere in this report. 



In the 1990s, marine geologists and geophysicists will begin a 

 major, decade-long study of the global mid-ocean ridge system 

 through the Ridge Inter-Disciplinary Global Experiment (RIDGE) 

 program^. The long-term goal of this program is to obtain a suffi- 

 ciently detailed spatial and temporal definition of the global mid- 

 ocean ridge system to construct quantifiable, testable models of 

 how the system works, including the complex interactions among 

 the magmatic, tectonic, hydrothermal, and biological processes 

 associated with crust formation. Among the goals that are achievable 

 in the next decade are a global characterization of the structure 

 and energy fluxes along the entire 50,000-kilometer-long mid-ocean 

 ridge system and the establishment of a permanent seafloor obser- 

 vatory on an active ridge segment to investigate the scales of 

 variability in tectonic, magmatic, hydrothermal, and biological 

 processes associated with the formation of new oceanic crust. 



The ancient ocean crust contains unique information about 

 mantle convection and composition. An improved understanding 

 of the chemical and isotopic record of mantle convection and the 

 variation of melt production through time is likely in the next 

 decade. Mapping crustal composition on an ocean basin scale 

 will require hundreds of shallow holes to be drilled into ocean 

 crust. Directly sampling the suboceanic mantle will require the 

 development of new drilling technology beyond that presently available 

 to the ocean drilling community. New seismic tomography tech- 

 niques for imaging the Earth's mantle will allow marine geolo- 

 gists to begin to relate mantle convection processes to melt pro- 

 duction rates, lithospheric stress and intraplate deformation, and 

 the variation in chemical and isotopic composition of the crust. 

 Vastly improved seismic images of the suboceanic mantle are pos- 

 sible if an array of seafloor seismic stations is established in the 

 1990s to augment the global digital seismic network. 



Continental margins are the locus of lithospheric deforma- 

 tion, sediment accumulation, and substantial and chemically dis- 

 tinctive magm^atism. Subduction and rifting processing at mar- 

 gins determine the size, shape, and distribution of continents and 

 result in complex and dynamic interactions among oceanic crust, 

 continental crust, and mantle systems. A basic description of the 

 nature and evolution of many margins is available today, but un- 

 derstanding of the dynamics of margin development is still very 

 limited. The development of new technology for probing the deeper 

 structure of continental margins, and new conceptual advances in 



