PLANKTON IN NITROOEN AND PHOSPHORUS CYCLES
181
3 r
Nitrite + Nitrate Nitrogen
,
1
,
,
,
1
,
1
1
.
1
1
1
1
-
.
1
.
1
1
1
1
~
~
.
~
M A M J J A S O N D J F M A M J J A S O N D J F M A
. 1964,
' I
1965
I 1966
FIQ. 12. The seasonal variation of nutrients, chlorophyll u and zooplankton at a station
in Harrington Sound, Bermuda. The nutrient data are the averages of observations
at three depths (1, 7 and 14 m) and the chlorophyll u values correspond to a depth
of 6 m: for zooplankton numbers, continuous line represents the total and the broken
line copepode only. (After Beers and Herman, 1969; Herman and Boers, 1969.)
levels decreased from a maximum in the morning (06.00-12.00 h) to a
minimum near midnight. However, the low levels of ammonia found
when zooplankton were at their peak may have resulted from the uptake of ammonia by phytoplankton during the night.
In contrast to the northern Sargasso Sea, Ryther and Menzel(l965)
found that stratification of the Arabian sea surface was permanent,
and that nutrient levels increased quickly with depth so that high