DISCUSSION 



In his original paper on the proportions of 

 organic derivatives in sea water, Redfield 

 (19B4) speculated that biological processes 

 might determine these proportions. Marine or- 

 ganisms contain in their protoplasm nitrogen 

 and phosphorus in approximately the same ratio 

 as in the ocean. The stoichiometric ratios have 

 been determined by previous workers (Redfield, 

 1934; Cooper, 1938; Fleming, 1940) to be— 

 : C : N : P = 276 : 106 : 16 : 1. Grill and 

 Richards (1964) obtained the silicate to phos- 

 phate ratio of 23 :1 during the biochemical oxi- 

 dation of organic matter in the laboratory. This 

 linear relationship existed only in an intermedi- 

 ate concentration range (15-40 ftg-at/L of sili- 

 cate). 



In order to compare the ratios found in the 

 Weddell Sea with the theoretical stoichiome- 

 tric ratios given above, the nutrient quantities 

 were converted to ratios by atoms and subjected 

 to a least squares regression. Using the general 

 mean values from the vertical sections for 

 IWSOE '69 (fig. 13-17), these ratios were ob- 

 tained : 



Continental Shelf N : Si : P = 15.8 : 31.2 : 1 

 Warm Deep Layer N : Si : P = 14.3 : 55.2 : 1 

 Bottom Layer _ _ N : Si : P = 14.4 : 55.1 : 1 



The ratios for nitrate and phosphate ob- 

 served in the Weddell Sea were in general a- 

 greement with the theoretical ratios. However, 

 there was a large deviation from the 23 : 1 

 silicate-to-phosphate ratio suggested by Grill 

 and Richards (1964), particularly in deep 

 water samples in which there were very high 

 (>40 ;Li,g-at/L) concentrations of silicate. Sili- 

 cate values in the Weddell Sea increased mono- 

 tonically with depth to concentrations greater 

 than 120 ,ig-at!L near the bottom of the basin. 

 These high silicate values distort the ratios of 

 silicate and phosphate from the classical stoich- 

 iometric values. 



The close correspondence of the nitrate-to- 

 phosphate ratios with 16 : 1, the theoretical 

 value, allowed the use of the preformed nutri- 

 ent concept in tracing water masses in the 

 Weddell Sea (Redfield, 1942). In calculating 

 preformed nutrients, the oxidation ratio of : 

 N : P = 276 : 16 : 1 was used. The good fit 

 between the observational values and the values 

 in the literature provide a valuable check on the 

 validity of the concept in the Weddell Sea. 



Hufford and Seabrooke (in press) used pre- 

 formed nutrient values from the Weddell Sea 

 to determine the water masses present. Analysis 

 of the data indicated three water masses : con- 

 tinental Shelf Water (PO4 = 1.81, NO3 = 23.07 

 ixg-at/L) ; a Warm Deep Layer (PO* = 1.35, 

 NO3 = 9.11 /ig-at/L (400-1600 meters); and 

 Antarctic Bottom Water (PO4 = 1.59, NO3 = 

 13.85 ,.g-at/L) (fig. 10, 11, 16, 17). There was 

 an excellent similarity between the distribu- 

 tions of temperature, salinity and the pre- 

 formed nutrients. 



Simultaneous observations of oxygen and the 

 nutrients can yield useful information regard- 

 ing the biological activity in the surface waters. 

 In the absence of physical dissipation and in 

 situ temperature changes, the degree of oxy- 

 gen supersaturation or negative apparent oxy- 

 gen utilization (AOU) in the surface layer 

 should represent the excess of photosynthesis 

 over respiration (Steffanson and Richards, 

 1964). Negative AOU and oxygen supersatura- 

 tion were calculated using the tables of Green 

 and Carrett (1967). Negative AOU and oxygen 

 supersaturation were found only in the south- 

 west region of the Weddell Sea indicating this 

 area to be more biologically active than the 

 central or southeastern regions. Distribution 

 of surface chlorophyll and carbon-14 measure- 

 ments in the Weddell Sea by El-Sayed (1968) 

 also indicate that the southwest portion is by 

 far the most productive; but there were con- 

 spicuous variations in productivity within areas 

 visited. 



