132 Alfred C. Redfield 



The concentrations of the organic derivative of sea water (phosphate, nitrate, and 

 carbonate), and of oxygen, have been shown to vary from place to place in proportions 

 related to the statistical composition of the plankton (Redfield, 1934). It is evident 

 that some broad-scale process of biological origin is responsible for the distribution 

 of these biogenetic properties in ways which are anomalous in respect to the purely 

 physical character of the circulation. 



The obvious mechanism for separating the organic derivative from the dissolved 

 materials in one mass of sea water, and transferring it to another, is the sinking and 

 subsequent decomposition of organisms into a deeper layer. Redistribution leading to 

 accumulation or attenuation is then dependent on the horizontal movement of the 

 respective layers. If such movements are consistently in opposite directions, great 

 differences in concentrations may be developed. The counter-current principle is 

 commonly employed in such physical mechanisms as heat exchangers. Its applications 

 in physiology have been discussed by Scholander (1954). 



The Gulf of Venezuela affords examples of two somewhat different types of counter- 

 current system which lead to the local accumulation of phosphorus, with attendant 

 depletion of oxygen in the deeper water. 



In the Outer Gulf the winds appear to produce an offshore movement of the 

 surface water, which is compensated for by an onshore counter-current at depth. 

 This is referred to as upwelling. Organic matter sinking from the surface layer is 

 carried landwards in the deep counter-current. The process leads to an attenuation 

 of phosphorus content of the surface layer with distance from shore, and its augmenta- 

 tion in the deeper water which increases as the coast is approached. The degree of 

 accumulation finally developed depends, of course, on a balance between this process 

 and the dissipating effects of the circulation, which mixes the water vertically or trans- 

 ports it horizontally across the region of upwelling. 



The situation in the Outer Gulf provides a small-scale example of the mechanism 

 of enrichment of ocean water which occurs wherever trade winds give rise to upwelling 

 along the continental coasts. 



In Calabozo Bay the counter-current system of the estuarine circulation is 

 engendered by the inflow of fresh water from Lake Maracaibo rather than by the wind. 

 Otherwise the process leading to the attenuation of phosphorus in the surface water 

 and its accumulation at depth is the same as in the upwelling system of the Outer Gulf. 

 The degree of accumulation attained is limited by the rate of circulation of the deep 

 water, which appears to move toward the head of the Bay, where it is most actively 

 incorporated into the surface outflow. The highest phosphorus and lowest oxygen 

 concentrations were found immediately off the outlet of the Lake, 



The estuarine circulation of Calabozo Bay provides an example of a mechanism 

 which must operate to varied degrees in many coastal embayments, fjords, and estu- 

 aries, and which may account in part for the greater fertility common to such enclosed 

 waters, when compared to the off-lying sea. 



REFERENCES 



Carter, Douglas B. (1954), Report on water balance of the Maracaibo Basin. Unpublished manu- 

 script on file, Woods Hole Oceanographic Institution. 



Corps of Engineers, U.S. Army (1938), Model study of channel improvements at outer bar, Lake 

 Maracaibo, Venezuela. U.S. Waterways Experiment Station, Corps of Engineers, U.S. Army, 

 Tech. Memo. No. 106-1, 3 vols, December 1, 1938. 



