Abyssal Benthic Organisms: Nature, Origin, 

 Distribution, and Influence on Sedimentation 



ANTON F. BRUUN and TORBEN WOLFF 



University Zoological Museum, Copenhagen, Denmark 



THE term "abyssal" is used here in the same sense as i \ the Treatise 

 on Marine Ecology and Paleoecology (Bruun, 1957) ; it thus includes 

 the depths from about 2000 m to about 6000 m, or more than one- 

 third of the surface of the globe. It does not, however, include those 

 depths in more enclosed areas such as the North Polar Sea, the 

 Mediterranean, the Japan Sea, or the Sulu Sea, where special con- 

 ditions create temperatures different from those usual for the open 

 ocean at these depths, namely about 1-4° C. 



By far the greater part of the abyssal region is covered with a 

 soft bottom, a fine ooze, or clay. Calcareous oozes, especially Globi- 

 gerina oozes, dominate in depths of less than 4000 m, whereas abys- 

 sal clay is encountered only in depths exceeding 4000 m. In many 

 places considerable debris of land plants is found (Bruun, 1959, 

 Fig. 7), which seems to be important for the production of food 

 with bacteria as the first link in the food chain. 



Fauna 



In general, the animal community of the abyssal zone may be 

 called a soft bottom community. In any case, rock surfaces without 

 any sediment covering exist only over a small fraction of the whole 

 abyssal area. It is no wonder then that the abyssal fauna in many 

 ways resembles soft bottom communities from shallower depths. 

 The nature of such a community has been discussed by Ekman 

 (1953), who also cites many examples of its representatives. 



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