with 8.4° to 8.7 °C in the adjacent oxygenated 

 water in the Inner Bay (Figure 4). Calculated 

 density values (Figure 5) show that the water 

 within the affected mass was more dense {o^, 

 23.6) than the overriding water within the Inner 

 Bay {a , 22.6 to 23.4). The two features com- 

 mon to anoxic situations in fjords were present 

 — a shallow sill and an adjacent pycnoline. The 

 situation at Little Port Walter was typical of 



STATIONS 

 I 2 3 



Figure 2. — Dissolved oxygen (mg/liter) contours in 

 anoxic estuary, Inner Bay, Little Port Walter, 6 October 

 1971. 



Figure 5. — Density (a.) contours in anoxic estuary. 

 Inner Bay, Little Port Walter, 6 October 1971. 



anoxic fjords; the pycnocline existed because of 

 a strong halocline. 



The mass of anoxic water was abruptly flushed 

 out of the bay sometime between midday of 

 6 October and early evening of 7 October. On 

 the evening of the 7th, divers found that the 

 water was clear. Live benthic animals (mostly 

 shrimp) were seen, although not abundantly, 

 in the area where none had been seen the pre- 

 vious 3 days. Also, most of the dead organisms 

 had disappeared. 



Figure 3. — Salinity (%o) contours in anoxic estuary. Inner 

 Bay, Little Port Walter, 6 October 1971. 



Figure 4. — Temperature (°C) contours in anoxic estuary. 

 Inner Bay, Little Port Walter, 6 October 1971. 



Possible Causes of Formation and Destruction 

 of Anoxic Condition 



Depletion of dissolved oxygen to the point 

 of anoxia in Little Port Walter is probably the 

 result of the biochemical oxidation of organic 

 matter (mainly salmon carcasses) both in Sashin 

 Creek and in the Inner Bay. Richards (1965b) 

 explains a mechanism which could account for 

 the situation observed at Little Port Walter. 



As long as appreciable quantities of dissolved 

 oxygen are present in the water, it is the pre- 

 ferred hydrogen acceptor for the biochemical 

 oxidation of organic matter, being the richest 

 available source of free energy. The decompo- 

 sition can be pictured as the hydrolytic release 

 of ammonium and phosphate ions, and the oxi- 

 dation of the organic residues to carbon dioxide 

 and water. The released ammonia is a transient 

 form, because in oxygen-bearing waters it enters 

 upon nitrification and is oxidized through nitrite 

 to nitrate — the most abundant form of combined 

 inorganic nitrogen in the ocean. 



When all, or nearly all, of the dissolved oxygen 

 is consumed, nitrate and nitrite ions become the 



898 



