Chapter II 



The Sea- water and its Physical and 

 Chemical Properties 



1. Collecting Oceanographic Samples 



The ocean basins are filled with a liquid that is essentially the same as rain water 

 formed by the condensation of water vapour. An accurate knowledge of the different 

 contents of sea-water is indispensable in order to be able to learn something of the 

 geophysical-chemical structure of the ocean. This knowledge of the structure must be 

 derived from samples collected at oceanographic stations. It cannot be limited to the 

 surface layers of the sea but must include all layers down to the sea bottom and must 

 be based on a network of observation stations placed as systematically as possible. 

 The precise determination of the spatial distribution of the oceanographic factors is a 

 major achievement of modem oceanography and its observational technique. 



Collecting samples from the surface of the sea offers no real difficulties, or at the 

 most only those that can be overcome by simple means. The collection of unob- 

 jectionable and homogeneous material of definite origin from deep layers of the sea 

 is, however, not easy and it has required the work of several decades to overcome the 

 difficulties. The differences in the oceanographic factors (such as temperature and 

 salinity) at deeper levels become continuously smaller both in horizontal and vertical 

 direction; the accuracy of measurements at great depths must therefore be increased, 

 and it has only been possible by the use of modern analytical techniques to do this 

 with the degree of accuracy needed to follow small local variations. 



Almost all the properties of sea-water, apart from the temperature, can be deter- 

 mined if genuine samples of water are available from each particular depth, because 

 these properties show no appreciable alteration when the sample is brought from the 

 deep sea to the surface. The temperature of the water must, however, be determined at 

 the place and at the depth from which the water sample was taken {in situ). 



To collect oceanographic data at a station it is necessary to lower a thermometer in 

 order to measure the temperature at different depths, and to bring back genuine samples 

 of water from these depths in sampling bottles. The work at such an oceanographic 

 station is done with a series-machine so-called because it is usually used for series 

 observations, that is, the sampling bottles and thermometers are lowered at the same 

 time to predetermined depths and a series of samples is collected and brought back 

 together with temperature measurements. More recently, specially built machines 

 have been used for this, but sounding winches or hydrographic winches were used 

 previously. The oceanographic series machine and its operation on board ship will not 

 be described here, but details are given "'Meteor'" Work, 4, No. 1 (WiisT, Bohnecke 

 and Meyer, 1932, Berlin). 



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