BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
297 
of the water were made out at the areas mentioned below during the spring and summer 
cruises, but the current velocities, according to current-meter records, were quite 
low. During the fall and winter cruises, however, when the current velocities were 
a little higher, the alternating incoming and outgoing currents characteristic of tides 
were usually not so evident, judging from our data obtained during 24-hour obser- 
vations at area U, near Baltimore, and at areas R, L, and Q, lower down in the bay. 
These results are of interest in connection with the observations made by Canadian 
observers. (See Dawson, 1897.) Changes due to local precipitation and evaporation 
can not be made out, as a rule, from our data. Other changes due to more dominant 
causes mask them. 
The fact that the water at 30 meters as far north as a little below Baltimore 
(area R) may have a salinity of 20.00 shows, of course, that water of partly marine 
origin makes its way up in the bay. It is difficult to ascertain what factors bring this 
condition about and whether the higher salinities sometime after the spring freshets 
are due to decreased pressure from the fresh water, to reaction currents resulting 
from outflow of surface fresh water, to the pressure of oceanic water resulting from the 
northerly drift of the highly saline water of equatorial regions, to a combination of 
these factors, or to other factors. Irregularities in tidal flow due to hydrological 
conditions in the upper part of the bay, the occurrence of spring and neap tides, and 
probably many other factors which add complexity make it difficult to analyze the 
movements of the waters of Chesapeake Bay. 
Current records, however, at 24-hour stations do show at times what appears to 
be a persistent, although not continuous, tendency for the rather highly saline waters 
of the lower layers to move slowly into the bay. Areas L and R are both deep-water 
areas situated in the deep channel where the movements of the more saline water 
may be observed. The records indicated that with the approach of autumn and 
during the winter months there was at times a persistent tendency for the highly 
saline water of the lower layers to push its way slowly inwards, thus masking the 
tidal movements, and that during the spring and summer cruises this tendency was 
not so evident, with the result that the tidal currents were more clearly seen. A 
similar condition has been observed in Christiana Fiord by Hjort and Gran (1900). 
The movement inward during the autumn and winter cruises did not seem to be 
dependent on the conformation of the bottom, nor could it be related clearly to the 
occurrence of spring and neap tides. Undoubtedly, however, a nontidal factor (see 
Marmer, 1925, and Zeskind and LeLacheur, 1926) was responsible for this ingoing 
current. The wind, as an example, blows more frequently from a northerly direction 
during the winter, while during the summer the more common direction is southerly, 
according to Spencer. This would tend to move the fresher surface water oceanward 
in the winter and as a result produce the so-called “reaction stream” of Ekman 
(1876); the “reaction current” of Helland-Hansen and Nansen (1909); “compen- 
satory bottom current,” Johnstone (1923); “induction current,” Cornish (1898); 
“undercurrent,” Dawson (1896), in which the deeper more saline water moves 
inward from the sea. In summer, on the other hand, with the wind from the opposite 
direction such a tendency would not exist. 
The discharge from rivers (another nontidal factor) would also bring about 
conditions such as those just described, but it is not clear why the undercurrent 
moving in an ingoing direction is so marked during the winter months, when the 
discharge from the rivers is not ordinarily at is height. 
