SOUTHEASTERN 

 ALASKA 



SITKA 



) ANOXIC AREA 

 • SAMPLING STATION 



Figure 1. — Little Port Walter estuary, Baranof Island, 

 southeastern Alaska. 



directly with Chatham Strait through a channel 

 approximately 36 m. deep. 



The basins of both Inner and Outer Bays are 

 steep sided, with practically no shelf formation 

 except for a small shoal area at the head of Inner 

 Bay. The surface area of the estuary consequent- 

 ly undergoes little change between low and high 

 waters. Basins of this type are characteristic of 

 Bai-anof Island as well as much of the rest of 

 southeastern Alaska. The coastline is frequently 

 indented by long narrow, deep embayments 

 from which mountains rise sharply to heights 

 of several thousand feet. 



Tides in the estuary exhibit the exaggerated 

 diurnal inequality typical of the west coast of 

 North America. The range of spring tides at 

 Little Port Walter is as much as 4.6 m., the 

 range of neap tides less than half of this. With- 

 in the estuary, the tide has the characteristics 

 of a standing wave, with high and low slack 

 waters occurring at about the same time over 

 the entire basin. 



The surface area of Inner Bay, where the 

 anoxic condition was observed, is about 0.25 

 km-, and the approximate area of the affected 

 water was about 0.02 km- (Figure 1). 



Observations During Anoxic Period 



The first time the anoxic condition was ob- 



served was on 4 October 1971, when two biolo- 

 gists (including the senior author) from the 

 Auke Bay Fisheries Laboratory made a night 

 dive in Inner Bay. The purpose of the dive was 

 to count shrimp along underwater transects 

 close to the shallow sill that separates Inner 

 and Outer Bays. In a restricted area near the 

 sill and below a depth of 12 m, the divers saw 

 numerous dead animals on the bottom; most 

 of them were shrimp, but there were also nu- 

 merous chitons, limpets, clams, anemones, sea 

 stars, crabs, and a few fish. No animals definitely 

 known to be living were seen in the anoxic zone. 

 No indication of the deeper affected zone was 

 evident at the surface or in the water column at 

 depths less than 12 m. 



During the next 2 days (5 and 6 October) 

 additional dives were made into the affected 

 area to make more observations and to collect 

 water samples. The water mass in the area of 

 the die-off was obviously different from that in 

 the rest of the bay; the water was milky, and 

 visibility within the area ranged from a few 

 centimeters to a meter. Outside of that area the 

 water was clearer, and visibility was 6 m or 

 more. Within the milky water of the die-off 

 area, there was an odor of hydrogen sulfide — 

 strong enough, in fact, to be smelled by the 

 divers under water. 



Three stations (Figure 1) were set up at which 

 measurements of salinity, temperature, and dis- 

 solved oxygen were taken. Two of the stations 

 were within the Inner Bay — station 2 in the 

 affected area and station 1 in an unaffected area 

 immediately adjacent to the affected water mass. 

 The third station (station 3) was in the Outer 

 Bay. Water samples collected on the third day 

 of observations (6 October) in the area where 

 the die-off had occurred had extremely low levels 

 of dissolved oxygen (less than 0.08 to 0.45 mg 

 02/liter); those collected outside of this area 

 had much higher levels (4.23 to 8.29 mg O2/ 

 liter). Approximate contours of distribution of 

 dissolved oxygen are shown in Figure 2. The 

 affected water mass had higher salinity than the 

 surrounding waters within the Inner Bay; near 

 the bottom salinity was 30.4"/oo in the anoxic 

 water and 30.17oo in the adjacent oxygenated 

 water (Figure 3). Similarly, temperature was 

 higher in the anoxic water — 9.2 °C compared 



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