188 



there is need of additional research on the conductivity - chlorinity relationships 

 for different waters, existing information appears adequate as a basis for calcu- 

 lating dynamic topography. 



There is a present trend towards increased use of micro or semi-micro 

 analytical methods for which ever smaller water samples are collected and 

 stored prior to analysis. I would like to emphasize that the collecting and stor- 

 ing of small samples requires special care to insure that the sample is repre- 

 sentative of the sea water in question, and that contamination is kept to a mini- 

 mum. Contamination is largely an interface problem, usually between the wa- 

 ter and the air or the impounding container. In sinailarly shaped containers of 

 the same material, the surface area increases as the square of a linear dimen- 

 sion and the volume as the cube; thus decreasing the dimensions of the container 

 tenfold will increase the potential contamination an order of magnitude. Several 

 instances of difficulty experienced by different activities resulting from the use 

 of smaller screw cap bottles of 60 to 240 ml capacity instead of the conventional 

 citrate bottle of over 300 ml capacity have come to miy attention during the past 

 few years. The method of closure has no doubt caused much of the undesirable 

 variability, and this is perhaps particularly the case in using screw top poly- 

 ethylene bottles. Nevertheless the larger containers are preferable to the 

 smaller for keeping changes on storage to a minimum. For some purposes 

 these changes are of no consequence. It is another example of tailoring the 

 instrument or technique to the job at hand. 



DISCUSSION: Dayton E. Carritt 



I wish to expand on Clifford Barnes' remarks on my paper. All of his 

 remiarks are pertinent and I'm especially pleased to have tais comments on the 

 results with the Wenner bridge together with the reference to his paper with 

 Floyd Soule. 



Now there is one point raised that I would like to amplify. His comment 

 "An instrumental accuracy of a few tenths of a part per mille of salinity is more 

 than adequate to track the movemients of these 'fronts' between water parcels 

 (here he refers to shallow inshore water) " I think should be expanded. 



For some purposes Dr. Barnes' statement is correct. There are, how- 

 ever, circumstances for which a much greater instrumental accuracy and sensi- 

 tivity are needed. In the study of turbulence, for example, from which we can 

 expect to learn how different waters get mixed, theoretical approaches require a 

 knowledge of mean values of salinity and velocity as well as ternms which involve 

 random fluctuations from the nneans. In the treatment of mixing and circulation 

 in a coastal plain estuary, Pritchard (1952) developed a salt balance equation 

 in which terms involving the mean product of random velocity and salinity are 

 retained, rather than resorting to the usual substitution of the mean salinity 

 times a coefficient of diffusion. It turns out that salinity observations which are 

 "good to 0.1 o/oo" are just good enough to obtain an indirect measure of the ran- 

 dom terms. Ideally, we would like a direct measure of these terms. To get 

 this, an instrument with fast response and high sensitivity, one that will look at 

 changes of the order of 0.01 '-'/oo, appears necessary. 



Applying the same approach to the open ocean, where the random fluctu- 

 ations are smaller, it would appear that a fast response instrument that can look 

 at changes of the order of 0.001 °/oo miight be necessary. 



All of this further emphasizes Dr. Barnes' remarks concerning 



