Description and Evaluation of Methods for Determining 



Incident Solar Radiation, Submarine Daylight, 



Chlorophyll A, and Primary Production 



Used by Scripps Tuna Oceanography Research Program in the 

 Eastern Tropical Pacific 



By 



ROBERT W. HOLMES, Associate Research Biologist 



Institute of Marine Resources, Scripps Institution of Oceanography- 

 University of California, La JoUa, Calif. 92037 



ABSTRACT 



A detailed account and evaluation are presented for certain methods used by the 

 STOR (Scripps Tuna Oceanography Research) Program, This description should as- 

 sist readers and users of the STOR data and be of general interest to workers in 

 the field. 



An Eppley 10-junction 180° pyranometer was used in conjunction with a Speed- 

 omax recorder for the naeasurement of incident solar radiation. Daily incident 

 radiation was obtained by integration of the daily record with a polar planimeter. 

 Errors due to integration and failure of the gimbals to stabilize the pyranometer 

 completely are estimated to be t 1 percent and t5 percent, respectively. A com- 

 parison between observed daily radiation and computed radiation from four standard 

 climatological equations revealed the inaccuracy of using indirect methods for daily 

 totals. 



The deck and submarine irradiance meters were equipped with cosine collectors; 

 their construction, calibration, and operation are described. A blue-green Wratten 

 filter (No. 45) was routinely used with both detectors. The relative spectral sensi- 

 tivity in air and Jerlov ocean water type I was calculated. In air, the maximum 

 transmittance was at 490 m>i and the half-band width was roughly 63 mfi. At lOO-m. 

 depth in type I water, this value shifted to 475 rrifi with a 50 mfi band width. By 

 assuming the universal validity of the Jerlov sea-water transmission curves, it 

 was possible to obtain estimates of total visible downwelling irradiance at depth 

 from a single attenuation coefficient measurement. Under ideal conditions and with 

 no depth measurement error, a coefficient of variation of + 10.5 percent was ob- 

 tained for the attenuation coefficient. This error increased appreciably when vessel 

 motion and errors of depth measurement occurred. 



Chlorophyll a measurements were obtained by spectrophotometric method with 

 acetone extracts of membrane -filtered water samples. Corrections for blank values 

 at 750 m// were applied, and concentrations computed with the equations of Richards 

 with Thompson. The coefficient of variation for surface samples varied between 14 

 and 27 percent and increased with depth. 



Primary production was measured with C ; the details of the methodology and 

 standardization are given. Because a number of different incubation techniques 

 were used (i.e., in situ, deck incubator, trailing bottle, and laboratory incubator), 

 an attempt was made to compare these procedures with the in situ method. All of 

 the methods yielded results which were correlated with those obtained by the in situ 

 method. Thus unbiased estimates of in situ production may be obtained from the dif- 

 ferent incubation techniques. 



