THE KARA SEA 229 



(4) Atlantic saline and relatively warmer waters which penetrate into the 

 Kara Sea by three ways : 



(a) from the north from the central parts of the Arctic basin from its 

 intermediate 'warm' layer, 



(b) from the northwest from the Barents Sea, between Franz Joseph 

 Land and Novaya Zemlya, and 



(c) from the southwest through the Kara Gates. 



(5) Cold and saline deep waters, which penetrate into the northern parts of 

 the Sea from the lower layers of the central part of the Arctic basin. 



Soils 



Silts and clayey ooze are preponderant in the central, northern and north- 

 eastern deep parts of the Sea (Fig. 97). In its eastern part, mainly in the shal- 

 lows opposite the Ob and the Yenisey estuaries, silty sand and sand floors are 

 preponderant. The finer-grained bottoms of the Kara Sea are usually coloured 

 brown in their upper layer ; this is explained, as in other cases, by the presence 

 of manganese and iron oxides. The boundaries of the brown mud distribution 

 are given in Fig. 98. Brown muds and the ferromanganate concretions so 

 characteristic of them are more widely distributed in the Kara Sea than in 

 any other body of water in our Arctic. In the Kara Sea the brown mud 

 attains a thickness of 18 cm, lying over the silts and grey-blue clays. In the 

 deeper parts of the Sea the brown mud is usually thicker (Fig. 98). The deep- 

 water troughs running out of the Arctic basin from the north are also covered 

 with brown mud. 



Manganese is particularly active in this process. Getting into the deeper 

 layers of the silt (the reduction zone) manganic oxides are reduced to the 

 manganous state. These soluble compounds are dissolved in deep water, get 

 oxidized again and are precipitated on to the sea-bed, where reduction may 

 occur again. Hence there is an active consumption of oxygen in the deep layer 

 and brown mud is characterized by the presence of both managanese and 

 iron in an oxidized state. 



There is much that is still not clear about the zones of formation of brown 

 muds, the chemical state of the overlying deep-water layer, and the effect of 

 such a sea-bed on organisms. One might suppose that an accumulation of 

 brown mud takes place where there is an inflow of river waters, which drain 

 the marshland and carry out into the sea large amounts of iron and man- 

 ganese. However, the northern part of the Barents Sea and the central part 

 of the Arctic basin are too far removed from river estuaries for this. The 

 brown muds are most widely developed in the deeper parts, more or less 

 stagnant, of the water bodies; at the same time oxygen is required in sufficient 

 amounts for the oxidation of the iron and manganese. A large number of 

 ferromanaganese concretions, frequently of large size, are characteristic of 

 the Kara Sea. 



The intensity of the oxidation-reduction reactions in the deep-water layer 

 above the brown mud is indicated by a high oxidation-reduction potential ; 

 the index of the active reaction, however, is lower, probably as a consequence 

 of the presence of carbon dioxide. This is connected also with the small 



