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50 Years of Ocean Discovery: National Science Foundation 1950—2000
gator tends to be limited to a small range of time scales of processes and resulting spatial scales of sedimentary features. The investigator is familiar with the next lower time-space scale of research, since his/her investigation likely uses the tools of that research (i.e., sediment-transport equations) or relies on its conclusions; the investigator is likely also aware of the implications of his or her research to the next higher time-space scales. While it is seldom that an individual can meaningfully cover an appreciable area of the time-space graph, it is through collaborative research efforts and modeling that connections can be made that lead to a more comprehensive understanding of the processes that are presently important, and were important in the past, to the sediments and sedimentary record of the margin system. A deeper understanding in the future will therefore depend on increased support for such collaborative research efforts.
As we enter the twenty-first century, seventy percent of the world' s population will live and work alongside the sedimentary province of the ocean margins. The deposits of the coastal plain, shoreface and shelf, slope, and rise consist of particles and pore fluids arranged in a complex architecture of bedforms, layers, wedges, aprons, and lenses that define the anatomy of the province.
For over a century, human activity has perturbed the coastal sedimentary province by the filling of wetlands and the reclamation of estuaries, through the construction of sea-walls and breakwaters, and by starvation of the sediment supply as a consequence of damming rivers for hydroelectricity, irrigation, and flood control. Many of the environments of this province are "diseased" from thoughtless use, over-exploitation, and even well-intentioned but ignorant attempts at mitigating the problems that come with human influences. Millions of dollars are spent annually to pump sand back to the shore to replenish beaches, only to have these grains disappear into the sea again following northeasters, hurricanes, or typhoons. Much of this province has been alternately submerged and exposed in the past. Some of it will experience renewed flooding if global warming predictions are correct. Some sectors, such as the extremely populated Nile Delta and portions of the Mississippi Delta, are currently in a state of crisis in the wake of severe coastal erosion. The megalopolis of Bangkok is sinking at an alarming rate of one meter in a human lifetime due to a combination of diminished sediment supply and aquifer depletion.
True stewardship of the sedimentary resource will require an improved understanding of its anatomy. The piecemeal, ad hoc examination typical of past research will not provide a sufficiently integrated understanding of the character of the system. A new approach must incorporate the next generation of Earth and environmental scientists trained with greater engineering skills and an integrated knowledge of the physical/chemical/biological metabolism of the sedimentary environment. This is necessary preparation for the challenge of quantitative modeling and measurement that lies ahead. A new, integrarive science must be the hallmark of future sedimentological research. In order to achieve new goals of understanding the ocean margin, the science of sedimentology must evolve into a systems approach that integrates theories and concepts of biochemistry, geophysics, meteorology, climatology, population statistics, ecology, and hydrodynamics.
GROUP #4: FLUIDS IN THE OCEANIC LITHOSPHERE AND MARGINS
The importance of water to essentially all aspects of Earth science probably cannot be overstated. Water is a ubiquitous agent of geological creation and transformation and of life. The charge of Working Group 4 was to construct a vision for the next 10+ years of marine geological and geophysical research involving fluids, fluid processes, and fluid products. This vision is to include an assessment of the most important unresolved questions, the means by which these questions should addressed, and the infrastructure and facilities that will be required to do so. The completion of our assignment was complicated by the nature of fluids themselves: they exist at an astonishing array of temperatures, pressures, chemistries, and physical properties, within many different geological systems.
While many questions associated with lithospheric fluids may be addressed successfully through the use of steady-state assumptions, it is becoming increasingly clear that fluid flow and associated processes and properties are inherently transient and interdependent. We suggest that issues associated with fluid flow and resulting reactions, chemistry, biology, and physical properties can be considered in the context of conservation of mass and conservation of energy. The simplest example of this concept is illustrated through examination of the one-dimensional, steady-state diffusion equation (used for chemical, thermal, electrical, and fluid transport): q =-D dP/dl. This equation states that the flux (q, mass or energy) is a function of the driving force (dP/dl , a gradient in potential) and the properties of the system that govern transmission (D). If one knows any two of the above terms, the third can be calculated. Ideally, all three would be determined independently so that internal consistency can be established.
Other modes of transport can be described in such an equation through inclusion of additional terms (advective, dispersive, reactive, decay, etc.). When such a construction is applied to a volume of the oceanic lithosphere or margin, multidimensional and transient processes can be considered, including the importance of storage terms (for both energy and mass) and tensor properties. With this framework in mind, key questions can be considered:
What are the mechanisms influencing hydrothermal fluxes associated with dike injection, transient magma chamber output, and penetration of a cracking front (extent of water-rock reactions, creation and modification of fluid pathways).