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FUTURE DIRECTIONS IN OCEAN SCIENCES 89 



and electromagnetic methods to increase their sensitivity to the 

 detection of fluids will be particularly relevant. 



Recycling 



Mass flux studies needed to understand convergent margins as 

 dynamic systems will involve integrated field, analytical, experi- 

 mental, and theoretical studies that draw from geochemistry, pe- 

 trology, and geophysics. Such projects require marine as well as 

 land-based studies and careful integration of results from the two. 

 Sampling must include fluids, melts, sediments, crust, and gases 

 from the entire subduction zone, the subducting plate to the back- 

 arc zone. Theoretical and experimental studies are an essential 

 addition to these geochemical and geophysical programs. Existing 

 studies have related only to isolated aspects of mass fluxes at 

 convergent margins. However, the results of these studies can be 

 used in conjunction with samples from existing and planned Deep 

 Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) 

 holes drilled offshore of various trenches to formulate an inte- 

 grated, multidisciplinary plan for studying these complex systems. 



Ocean Basin Sediments 



Marine sediments provide important records for important Earth 

 processes. For example, marine sediments furnish a history of 

 regional and global volcanic activity, a record of the long-term 

 changes in Earth's magnetic field, and a tool for studying large- 

 scale tectonic processes, such as continental accretion and rifting. 

 An active area of research is the study of past global climates. 



Evidence of global environmental change comes from the 

 paleoclimate record, which is the only long-term record available. 

 The paleoceanographic record provides information necessary to 

 understand environmental changes (see "Directions for Marine 

 Geochemistry"). The paleoceanographic record also places obser- 

 vations of the present ocean in a historical context of long-term 

 environmental variability. It affords a unique opportunity to test 

 our understanding of the climate system as represented by nu- 

 merical models of the ocean-atmosphere system. If models of the 

 present ocean are capable of hindcasting oceanographic conditions, 

 then we should have more confidence in their predictive capabil- 

 ity. Whereas satellites provide a global means to observe the 

 ocean surface, ocean sediments and the proxy indicators of oceano- 



