At 100 Metres (Chart 26). — Throughout the area at this level the 

 salinities were very uniform with values about the same as at the 75-metre 

 level. There is no indication of the low-salinity water which was found 

 off Palawan at this depth during the north-east monsoon (Chart 21). 



At 200 Metres (Chart 27). — At this level the range of salinity values 

 is 0-03 Voo, from 34-42 °/oo to 34-45 %o- This is even less than the range 

 found at this level during the north-east monsoon. 



Summary of Salinity Distribution 



The study of the salinity distributions at the various levels during 

 the two seasons brings out several important features. 



The lower-surface salinities during the north-east monsoon may be 

 due to local weather conditions, but is more likely the result of a lag in 

 the changes of salinity which follow the changes in currents effected by 

 the south-west monsoon. The south-west monsoon begins in May or 

 June, at which time it can be expected that water from the China Sea 

 will begin to enter the Sulu Sea. By July, when the " Baird " surveyed 

 the south-western half of the Sulu Sea, this China Sea water will have 

 exerted its influence almost halfway across the area, as shown by reduced 

 salinities, but in June, when the " Baird " surveyed the north-eastern 

 half of the sea, the water still had the high salinities characteristic of the 

 north-east monsoon. The south-west monsoon ends about September in 

 the north and about November in the south, and at this time the surface 

 saUnities throughout the Sulu Sea can be expected to have reached their 

 lowest values. This is corroborated by the low surface salinity found by 

 the " Snellius " is September. 



The north-east monsoon begins in October toward the north and in 

 December toward the south. Thus the conditions found by the " Baird " 

 in October in the north-eastern half of the Sulu Sea are probably an 

 expression of the conditions set up during the south-west monsoon. By 

 December, when the " Baird " surveyed the south-western half of the area, 

 the north-east monsoon probably was ahead}' effective in some areas, 

 but oceanographic conditions were probabty still in a transition toward 

 the conditions characteristic of the north-east monsoon, which might be 

 expected to reach a maximum about March. 



" Dana " station 3685 occupied in April in the south-eastern Sulu 

 Sea shows a high surface salinity and probabty represents conditions 

 more characteristic of the north-east monsoon. 



The lower subsurface salinities along the east side of Palawan perhaps 

 can be explained in much the same way. The reduction in salinity in 

 June and July did not extend to the 50-metre level. It is probable 

 that in the early part of the south-west monsoon the north-east current 

 in this region is very shallow. During October and December — that is, 

 during the beginning of the north-east monsoon — there are pockets of 

 low-salinity water extending to 100 metres depth. Possibly the north- 

 east current extends to 100 metres during the end of the south-west 

 monsoon and is composed of low-salinity water characteristic of the 

 South China Sea. As this current is obliterated during the north-east 

 monsoon, complex eddies and remnants of China Sea water might be 

 expected to persist for some time, creating conditions as found by the 

 " Baird " in October and December. 



252 



