GULF OF MEXICO 



121 



Fku're 34. — Surface ocean currents in the Gulf of Mexico in June. 



Conclusions concerning currents sot up by the 

 wind are mostly based upon theoretical consider- 

 ations. A few observations have been made in 

 landlocked bays to show the piling up of water by 

 the wind. However, in the open ocean no sys- 

 tematic data are available. The drilling plat- 

 forms off the Gulf coast permit the accumulation 

 of data which will make possible a practical 

 analysis". 



The ciuTents related to the distribution of 

 density are the major semipermanent currents of 

 the oceans. Little is known about these currents 

 in the Gulf of Mexico. The chief source of infor- 

 mation is the pilot charts of the United States 

 Navy Hydrographic Office (figs. 34 and 35) . These 

 are based upon the navigation reconis of the ships 

 sailing in the Gulf over many jears. 'i'hev do 

 indicate the general drift in various regions, but 

 the individual observations upon which they are 

 based are subject to many errors. For example. 



the deviation of a ship from its course may be 

 caused by the wind rather than by the current. 

 Also, it is difficult to determine positions at sea 

 accurately. A survey of the pilot charts for the 

 Gulf indicates that these may not describe all of 

 the cm-rents present. They show waters flowing 

 into the western part of the area at all latitudes 

 but no water flowing out. This situation cannot 

 exist unless theic is a submarine return current of 

 equal nuignitude,»which seems unlikely. 



In the deep waters, direct observation of current 

 velocities has been almost impossible until recently 

 because of difficulty in anchoring vessels. Ac- 

 cordingly, few such observations have been made. 

 Instead, oceanographers have developed a method 

 based upon principles of [ihysics. By use of this 

 method the ocean currents present may be 

 inferred fnun the (listril)ution of density as deter- 

 mined l)y relatively simple observations of tem- 

 perature, salinity, and pressure. Two forces again 



