the winter values. In deeper water (20 to 50 m) the salini- 

 ty remained rather constant at 30 to 31 °/°° through the 

 year. The salinity of surface waters varied 3 to 5°/»» in a 

 few days during the spring-fall period while short-term 

 variations in the deeper water seldom exceeded l%o. 

 Two distinct layers of water — surface (to 30 m) and 

 deep (below 30 m) — appear in the vertical profiles of 

 salinity in Auke Bay (Fig. 9). Between January and 

 April, isohaline conditions exist from the surface to 50 m. 

 The salinity of the surface layer decreases continuously 

 from April through July or August, and a strong salinity 

 gradient forms in the top 10 to 12 m. The strongest 

 halocline occurs in July with salinities near 20 %o at 5 

 m, 27°/oo at 10 m, and 31%o at 30 m. Surface salinity 

 remains low through September and increases in Oc- 

 tober as a result of autumn storm mixing. The strong 

 halocline of July and August is the result of peak runoff 

 from the large, glacial-fed streams. Runoff from the low 

 elevation, forested watersheds does not affect surface 

 salinities as much as runoff from the glacial streams. 

 Runoff from lower elevations peaks in both the spring 

 and the fall, but not during the summer (McLain 1969). 

 Often in the summer silty glacial Mendenhall River 

 water intrudes from neighboring Fritz Cove into the 

 clearer waters of Auke Bay. 





1G 



17 18 19 10 



21 



SALINITY (°/oo) 

 22 23 24 25 



26 



27 



28 



29 



30 31 



2 



s 



10 

 15 





& JANUARY 

 X APRIL 















1 





20 





O JULY 



















= » 





D OCTOBER 















HI 





po 



















b M 





°3S 























US 



- 





















so 



- 





















55 













































Figure 9.— Typical profiles of salinity (V..) in Auke Bay, Alaska, 

 for January, April, July, and October; data are averages for 1960-G8. 



Density 



Water density, a function of temperature and salinity, 

 is used to identify water masses and to assess the stabili- 

 ty or stratification and probable circulation of these 

 water masses. Over the range of values observed in Auke 

 Bay density is affected more by salinity variation than by 

 temperature variation. 



The annual cycle of water density of Auke Bay from 

 1960 to 1968 expressed in terms of a , 3 is shown in Figure 

 10. The density of the surface water in Auke Bay varied 

 over a range of o, values between 9 and 24. Density was 

 greatest and varied little with depth from December to 

 April. In late April, density began to decrease at the sur- 



'Sigma-t (o t ) = 1,000 (p-1) where p is the density of the water. 



face 



and continued to decrease through July, rea 



ching a 



minimum in August (mean minimum a, = 11.0). The 



change in a t occurred progressively later with increasing 



depths (Fig. 10). The minimum a t at 30 m was 22.2 in 



October. At 50 m the density was relatively constant and 



had no obvious maximum or minimum. 



Figure 11 shows the seasonal vertical profiles of 



average a, t . From January to April the water in Auke Bay 



is well mixed and the density is uniform from the sur- ; 



face to 50 m. From July to October there is a strong den- 



25- 





•■ :» 



> : 



■■ =■:•■ 



















15- 













■ - ; ' 















" 



SURFACE 













* '..•' 











25- 













r f. 













-;- 





15- 













"-■ 















" 



5 M 

























I" 25- 



* , 



t " f 



iV- 



V 



.;-. . 

















> 



5 's- 















' ; : 







-:, 







5_ 



10 M 

























25- 



■ '.-,'• 



f '_- 



y. 





. % r. . 



- •£; 











. "■'•"" 







20 M 



















• - 4 ' 







15- 

 25- 



■>-" 



r 



.«-■ 





■■;■■ 





.-<■• 





. : . 



• ,. 









30 M 

























25- 



■■-; 





. c-. • 



-..-■ 











..-.-_■- 



-■• 











50 M 



























J 



F 



M 



A 



M 



J 



j 



A 



S 







N 



D 



MONTH 



Figure 10. — Observed densities (as o t ) at selected depths in Auke 



Bay, Alaska, 1960-68. 





DENSITY 1 c-,) 

 9 11 13 15 17 19 21 23 25 





~° ~ -—_____^ ^ ¥, 



to 



& JANUARY 4^ H*. 





K APRIL V*V 1 1 





° JULY \ ^\ \\ 



20 



a OCTOBER V N^ 





3 



1" 



1 







40 







SO 





1 



Figure 11.— Typical profiles of density (as o t ) in Auke Bay, Alaska, 



for 



Jt 



nuar 



y, Ap 



ril, Ji 



ily, a 



tidOt 



tobei 



; dati 



i are 



averages for 196 



3-68. 



