FISHERY BULLETIN: VOL. 76, NO 2 



Table 7. — Summary of slope water, ring, and Sargasso Sea primary productivity (mg C/m^ per day), phytoplankton carbon' (mg/m^), 



and chlorophyll a (mg/m^) measurements. 



'Based on counts of cells larger than 4-5 txm 



^The high value in average mg C m^ per day observed at this station is a consequence of one unusually high surface value. 



tion of rings to the northern Sargasso Sea as 

 explained earlier, and Ryther's estimate of a 

 twofold difference in annual production, the net 

 annual production of the geographic northern 

 Sargasso Sea is then 3 to 7% higher than if it 

 contained no rings (i.e., 6 x 1.5 = 9, 9 + 94 = 103 

 and 13 X 1.5 = 20, 20 + 87 = 107). Our assumption 

 of linear decay is most certainly an oversimplifica- 

 tion. In November 1975, the ring water column, 

 like the slope water, began its winter overturn 

 before the surrounding Sargasso Sea. Mixing 

 eroded the seasonal thermocline that had been 

 observed in Ring-D in August 1975. The decay we 

 have assumed was reversed, and ring productivity 

 was enhanced (Table 7). 



ZOOPLANKTON STANDING CROP.— Simi- 

 lar calculations can be made regarding the rela- 

 tive contribution of rings to the mean zooplankton 

 biomass of the geographic northern Sargasso Sea. 

 Neglecting one station which had anomalously 

 high values due to extreme salp dominance, the 

 average of slope water biomass values is 3.5 times 

 the observed Sargasso Sea biomass (Table 3). 

 Given this ratio and the same linear [i.e., (3.5 + 1) 

 -i- 2 = 2.25] and areal assumptions made earlier, 

 rings may augment the zooplankton standing crop 

 of the geographic northern Sargasso Sea by 8 to 

 16% (i.e., 6 X 2.25 = 14, 14 + 94 = 108 and 13 x 

 2.25 = 29, 29 + 87-1 16). Our ratio of slope water 

 to Sargasso Sea biomass may be compared with 

 that of Grice and Hart (1962), who reported the 

 slope water standing crop as three to four times 

 that of the Sargasso Sea. They also excluded ex- 

 tremely salp-rich samples in making this com- 

 parison. Our assumption of 2.25 as an annual 

 mean ring/Sargasso biomass ratio (i.e., linear de- 

 cay) may be an overestimate considering the aver- 

 age biomass ratio obtained on all cruises to date 



and the average ring age sampled (Table 3). On 

 the other hand some rings do last longer than a 

 year and the lowest ring:Sargasso Sea ratios that 

 we have observed are approximately 1.3 (i.e., 

 >1.0). 



We have noted a highly significant decline in 

 0-800 m biomass from August to November in 

 slope water, ring, and Sargasso Sea both in 

 data presented here and in data more recently 

 collected.'^ This observation is consistent with 

 those of Grice and Hart ( 1962) with respect to the 

 slope water. They noted, however, no such decline 

 in the Sargasso Sea. Neither is there a summer- 

 to-fall decline in the Sargasso Sea data of Deevey 

 (1971). The Sargasso Sea and slope water data of 

 Fish (1954) exhibit irregular fluctuations in 

 biomass throughout the summer and fall. Moore 

 ( 1949) presented some Sargasso Sea data indicat- 

 ing a progressive decline of biomass from a spring 

 maximum to a fall minimum. Their data substan- 

 tiate that interseasonal fluctuations in the Sar- 

 gasso Sea are less marked than in the slope water. 



Vertical Structure 



We have pointed out that, compared with either 

 the Sargasso Sea or slope water, an unusually 

 small percentage of 0-800 m biomass is present in 

 the upper 200 m of a ring. We found a relatively 

 large fraction of the 0-800 m zooplankton biomass 

 above 200 m in the northern Sargasso Sea. The 

 netting employed by Leavitt ( 1935, 1938) was rel- 

 atively coarse (1.0 mm) so it is difficult to compare 

 our results with his. Nonetheless, at his two Sar- 

 gasso Sea stations (2462, 2463) the percentages of 



^Some of this data is presented in figure 4 of Richardson, P, L,, 

 J, Schmitz, and P. H, Wiebe, 1977, Gulf Stream ring experi- 

 ment, Polymode News 25:3. Unpubl. manuscr. 



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