McCarthy and kamykowski : urea and other nitrogenous nutrients 



Table 3. — Comparisons of medians and variability of 

 the nitrate, nitrite, ammonium, and urea results from 

 stations sampled on the same day. 



for that day, it is reasonable to compare the 

 phaeo-pigment/chlorophyll ratios with the best 

 estimate of average ammonium and urea values 

 for the same area. This is supported by the find- 

 ings that the phytoplankton species composition 

 was similar at all three stations and that the 

 surface chlorophyll concentrations at Stations I 

 and III were significantly correlated with the 

 surface cell counts at Station II. Thus we 

 paired the phaeo-pigment/chlorophyll ratios 

 with the median ammonium and urea values at 

 each depth for the same day in the following 

 analysis. The phaeo-pigment/chlorophyll ratios 

 were not correlated with the median ammonium 



concentrations in either Period A (P = 0.189) 

 or Period C (P = 0.171) but were positively 

 correlated in Period B (P < 0.001) . The phaeo- 

 pigment/chlorophyll ratios were not correlated 

 with the median urea concentrations in Period A 

 (P = 0.382) , Period B (P = 0.397) , or Period C 

 (P = 0.166). Since each set of pigment and 

 nutrient data have been used in two correlations, 

 an appropriate a for significance is 0.05/2. Scat- 

 ter diagrams for phaeo-pigment/chlorophyll 

 ratios and the median ammonium and urea con- 

 centrations are presented in Figures 5 and 6 

 respectively. 



DISCUSSION 



Earlier studies in the Peru Current (Mc- 

 Carthy, 1970) , in the central Pacific (McCarthy, 

 1971), and the present study have shown that 

 great diflferences in both ammonium and urea 

 occur on a vertical scale of a few meters. If 

 during this study a small-scale inhomogeniety 

 had been prevalent in the horizontal as well as 

 vertical dimensions, it should have been evident 

 both within and between stations made on the 

 same day. If, on the other hand, there had been 

 horizontal patches large with respect to a 1.5 km 

 distance, the concentration at a particular depth 

 should have been similar at both stations; this 

 was apparently the case for nitrate, nitrite, and 



Table 4. — Normal deviates (z) and corresponding probabilities (P) 

 for comparisons between medians and variabilities of nitrate, nitrite, 

 ammonium, and urea for all three periods. 



1 P values are given for tVie two-sided test. To correct for multiple testing an or of 0.O5/2 

 should be used. Significant differences are in bold type. 



1269 



