130 Alfred C. Redfield 



water from Lake Maracaibo, which is on the average about 1 -4 [agA per litre, whereas 

 the Caribbean water contains about one-quarter this amount. The general pattern 

 of distribution of salinity and phosphorus in the surface waters (Figs. 8 and 10), 

 and in the axial section (Fig. 7), are so similar as to suggest that both properties vary 

 as the result of the system of circulation which mixes waters derived from the Lake and 

 Sea. 



In the deeper parts of Calabozo Bay and the eastern side of the Outer Gulf, con- 

 centrations of phosphorus occur which are too great to be accounted for by the 

 physical circulation (Figs. 6 and 7). In the former case the high salinity excludes an 

 origin from lake water; in the latter the high phosphorus content precludes Caribbean 

 water as the source. It is concluded that organisms and particulate matter have sunk 

 into these basins, carrying down from the surface layers the phosphorus which has 

 accumulated at depth. 



Oxygen 



In the Gulf of Venezuela the surface water, as well as that at greater depths, was 

 everywhere under-saturated, in amount varying from 1-4 to 9-6 per cent. Physically 

 this implies that the oxygen pressure was positive across the surface, and that oxygen 

 was diffusing downward into the water. This condition cannot be explained by the 

 cooling and consequent under-saturation of the surface, as is the case in higher latitudes 

 in winter (Redfield, 1948), because the annual range in temperature is too small. 

 It must be attributed to biochemical effects, arising from the excess of respiration over 

 photosynthesis in the water. 



The consumption of oxygen by respiration, in excess of its production by photo- 

 synthesis, can only persist if there is available some external source of organic matter, 

 as is the case in waters polluted by sewage. The undersaturation of the surface waters 

 of the Gulf of Venezuela may be the result of the high organic content of the outflow 

 from Lake Maracaibo. In the lake water two-thirds of the phosphorus (1 [J.gA/1) is 

 present in organic form, and while in the Lake much of this is probably present in 

 living organisms capable of photosynthesis. On introduction into the Gulf, however, 

 these organisms, which are fresh water or brackish species (Gessner, 1953 a), may be 

 killed by the higher salinity, and thus contribute to the quantity of organic matter 

 immediately available for oxidation. 



In support of this suggestion are the observations that the greatest under-saturation 

 of surface water occurs in the immediate offing of Tablazo Bay (Fig. 1 1), and that the 

 water of that bay is generally under-saturated with oxygen. 



In the deeper parts of Calabozo Bay and the eastern parts of the Outer Gulf, where 

 the total phosphorus was found to be anomalously high, the oxygen concentration is 

 reduced to less than 3 ml per litre. (Compare Figs. 5 and 6). The deficiency in oxygen 

 increases with the phosphorus content, and is about that to be expected from the 

 increase in phosphorus if it arises from the oxidation of planktonic material (see 

 Fig. 13). It may be concluded that the deficiency of oxygen in the deeper parts of the 

 Gulf is due to the accumulation of organic matter as the results of the sinking of 

 organisms and particulate matter from the surface layers of water, and that the 

 greater part of this material has undergone oxidation. 



At no place was the deeper water found to be completely devoid of oxygen. The 

 deep circulation appears to be sufficiently rapid to prevent the accumulation of enough 



