100. What causes the hydrogen sulphide concentration at the 

 bottom of the Black Sea? 



The Black Sea is landlocked with only a narrow, shallow outlet to the 

 Mediterranean Sea. As a result of its configuration, the bottom water is 

 stagnant. Although the surface water is well oxygenated and teeming 

 with life, water below the depth of about 200 meters contains no oxygen 

 and is inhabited only by bacteria that decompose organic matter drift- 

 ing down from above. 



Decomposition of organic material on the bottom uses up any avail- 

 able oxygen so that hydrogen sulphide is concentrated in a thick layer 

 of bottom water. This hydrogen sulphide colors the black mud on the 

 sea floor. 



Similar conditions occur in those Norwegian fiords that are separated 

 from the open ocean by shallow sills. 



Miller, Robert C. 



The Sea, Random House, 1966. 



Sverdrup, H. V., Martin W. Johnson, and Richard H. Fleming 



The Oceans, Their Physics, Chemistry and General Biology, Prentice- 

 Hall, 1946. 



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