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FUTURE DIRECTIONS IN OCEAN SCIENCES 117 



Air-sea fluxes of momentum and heat, for example, are not ad- 

 equately characterized in present models, which do not take into 

 account small-scale variability, directional offsets between the wind 

 and waves, limited fetch, and limited water depth (which charac- 

 terize the coastal environment; Geernaert, 1990). In addition, 

 thermal fronts, which occur throughout the coastal ocean, greatly 

 perturb the atmospheric layer directly above the sea surface and 

 sometimes perturb weather systems. Further, the coastal topogra- 

 phy helps to generate small-scale disturbances in the surface winds 

 that can affect currents over the shelf. Air-sea fluxes of particles 

 and chemicals, known to be important, must be a significant part 

 of any study. Until we can quantify the air-sea momentum, heat, 

 and chemical fluxes in this complex environment, we cannot un- 

 derstand the coastal ocean system as a whole. 



Air-sea exchange is complex, but answers to the questions 

 must be found. The atmosphere is the basic driving force of many 

 coastal ocean processes. Ocean fluxes, especially heat fluxes, are 

 critical to properties of the atmosphere. Air-sea exchanges that 

 govern the effects of ocean and atmosphere on each other need to 

 be quantified. 



Cross-Margin Transport 



The interaction of currents with bottom topography tends to 

 isolate continental shelves from the rest of the ocean, although 

 the strength of this isolation is significantly modulated by other 

 processes. Even when the isolation is especially strong, shelf 

 waters resemble the open ocean more than they resemble estuar- 

 ies. It is difficult to identify which processes determine the cross- 

 margin fluxes of water, particulates, chemicals, and organisms 

 within estuaries, between estuaries and the shelf, on the shelf, 

 and at the shelf-ocean boundary. The relative importance of such 

 factors as wind-driven motions, frontal instabilities, turbulent bound- 

 ary-layer transports, exchanges through submarine canyons, and 

 the sinking of dense waters has not been evaluated. The diffi- 

 culty is ultimately their episodic nature in terms of both location 

 and time. Each has distinct effects on biological, chemical, and 

 geological processes, so that interest in them is not limited to 

 physical oceanographers. 



Information on cross-margin transport is critical to all subdis- 

 ciplines of coastal ocean science. Alongshore gradients of most 

 characteristics tend to be small relative to cross-shelf gradients, 

 and alongshore currents are relatively well understood. It is cross- 

 shelf transport, or its absence, that shapes many distributions. 



