EAST OF SINGAPORE 



This location was selected as an example of an equatorial shallow water environment. 

 It also is isolated from open ocean influence. Six one-degree squares were processed to 

 provide a reasonable number of observations. This area is very shallow with bottom depths 

 ranging from about 25 m to 75 m. There were very few Nansen cast data in the set so 

 shallow profiles were retained and the sample was supplemented with a large percentage 

 ofXBT data. 



Strong seasonal variations would not be expected in the equatorial zone. However, 

 some seasonal pattern was evident from atlas sea surface temperature charts, so two six- 

 month seasons were selected based on this information. The northern hemisphere spring 

 and summer months (April-September) were combined for summer and the standard fall 

 and winter months (October-March) were processed as winter. Each season is briefly 

 described and associated figures containing statistical tables, composite plots and T-S 

 diagrams are located at the end of this section. 



Winter — The shape of the winter profiles resembles winter data observed at much 

 higher latitudes. The profiles are isothermal with weak positive sound speed gradients from 

 the surface to the bottom of the profiles. About 82 percent of the observations are classified 

 as positive gradient profiles. The one profile extending to 75 m has a strong negative 

 gradient near the bottom, indicating a local cool bottom layer. The T-S diagram shows 

 that a positive salinity gradient is relatively important in maintaining vertical stability at 

 this location. The selection of a single positive gradient sound speed profile to represent 

 the upper 50 m in this shallow water site for winter would seem to be supported. How- 

 ever, in water deeper than 50 m the presence of cooler deep water is suggested by the 

 single deep observation, which, if present would create a gradient change near the bottom. 



Summer — The strong seasonal signal in the upper layer temperatures and sound 

 speeds observed in the other examples is not apparent for this equatorial location. The 

 sound speed gradient in the upper 30 m primarily is positive, resulting in 60 percent of 

 the profiles being classified as having a positive gradient. A thermocline below this 

 depth is indicated on most of the profiles. Negative gradients with deep sound speed 

 values less than winter sound speeds are observed. A few profiles extending below 30 m 

 again indicate the presence of a cool bottom water while others do not. The data sample 

 is inadequate to support firm conclusions about the causes of the observed sound speed 

 structures. Both seasons indicate weak positive sound speed gradients in the upper 30 m. 

 Below this depth, the winter is still primarily positive, but the summer is less certain. 



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