306 
BULLETIN OF THE BUREAU OF FISHERIES 
Potomac River. The reduced temperatures at these two areas are probably due to 
the large volume of colder, fresh water forcing its way in from the Potomac River, 
as seen in density profiles. Ordinary daily variations in air temperature should not 
cause the irregularities mentioned at 30 meters, but the surface water temperature 
would, of course, be affected by them. 
Data for area G, which marks the main entrance into the bay, are included in 
the following discussion in order to show the influence of the oceanic water, although 
the depth at this area does not equal 30 meters (22 meters in January, 1916, 22.9 
meters in January, 1921, and 23.8 meters in January, 1922). The data for area S 
in 1916 were obtained from a station near area S. 
The decreasing range of temperature values from mouth to head shown in Table 
1 may be ascribed to a difference in latitude, but there is evidence which indicates that 
the higher temperature at G, the deepest area in the mouth of the bay, is due, in part, 
to the entrance of warmer water from the ocean. The bottom reading at G during 
the January, 1916, cruise was 6.1° C. (22 meters), a temperature higher than that 
observed at any area or any depth in the bay during that cruise — considerably warmer 
even, than those at area G', near Norfolk. The temperatures inside of the bay, then, 
show that the comparatively high bottom temperature at area G, in the mouth of the 
bay, has its origin from some other source. The data from the cruise of the U. S. S. 
Roosevelt off the mouth of Chesapeake Bay during January and February, 1916, (see 
Bigelow, 1917 b), show that the temperatures out to about the 20-meter contour were 
between 6° C. and 7° C. from the surface to the bottom, and that at the 200-meter 
contour they were considerably higher than nearer shore. These observations, how- 
ever, were made about two weeks after the time the observations were made at G, 
but it is very probable that similar relations existed two weeks earlier. Tempera- 
tures of 10° C. and 12° C. were found over the continental slope — for example, in the 
region of the 200-meter contour. It is evident that there was a gradual increase in 
temperature at the surface and at depths from the shore outward; and it is practically 
certain that the warmer water at G had a higher temperature, owing to the fact that 
its origin was largely oceanic. It is through this area that the bulk of the salt water 
usually finds its way into the bay. At the time the temperature observations were 
made at G, the salinity at 22 meters was 32.57, the highest found on that cruise in the 
mouth or anywhere else in the bay. During January, 1921 and 1922, the highest 
bottom temperatures for the whole bay were found again at G, with the exception that 
in the latter year the temperatures at F equalled those at G. It is quite probable that 
the comparatively warm water of the ocean during the colder months of the year has 
a tendency to raise the temperature of the water of Chesapeake Bay. The tempera- 
ture conditions at area G, the occurrence of water of fairly high salinity in the northern 
part of the bay, and the distribution of certain marine organisms are in keeping with 
this theory. 
The vertical distribution of temperature during the winter cruises was found to be 
characterized by a low temperature at the surface and an increasing range from the 
surface downward (Katothermous, following Krummel, 1911), as atarea G in January, 
1916, surface 4.1, 8 meters 4.9, 9 meters 5.6, 17 meters 5.8, 18 meters 5.9, 22 meters 
6.1 ; and at area R during the same cruise, surface 1.1, 5 meters 1.2, 9 meters 2.2, IS 
meters 3.4, 27 meters 3.6, 36 meters 3.8. A similar condition may be seen at area G 
in December, 1920, surface 10.5, 10 meters 10.8, 20 meters 11.3, 22.9 meters 11.6, and 
at many other areas. But there are times during the winter when close approaches 
to uniformity of water temperatures from surface to bottom occur. Such tempera- 
