OBSERVATIONS IN PHYSICAL OCEANOGRAPHY 43 



reversing the attached thermometers. A number of bottles can be 

 attached to the same wire rope. After reversing the first bottle, the 

 messenger releases another messenger that was attached to the wire clamp 

 before lowering. This second messenger closes the next lower bottle, 

 releasing a third messenger, and so on. 



The Ekman bottle, which can also be operated in series, consists of a 

 cylindrical tube and top and bottom plates that are fitted with rubber 

 gaskets. The moving parts are suspended in a frame that is attached to 

 the wire rope, and, when the bottle is lowered, the water can pass freely 

 through the cylinder. When struck by a messenger, the catch is released 

 and the cylinder turns through 180 degrees, thereby pressing the end 

 plates securely against the cylinder and enclosing the water sample. 

 Reversing thermometers are mounted on the cylinder. In recent years 

 the Nansen bottle has been generally used because of its more reliable 

 functioning. 



Messengers are essential for the operation of many types of oceano- 

 graphic equipment. Although their size and shape will vary for different 

 types of apparatus, they are essentially weights that are drilled out so that 

 they will slide down the wire rope. In order to remove and attach them 

 they are either hinged or slotted. 



Treatment and Analysis of Serial Observations 



Subsurface temperature and salinity observations obtained must be 

 carefully examined for possible errors before they are arranged into 

 convenient form for analyses, computations, or comparisons with other 

 data. First of all, the depths of sampling have to be determined. This 

 involves a considerable amount of practical experience, since depths 

 obtained by unprotected thermometers may be in error because of 

 improper functioning of the instruments, and also because unprotected 

 thermometers are generally attached only to two or three water bottles 

 of a string of bottles on a wire rope, the curvature of which is unknown. 



When the depths have been found, vertical distribution curves are 

 plotted by which temperature and salinity values that appear doubtful 

 may be readily recognized. Temperatures may be in error because of 

 faulty functioning of the thermometers or because the thermometers have 

 been reversed prematurely, and salinities may be in error because the 

 water bottles have closed prematurely or have leaked when being hauled 

 up. 



Besides plotting the vertical distribution curves, it is very helpful to 

 plot the temperature-salinity curve (T-S curve) in which the correspond- 

 ing values of temperature and salinity from a single station are entered in 



Fig. 5. The Nansen reversing water bottle. Left: Before reversing; first mes- 

 senger approaches releasing mechanism. Center: Bottle reversing; first messenger 

 has released the second. Right: In reversed position. 



