PLANKTON OF THE WOODS HOLE REGION 99 
TaBLE 1.—Salinity of surface water at Woods Hole from July to October, 1922 
Degree Degree Degree Degree Degree Degree 
Date of Date of Date of Date of Date of Date of 
salinity salinity Salinity salinity salinity salinity 
July 27_ 31.53 || Aug. 6_---| 30.30 || Aug.16_._| 31.58 |] Aug. 27 31.85 || Sept. 8__ 31. 22 || Sept. 24 31. 40 
July 28__- 46 || Aug. 7 31.20 || Aug.17_--| 31.53 || Aug. 28 31.31 || Sept. 9 31.18 || Sept. 27 31. 44 
July 29_ 31.62 || Aug.8__._| 31.29 }| Aug.18.-_) 31.82 |) Aug. 29 31. 49 || Sept. 10 31. 33 || Sept. 29__| 31.40 
July 30. 31.31 ug.9_---| 32.01 }| Aug.19-__| 31.60]} Sept. 1 31.36 || Sept.11__} 31.02] Sept. 30__| 31.62 
July 31 31.31 |} Aug.10---| 32.01]; Aug.20_-_| 31.65 |] Sept. 2 31. 36 || Sept. 12 31. 06 =.--|/ 30.88 
Aug. 1 31.31 || Aug. 11 31.73 |} Aug.21-__| 31.85 || Sept.3 31. 09 || Sept. 13 31.15 || Oct. 2-_--| 31535 
Aug. 2__-- 31. 56 |} Aug. 12 31. 82 || Aug. 22_ 31.85 || Sept. 4 30. 91 |} Sept. 14 318) || Oct onens 31.35 
Aug. 3----] 31.71 || Aug. 13. 31. 53 || Aug. 23_ 31.85 || Sept. 5 31.18 |} Sept. 16_-] 31.15 ]| Oct. 10__ 31.49 
Aug. 4... 31. 64 |} Aug. 14 31. 60 |} Aug. 24_ 31.65 || Sept. 6__ 31. 04 |} Sept. 17_- 31. 06 || Oct. 11_ 31.20 
Aug. 5.. 31.46 |} Aug. 15 31. 67 |} Aug. 25_ 31.71 |} Sept. 7 31. 49 
After southerly winds a slight increase in salinity usually can be noted. This 
would naturally be expected, for the outlying waters always have a higher salinity— 
in the case of the Gulf Stream upwards of 35 per mille. It was to determine to what 
extent this influx of ocean waters takes place after storms that the titrations were 
made in Great Harbor. They covered the period when most tropical oceanic 
animals appear in the plankton. The results showed that very little change takes 
place even during hard southerly winds unless they extend over a long period of 
time. ‘This is probably due to a dilution resulting from a mixture with the fresher 
waters of the southern part of the bay. Marked changes may have occurred in 
Vineyard Sound but were not evident farther inland. 
On August 6 and 7 a heavy southwest storm took place, reaching its height on 
the second day. During this time the wind blew continuously and much Sargassum 
was noticed in the sound. A slight increase in salinity from 31.29 to 32.01 per mille 
on August 9 and 10, followed by a gradual decline, was the only evidence of outside 
water, and this was below the usual average for theSound in August. However, 
this again may have represented a mixing of the bay water with that of a higher 
salinity than is usually found in the sound. 
Hard southerly winds extending over a long period of time replace the waters 
of the region to such an extent that the dilution by bay water is hardly noticeable 
except after a hard rain or a period of melting snow. This was shown by the 
density records during the spring of 1922. Figures 2 and 3 give the daily variation 
in the density at Great Harbor, taken by Mr. Hamblin at the Fisheries dock at 12 
o’clock noon. As these unfortunately have no relation to the tides, they can only 
indicate in a general way the conditions existing at any particular time. Standard 
hydrometers, certified by the Bureau of Standards, were used, the error being 
probably not greater than + 0.0001. 
The density in shallow waters is governed by two factors, temperature and 
salinity, the comparative influence of each being clearly shown in Figures 2 and 3. 
A comparison of Figures 2 and 3 with Figures 4 and 5 indicates the effect of the 
temperature. Durmg the warmest seasons a minimum density is found, and 
during the coldest months it reaches its highest pot. Were there no change in 
the salinity the curve would rise and fall evenly, corresponding to the rise and fall 
in the temperature of the water. The sudden increase or decrease in the curve at 
any particular time is due to an increase or decrease in salinity. As previously 
