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84 OCEANOGRAPHY IN THE NEXT DECADE 



Physical, Chemical, and Biological Processes 

 Involved in Interactions Between Circulating Seawater 

 and the Lithosphere 



Hydrothermal plumes that issue from seafloor vents link the 

 oceanic lithosphere, hydrosphere, and biosphere through complex 

 physical, chemical, and biological interactions (Rona et al., 1986). 

 A detailed understanding of the individual processes that consti- 

 tute a hydrothermal system will provide insight into many prob- 

 lems in biological, chemical, geological, and physical oceanogra- 

 phy. Although present 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 interdiscipli- 

 nary view. 



Distribution and Intensity of Mid-Ocean 

 Hydrothermal Venting 



The character of hydrothermal plumes is determined by both 

 crustal processes and 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 hy- 

 drothermal plumbing, and shifting bottom currents. To under- 

 stand 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 1,000-kilometer scale of the large ocean-basin 

 plumes estimated to contain the integrated output from 100 years 

 of hydrothermal venting. An important new research direction is 

 to move from the realm of general observation to the quantifica- 

 tion of rates and processes in hydrothermal plumes. 



In summary, an improved understanding of the mid-ocean ridge 

 system will require focused efforts. Present technologies are rela- 

 tively well developed for establishing the occurrence of spatial 

 variations within the ridge system, but obtaining observations of 

 temporal change will be challenging. Global-scale reconnaissance 

 surveys can help in selecting sites for more focused regional stud- 

 ies in which coordinated experiments would involve a range of 

 long-term measurements. A common requirement of many of the 

 recommended studies is accurate age information on time scales 

 between a decade and a million years. Innovative approaches to 

 dating hydrothermal fluids, rocks, and biological materials will be 

 necessary to meet this requirement. 



