in situ rates and are useful substitutes for 

 the tinne -consuming and costly in situ method. 

 In the present investigation deck incubation 

 soon replaced the trailing bottle method of 

 surface sample incubation. This change was 

 a matter of convenience, since trailing bottle 

 assemblies of the type employed required 

 attention whenever the vessel slowed down or 

 stopped. These two methods appear to yield 

 comparable results (table 14), although a 

 comparison of these methods with simul- 

 taneous in situ measurements would be worth- 

 while. 



SUMMARY 



1, Incident solar radiation was measured 

 on shipboard with a gimbals -mounted 10- 

 junction Eppley pyranometer and poten- 

 tiometric recorder. Daily radiation totals were 

 obtained by integrating the unsmoothed daily 

 records with a polar planimeter. The daily 

 totals are believed to be accurate to within +7 

 to 10 percent. One hundred and four of the daily 

 radiation totals were compared with estimates 

 obtained from the climatological equations of 

 Kimball, Savino-An g s t r bm. Black, and 

 Laevastu, by using multiple linear regression 

 techniques. All these indirect methods yielded 

 daily means which were significantly corre- 

 lated with the measured values. The regression 

 coefficients were all significant at the one 

 percent level and only the Laevastu equation 

 yielded an intercept value significantly dif- 

 ferent from zero. On cloudless days all of the 

 climatological equations except that of Laevastu 

 overestimated the daily total. 



2. Submarine irradiance H, 



,7r/2 



where H 



N cos du, 



9 is the angle of incidence, and ai the solid 

 angle measure, was measured with a sinnple 

 waterproof housing containing a Weston photo- 

 voltaic cell, Wratten No. 45 filter, and a 

 cosine collector. The attenuation or extinction 

 coefficient (k) was calculated from downwelling 

 irradiance values at two depths z and z (both 

 in m.; Zj deeper than z^^) according to the 

 following expression: 



loge Hzj^ - loge Hzj 



Z2 - Zl 



The outputs of the deck and submerged 

 irradiance meter were read simultaneously at 

 a given depth on electrically damped low 

 resistance microampere meters. Corrections 

 for departures in linearity of response of the 

 detector and ambient irradiance were made at 

 each depth at each station before calculating k. 



Calculations show the detector has a maxi- 

 mum sensitivity at 490 m^ with a half -band 

 width of approximately 63 m^. These charac- 

 teristics shift to 475 mfi and 50 m/j at 100 m. 

 depth in Jerlov Type I ocean water. In Type III 

 ocean water the peak remains at 475 m/j while 

 the half-band width increases to 70 mu. 



A method is described for obtaining the per- 

 centage of incident "visible" energy at any 

 depth in the upper 100 to 200 m., based on 

 measurements of the attenuation coefficient 

 at 475 m/j in Jerlov ocean water Types I, II, 

 III, and intermediate types. 



A statistical treatment of replicate deter- 

 minations of attenuation coefficient under ideal 

 conditions with negligible depth error yielded 

 a coefficient of variation of 10 percent 

 (k = 0.1805, standard deviation 0,0189). It is 

 doubtful that this precision can be exceeded 

 with the equipment described. Under adverse 

 field conditions the precision is obviously 

 much worse although measurements of this 

 type have not been evaluated. 



Errors in depth measurement cause ir- 

 radiances to be assigned to incorrect depths; 

 k values likewise will be in error and be 

 assigned to incorrect depth intervals. Com- 

 parisons of depths computed from wire angle 

 and length and depths measured with a pre- 

 cision depth sensor show the computed depth 

 to be almost invariably less than the measured 

 depth when wire angles exceed about 25 

 degrees. In the two examples discussed, these 

 differences amounted to 5 and 8 m. with wire 

 length 100 m. and wire angles of 40 to 45 

 degrees. Such differences become less as wire 

 length is decreased but may amount to 1 or 2 

 meters with only 20 meters of wire. Depth 

 intervals derived from indirect depth measure- 

 ments can cause a k value to be 22 percent 

 too low, as well as being referred to an in- 

 correct depth interval. 



3. Chlorophyll a^ was measured spectro- 

 photometrically with dried extracts by using 

 the equations of Richards with Thompson 

 (1952). Pigment-bearing materials were col- 

 lected on HA Millipore filters. Absorption at 

 750 m^ was subtracted from that at 665 m^ 

 before calculating chlorophyll a concentration. 

 Wavelength settings on the spectrophotometer 

 were periodically checked by using chlorophyll 

 a extracts or occasionally with didymium 

 glass. 



The variability in chlorophyll a under dif- 

 ferent sampling conditions was investigated. 

 When certain statistical assumptions were 

 used, it was found that the coefficient of 

 variation for surface samples never exceeded 

 27 percent and most frequently was less. At 

 depths between 10 and 40 meters the coeffi- 

 cient of variation increased appreciably. It 

 is suggested on the basis of indirect evidence 

 that a significant part of this variability re- 

 sults from the failure of the sannplers to 



28 



