latter value Is very similar to the average value 

 reported above for the group exhibiting the low 

 assimilation factor when the difference in light 

 intensities between the two sets of experiments 

 are equated. Tailing (personal communication) 

 has observed similar rates in cultures of the 

 marine diatom, Chaetoceros aff inis . 



The high values (ca. 20 mg C/hr/mg chlorophyll 

 "a") observed at a few stations are somewhat 

 anomalous and difficult to interpret. The sta- 

 tions where such high values were observed were 

 all located in the region of the thermal anti- 

 cline. These higher photosynthetic rates may 

 be associated with differences in the species 

 composition and/or some difference in the physio- 

 logical state of the organisms. 



The "average" in situ rates (see Fig. 6) observed 

 on the expedition on a per-hour basis (assuming 

 a 12-hour day) are somewhat lower than the rates 

 observed in the incubator, averaging about U.2 

 mgC/hr/mg chlorophyll "a". Again, the highest 

 ratios are observed at stations in the region 

 of the thermal anticline off Costa Rica. The 

 lower "average" value may be the result of in- 

 hibition of photosynthesis during the brightest 

 portion of the day. 



As mentioned above, there is considerable vari- 

 ability among individual values. Some of the 

 variability is doubtless associated with the 

 techniques employed but much of it is certainly 

 quite real. A study of the possible effect of 

 differences in species composition of the phy- 

 toplankton on the productivity-chlorophyll ratio 

 will be examined in the near future. 



These data yield further confirmation of Ryther's 

 suggestions (1956) that it should be possible to 

 estimate productivity from the concentration of 

 chlorophyll "a" in sea water. However, the pre- 

 cision of such an estimate from chlorophyll "a" 

 concentration would be rather poor in the Eastern 

 Tropical Pacific. Furthermore, it appears that 

 departures from the "average" value of carbon 

 assimilation per unit chlorophyll "a" that is 

 observed in the surface water become more pronounc- 

 ed in samples collected deeper in the photic zone. 



BIBLIOGRAPHY 



Clendenning, K. A., T. E. Brown, and 



H. C. Eyster. 1956. 



Comparative studies of photosynthesis in 

 Nostoc muscorum and Chlorella pyrenoidosa . 

 Can. J. Bot., Vol. 3^, PP- 9^3-966. 



Holmes, R. W., M. B. Schaefer, and 



B. M. Shimada. 1957. 



Primary production, chlorophyll, and 

 zooplankton volumes in the Eastern 

 Tropical Pacific Ocean. Inter-Am. Trop. 

 Tuna Comm. , Bull., Vol.2, No. h. 



Manning, W. H., and R. E. Juday. 1951. 



The chlorophyll content and productivity 

 of some lakes in northern Wisconsin. 

 Trans. Wis. Acd. Sci., Arts, and Let., 

 Vol. 33, PP. 363-393. 



Rabinowitch, E. I. 1956. 



Photosynthesis and related processes 

 Vol. 2, Part 2, Kinetics of photo- 

 synthesis, pp. 1211-2088, Interscience 

 Publishers, N. Y. 



Ryther, J. H. 1956. 



The measurement of primary production. 

 Limm. and Ocean., Vol. 1, No. 2, pp. 79-93- 



Ryther, J. H., and C. S. Yentsch. 



The estimation of phytoplankton produc- 

 tion in the ocean from chlorophyll and 

 light data. Limn, and Ocean., Vol. 2, 

 No. 3, PP- 281-286. 



Steemann Nielsen, E. 1952. ^ 



The use of radio-active carbon (C ) 

 for measuring the organic production in 

 the sea. J. du Conseil., Vol. l8, No. 2, 

 pp. 117-11*0. 



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