UNITED STATES 



ZOOPLANKTON 0-300 M. 



JANUARY -JUNE (DAY a NIGHT) 



ML /lO* M* 



Figure 5. — Geometric means and (In parentheses) num- 

 bers of observations of surface primary productivity in 

 milligrams of carbon per cubic meter per day, for each 

 of the areas 1 to 14, in January to June. Daylight data 

 only; asterisk indicates <10 observations; for further 

 explanation see text. 



increasing depth of thermoclme). The relation 

 to thermocline depth may be understood as 

 follows: shoal thermoclines can be depressed 

 by wind-mixing, so as to enrich surface waters 

 chemically without carrying all the resulting 

 plant crop below the compensation depth (Black- 

 burn, 1962); in well-lighted tropical areas with 

 shoal thermoclines, primary production can be 

 significant below the mixed layer (Holmes, MS., 

 see footnote 1); on the other hand, in areas 

 where thermoclines lie deep, ascent of nutri- 

 ent-rich water is unlikely, and part of what- 

 ever plant crop is formed is likely to be 

 carried below the compensation depth. Pro- 

 duction below the mixed layer could be ex- 

 pected to be more important in the eastern 

 tropical Pacific than the eastern tropical 

 Atlantic; both have shoal thermoclines, but the 

 eastern tropical Pacific has fewer large rivers 

 and is, therefore, probably less turbid. 



Holmes (MS., see footnote 1) and Blackburn 

 (1966; and MS., see footnote 2) have de- 

 scribed areal distributions of water-column 

 chlorophyll a and water-column productivity, 

 and of micronekton. Although these distribu- 



Figure 6. — Geometric means and (in parentheses) num- 

 bers of observations of zooplankton in milliliters per 

 1,000 m.^ at to 300 m., for each of the areas 1 to 14, 

 in January to June. Day and night data; asterisk indi- 

 cates <iO observations; for further explanation see text. 



tions were based on much smaller numbers of 

 observations than those for surface chlorophyll 

 a, surface productivity, and zooplankton, they 

 are broadly similar to the distributions of those 

 properties as determined from more extensive 

 data. 



SEASONAL (HALF-YEARLY) DISTRIBUTION 

 OF BIOLOGICAL PROPERTIES 



Tests were made of statistical significance 

 of difference (t test) between means of the 

 logarithms of the same property for the same 

 area for the 2 half-years, when the number of 

 observations exceeded 10 for each period. 



Tests were possible as follows: chlorophyll 

 a (figs. 1 and 4), areas 2, 3, 4, 5, 6, 7, 9, and 

 11; primary productivity (figs. 2 and 5), areas 

 2, 3, 4, and 5; and zooplankton (figs. 3 and 6), 

 areas 2, 3, 4, 5, 6, 7, 9, 10, and 11. The fol- 

 lowing differences were significant at the 

 5 -percent level of probability: chlorophyll a, 

 in area 6; zooplankton in area 9. The following 

 differences were highly significant (1 -percent 

 level of probability): chlorophyll a in areas 2, 



11 



