42 
PACIFIC SCIENCE, Vol. XII, January, 1958 
Fig. 17. Distribution of oxygen and oxygen saturation anomaly at the sea surface, in February and March, 1939- 
salinity. The effect of evaporation increases 
as one proceeds toward the northwest. 
The circulation in the surface layers is pre- 
dominantly wind driven. Since the winds 
transport water of different origin towards the 
entrance of the Gulf, it is a transition region 
marked by the existence of fronts of which 
the San Lucas front is the best developed and 
best known. 
In the Gulf, as elsewhere, upwelling, sink- 
