314 



20 iO 

 Shallow Water 

 Bab-el-Mandab 



60 



80 100 /am D -* 



FIGURE 26. LSL-technique compared with Aminco- 

 Sc.-Light measurement. 



comparable locations are shown which were carried 

 out on the occasion of the Indian Ocean expedition 

 of the "Meteor". For the investigations, which 

 have been made by Krey et al. (1971), the so-called 

 inverted microscope and 1:he Zeiss particle-counter 

 were used. These results lie always one magnitude 

 above the "Sydney Express" measurements for the 

 operating revolution (n = 101 rpm) . In case of the 

 low revolution number of n = 60 rpm the nuclei 

 concentration measured at the "Sydney Express" 

 expedition (Co = 15 N/cm ) reaches the values from 

 the "Meteor" expedition in the range 20 - 35 ym 

 and exceeds in the range 35 - 92 ym. Since, further- 

 more, the water sample tests carried out with the 

 Aminco scattered light device do not show any 

 difference between filtered and unfiltered water 

 (medium diagram - Figure 27) it is justified to 

 state that witih the LSL measurement mainly bubbles 

 were recorded. The investigation of Keller et al. 

 (1974) of the optical qualities of the latex spheres, 

 applied for the calibration, supports this fact. 

 According to his investigation the latex spheres 



|cm3 



lO^H 



10^- 



iC- 



912 



116 / 



10 m 

 Depth 



"Meteor" Suspended 

 195i/65 Particles 



2m 

 Depth 



^8 Station 179 



10' 



10^- 



10' 



Sydn.-Expr " Test No 70 



n = 101.7 RPM 



1i.5 



Aminco -Sc-Light: 

 A(Rel.-lnt.) =0 



20 40 

 Deep Water 



60 80 100 /^ m D — 



FIGURE 27. LSL-technique compared with other 

 investigations . 



10' 



10^ 



10' 



' Sydn.- Expr. " 

 n = 103.1 RPM 



Test No 99 



Aminco-Sc-Light 

 |A(Rel.-lnt.)=0 



20 



40 



60 80 100 /um—^D 



Deep Water 

 Gult of Aden 



FIGURE 28. LSL-technique compared with other 

 investigations . 



show scattering characteristics similar to the 

 bubbles. Therefore, it can be said that the 

 sensitivity of the LSL measurements is - to a 

 certain extent - adjusted to the scattering 

 behavior of bubbles via the calibration. With the 

 LSL technique mainly bubbles are measured whose 

 number is always smaller than that of all solid 

 and gaseous nuclei. It is known, for instance, 

 that silica algae are almost transparent. It is, 

 therefore, understandable tihat there must exist 

 differences between the LSL method on the one hand 

 and the microscope method (with coloration perhaps) 

 and the conductivity measurement with Coulter 

 Counter on the other hand. The assumption that, 

 with the LSL method, mainly bubbles are measured is 

 supported by the good conformity of the LSL method 

 with the holographic method of an ITTC-comparison 

 measuring, Peterson et al. (1975) . In this investi- 

 gation a holographic method, the laser scattering 

 light method, and a microscope method have been com- 

 pared with each other . The first two methods agreed 

 well with each other in the range of the bubble sizes 

 20-40 ym, whilst the microscope method also showed 

 a nuclei concentration higher by one order of 

 magnitude. The higher concentration of nuclei 

 according to tihe microscope method apparently 

 results from mistakes arising from the focusing of 

 the nuclei. Similar difficulties might also occur 

 with the inverted microscope applied at the "Meteor" 

 expedition. This argument, however, does not say 

 that the highest nuclei concentration of the "Sydney 

 Express"-investigation, frequently occurring in 

 the smallest ranges of size, results from bubbles 

 only. (See, for instance. Test 70 - Figure 27 and 

 Test 99 - Figure 28 or all diagrams of Figure 20) . 

 In the class of the smallest size nuclei solid 

 particles which always exist in the sea water have 

 certainly also been measured. 



Oceanographic studies with t:he Coulter Counter, 

 for instance, carried out in the Gulf of California 

 by Zeitzschel (1970) show a strong increase in the 

 number of particles with a diameter of 14 to 4 ym. 

 In addition, Zeitzschel cites the size distribution 

 of particulate carbon in the Indian Ocean by means 

 of fractional filtration investigated by Mullin 



