274 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



The sea-bed 



A preponderance of sand, gravel and at times a rocky floor, are the character- 

 istic features of the sea-bed in the shallow zone (down to 50 m) of the Baltic. 

 Ooze bottoms are found only in stagnant bottom hollows. The deeper parts 

 of the bottom (over 50 m in depth) are occupied for the most part by clayey 

 mud with sand, at times by black ooze, rich in organic detritus. The sea 

 bottom is usually brown-red, especially in the Gulf of Bothnia; this colour 

 is due to an admixture of ferric hydroxide. This kind of distribution of brown 

 mud deposits is very characteristic of the floor of the Kara Sea and to a 



Fig. 115. Bottom deposits in southern part of Baltic Sea (Demel). Unhatched areas 

 are sand; vertically hatched are sandy silt; horizontally hatched, silts. 



lesser extent of that of the White Sea. This kind of bottom contains a large 

 amount of concretions. Z. K. Demel and Z. Mulicki (1954) have given a map 

 showing the distribution of the different soils of the southern part of the Baltic 

 (Fig. 115). As is shown in Fig. 115, sand and sandy silts are preponderant here. 

 Soft ooze is concentrated in the deepest places (more than 80 to 100 m). 



The Swedish research scientist B. Kullenberg (1952) studied the salinity of 

 the solutions of cores up to 15m long taken from several sites in the Baltic. 

 The core taken near Bornholm, from a depth of 86 m, is particularly demon- 

 strative. 



Interstitial water taken from a layer 2 m below the sea-floor indicated 

 salinity of 15% ; salinity decreased with depth down to 6% at 12 to 15 m 

 (Fig. 1 16). In B. Kullenberg's opinion (1954) this corresponds to the early period 



