100 
BULLETIN OF THE BUEEAU OF FISHERIES 
stated, there are no rivers in the immediate vicinity of Great Harbor, although 
melting snow and hard northerly winds cause the sudden appearance of waters 
of comparatively low density. Prevailing southerly winds extending over a long 
period of time cause high density. In the spring of 1922 (fig. 2), combined with 
the usual low temperature, the density almost equaled that of ocean water and 
remained that way until the middle of May. 
The effect of melting snow shows clearly (fig. 2) in the first week of April, 1922, 
and (fig. 3) on January 2 and 3, 1923. On the latter dates a marked increase in the 
number of diatoms was also noticeable. The greatest change took place on March 31, 
when the density dropped from 1.0260 to 1.0244 in one day. A heavy snowstorm 
had occurred on March 30, followed by rain and snow on March 31 and April 1. 
The rapid rise took place during a period of constant hard southwesterly winds. 
The extreme point reached on April 9 (1.0270), accompanied by a drop of 1° in 
temperature, is impossible to explain on the basis of local conditions. Southerly 
winds prevailed, but were not unusually strong. Some hydrographical change 
beyond the limits of the immediate region must have accounted for it. 
It is probable that the salinity plays little or no part in the seasonal distribution 
of the planktonic animals of this region. The fresh waters of the upper bay no 
doubt form a barrier for the oceanic species and the brackish water forms probably 
do not go far out to sea. Such conditions, however, are not found in this immediate 
region. 
TEMPERATURE 
The subject of the temperatme at Woods Hole and adjacent regions is so fully 
discussed by Stminer in his report that only the particular conditions existing in 
Great Harbor dm-ing the past two years need be considered here. 
Figiu-es 4 and 5 show the variations in the temperature of the air and water 
for the years 1922-23, inclusive, to December 31. The figures were obtained from 
the records taken daily at 8 a. m. by Mr. Hamblin, of the Bmeau of Fisheries. 
This hour was selected because it eliminates the temporary midday rise of surface 
temperature typical of all shallow water. Figure 6 was compiled by Sumner to 
show the mean average temperatme of the air and water for a period of five years. 
A comparison of this chart with that of the past year shows many important points. 
The fact that Sumner's chart is based on noon records must be considered, although 
it probably had little effect on the water curve. The highest point on this curve is 
on August 12, when the mean temperatme was slightly over 71° F. The highest 
point reached in 1922 was 71° F., on August 8. The curve for 1922 agrees well 
with that of the average temperature for other years. The lower point of the 
latter (30° F.) was reached only once, on February 19. In 1922 the curve feU 
below this on two occasions (January 25 and February 17-19), and reached it on 
February 4. 
During the spring of 1923 very unusual conditions prevailed. The tempera- 
ture went below 30° F. on January 29, and never rose above this point imtil March 
14. Throughout this period the temperatures fluctuated between 28.5 and 29° 
F., reaching 28° F. on February 24. This unusually cold water, occurring for such 
an extended period, accounts for certain peculiarities in the plankton of the present 
