PLANKTON OF THE GULF OF MAINE 
481 
In the western coastal zone, south of Cape Elizabeth, and in the basin generally, 
the vernal period of vertical mixing is brief, its activity lessening as soon as the 
combined effect of solar warming and of the freshening of the surface increases 
the vertical stability of the water. This becomes very stable indeed by the early 
summer with very little interchange taking place between the upper and deeper 
strata from that time until into the autumn. But strong tidal currents keep the water 
in the northeastern corner of the gulf in a state of more active vertical circulation 
throughout the year, especially in the Bay of Fundy, along western Nova Scotia, 
and locally on Georges Bank. In the Grand Manan Channel, an extreme example, 
the water is kept practically uniform in temperature from surface to bottom, even 
in midsummer. 
Planktonic diatoms, with their silicious frustules and without power of locomo- 
tion, tend to sink unless kept afloat mechanically by some movement of the water. 
Although sinking is more or less hindered by their spines, slime threads, disclike 
outlines, etc., 92 they are more liable to sink than other members of the phytoplankton 
are, as Gran (1915, p. 136) has emphasized. 
The mechanical influence of the state of circulation of the water on the flotation 
of diatoms or on small objects of any sort is obvious. Indeed, particles as heavy as 
sand may be kept in suspension by active vertical currents, as just remarked; and 
from what has just been said it is evident that diatoms are more apt to remain in 
suspension in the coastal waters of the Gulf of Maine from midwinter on through 
spring, when the water is actively mixing, than in summer. The flotation of diatoms 
or of any of the unicellular planktonic organisms is likewise made more easy in winter 
and early spring than in summer by the more viscous condition of the water during 
the cold season. The importance of viscosity in this respect, first appreciated by 
Ostwald (1903), is now so generally recognized (Steuer, 1910; Gran, 1912; Murray 
and Hjort, 1912) that no general discussion of it is called for here. 93 It is in waters 
such as those of the Gulf of Maine, where a cold winter alternates with a warm 
summer in the sea as well as in the air, that seasonal differences in this respect are 
greatest, because the viscosity of the water depends almost wholly on its temperature 
within the range of salinities there obtaining (say 27 to 34 per mille). The following 
table is compiled, in a slightly modified form, from Krummel (1907, p. 282), Murray 
and Hjort (1912, p. 690), and Murray (1913, p. 102). 
Viscosity for sea water of SO to S3 per mille salinity, 100 being that of distilled water at 0° temperature 
Temperature in degrees centigrade 
Viscosity 
Temperature in degrees centigrade 
Viscosity 
0 
104. 5-105. 2 
100. 4-101. 1 
97. 3- 98 
94. 3- 95 
5_ 
89. 1-89 
77. 2-77. 8 
67. 5-68. 2 
59. 9-60. 6 
1 .. 
10. 
2 
15 
3 
20 
43 For a summary of these arrangements for flotation see Steuer, 1910, p. 193. 
43 As a homely and extreme illustration of the effect of differences in viscosity in fluids familiar to every biologist, consider how 
much more rapidly a round cover glass, resting on its flat surface (which we may conceive as representing a Coscinodiscus), will 
sink in water than in ordinary xylol-balsam, fluids hardly differing in specific gravity but of which the latter is much the more 
viscous. 
