BIOLOGICAL STUDY OF CHESAPEAKE BAY WATERS 
307 
tures were observed during the month of January, 1921, which was an exceptionally 
mild month in Maryland at least. Ice floes were so common during the cruise in the 
upper part of the bay that they interfered with the instruments. The 24-hour current 
meter records at area L near the mouth of the Potomac River showed a dominating 
outgoing current from surface to bottom, which, however, was as usual of low velocity. 
The salinities were remarkably low at all depths for that time of the year, and at 
many areas there was, for such a body of water as Chesapeake Bay with its highly 
variable temperatures, a rather close approach to uniformity from the surface to the 
bottom. So there is much evidence to show that the bay had been flooded, probably 
gradually, with almost homothermous water of low salinity similar to that of the 
spring freshets. This condition combined with the freezing air temperatures, which 
occurred at the lower end of the bay during the January cruise (see U. S. Weather 
Bureau records for Norfolk, two days before our observations were made) and which 
chilled the upper layers, was undoubtedly largely responsible for the almost homother- 
mous gradient from surface to bottom. 
TEMPERATURE OF WATER DURING SPRING 
The data collected on the spring cruise, as for the winter cruise, range decreasingly 
for the most part from the mouth toward the head. This is shown in Table 2, 
although it will be seen that there are some irregularities — for example, high surface 
temperatures at the upper end of the bay during March, 1922, and March-April, 
1921, cruises. The temperature values for the bay were somewhat higher during 
three of the spring cruises, but in March, 1916, the readings, especially at the bottom, 
ran lower than during any of the winter cruises. According to the United States 
Weather Bureau this was an exceptionally cold March for Maryland. There was a 
remarkable unbroken period of low daily air temperatures recorded. The tempera- 
ture observations made at G during the March cruise, 1916, were the highest observed 
in the whole bay, as was the case during the winter cruises, but in the data for the 
April, 1916, March, 1922, and March-April, 1921, cruises this relation was not so 
evident. Apparently during those months the change was taking place from the 
winter condition to that found during the summer cruises in which the bottom 
water temperatures at G were cooler than those observed at other areas in the bay. 
The vertical distribution during the spring cruises varied like that of the winter 
season. On the March cruise of 1916 — the exceptionally cold March — the tempera- 
tures showed a close approach to uniformity (homothermous), as at area G where 
the following readings were made: Surface 3.7, 5 meters 3.8, 10 meters 3.7, 20 meters 
3.5, 22 meters 3.6. Occasionally the surface water was a little warmer than the inter- 
mediate layers, and below the latter the temperatures increased again (dictothermous), 
as during the March-April cruise, of 1921, at area A: Surface 12.1, 10 meters 11.2, 
20 meters 11.3, 30 meters 11.4, and 42.5 meters 11.5 — or as during the March cruise 
of 1922 at area J: Surface 8.1, 10 meters 6.2, 20 meters 6.2, 30 meters 6.5, 40 meters 
6.2, 43 meters 6.6. Often on the March cruise and more often on the March-April 
cruise, however, the surface water was the warmest, and there was a decrease in tem- 
peratures passing downward (anothermous). In March, 1922, at area G, as an 
example, the temperatures were as follows: Surface 8.9, 10 meters 6.6, 24 meters 
6.5; and at area X, surface 8.2, 10 meters 7.2, 20 meters 4.5, 26.5 meters 4.0. 
1988—30 3 
