THE PRODUCTION O F MARINE PLANKTON
127
the water. Light is relatively very rapidly reduced in the sea, being
partly absorbed and partly scattered. Particlies in the water, whether
inorganic or organic detritus, as well as living plankton, all reduce
transparency; there is also some dissolved “yellow substance” which
absorbs light. Greater light penetration is t,ypical of less productive
waters, since algal cells are sparser, but the relatively rapid reduction
of light in richer seas is partly due to greater quantities of detritus (cf.
Ryther, 1963). The compensation depth is greatly affected by latitude
and season, but it is not an absolute value - it will depend aIso on the
time of day. At night it does not exist.
Light is absorbed logarithmically in sea water, and even for the
clearest oceanic waters about SOYo of the total solar radiation is absorbed in the upper 10m. Although infrared rays are especially rapidly
absorbed, even of the visible wavelengths only some 50% remains for
the clearest water at 10m depth. Whereas about 1% of incident visible
light reaches some 120m in clear tropical oceans, the same reduction to
1% is reached at ca. 50m depth in boreal waters, and in turbid inshore
areas the 1 Yo level is reached at depths approaching only 10 or 20m.
TABLE I1
Culture Experiment 22-25 Nwch, 1916
Average Increase in 24 hours (from Bmvder and Bran, 1927)
yo Increase i n Cell Numbers
Depth,
Oxygen,
Lauderia
Tlialassiosira Thalaseiosira
m
cm8/1
glacialis
gravida
nordenekioldii
0
+ 0.20
77
59
10
2
+ 0.19
79
58
73
5
+ 0.13
70
55
67
10
0
28
34
23
20
- 0.03
0
0
0
30
- 0.05
0
0
0
40
- 0.07
0
0
0
In the oxygen bottle experiments such as those of Gaarder and Gran
(Table 11), the decrease in the amount of oxygm produced with increase
in depth of the water reflects the rapid reduction in light intensity.
These experiments were conducted over a 24-hour period; had shorter
term experiments been made during daylight hours only, there would
have been greater oxygen production at each depth and the estimated
compensation depth would have been greater. Frog the view point of
overall primary production, the 24-hour experiment is the most satisfactory. The compensation depth will vary with season in a temperate
127
the water. Light is relatively very rapidly reduced in the sea, being
partly absorbed and partly scattered. Particlies in the water, whether
inorganic or organic detritus, as well as living plankton, all reduce
transparency; there is also some dissolved “yellow substance” which
absorbs light. Greater light penetration is t,ypical of less productive
waters, since algal cells are sparser, but the relatively rapid reduction
of light in richer seas is partly due to greater quantities of detritus (cf.
Ryther, 1963). The compensation depth is greatly affected by latitude
and season, but it is not an absolute value - it will depend aIso on the
time of day. At night it does not exist.
Light is absorbed logarithmically in sea water, and even for the
clearest oceanic waters about SOYo of the total solar radiation is absorbed in the upper 10m. Although infrared rays are especially rapidly
absorbed, even of the visible wavelengths only some 50% remains for
the clearest water at 10m depth. Whereas about 1% of incident visible
light reaches some 120m in clear tropical oceans, the same reduction to
1% is reached at ca. 50m depth in boreal waters, and in turbid inshore
areas the 1 Yo level is reached at depths approaching only 10 or 20m.
TABLE I1
Culture Experiment 22-25 Nwch, 1916
Average Increase in 24 hours (from Bmvder and Bran, 1927)
yo Increase i n Cell Numbers
Depth,
Oxygen,
Lauderia
Tlialassiosira Thalaseiosira
m
cm8/1
glacialis
gravida
nordenekioldii
0
+ 0.20
77
59
10
2
+ 0.19
79
58
73
5
+ 0.13
70
55
67
10
0
28
34
23
20
- 0.03
0
0
0
30
- 0.05
0
0
0
40
- 0.07
0
0
0
In the oxygen bottle experiments such as those of Gaarder and Gran
(Table 11), the decrease in the amount of oxygm produced with increase
in depth of the water reflects the rapid reduction in light intensity.
These experiments were conducted over a 24-hour period; had shorter
term experiments been made during daylight hours only, there would
have been greater oxygen production at each depth and the estimated
compensation depth would have been greater. Frog the view point of
overall primary production, the 24-hour experiment is the most satisfactory. The compensation depth will vary with season in a temperate