409 



FUTURE DIRECTIONS IN OCEAN SCIENCES 75 



estimation of variability of fluxes. Weathering processes are tra- 

 ditionally regarded separately from oceanography, but oceanic tech- 

 niques are essential to trace the pathways by which material en- 

 ters estuarine mixing zones through rivers, progresses across the 

 shelf, and finally moves into the deep sea. For some elements 

 (e.g., iron), delivery to the world ocean by this route is negligible 

 because of their insolubility in seawater. Soluble elements pass 

 through the coastal ocean with little loss. Research on this topic 

 has great societal importance because chemical fluxes substan- 

 tially alter global climate, coastal pollution, and possibly harmful 

 algal blooms and fisheries production. 



The strength of airborne transport of particles is known to 

 vary widely with climatic conditions. Airborne transport is the 

 one direct pathway between the continents and the surface waters 

 overlying the deep ocean, and its importance as a supplier of mi- 

 cronutrients (e.g., iron and selenium) needs to be more firmly 

 established. It is possible that the productivity of some areas of 

 the ocean is controlled partially by the amount of airborne trace 

 metals. This area of research is an active one. 



Estimates of the hydrothermal flux range over a factor of five. 

 The mechanisms responsible for the wide salinity variations and 

 the temporal stability of the values at a given site are not under- 

 stood. Both of these problems can be resolved only by systematic 

 investigation of vent fluids from different sites and by develop- 

 ment of additional tracers of both the subsurface reaction pro- 

 cesses and the characteristic hydrotheimal inputs to the global 

 reactor. 



Fluid inputs from the mid-ocean ridge flanks and from sub- 

 duction zones are perhaps best studied by drilling and pore water 

 sampling because the flow across the seafloor-water interface may 

 be too diffuse for discrete sampling in the water column. Much 

 improved down-hole sampling and measurement capabilities are 

 required. Systematic sampling of representative ridge flanks and 

 subduction zone complexes is needed, using the complete range 

 of modern geophysical tools. 



Understanding Redistribution and Removal in the Ocean 



The general circulation of the global ocean has been relatively 

 well described. From the geochemical point of view, much re- 

 mains to be learned about the relative importance of the removal 

 of elements at ocean boundaries versus in situ removal by settling 

 particles. The spatial and temporal variability of processes con- 



