LARRANCE: PRIMARY PRODUCTION IN MID-SUBARCTIC REGION 



Table 5. — Changes of dissolved phosphate in upper 50 m of mid-Subarctic 

 Pacific Region (attributable to vertical transport and assimilation by 

 phytoplankton) and their relation to measured concentrations (shown 

 in parentheses). 



mg ?/m~ per day 

 (mg P/m-) 



mg P/m2 per day 

 (mg P/m-) 



mg P/m2 per doy 

 (mg P/m2) 



Residual change 



of P' 



mg P/m2 per day 



(mg P/m2) 



1 See text for definition. 



ward motion; the net upward flux of phosphate, 

 therefore, is underestimated when mean vertical 

 velocities are applied. 



Values of P,, for the periods between cruises 

 were estimated from productivity data. The 

 lesser values of the two productivity estimates 

 (Pk or Pr) from each of two succeeding cruises 

 were averaged, as were the greater values. 

 These averages represented the limits of the 

 range of mean productivity during the period 

 between cruises. For example, in the summer of 

 1966 (when in June, Pk = 238 and Pr = 426 mg 

 C/m^ per day, and in September, Pk = 2-50 and 

 Pr = 201 mg C/m- per day) , the range of mean 

 productivity during the period was from 220 

 (the average of 238 and 201) to 338 (the average 

 of 426 and 250) mg C/m^ per day. The limits 

 of the ranges were divided by the C:P ratio 

 (40) to obtain the daily rate of phosphorus up- 

 take in milligrams within a 1-m- cross-sectional 

 column of the euphotic zone (Table 5). This 

 rate was considered equivalent to the uptake in 

 the upper 50 m. No error was incurred by this 

 approximation when the euphotic zone was no 

 deeper than 50 m. The "residual changes" of P 

 were the changes unaccounted for by P„ and P„ ; 

 thus they included regeneration, other changes 

 not evaluated, and measurement errors: 



residual change 



Po — (Pa + P„). 



Although the accuracy of these estimates was 

 low, the direction that Pa and P„ are likely to be 

 in error is known and the direction of error of the 



residual changes can be deduced. As the absolute 

 values of Pa were minimal and those of P„ were 

 too large (and P„ was either positive or negative 

 and P„ was always negative) , the sum Pa + Pu 

 tended to be underestimated. The residual 

 changes, therefore, tended to be overestimated. 



The residual changes during similar seasons 

 in the 2 years indicate similar trends (Table 5). 

 Negative values during spring 1966 show that 

 phosphorus assimilation, and hence primary 

 in-oductivity, must have averaged more than 

 that calculated, even if no regeneration occurred. 

 If phosphate regeneration is assumed to be 

 zero, the productivity during spring 1966 could 

 have been as much as 40 ''r higher than that 

 calculated to account for the changes in measured 

 phosphate. Although regeneration rates were 

 probably lower than in summer, some regener- 

 ation probably occurred, and therefore the re- 

 sidual change would have been greater and the 

 productivity even higher. Clearly, spring phy- 

 toplankton production in 1966 must have been 

 substantially greater than the measured pro- 

 ductivities. 



Larger residual changes in the summer in- 

 dicate higher phosphate regeneration rates than 

 in spring. Phosphate turnover times ranging 

 from about one to several months have been re- 

 ported (Ketchum, 1962). According to Ketch- 

 um, excretion by zooplankton accounts for large 

 portions of regenerated phosphate as well as in- 

 organic niti'ogenous compounds. The residual 

 changes were correlated with zooplankton 



609 



