BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
293 
air temperatures were exceptionally low. During the night of March 5, 1920, an 
exceptionally large drop in temperature occurred — from 46° F. (7.8° C.) to 18° F. 
( — 7.8° C.), a drop of 28° F. (15.6° C.), in Baltimore. 
SALINITY OF WATER DURING SUMMER 
A discontinuity in the vertical distribution of salinity was distinctly seen on the 
summer cruises. This might be expected, since the time for spring freshets was over 
and there was less chance of a disturbance in the stability of the layers. The maxi- 
mum rains in the Chesapeake Bay region usually occur during the summer months. 
While they may cause a distinct decrease of temperature in the surface layers and 
while, of course, the surface layers are diluted to some extent, our data, except for the 
July, 1916, cruise in the upper part of the bay, do not show any appreciable decrease 
in the salinity at the surface or in the deeper layers during the months of maximum 
precipitation. (Table 3.) The indications are that the effects of precipitation on the 
bay itself are not very important in changing the salinity. No tendency toward a 
homohaline condition was observed during the summer cruises along the deep-water 
channel, and even in shallow water the range from surface to bottom was usually 
considerable. Typical summer conditions for U, July 3, 1920, were as follows: Sur- 
face, 6.80, 5 meters 8.49, 10 meters 12.24, 12.5 meters 13.31, at 11.28 p. m.; and fori 
at 10.19 a. m., July 6, 1920, surface 12.50, 10 meters 14.66, 20 meters 19.72, 30 meters 
20.20, 36.6 meters 20.22. That the salinity values of the midsummer and late sum- 
mer cruises showed an increase over the low salinity values of the spring cruises may 
be seen from the data given under the section “Salinity at 30 meters and averages of 
salinities.’' 
SALINITY OF WATER DURING AUTUMN 
So far as our records show, the discontinuity in vertical distribution of salinity 
persists in a striking manner into the autumn. During this season the discharge 
from rivers is at its minimum and the weather is usually exceptionally mild on Chesa- 
peake Bay. Possibly, but not probably, almost homogeneous vertical distribution of 
salinity, occurred at times, but our records do not show that such changes have taken 
place. However, only two cruises have been made during the autumn — one in Sep- 
tember, 1916, and the other in October, 1920. During the cruises of the autumn 
months just mentioned the salinities, like those of the summer, were higher than those 
of the spring cruises. (Table 4.) 
Table 3. — Temperatures and salinities at surface, 20 meters, and 30 meters, during July and August, 
for various years and areas 
July, 1916 August, 1920 
Areas 
Tempera- 
ture, ° O., 
surface 
Salinity, 
Temperature, 
°C. 
Salinity 
surface 
Surface 
20 meters 
30 meters 
Surface 
20 meters 
30 meters 
G 
23.5 
24. 90 
27.0 
17.2 
22. 73 
31. 26 
27. 43 
A 
24. 3 
22. 54 
27. 0 
22.2 
21. 3 
22. 36 
28.09 
J 
26.0 
26.0 
25. 2 
L 
25.5 
25.5 
25.0 
13. 72 
13. 77 
19. 76 
R 
25.2 
10.21 
24.2 
12. 83 
s . 
26. 0 
8. 46 
X 
25.2 
5.41 
23.7 
10. 65 
Y 
26.0 
4.02 
23.5 
9. 46 
U - 
23.5 
4. 75 
