40 
creases and reaches a second minimum around 
December. The salinity ranges between 35.5 
and 36.5°/oo in La Paz and between 35.8 and 
37.1°/oo in Guaymas. Both places are situated 
at the head of shallow bays where evaporation 
is extensive. These values are, therefore, not 
representative for the open Gulf. 
In Mazatlan the salinity varies between 32.8 
and 35.8°/ 00 . The very low value found in 
September (32.8°/ 00 ) is possibly caused by 
extensive runoff from Rio Presidio during the 
rainy season. 
Figure 15 illustrates that there is a very 
good agreement between net evaporation and 
salinity. The slight differences seen can be 
attributed to the different years in which the 
salinity was observed and for which the net 
evaporation was computed. 
DISTRIBUTION OF PHYSICAL AND CHEMICAL 
PROPERTIES IN THE GULF 
A preliminary discussion of the distribution 
of temperature, salinity, and oxygen in Feb- 
ruary and March, 1939, was published by 
Sverdrup (1941). A short report on the dis- 
tribution of silicate and phosphate from Oc- 
tober to December, 1940, was given by the 
same author (Sverdrup and staff, 1940). Here 
only a few conclusions will be drawn from the 
distribution of these properties. The distribu- 
tion of phosphate and silicate in the Gulf can 
be discussed only qualitatively, because the 
measured data are such that they do not war- 
rant a quantitative discussion. 
Vertical Distribution 
The Gulf can be divided vertically into a 
shallow upper layer (20 to 40 m. deep) where 
the distribution of properties is rather uniform 
due to wind stirring; a layer between roughly 
50 and 150 m., varying with season, where the 
temperature, salinity and oxygen content de- 
crease rapidly; and a deep layer, between the 
thermocline and the bottom, where the con- 
centrations remain fairly constant from one 
season to another. 
PACIFIC SCIENCE, Vol. XII, January, 1958 
In the upper layer the concentrations vary 
considerably with time due to the amount of 
heating, cooling, stirring, evaporation, preci- 
pitation, runoff and various biological ac- 
tivities. Shallow and semi-enclosed bays show 
greater variations than the open Gulf. The 
layer of rapid density increase is generally 
closer to the surface during the warm season 
than during the cold season, but the available 
data are too few to give accurate depth ranges. 
Below the layer of rapid density increase the 
temperature decreases more or less slowly 
toward the bottom, but in a few deep basins, 
below 2000 m., a slight increase is observed 
due to the adiabatic effect. 
The salinity shows a minimum (34.48- 
34.54°/oo) between 600 and 800 m. and in- 
creases slightly toward the bottom. 
The amount of dissolved oxygen has a very 
pronounced minimum (less than 0.1 ml/1) 
between 300 and 700 m. and increases again 
toward the bottom. 
The silicate content increases with depth 
and equals about 160 fig- at/1 in the central 
part of the Gulf where the bottom deposits 
are largely diatomaceous oozes. 
Horizontal Distribution 
The horizontal distributions of tempera- 
ture, salinity and oxygen in February and 
March, 1939, are illustrated in Figures 16, 17, 
18 and 19. 
At the surface (Figs. 16 and 17) the distribu- 
tion of these properties is very complicated. 
The high oxygen values (more than 50 per 
cent supersaturated in places) are probably 
the result of extensive phytoplankton pro- 
duction. The southern half of the Gulf is 
slightly undersaturated with respect to oxy- 
gen. Upwelling as indicated by a low tem- 
perature (and salinity) can be seen to occur 
in Bahia Guaymas and Topolobampo. 
At subsurface depths (Figs. 18 and 19) the 
two outstanding features are a tongue of 
warm, high saline and oxygen-rich water mov- 
ing to the south along the coast of Baja 
California and a tongue of low saline, cool 
