420 



Anton Fr. Bruun and A. Kiilerich 



km) (Fig. 4). This agrees well with the general concept that the Pacific Deep Water 

 is derived from the region south of AustraUa with roots in the Indian Ocean, and 

 furthermore that there is a slow movement from south to north in the West Pacific. 

 The velocity of this current is probably so slow that a renewal of the bottom 

 water in the PhiUppine Trench would require very many years. We know Httle about 

 the abundance of the organisms in the trenches (Bruun 1951, 1953 a, b; ZoBell, 

 1952; Zenkevitch, Birschtein and Beuaev, 1954; Zenkevitch, 1955); but in 

 any case they require a certain amount of oxygen. The content of oxygen is relatively 

 high. Therefore, as an additional possibility, acting in the renewal of the trench 



Fig. 2. Four sections of the Philippine Trench. Base Une of all sections at 10000 m; distance between 

 any two sections is a little more than 100 km (From Kiilerich, 1953). 



water, turbidity currents are suggested. The deepest part of the trench (ca. 10000 m) 

 is nowhere more than 90 km distant from the narrow coastal shelf of the Phihppines 

 (Fig. 2). Here turbidity currents can easily get started; typhoons will disturb the 

 bottom of the shelf and add to the velocity of the strong tidal currents in the narrow 

 straits of the islands. Eruptions of submarine volcanoes or the frequent earthquakes, 

 which have their epicentres on the western slope (Repetti, 1931 ; 199) should also be 

 considered as the cause of bottom sediment shdes. The many stones with rounded 

 edges found by Galathea must have been carried down in some such way. (Fig, 3); 

 this is also in agreement with Shepard (1951). 



