known as "the minimum oxygen zone." Below and above this depth, the dissolved 

 oxygen content starts to increase. The underlying causes of the minimum oxygen 

 zone are still imperfectly understood. 



Biological Activity 



Rock Samples . Rock specimens were desired from this area to study any fouling 

 organisms attached to the rocks, since they could be expected to attach themselves 

 to other materials placed there. Prior to placing the STU at this site, a pipe dredge 

 — a 10-inch-diameter by 36-inch-long steel pipe with retaining rods welded across 

 the lower end of the pipe — was lowered to the ocean floor from an oceanographic 

 vessel, USNS DAVIS, and the area dredged for rock specimens. Several passes were 

 made across the area but no specimens could be obtained. 



Sediment Samples. Marine bacteria are one of the major biological agents in 

 the deterioration and fouling of various materials and equipment submerged in the 

 sea. To detennine the type and activity of bacteria in this deep-ocean area, sediment 

 samples for bacteriological and biological analysis by standard microbiological methods" 

 were obtained with: 



1. A gravity core sampler, which takes cores up to 4 feet long. 



2. NCEL's scoop-type bottom sampler, which collects about 225 cubic inches 

 of sediment from a soft bottom. 



3. A modified ZoBell bacteriological sampler, used to collect a mixture of sea 

 water and sediment.! 



Approximately 1,500,000 aerobic and 5,000 anaerobic bacteria were found in 

 a gram of sediment (net weight) collected at the sediment -sea water interface. 

 Sulfate-reducing bacteria were also present in the samples. The sulfate reducers are 

 anaerobic bacteria which obtain their energy by the reduction of sulfate and sulfites 

 in water in the absence of free oxygen. The end product of their metabolic process 

 is hydrogen sulfide (H2S). These microbes are considered to be responsible for the 

 anaerobic corrosion of metals. 



The sediment samples obtained with the scoop sampler were washed through a 

 screen to collect mud-dwelling organisms. The animals were bottled and preserved 

 in a 5-percent glycerol-alcohol solution for laboratory analysis. 



A variety of animals were found in these samples. Amphipods and annelids 

 were the most abundant marine organisms collected in the vicinity of STU Test Site II 

 (Figures 3 and 4). 



