Richards with Thompson (1952), except those 

 for operation 29. There the concentrations were 

 calculated from the equation of Parsons and 

 Strickland (1963) and are so given in the data 

 list for the cruise (Forsbergh and Broenkow, 

 1965), but for the purpose of this paper they 

 were multiplied by 1.345 (the Richards -Thomp- 

 son Dggg constant divided by the corresponding 

 P arsons -Strickland constant) to mal^e them 

 reasonably comparable with the rest of the 

 data. Data on chlorophyll a from operation 9 

 are ignored; only 21 measurements were made 

 from the eastern tropical Pacific, and they 

 may not be comparable with others because of 

 differences in methods (King et al., 1957; 

 Robert W. Holmes, personal communication). 

 Night observations were omitted because of 

 possible diurnal variation, and also because 

 they were scanty. 



Many more observations were made on 

 chlorophyll a^ at the sea surface than at other 

 depths, auid on some operations (25, 26, 28, 29) 

 only surface observations were made. (A few 

 samples collected at depths of 1, 2, or 3 m. 

 have been considered surface samples.) Sub- 

 surface observations were made at four to eight 

 depths in the upper 1 50 m. The sampling depths 

 were frequently the same as those used in 

 studying vertical distribution of primary pro- 

 ductivity; at other times they were chosen to 

 agree with features of temperature -depth 

 curves obtained by bathythermograph, or were 

 arbitrary and standard (Holmes, MS., see 

 footnote 1). 



Primary Productivity 



The well-known C !■* -uptake nnethod was 

 used, sometimes with incubation under constant 

 artificial illumination--the original method of 

 St eem an -Nielsen (1952) --and sometimes under 

 in situ or simulated in situ conditions of illum- 

 ination. In situ incubation means suspension of 

 inoculated samples from a buoy at depths cor- 

 responding to those from which they were ob- 

 tained, for half a solar day immediately follow- 

 ing collection and inoculation of samples. In 

 simulated in situ incubation (sometimes called 

 "deck incubation"), the samples are individu- 

 ally screened with neutral filters of varying 

 density, so as to receive illumination com- 

 parable with that at the depths from whichthey 

 came, and then placed in circulating sea sur- 

 face water on the unshaded deck of a ship for 

 half a solar day. Another method of in situ 

 incubation, suitable only for surface samples, 

 is to trail inoculated samples in the wake of the 

 ship for half a solar day ("trailing bottle 

 technique"). Details of these incubation tech- 

 niques, and other aspects of the C ^^ method 

 were given by Holmes et al. (1957), Holmes 

 and Blackburn (1960), Blackburn et al. (1962), 

 Forsbergh and Joseph (1964), and Holmes (MS., 

 see footnote 1). The photometry to determine 

 depths at which irradiance corresponds to that 



through the neutral filters was fully discussed 

 by Holmes (MS., see footnote 1). 



Only surface values (in milligrams of carbon 

 per cubic meter per day) are used in the later 

 sections of this paper which deal with hori- 

 zontal and seasonal variations in primary pro- 

 ductivity, since observations were much fewer 

 at other depths. On the basis of analysis and 

 discussion of incubation methods by Holmes 

 (MS., see footnote 1), only in situ, simulated 

 in situ, and "trailing bottle" observations are 

 used. When estimates of primary productivity 

 were available from more than one of these 

 incubation methods at the same station, only 

 one was used; in situ was preferred to simu- 

 lated in situ, and the latter to "trailing bottle." 

 Both Holmes and Forsbergh used dark bottles 

 as controls to some extent in their incubations; 

 Holmes did not routinely subtract dark-bottle 

 values, which were usually low, but Forsbergh 

 did (except on operation 28). Hence, the avail- 

 able surface data discussed are a mixture of 

 light-bottle values and light-bottle minus dark- 

 bottle values; they are heterogeneous also in 

 incubation method, although they do not include 

 any values resulting from incubations under 

 constant artificial illumination. Measurements 

 of primary productivity from operations 1, 8, 

 and 13 are excluded because of constant arti- 

 ficial incubation. Operation 18 yielded data for 

 18 stations in the eastern tropical Pacific 

 (Holmes, 1963); deck incubation was used, but 

 because of possible differences intechnique as 

 compared with those used by Holmes and 

 Forsbergh, this small group of observations is 

 neglected in this paper. 



Thomas (1964), who compared uptake ofCl"* 

 with net and gross O2 production, pH changes, 

 and growth in phytoplankton cultures, concluded 

 that the C''* method provides a reliable meas- 

 ure of net photosynthesis and increase in 

 bionnass both under good growing conditions 

 and under conditions of incipient nitrogen de- 

 ficiency. 



Zooplankton 



Most investigators in the eastern tropical 

 Pacific --including those at the BCF Biological 

 Laboratory, Honolulu, in the central tropical 

 Pacific and CalCOFI investigators in the Cali- 

 fornia Current region- -have used the same net. 

 This net, described by King and Demond (1 953), 

 has a mouth diameter of 1 m. and mesh- 

 apertures of 0.65 mm. in the front and middle 

 sections and 0.31 mm. in the rear section; 

 volume of water strained is estimated from 

 readings of a calibrated flowmeter in the mouth 

 of the net. 



The BCF Biological Laboratory in Honolulu 

 has used this net in oblique hauls to a depth of 

 about 200 m. on cruises which extended into 

 the eastern tropical Pacific (operations 3, 6, 8, 

 and 13 of table 1, and references there); 

 CalCOFI agencies have used it in oblique 



