354 



BosTWiCK H. Ketchum and D. Jean Keen 



400 times as great as the product SyAf/i\y for the winter distribution and the 30 

 fathom contour. This product for the direction parallel to the coast never exceeds 

 one per cent of the value normal to the coast. 



As has been shown above, there is a decrease of salinity for this area between the 

 spring and summer conditions, and a corresponding increase between the summer 

 and winter conditions, with httle or no change between the winter and spring condi- 

 tions. Since the flushing time of the area is a year and a half, and these changes 

 occur in shorter periods, the distribution cannot be treated as a steady-state. How- 

 ever, it is possible to evaluate the flux of salt from the seasonal changes, and to 

 compute average mixing coefficients from these data. The necessary data are pre- 

 sented in Table IV, and the coefficients are given in Table V, 



Table IV 

 The mean salinities at three seasons of year, and the flux of salt across different depth 

 boundaries on the continental shelf between Cape Cod and Chesapeake Bay. The 



contours selected average 28 kilometers apart 



Table V 

 The coefficients of horizontal diffusion computed from the changes in salinity at different 



seasons of the year 



Depth 

 Contour 

 Fathoms 



30 



40 



100 



Horizontal Diffusion Coefficients 



IQ^cm^ I sec. 

 Sp.-Su. Su.-Wint. 



2-52 

 1-72 

 0-58 



4-96 

 3-41 

 1-48 



The net flux of salt is positive for the change from spring to summer, since salt is 

 being transported oflFshore in the plus x direction, and negative for the change from 

 summer to winter when the salinity increases again. The net flux of salt resulting 

 from changes from season to season range from about 15 to 50% of the offshore 

 advection of salt with the river water escaping from the area. The coefficients of eddy 

 diffusion (Table V) obtained for the spring-summer change range from 0-58 to 2*52 

 X lO^cmVsec, and the values obtained for the summer-winter change vary from 

 1-48 to 4-96 X 10® cmVsec. At both times the value decreases with increasing depth 

 and distance from shore. Although the vertical component of turbulence has been 



