FUTURE DIRECTIONS IN OCEAN SCIENCES 



Observed 



111 



FIGURE 3-4 Observed {solid line] and modeled [dashed line] alongshore 

 currents from over the continental shelf off Oregon, summer 1978. Posi- 

 tive velocity denotes northward ilovf. After Battisti and Hickey (1984). 



the other hand, owe their high biological productivity to nutrient 

 inputs from the land and density-driven internal circulation that 

 serves to retain and enhance the recycling of these nutrients. 



Sea ice is important in controlling air-sea fluxes in coastal 

 regions when it forms there. Ice cover decreases heat, moisture, 

 and gas fluxes and modifies momentum fluxes. During the for- 

 mation of ice, salt is excluded, creating saltier adjacent water. 

 These dense water masses can sink, impacting an entire basin 

 through thermohaline circulation (see "Directions for Physical 

 Oceanography"). Freshwater generated by ice melting stabilizes 

 the water column, thus helping to prompt the spring phytoplank- 

 ton bloom. 



Tidal currents are sometimes enhanced over the continental 

 shelves by physical resonances taking place in bays, such as in 

 the well-known Gulf of Maine-Bay of Fundy example. Strong 

 tidal currents intensify near-bottom mixing that can extend to 

 the sea surface in shallow regions such as Georges Bank. This 

 mixing and the resulting circulation enhance nutrient availability 

 in the upper ocean, cause high primary productivity, enrich fish- 

 eries, and increase the transfer of organic material to underlying 

 sediments. Energetic tidal currents can reinforce the many physi- 

 cal processes (including waves and wind-driven currents) that in- 

 crease sediment resuspension and transport as well as the trans- 

 port of chemicals that adhere to the particles. 



Continental shelves are the transition zone between the land 

 and the ocean and are thus particularly important in processes 

 involving sediment and chemical fluxes. Freshwater outflows propel 

 currents with distinct properties. Sediments from the land are 



