ORTNER ET AL.: SARGASSO SEA ZOOPLANKTON BIOMASS DISTRIBUTION 



upper 200 m in the ring (Table 6). This apparent 

 contradiction results from the fact, already noted, 

 that the percentage of 0-800 m biomass present in 

 the upper 0-200 m was very much greater in the 

 Sargasso Sea. Day/night ratio of biomass in the 

 upper water column is often used to measure in- 

 tensity of diel migration; clearly the meaning of 

 this ratio is highly dependent upon average verti- 

 cal biomass distribution. 



Slope water day/night sample pairs may be in- 

 terpreted as documenting diel migration, but the 

 data are extremely variable both within and be- 

 tween cruises (Table 4). There may have been a 

 less well-developed migration in the fall, but the 

 generality of this is questionable. 



Table 6. — Day night differences in slope water, ring, and Sar- 

 gasso Sea zooplankton biomass in the upper 200 m. 



'Based on 0-200 m tows 

 2Based on 0-800 m tows 

 3Ratio affected by extreme salp dominance. 



Shallow Biomass Structure 



In the 0-200 m biomass profiles, an intermediate 

 biomass peak occurred between 50 and 100 m 

 depth at nearly every station in August 1975 (Fig- 

 ure 1: MOC 1, 3, 6, 7, 10, 16, 17). At all butone of 

 the Sargasso Sea and ring stations this inter- 

 mediate peak is the highest observed value in the 

 0-200 m tows. At slope water stations of the same 

 cruise this intermediate peak is the second highest 

 observed value. If we rank each interval in a 

 profile in order of zooplankton abundance, we can 

 test the significance of this observation. For in- 

 stance, the individual summer tows in the ring 

 and the Sargasso Sea exhibit significant concor- 

 dance as to which depth intervals have the larger 

 and which the smaller zooplankton biomass 

 (Friedman 2-way analysis of variance on ranks, 

 P<0.005). Given this result, the best estimate of 

 the differences between intervals is the order of 

 their summed ranks (i.e., 50-75 m>75-100 

 m>100-125 m>25-50 m>0-25 m>150-175 

 m>125-150 m>175-200 m). Applying a procedure 

 for testing differences between individual depth 

 intervals (Nemenyi 1963), we see that concor- 

 dance results from the fact that the 50-75 m 

 biomass is significantly greater than the biomass 



in the intervals 125-150, 150-175, and 175-200 m, 

 and the 75-100 m biomass is greater than the 

 175-200 m biomass (P<0.05). An intermediate 

 peak is not a notable feature of any of the 0-200 m 

 profiles taken on the fall cruise with the exception 

 of the Sargasso Sea sample pair (Figure 2: MOC 

 23, 26). 



DISCUSSION 



Wiebe, Hulburt, Carpenter, Jahn, Knapp, Boyd, 

 Ortner, and Cox ( 1976) have discussed the forma- 

 tion and decay of an idealized cold core ring. Ini- 

 tially conditions inside a ring core are identical to 

 those in the slope water just northward of the Gulf 

 Stream at the time of ring formation. Through 

 time the ring decays; the isotherms deepen, the 

 water becomes more saline, the O2 minimum 

 deepens, and the constituent flora and fauna 

 either die off or become diluted by populations 

 from the surrounding Sargasso Sea. Because zoo- 

 plankton populations are generally suited to the 

 environmental conditions they encounter within 

 their normal range, this decay process may be 

 viewed as the gradual imposition of a complex 

 environmental stress upon an entire community. 

 Wiebe, Hulbert, Carpenter, Jahn, Knapp, Boyd, 

 Ortner, and Cox ( 1976) have documented some of 

 the intermediate stages in this idealized process. 

 In fact, this process can be aborted when a ring is 

 reabsorbed by the Gulf Stream (Fuglister 1972; 

 Richardson et al. 1977). All biological and physical 

 properties are not equally conservative so their 

 decay rates would not be the same. 



Regional Contribution of Cold Core Rings 



PRIMARY PRODUCTIVITY.— It is well 

 known that slope water is more productive than 

 the Sargasso Sea. Ryther (1963) estimated that 

 slope water is about twice as productive on an 

 annual basis ( 120 g C/m^ per yr versus 60 g C/m^ 

 per yr). Although our own data are scanty, rings 

 on the average are intermediate between slope 

 water and the Sargasso Sea (Table 7). A few 

 simplifying assumptions permit budgetary com- 

 putations to be made regarding the overall effect 

 of rings on the carbon budget of the northern Sar- 

 gasso Sea. Let us assume an average ring life of 1 

 yr and a linear rate of decay of productivity (i.e., 

 that annual ring production is the arithmetic 

 mean of annual Sargasso Sea and slope water pro- 

 duction). Allowing 6 to 13% as the areal contribu- 



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