416 BOUNDARIES OF THE SEA 



of successive fractions increases considerably after removal of the 

 largest particles. 



Gaseous Exchange 



For particulate matter, it was found that the rate of exchange 

 could be described by a transport velocity times the concentration 

 of sea salt per unit \'olume. A likely figure for this transport velocity 

 is 1.5 cm sec~^ Only diffusion processes operate for gaseous matter, 

 but despite this it may be of interest to see if gaseous exchange 

 also can be formulated as transport velocity times the concentra- 

 tion. Dimensional ly this can be inferred and can also be derived as 

 follows. 



For two substances a and b we can write the fluxes: 



Fa - -k/-^ (4a) 



dz 



dz 



If it is assumed that the fluxes are constant and that Ka = Kb in 

 the whole region, we can write 



Fadpb = Fbdpa (5) 



and integrate between two levels s^ and z.,. If the differences of 

 Pa and pb at these levels are designated Apa and Apt, we have 



Fa ^^ —^ ■ Apa (6) 



Ap6 



and writing Fb/Apb = w, 



Fa = IV A Pa (7) 



i.e., the flux of the substance a is a product of a transport velocity 

 w and a concentration difference Apa. This transport velocity is, 

 of course, the same for all gaseous substances considered under the 

 conditions given. 



Consider now exchange between the air at a certain point and the 

 sea surface, the exchange not being limited by conditions in the 

 sea. We chose the lower level of integration to be at the air-sea 



