36 
Lucas transition represents a very sharp boun- 
dary between warm and high-saline Gulf 
water, and cool, low-saline water from the 
California region. It was first described by 
Thorade (1909), who pointed out that the 
intensity of the front is seasonal in character 
and that the maximum intensity occurs in 
late spring when the temperature differences 
between the Gulf and California Current water 
are greatest. 
The San Lucas front is illustrated in Figure 
13 (unpublished data). It is seen that the 
front is marked by a narrow band across which 
the temperature decreases from 21° to 18°C. 
and the salinity from 34.6 to 34. 1 /oo- 
It is possible that when the more saline 
Gulf water is cooled rapidly some sinking of 
this water takes place at the front, but this 
PACIFIC SCIENCE, Vol. XII, January, 1958 
feature has not been investigated. The tem- 
perature structure below the San Lucas front 
is shown in Figure 14. The bathythermograph 
section from Cabo Corrientes to Cabo San 
Lucas was prepared from hourly temperature 
observations made aboard the U. S. vessel 
''Golden Bear” and led to the discovery of 
another front in the vicinity of Cabo Cor- 
rientes. It is seen that the temperature differ- 
ences across the front increase with increasing 
depth. The increase could be explained as the 
result of decreased mixing at greater depth, 
but the feature needs further investigation. 
Since the winds were northerly in April, 
1949, when the "Golden Bear” crossed the 
Gulf Entrance it can be assumed that an 
already warmed water mass was driven out of 
the Gulf and pushed the cooler water north 
Fig. 12. Observed fronts (solid black) and transition regions (shaded) near the Gulf of California. 
