BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
303 
VARIATION OF SURFACE TEMPERATURE ACROSS BAY 
Referring to the map showing the surface temperatures for June, 1916 (fig. 15), 
one sees at once that the isotherms are arranged quite differently from those of 
August, 1920. Here we see a condition which is more characteristic of the warmer 
months. The isotherms, during this cruise at least, run, more or less, up and down 
the bay. This condition results from the warmer water being on the western side of 
the bay, except along the line J, I, K, and also from the fact that temperatures from 
north to south are close to uniformity. 
After a study of the data for all the cruises it seems to be difficult to formulate 
any very definite rule for the distrubution of surface temperature with reference to 
the east and west sides of the bay. However, it may be stated that, judging from 
data collected during winter and summer cruises, warmer water lies decidedly more 
often at area G than at area E. These areas mark the line across the mouth of the 
bay. 
BOTTOM TEMPERATURE AT MOUTH AND HEAD 
The highest and lowest bottom temperatures for area G at the mouth of Chesa- 
peake Bay, as recorded on our cruises, were 21.0° C. in July, 1916, and 3.6° C. in 
March, 1916, while at the head of the bay the highest and lowest temperatures at 
U were 24.4° C. in August, 1920, and 0.9° C. in January, 1921. It will be noted that 
the range was considerably less for the bottom water than for the surface water both 
at area G and at area U (surface 27.0° C. to 3.7° C. at G and 24.8° C. to 0.3° C. at U). 
A smaller range would be expected at the bottom, since that water is not subject so 
much to the effect of great changes in air temperatures. 
DEEP-WATER TEMPERATURE FROM MOUTH TO HEAD 
The decrease in water-temperature values passing from the line Z>, C, B, A just 
inside of the mouth of the bay to the region near Baltimore (this leaves out of con- 
sideration for the moment the region between D, C, B, A and G, F, E ) was as marked 
for the deep water during the cruises of the colder months as for the surface water. 
This relation can be seen by inspection of the data for 20 and 30 meters. (See 
Tables 1, 2, and 4.) As in the case of the salinity, the data could not be collected 
simultaneously at all areas, but notwithstanding this they show consistently a de- 
creasing range. 
The greatest differences in deep-water temperature per unit of distance from 
mouth to head were found near the mouth of the bay between D, C, B, A and G, F, E, 
as in the case of the surface water. It was during the cruises of the warmest months 
of the year that the greatest range occurred. As examples, the difference in the 
bottom temperatures between G and A (21.0° C., 24.2° C.) or G and D (21.0° C., 
25.5° C.) in July, 1916, G and A (15.5° C., 21.3° C.) or G and D (15.5° C., 24.0° C.) 
in August, 1920, and G and A (15.2° C., 17.1° C.) or G and D (15.2° C., 19.1° C.) in 
May, 1921, are of interest, especially those between G (the area through which most 
of the oceanic water enters) and A, where the bottom temperatures for G, at about 20 
meters, are much lower even than those for A (about 43 meters). This condition sup- 
ports the statement that the bottom water, as well as the surface water, entering 
the bay during the warmer months has a lower temperature than that inside of the bay. 
Deep-water temperatures, as in the case of the surface temperatures, show 
almost invariably a decreasing range in the warmest months passing from D, C, B, 
A through G, F, E and an increasing range during the coldest months. 
