68 



The Sea-water and its Physical and Chemical Properties 



below 2000 m and the high oxygen content proves the possible presence of con- 

 vection descending to great depths and the considerable ventilation it would give. 



The renewal of the deeper water layers has a major effect on the oxygen distribution 

 in them. If renewal did not occur oxygen depletion processes would in time reduce the 

 oxygen content until it would be finally zero. It is to be expected that enclosed, stag- 

 nating water masses will always have a very low oxygen content when their thermo- 

 haline structure prevents the thermal circulation from the surface reaching the bottom. 

 If the surface layer density is so low that it does not become heavy enough when the 

 temperature decreases in the autumn and winter in order to change places with the 



6t 35 26 

 02% 20 I W 



500 



1000 



1500 



2000 



2500 



3000 



Fig. 37. Left : Vertical distribution of oxygen and density at about 10° S. in the South Atlantic 



(according to the values of the "Meteor" Expedition). Right: the same for "Meteor" station 



122 (Greenland, ^ = 55° 3' N., A = 44° 46' W). 



more saline deeper layers thus carrying oxygen to the layers beneath, the oxygen 

 content of the deep stagnating layers may fall to zero, especially when a lateral 

 addition of fresh water, due to the orographic conditions, is hindered or completely 

 missing. In this case hydrogen sulphide will be formed either by the decomposition of 

 proteins or by the reduction of sulphate by the carbon compounds of organic material 

 under the action of certain bacteria. The classic example of these conditions is the 

 Black Sea, where the water from about 200 m down to the greatest depths contains 

 considerable amounts of free hydrogen sulphide and thus forms a "Kingdom of the 

 Dead" from which all life has disappeared and where the organic world is represented 

 only by the lowest forms of plant life (Schokalski, 1924; Nikitin, 1927; Neumann, 

 1942, 1944). The thermo-haline structure of the Black Sea is indicated in Fig. 38 which 

 shows the vertical distribution of temperature, salinity, density, oxygen content and 



