38 
Upwelling is not uniformly distributed 
along the east coast with northerly winds but 
seems rather to be confined to certain places. 
Such places are in the lee of Isla Tiburon, in 
Bahia Guaymas, in Bahia Yavaros and in the 
vicinity of Topolobampo (Allen, 1937). It is 
interesting to note that all these places are in 
the lee of islands or headlands, which sug- 
gests that upwelling is largely controlled by 
the irregularities of the coast line as well as 
by the winds. 
Upwelling is important in the Gulf as a 
means of replenishing the depleted surface 
layers with plant nutrients from below. There 
are, unfortunately, no data on the concentra- 
tion of plant nutrients available for the re- 
gions where upwelling occurs, and it is for 
the time being not possible to investigate the 
biological role of upwelling in a quantitative 
manner. The high concentration of phyto- 
plankton in the upwelling areas in spring 
(Allen, 1937) is indicative, however, of a 
sufficient concentration in plant nutrients to 
support the large standing crop. 
It should be pointed out that upwelling is 
not the only process to fertilize the surface 
layers with plant nutrients. Increased wind 
mixing and winter convection may be of 
equal importance. The latter process is effec- 
PACIFIC SCIENCE, Vol. XII, January, 1958 
tive in the northernmost part of the Gulf 
(Sverdrup, 1941) whereas the former is bene- 
ficial everywhere. 
SEASONAL VARIATION OF TEMPERATURE 
AND SALINITY IN THE GULF 
Information on the monthly variation of 
temperature and salinity at the sea surface in 
the Gulf is very scanty. 
The first attempt to draw charts of monthly 
average sea surface temperatures was made by 
Thorade (1909). He collected data from ships’ 
observations for many years and averaged 
them. These pre- World War I charts are still 
the only ones in existence (Fig. 3). Since the 
Second World War the U. S. Coast and Geo- 
detic Survey has published sea surface tem- 
peratures from a few shore stations in the 
Gulf. These are given in Table 4. It is seen 
that the minimum temperatures occur in Jan- 
uary and February and the maximum tem- 
peratures in August and September. The mean 
annual range lies between 23°C. and 28°C. in 
Mazatlan and between 16°C. and 32°C. in 
Guaymas. In the northern half of the Gulf 
the mean monthly temperatures are not known. 
The minimum in the northernmost part seems 
to be above 10°C. since this is the temperature 
of the bottom water found there (Sverdrup, 
1941). 
TABLE 4 
Monthly Variation of Sea Water Temperature and Salinity for La Paz, Guaymas, and MazatlAn 
(USCGS 1951, Schott, 1935) 
LA 
PAZ 
GUAYMAS 
mazatlan 
t°C. 
S%o 
t°C. 
S%o 
t°C. 
S7oo 
January 
19-1 
35.5 
16.3 
36.2 
24.0 
34.8 
February 
19-3 
35.8 
17.6 
36.0 
23-0 
34.9 
March 
20.0 
36.4 
18.2 
35.8 
24.0 
35.0 
April 
22.0 
36.6 
21.0 
36.2 
24.5 
35.1 
May 
24.4 
36.6 
24.8 
36.4 
25.5 
35.5 
June 
26.0 
36.4 
29.3 
37.0 
26.7 
35.8 
July 
28.2 
36.6 
31.7 
37.1 
27.5 
34.8 
August 
29.8 
36.2 
31.4 
36.3 
28.2 
3 4.6 
September 
29.0 
36.2 
31.9 
36.3 
28.0 
32.8 
October 
28.3 
36.2 
30.0 
36.7 
27.8 
34.5 
November 
24.7 
35.9 
25.4 
36.2 
26.9 
35.1 
December 
21.2 
35.7 
19.6 
36.2 
26.1 
35.0 
Year 
24.3 
36.2 
24.8 
36.3 
26.0 
34.9 
Minimum 
17.8 
34.1 
11.0 
31.4 
— 
11.1 
Maximum 
33.3 
40.4 
36.2 
41.0 
36.7 
