12 - 



d. 



adjusted to a constant but arbitrary Incident 

 radiation value. 



Maximum instrument depth was frequently ob- 

 tained from a BT or Vibrotron depth element at- 

 tached to the photometer. Intermediate depths 

 were calculated from wire angle/wire length re- 

 lationship. Agreement between the maximum 

 (usually about 100 m) computed and observed 

 depths was fair ( ± 3 m) providing the wire angle 

 remained under 45°. Whenever the wire angle 

 exceeded 45°, depth determinations obtained by 

 the two methods rarely agreed, the wire angle/ 

 wire length determinations almost always indi- 

 cating that the maximum instrument depth was 

 less than that shown on the BT. In such cases 

 the maximum depth indicated by BT or Vibrotron 

 was used and the intermediate depths were cal- 

 culated from wire angle/wire length relationship 

 if the wire angle was less than 45°; in the few 

 cases where the wire angle exceeded 45°, inter- 

 mediate depths were rather arbitrarily chosen 

 using a variety of subjective and objective 

 criteria. 



The diffuse attenuation coefficient per meter was 

 calculated tor both downwelling and upwelling 

 radiation using the following formula: 



K = In I " ^" ^ X 



^1 ^2 



Z - Z 



2 1 



this report, under the Regular Forenoon Station or 

 In Situ Productivity Station of the day (occasionally 

 under a Special Station). 



Chlorophyll a Standing Crop 



The water samples used for the determination of 

 chlorophyll a content were collected from the sur- 

 face with a plastic bucket; subsurface samples were 

 collected with a Van Dorn-type plastic sampler. The 

 water sample, 3.0-6.0 1 in volume, was shaken after 

 the addition of a small amount of magnesium carbon- 

 ate, and filtered through a plain white 47-mm type 

 HA Millipore filter. The filter membranes were 

 dried in a vacuum desiccator with silica gel for 18-20 

 hours and then extracted with 3 ml of 90 percent ace- 

 tone (glass redistilled) in the cold (ca. 10°C) and dark 

 for approximately 10-12 hours. The sample was then 

 centrifuged until clear. The supernatant was next de- 

 canted into a volumetric flask or cylinder and the re- 

 maining precipitate in the tube resuspended with 1-2 

 ml of 90 percent acetone, centrifuged, and the super- 

 natant combined with that obtained previously. Recen- 

 trifugation of the combined extracts was frequently 

 necessary to reduce turbidity. This extract was 

 finally diluted to 6 ml, and its optical density was 

 measured in a 10 cm semicro-absorption cell at 750, 

 665, 645, and 630 m\x with a Beckman model DU 

 Spectrophotometer. Turbidity corrections were made 

 on the basis of the sample transmission at 750 mji 

 and the concentrations of chlorophyll are calculated 

 from the equations of Richards with Thompson (Jour. 

 Mar. Res. , 11 (2) pp. 156-172, 1952). 



where I is the corrected output of the submerged 

 cell, Z is the depth in meters, and X refers to 

 the spectral sensitivity of the Photronic cell- 

 filter combination employed (assumed to be a 

 constant). 



At a number of stations the ratio of upwelling to 

 downwelling radiation, alpha (a), is given. In these 

 computations the difference in sensitivity of the up- 

 looking and downlooking cells was taken into account. 



Incident Solar Radiation 



A gimbals-mounted Eppley 10-junction pyrheliometer 

 was mounted above all superstructure on the A-frame 

 of the ship. The signal was recorded with a 0-10 mv 

 Speedomax recorder. The daUy curve was integrated 

 with a planimeter. The daily incident radiation total 

 and day length are given in the station data section of 



The integrated chlorophyll a_ value given at the bot- 

 tom of the table for each station ("water column" 

 value) was obtained by integration with a polar plani- 

 meter of smoothed profiles. 



Zooplankton Standing Crop 



Measurements by volume of the standing crop of zoo- 

 plankton were made by means of plankton net hauls, 

 using equipment comparable to that currently used in 

 the California Cooperative Oceanic Fisheries Inves- 

 tigations. Both types of nets employed (regular and 

 closing type) had a mouth-diameter of one meter; the 

 main body of the net was made of 30XXX nylon grit 

 gauze, while the rear section and cod end consisted of 

 56XXX nylon grit gauze. A flowmeter, mounted in 

 the center of the mouth of each net, measured the 

 volume of water filtered during each tow. Flow- 

 meters were calibrated before and after the expedition. 



