EXPLANATION OF NUMERICAL RATINGS 



Because the sea floor is never perfectly flat, the rating zero is not used. The rating 1 denotes 

 minimum but recognizable roughness; the rating 5 denotes maximum roughness. Some descriptive notes 

 on the ratings follow: 



1. Almost smooth surfaces formed on clays, oozes, and silty clays in abyssal areas between, and 

 on, major and intermediate topographic features. Visible evidence of churning is lacking, with a 

 minimum of epifauna and infauna present. Rock fragments and manganese nodules occur in scattered 

 patches, varied according to chemical composition of water. 



Height of churning 3 cm. 



Normal range of microrelief to 1 cm. 



2. Low-order bottom relief formed by fauna churning on clays, oozes, and silty clays in areas of 

 gentle relief. Such low-order relief also occurs on marine slopes, valleys, basins, and other gentle 

 topographic features. More epifauna visibly present but not in great numbers in deeper areas. Occa- 

 sional occurrences of small manganese nodules and rock fragments in tightly packed or scattered 

 patterns of distribution, again dependent on seawater conditions. Occasional occurrences of loosely 

 scattered and larger manganese nodules with visible churning between targets. Oozes are normally in 

 shoaler areas and are coarser grained. 



Height of churning 3 to 6 cm. 



Normal range of microrelief 3 to 20 cm. 



3. Maximum churning of clay and silty sediments. Ripple marks occur where fine sands and 

 sandy silts are present. Greater occurrence of larger manganese nodules, pumice slobs, and rock 

 fragments. Chemical crusting of sediments sometimes present. Major and intermediate features 

 predominantly island slopes, hills, ridges, highs, and irregular topography. 



Height of churning 6 to 15 cm. 



Normal range of microrelief 6 to 30 cm. 



4. Rock fragments, outcrops, boulders, and coarse sediments predominate in this shoaler 

 environment. Fauna churning maximum where silty sediments exist. Ripple marks often present in 

 sandy sediments. Greater abundance of epifauna on rocky surfaces. 



Height of churning, where present, 15 cm. 

 Normal range of microrelief 6 cm to 1 meter. 



5. Jagged rocks, phosphorite nodules, large boulders, and coarse sediments on upper surfaces 

 and slopes of underwater features such as ridges, mountains, banks, cliffs, walls of canyons, and 

 other topographic highs. Fauna churning of coarse sediments variable and dependent on presence of 

 organic matter. Predominance of attached and unattached epifauna on rock exposures. 



Height of churning highly variable up to 15 cm. 

 Normal range of microrelief 3 cm to 2 or 3 meters. 



Summary of Microrelief Characteristics 



1. In general, microroughness is directly related to 

 the intermediate and major topographic relief on which it 

 is superimposed. 



2. With some exceptions, microrelief diminishes in 

 magnitude with increasing depth. Outcrops are fewer in 

 deeper water where less infauna and epifauna are present 



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