sity gradient from the surface down to 30 m. The data for 

 all years of this study show the same seasonal pattern of 

 density distribution. 



Stability 



Stability of a water column 1 is determined by the rate 

 of change of density with depth, the vertical gradient of 

 density. Where stability is high, vertical movement and 

 vertical mixing are inhibited. The water column in a 

 strong vertical gradient of density (a marked pycnocline) 

 is very stable, and much more energy is required to dis- 

 place particles of water upward or downward than in a 

 region where the gradient is weak. This mechanism 

 greatly restricts the vertical transfer of water from the 

 deep layer to the upper layer in Auke Bay. Tidal-in- 

 duced turbulence is unable to penetrate the pycnocline. 



Table 1 gives numerical values for the stability of Auke 

 Bay water during July and August 1965. All the stability 

 values in Table 1 are positive and relatively high, in- 

 dicating a highly stable water column. Data from other 

 years show the same general density distribution as in 

 1965; all depict a highly stable water column during the 

 summer. The similarity between seasonal cycles of 

 salinity and density in Auke Bay (Figs. 8 and 10) is ex- 

 pected because of the strong dependency of density on 

 salinity at the relatively low temperatures common in 

 Auke Bay. 



The development of a stable water column is one of the 

 most ecologically significant features of the 

 oceanography of Auke Bay because stability of the water 



'For depths to 100 m, stability (E) can be expressed by 



E = 10 ' (Sverdrup et al. 1942, p. 417), 



dZ 



or in different form 



3 [ : 



E = 10 



,) 



( z , - z , ) 



where Z = depth 



dZ = Z, - Z, = change in depth 



do, s (", , 0",,) = change in a, 



o, = 1.000 ( p- 1) where p= density of the water. 



column is a prerequisite for the onset of spring 

 phytoplankton bloom (Riley 1942; Sverdrup 1953; Steele 

 1966). Gilmartin (1964) found that seasonal variability in 

 the stability of the water column in a British Columbia 

 fiord was the primary factor controlling phytoplankton 

 growth. We observed a strong burst of phytoplankton 

 growth each year in April or early May as solar radiation 

 increased and a stable water column began to form. It is 

 clear that stratification has a pronounced effect on the 

 basic productivity of Auke Bay throughout the spring- 

 summer growing season. 



Dissolved Oxygen 



Oxygen is one of the common gases dissolved in 

 natural waters and is critically important because of its 

 key role in biological energy transfers. Although aquatic 

 organisms respire efficiently at oxygen concentrations 

 considerably below saturation values, metabolic rates 

 and efficiencies are dependent on the availability of dis- 

 solved oxygen. Consequently, the dissolved oxygen con- 

 centration is a major determinant of the environmental 

 quality of water. The oxygen requirement of organisms is 

 given generally in terms of absolute concentration ex- 

 pressed in appropriate units such as mlAiter or mg/liter. 



Concentrations of dissolved oxygen at selected depths 

 in Auke Bay are shown in Figure 12. Dissolved oxygen in 

 the upper 5 m generally remained above 6 ml/liter, and 

 spring and summer concentrations were above 8 ml/liter. 

 Highest concentrations occurred from April through 

 June and maximum observed value was 11.4 ml/liter. 

 Below 10 m the concentration of dissolved oxygen 

 decreased with depth. In winter the concentrations 

 varied less with depths. The lowest concentrations of 

 oxygen at or near the bottom occurred in September and 

 October. 



The degree of oxygen saturation provides information 

 on the relative intensities of processes which affect the 

 oxygen content of the water. Supersaturation is ob- 

 served frequently and is essentially a result of high 

 photosynthetic activity by plants in the upper layer of 

 the water. Under conditions of high solar radiation dur- 

 ing the day and abundant nutrients, the rate of oxygen 

 production may exceed the rate at which oxygen is given 



Table 1.— Stability (E)' at Auke Bay monitor station in July and August 1965. 







21 July 1965 







10 August 1965 





Depth 

 (m) 



Temp. 

 (°C) 



Salinity 



o-l 



10 S E 



Temp. 

 (°C) 



Salinity 

 (%,„ ) 



"l 



10 6 E 







13.48 



16.30 



11.94 





16.55 



16.30 



11.37 





10 



7.84 



29.50 



23.01 



1,107 



7.98 



29.85 



23.26 



1,189 



20 



5.82 



31.10 



24.52 



151 



6.21 



30.85 



24.27 



101 



30 



4.76 



31.57 



25.01 



49 



5.66 



31.30 



24.70 



43 



50 



4.28 



31.90 



25.32 



16 



4.70 



31.72 



25.13 



22 



•See text footnote 4. 















