explained by the .seasons in which the stations were occupied. The 

 " Dana " data are for April, when the high salinities of the north- 

 east monsoon still persisted. The " Snellius " station was occupied in 

 September, when the water was of low salinity characteristic of the 

 south-west monsoon. The " Baird " curve is significant^ different in 

 showing high temperatures in the upper layers. This station was occupied 

 in October, 1947, when the temperatures were very high. Curves for 

 " Baird " stations occupied in December resemble closely the " Dana " 

 curve. 



In the Sulu Sea there is no indication of a salinity maximum at the 

 100 to 200 metre level as found in the western Pacific. The Sulu Sea is 

 effectively isolated from the Pacific at these levels. The South China 

 Sea, with which it is in communication at this depth, does not have 

 this layer of high salinity. 



The study of the data on the chemical constituents, which are of 

 biological importance such as oxygen, phosphate, silicate, &c., has not 

 been completed. A knowledge of the distribution of these substances 

 throughout the waters is of great importance to an understanding of 

 the biological conditions, and the " Baird " data are expected to be of 

 considerable significance in this connection. 



Plankton collections also are being made and are being studied in 

 relation to the distribution of specific chemical substances. Both the 

 hydrographic conditions, per se, and the plankton factors are related to 

 the production and distribution of fish. 



It is confidently hoped that some relationships between all these 

 various factors will be demonstrated before the Philippine investigations 

 are -completed. 



Summary 



1. This report is based on data collected by the " Spencer F. Baird " 

 on four cruises to the Sulu Sea, constituting two surveys — the first 

 during the early part of the north-east monsoon, in October and December, 

 1947 ; the second during the early part of the south-west monsoon, in 

 June and July, 1948. Seventy-nine stations were occupied, at which 

 serial temperatures and water samples were collected. 



2. The Sulu Sea is an enclosed basin with maximum sill depth of 450 

 metres between it and the South China Sea to the north. It joins this 

 sea to the west over a sill less than 100 metres in depth. Communication 

 with the open Pacific is at still shallower depths, but a connection with 

 the Celebes Sea to the south exists to a depth of 275 metres. 



3. The surface currents in the Sulu Sea, as indicated b}- studies of 

 dynamic topography, are dominated by two large eddies — a North 

 Central Eddy and a South Central Eddy. These and a flow of water 

 from the Mindanao Sea appear to be permanent features of the surface 

 circulation. 



4. During the early part of the south-west monsoon there is a strong 

 inflow of water from the South China Sea which very noticeably lowers 

 the surface salinities. 



5. During the south-west monsoon a north-easterly current flows along 

 the coast of Palawan. 



258 



