concentration of total phosphorus at Station 6 was only 0.18 ;ig-at/L (see 

 table h). 



In May when observations extended to Station 8 the surface waters were 

 warming but the colder bottom water at I4.0 fathoms (Station 7) was maintained. 

 The phosohorus content was high at the bottom, again similar to the water 

 at 135 meters at Station 8. In this case, however, the high phosphorus was 

 represented by organic phosphorus. Perhaps the upwelled water of the pre- 

 vious month had been maintained while the inorganic phosphorus was converted 

 to organic. 



In June considerable surface heating had taken place and a thermocline 

 was developed at all stations. The phosphorus concentration was low at ail 

 depths at Stations 6 and 7 and in the upper layers at Station 8 except at 

 the surface. 



In July the surface temperature had continued to increase and the bot- 

 tom temperature had also increased at Station 7. The phosphorus content of 

 the water in the upper layers was higher than usual. 



In August the temperature had reached its yearly maximum at the sur- 

 face at the offshore stations while the bottom temperature at Station 7 was 

 unchanged over July. At Station 8 the thermocline was well developed with 

 a decrease in temperature to the bottom. The phosphorus content of the 

 water in the upper UO meters was low from Station 5 outward. 



It can be concluded from this study of the phosphorus distribution to 

 the 100-fathom line that, although upwelling does occur at certain times, it 

 does not produce abnormally high concentrations of phosphorus in the coastal 

 waters where the red tide occurred. 



Another point brought out by this study is that the concentrations of 

 inorganic phosphorus in the upper layers of the open Gulf are always extremely 

 low. 



At the surface at Stations $, 6, 7 and 8 the concentration of inorganic 

 phosphorus was almost always less than O.l^ug-at/L. In fact, the values 

 recorded are practically within the experimental error of the method of deter- 

 mination. 



Any inorganic phosphorus that was brought to the photic zone, either 

 by vertical or horizontal movement or run-off from land during the l6-month 

 period of observation, in the entire area from the 10-fathom line outward, 

 was quickly removed from the water by the phytoplankton. The concentration 

 0.0$ to 0.1 _ug-at/L orobably represents the minimum value to which the phyto- 

 plankton can deplete the water. 



In our observations there is nothing to indicate that the bottom of 

 the Gulf is a source of phosphorus. If quantities of soluble phosphate 



38 



