310 
BULLETIN OF THE BUREAU OF FISHERIES 
On the other hand, during some of the midsummer cruises, such as July, 1916, 
and August, 1920, the thermocline was practically obliterated in the bay, owing to 
rain in the first case and cool weather in the second, aided probably by wind and 
currents. The records show, as would be expected, that the temperature of the 
upper layers drops during the night and rises during the day; but, independently of 
this, discontinuity layers occur corresponding to the warm and cold parts of the year 
and often in accordance with the origin of the upper and lower layers of water. On 
the August cruise the temperature and salinity data were as shown in Table 8. 
Table 8. — Temperatures and salinities at various depths on August, 1920, cruise 
Date 
Area 
Tempera- 
ture, ° C. 
Salinity 
Depth, 
meters 
Date 
Area 
Tempera- 
ture, 0 C. 
Salinity 
Depth, 
meters 
August, 1920 
U 
23.5 
4.75 
0 
August, 1920 
L 
25.0 
19.76 
30 
24.4 
14. 21 
5 
24.8 
20. 50 
37 
24.2 
15. 21 
11 
Do 
G 
27.0 
22.73 
0 
Do 
L 
25.5 
13.72 
0 
20.2 
29.05 
10 
25.5 
13.72 
10 
17.2 
31.26 
20 
25.5 
13. 77 
20 
15.5 
31.74 
23 
It will be noted that the thermocline is conspicuous at G, the result of high air 
temperature in that region. Farther north, where the thermocline was not so evident 
or lacking, the air temperature was about 10° C. lower than in the region of G. 
While the thermocline is more or less characteristic of the waters of Chesapeake 
Bay during the warmer months, a discontinuity in the degree of temperature and 
salinity often occurs during the winter. This condition is the reverse of that during 
the summer because there is an upper layer of water which is distinctly colder than the 
water below. This is most conspicuous along the deep-water channel. The fresher 
and lighter, although colder, water from the rivers lies over the much warmer but 
much heavier saline water having its origin from the ocean. Excellent examples of 
the discontinuity just mentioned occurred when the cruise of December, 1920, was 
made. Data for areas U, L, and G are shown in Table 9. 
Table 9. — Temperatures and salinities at various depths on December, 1920, cruise 
Date 
Area 
Tempera- 
ture, 0 C. 
Salinity 
Depth, 
meters 
Date 
Area 
Tempera- 
ture, 0 C. 
Salinity 
Depth, 
meters 
December, 1920 
U 
5.8 
6.70 
0 
December, 1920 
G 
10.5 
25.20 
0 
5.9 
6. 02 
5 
10.8 
28.76 
10 
9.0 
14. 02 
11 
11.3 
30.22 
20 
Do 
L 
8.7 
15. 03 
0 
11.6 
30.96 
22 
8.6 
15. 21 
10 
10.0 
20. 01 
20 
10.1 
20. 13 
30 
10.1 
20. 21 
37 
DELAY IN SEASONAL CHANGE OF TEMPERATURE 
The “Phasenverzug,” a condition described by Krummel (1907) in which there 
is a delay in the change of temperature of the bottom water, so that it does not reach 
its maximum temperature in midsummer but in the fall and does not reach its mini- 
mum temperature in the midwinter but in the spring, can not be said to be a fixed 
condition in Chesapeake Bay, such as it is in the English Channel according to Dickson 
(1893). The time of occurrence of maximum and minimum temperatures varies 
somewhat with the year. There are indications from the data obtained on our cruises 
that the minimum bottom temperature occurs sometimes in midwinter and sometimes 
